Effects of cloud condensation nuclei and ice nucleating particles on precipitation processes and supercooled liquid in mixed-phase orographic clouds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fan, Jiwen; Leung, L. Ruby; Rosenfeld, Daniel

How orographic mixed-phase clouds respond to the change in cloud condensation nuclei (CCN) and ice nucleating particles (INPs) are highly uncertain. The main snow production mechanism in warm and cold mixed-phase orographic clouds (referred to as WMOCs and CMOCs, respectively, distinguished here as those having cloud tops warmer and colder than -20°C) could be very different. We quantify the CCN and INP impacts on supercooled water content, cloud phases, and precipitation for a WMOC case and a CMOC case, with sensitivity tests using the same CCN and INP concentrations between the WMOC and CMOC cases. It was found that depositionmore » plays a more important role than riming for forming snow in the CMOC case, while the role of riming is dominant in the WMOC case. As expected, adding CCN suppresses precipitation, especially in WMOCs and low INPs. However, this reverses strongly for CCN of 1000 cm -3 and larger. We found a new mechanism through which CCN can invigorate mixed-phase clouds over the Sierra Nevada and drastically intensify snow precipitation when CCN concentrations are high (1000 cm -3 or higher). In this situation, more widespread shallow clouds with a greater amount of cloud water form in the Central Valley and foothills west of the mountain range. The increased latent heat release associated with the formation of these clouds strengthens the local transport of moisture to the windward slope, invigorating mixed-phase clouds over the mountains, and thereby producing higher amounts of snow precipitation. Under all CCN conditions, increasing the INPs leads to decreased riming and mixed-phase fraction in the CMOC as a result of liquid-limited conditions, but has the opposite effects in the WMOC as a result of ice-limited conditions. However, precipitation in both cases is increased by increasing INPs due to an increase in deposition for the CMOC but enhanced riming and deposition in the WMOC. Increasing the INPs dramatically reduces supercooled water content and increases the cloud glaciation temperature, while increasing CCN has the opposite effect with much smaller significance.« less

Effects of cloud condensation nuclei and ice nucleating particles on precipitation processes and supercooled liquid in mixed-phase orographic clouds

DOE PAGES

Fan, Jiwen; Leung, L. Ruby; Rosenfeld, Daniel; ...

2017-01-23

How orographic mixed-phase clouds respond to the change in cloud condensation nuclei (CCN) and ice nucleating particles (INPs) are highly uncertain. The main snow production mechanism in warm and cold mixed-phase orographic clouds (referred to as WMOCs and CMOCs, respectively, distinguished here as those having cloud tops warmer and colder than -20°C) could be very different. We quantify the CCN and INP impacts on supercooled water content, cloud phases, and precipitation for a WMOC case and a CMOC case, with sensitivity tests using the same CCN and INP concentrations between the WMOC and CMOC cases. It was found that depositionmore » plays a more important role than riming for forming snow in the CMOC case, while the role of riming is dominant in the WMOC case. As expected, adding CCN suppresses precipitation, especially in WMOCs and low INPs. However, this reverses strongly for CCN of 1000 cm -3 and larger. We found a new mechanism through which CCN can invigorate mixed-phase clouds over the Sierra Nevada and drastically intensify snow precipitation when CCN concentrations are high (1000 cm -3 or higher). In this situation, more widespread shallow clouds with a greater amount of cloud water form in the Central Valley and foothills west of the mountain range. The increased latent heat release associated with the formation of these clouds strengthens the local transport of moisture to the windward slope, invigorating mixed-phase clouds over the mountains, and thereby producing higher amounts of snow precipitation. Under all CCN conditions, increasing the INPs leads to decreased riming and mixed-phase fraction in the CMOC as a result of liquid-limited conditions, but has the opposite effects in the WMOC as a result of ice-limited conditions. However, precipitation in both cases is increased by increasing INPs due to an increase in deposition for the CMOC but enhanced riming and deposition in the WMOC. Increasing the INPs dramatically reduces supercooled water content and increases the cloud glaciation temperature, while increasing CCN has the opposite effect with much smaller significance.« less

Cloud Condensation Nuclei in FIRE III

NASA Technical Reports Server (NTRS)

Hudson, James G.; Delnore, Victor E. (Technical Monitor)

2002-01-01

Yum and Hudson showed that the springtime Arctic aerosol is probably a result of long-range transport at high altitudes. Scavenging of particles by clouds reduces the low level concentrations by a factor of 3. This produces a vertical gradient in particle concentrations when low-level clouds are present. Concentrations are uniform with height when clouds are not present. Low-level CCN (cloud condensation nuclei) spectra are similar to those in other maritime areas as found by previous projects including FIRE 1 and ASTEX, which were also supported on earlier NASA-FIRE grants. Wylie and Hudson carried this work much further by comparing the CCN spectra observed during ACE with back trajectories of air masses and satellite photographs. This showed that cloud scavenging reduces CCN concentrations at all altitudes over the springtime Arctic, with liquid clouds being more efficient scavengers than frozen clouds. The small size of the Arctic Ocean seems to make it more susceptible to continental and thus anthropogenic aerosol influences than any of the other larger oceans.

Effects of turbulence on warm clouds and precipitation with various aerosol concentrations

NASA Astrophysics Data System (ADS)

Lee, Hyunho; Baik, Jong-Jin; Han, Ji-Young

2015-02-01

This study investigates the effects of turbulence-induced collision enhancement (TICE) on warm clouds and precipitation by changing the cloud condensation nuclei (CCN) number concentration using a two-dimensional dynamic model with bin microphysics. TICE is determined according to the Taylor microscale Reynolds number and the turbulent dissipation rate. The thermodynamic sounding used in this study is characterized by a warm and humid atmosphere with a capping inversion layer, which is suitable for simulating warm clouds. For all CCN concentrations, TICE slightly reduces the liquid water path during the early stage of cloud development and accelerates the onset of surface precipitation. However, changes in the rainwater path and in the amount of surface precipitation that are caused by TICE depend on the CCN concentrations. For high CCN concentrations, the mean cloud drop number concentration (CDNC) decreases and the mean effective radius increases due to TICE. These changes cause an increase in the amount of surface precipitation. However, for low CCN concentrations, changes in the mean CDNC and in the mean effective radius induced by TICE are small and the amount of surface precipitation decreases slightly due to TICE. A decrease in condensation due to the accelerated coalescence between droplets explains the surface precipitation decrease. In addition, an increase in the CCN concentration can lead to an increase in the amount of surface precipitation, and the relationship between the CCN concentration and the amount of surface precipitation is affected by TICE. It is shown that these results depend on the atmospheric relative humidity.

Process-model Simulations of Cloud Albedo Enhancement by Aerosols in the Arctic

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kravitz, Benjamin S.; Wang, Hailong; Rasch, Philip J.

2014-11-17

A cloud-resolving model is used to simulate the effectiveness of Arctic marine cloud brightening via injection of cloud condensation nuclei (CCN). An updated cloud microphysical scheme is employed, with prognostic CCN and cloud particle numbers in both liquid and mixed-phase marine low clouds. Injection of CCN into the marine boundary layer can delay the collapse of the boundary layer and increase low-cloud albedo. Because nearly all of the albedo effects are in the liquid phase due to the removal of ice water by snowfall when ice processes are involved, albedo increases are stronger for pure liquid clouds than mixed-phase clouds.more » Liquid precipitation can be suppressed by CCN injection, whereas ice precipitation (snow) is affected less; thus the effectiveness of brightening mixed-phase clouds is lower than for liquid-only clouds. CCN injection into a clean regime results in a greater albedo increase than injection into a polluted regime, consistent with current knowledge about aerosol-cloud interactions. Unlike previous studies investigating warm clouds, dynamical changes in circulation due to precipitation changes are small.« less

Ship Tracks

Atmospheric Science Data Center

2013-04-19

... into a moist layer of atmosphere. The particles become cloud condensation nuclei (CCN), which may either produce new cloud particles where ... visualization of the vertical structure of the condensation trails. It was created using a combination of red band data from ...

Environmental conditions regulate the impact of plants on cloud formation

PubMed Central

Zhao, D. F.; Buchholz, A.; Tillmann, R.; Kleist, E.; Wu, C.; Rubach, F.; Kiendler-Scharr, A.; Rudich, Y.; Wildt, J.; Mentel, Th. F.

2017-01-01

The terrestrial vegetation emits large amounts of volatile organic compounds (VOC) into the atmosphere, which on oxidation produce secondary organic aerosol (SOA). By acting as cloud condensation nuclei (CCN), SOA influences cloud formation and climate. In a warming climate, changes in environmental factors can cause stresses to plants, inducing changes of the emitted VOC. These can modify particle size and composition. Here we report how induced emissions eventually affect CCN activity of SOA, a key parameter in cloud formation. For boreal forest tree species, insect infestation by aphids causes additional VOC emissions which modifies SOA composition thus hygroscopicity and CCN activity. Moderate heat increases the total amount of constitutive VOC, which has a minor effect on hygroscopicity, but affects CCN activity by increasing the particles' size. The coupling of plant stresses, VOC composition and CCN activity points to an important impact of induced plant emissions on cloud formation and climate. PMID:28218253

Environmental conditions regulate the impact of plants on cloud formation.

PubMed

Zhao, D F; Buchholz, A; Tillmann, R; Kleist, E; Wu, C; Rubach, F; Kiendler-Scharr, A; Rudich, Y; Wildt, J; Mentel, Th F

2017-02-20

The terrestrial vegetation emits large amounts of volatile organic compounds (VOC) into the atmosphere, which on oxidation produce secondary organic aerosol (SOA). By acting as cloud condensation nuclei (CCN), SOA influences cloud formation and climate. In a warming climate, changes in environmental factors can cause stresses to plants, inducing changes of the emitted VOC. These can modify particle size and composition. Here we report how induced emissions eventually affect CCN activity of SOA, a key parameter in cloud formation. For boreal forest tree species, insect infestation by aphids causes additional VOC emissions which modifies SOA composition thus hygroscopicity and CCN activity. Moderate heat increases the total amount of constitutive VOC, which has a minor effect on hygroscopicity, but affects CCN activity by increasing the particles' size. The coupling of plant stresses, VOC composition and CCN activity points to an important impact of induced plant emissions on cloud formation and climate.

Plume-exit modeling to determine cloud condensation nuclei activity of aerosols from residential biofuel combustion

NASA Astrophysics Data System (ADS)

Mena, Francisco; Bond, Tami C.; Riemer, Nicole

2017-08-01

Residential biofuel combustion is an important source of aerosols and gases in the atmosphere. The change in cloud characteristics due to biofuel burning aerosols is uncertain, in part, due to the uncertainty in the added number of cloud condensation nuclei (CCN) from biofuel burning. We provide estimates of the CCN activity of biofuel burning aerosols by explicitly modeling plume dynamics (coagulation, condensation, chemical reactions, and dilution) in a young biofuel burning plume from emission until plume exit, defined here as the condition when the plume reaches ambient temperature and specific humidity through entrainment. We found that aerosol-scale dynamics affect CCN activity only during the first few seconds of evolution, after which the CCN efficiency reaches a constant value. Homogenizing factors in a plume are co-emission of semi-volatile organic compounds (SVOCs) or emission at small particle sizes; SVOC co-emission can be the main factor determining plume-exit CCN for hydrophobic or small particles. Coagulation limits emission of CCN to about 1016 per kilogram of fuel. Depending on emission factor, particle size, and composition, some of these particles may not activate at low supersaturation (ssat). Hygroscopic Aitken-mode particles can contribute to CCN through self-coagulation but have a small effect on the CCN activity of accumulation-mode particles, regardless of composition differences. Simple models (monodisperse coagulation and average hygroscopicity) can be used to estimate plume-exit CCN within about 20 % if particles are unimodal and have homogeneous composition, or when particles are emitted in the Aitken mode even if they are not homogeneous. On the other hand, if externally mixed particles are emitted in the accumulation mode without SVOCs, an average hygroscopicity overestimates emitted CCN by up to a factor of 2. This work has identified conditions under which particle populations become more homogeneous during plume processes. This homogenizing effect requires the components to be truly co-emitted, rather than sequentially emitted.

Lagrangian condensation microphysics with Twomey CCN activation

NASA Astrophysics Data System (ADS)

Grabowski, Wojciech W.; Dziekan, Piotr; Pawlowska, Hanna

2018-01-01

We report the development of a novel Lagrangian microphysics methodology for simulations of warm ice-free clouds. The approach applies the traditional Eulerian method for the momentum and continuous thermodynamic fields such as the temperature and water vapor mixing ratio, and uses Lagrangian super-droplets to represent condensed phase such as cloud droplets and drizzle or rain drops. In other applications of the Lagrangian warm-rain microphysics, the super-droplets outside clouds represent unactivated cloud condensation nuclei (CCN) that become activated upon entering a cloud and can further grow through diffusional and collisional processes. The original methodology allows for the detailed study of not only effects of CCN on cloud microphysics and dynamics, but also CCN processing by a cloud. However, when cloud processing is not of interest, a simpler and computationally more efficient approach can be used with super-droplets forming only when CCN is activated and no super-droplet existing outside a cloud. This is possible by applying the Twomey activation scheme where the local supersaturation dictates the concentration of cloud droplets that need to be present inside a cloudy volume, as typically used in Eulerian bin microphysics schemes. Since a cloud volume is a small fraction of the computational domain volume, the Twomey super-droplets provide significant computational advantage when compared to the original super-droplet methodology. Additional advantage comes from significantly longer time steps that can be used when modeling of CCN deliquescence is avoided. Moreover, other formulation of the droplet activation can be applied in case of low vertical resolution of the host model, for instance, linking the concentration of activated cloud droplets to the local updraft speed. This paper discusses the development and testing of the Twomey super-droplet methodology, focusing on the activation and diffusional growth. Details of the activation implementation, transport of super-droplets in the physical space, and the coupling between super-droplets and the Eulerian temperature and water vapor field are discussed in detail. Some of these are relevant to the original super-droplet methodology as well and to the ice phase modeling using the Lagrangian approach. As a computational example, the scheme is applied to an idealized moist thermal rising in a stratified environment, with the original super-droplet methodology providing a benchmark to which the new scheme is compared.

A Balloon-Borne Cloud Condensation Nuclei Counter

NASA Technical Reports Server (NTRS)

Delene, David J.; Deshler, Terry; Wechsler, Perry; Vali, Gabor A.

1997-01-01

A balloon-borne instrument was constructed for observations of vertical profiles of cloud condensation nucleus (CCN) concentrations, active at 1% supersaturation. Droplet concentration in the static thermal-gradient diffusion chamber is deduced from the amount of scattered laser light detected by a photodetector. The photodetector is calibrated using a video camera and computer system to count the number of droplets produced from NaCl aerosol. Preliminary data are available from nine early morning profiles obtained at Laramie, Wyoming, between June 1995 and January 1997. To complement the CCN measurements, instruments that measure condensation nuclei (CN) and aerosols with diameter greater than 0.30 micrometers (D(sub 0.3) were also included on the balloon package. CCN concentrations exhibited a general decrease from the surface to the top of the boundary layers, were generally uniform through well-mixed layers, and show variability above well-mixed layers. In general, the structure of the CCN profile appears to be closely related to the structure in the CN and D(sub 0.3) profiles. Summer profiles generally have CCN concentration greater than 200/cu cm up to 500 mbar, whereas winter profiles are less than 200/cu cm at all levels.

Cloud Condensation Nuclei Activity of Aerosols during GoAmazon 2014/15 Field Campaign Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, J.; Martin, S. T.; Kleinman, L.

2016-03-01

Aerosol indirect effects, which represent the impact of aerosols on climate through influencing the properties of clouds, remain one of the main uncertainties in climate predictions (Stocker et al. 2013). Reducing this large uncertainty requires both improved understanding and representation of aerosol properties and processes in climate models, including the cloud activation properties of aerosols. The Atmospheric System Research (ASR) science program plan of January 2010 states that: “A key requirement for simulating aerosol-cloud interactions is the ability to calculate cloud condensation nuclei and ice nuclei (CCN and IN, respectively) concentrations as a function of supersaturation from the chemical andmore » microphysical properties of the aerosol.” The Observations and Modeling of the Green Ocean Amazon (GoAmazon 2014/15) study seeks to understand how aerosol and cloud life cycles are influenced by pollutant outflow from a tropical megacity (Manaus)—in particular, the differences in cloud-aerosol-precipitation interactions between polluted and pristine conditions. One key question of GoAmazon2014/5 is: “What is the influence of the Manaus pollution plume on the cloud condensation nuclei (CCN) activities of the aerosol particles and the secondary organic material in the particles?” To address this question, we measured size-resolved CCN spectra, a critical measurement for GoAmazon2014/5.« less

Cloud Condensation Nuclei Measurements During the First Year of the ORACLES Study

NASA Astrophysics Data System (ADS)

Kacarab, M.; Howell, S. G.; Wood, R.; Redemann, J.; Nenes, A.

2016-12-01

Aerosols have significant impacts on air quality and climate. Their ability to scatter and absorb radiation and to act as cloud condensation nuclei (CCN) plays a very important role in the global climate. Biomass burning organic aerosol (BBOA) can drastically elevate the concentration of CCN in clouds, but the response in droplet number may be strongly suppressed (or even reversed) owing to low supersaturations that may develop from the strong competition of water vapor (Bougiatioti et al. 2016). Understanding and constraining the magnitude of droplet response to biomass burning plumes is an important component of the aerosol-cloud interaction problem. The southeastern Atlantic (SEA) cloud deck provides a unique opportunity to study these cloud-BBOA interactions for marine stratocumulus, as it is overlain by a large, optically thick biomass burning aerosol plume from Southern Africa during the burning season. The interaction between these biomass burning aerosols and the SEA cloud deck is being investigated in the NASA ObseRvations of Aerosols above Clouds and their intEractionS (ORACLES) study. The CCN activity of aerosol around the SEA cloud deck and associated biomass burning plume was evaluated during the first year of the ORACLES study with direct measurements of CCN concentration, aerosol size distribution and composition onboard the NASA P-3 aircraft during August and September of 2016. Here we present analysis of the observed CCN activity of the BBOA aerosol in and around the SEA cloud deck and its relationship to aerosol size, chemical composition, and plume mixing and aging. We also evaluate the predicted and observed droplet number sensitivity to the aerosol fluctuations and quantify, using the data, the drivers of droplet number variability (vertical velocity or aerosol properties) as a function of biomass burning plume characteristics.

Cloud condensation nuclei in Western Colorado: Observations and model predictions

NASA Astrophysics Data System (ADS)

Ward, Daniel Stewart

Variations in the warm cloud-active portion of atmospheric aerosols, or cloud condensation nuclei (CCN), have been shown to impact cloud droplet number concentration and subsequently cloud and precipitation processes. This issue carries special significance in western Colorado where a significant portion of the region's water resources is supplied by precipitation from winter season, orographic clouds, which are particularly sensitive to variations in CCN. Temporal and spatial variations in CCN in western Colorado were investigated using a combination of observations and a new method for modeling CCN. As part of the Inhibition of Snowfall by Pollution Aerosols (ISPA-III) field campaign, total particle and CCN number concentration were measured for a 24-day period in Mesa Verde National Park, climatologically upwind of the San Juan Mountains. These data were combined with CCN observations from Storm Peak Lab (SPL) in northwestern Colorado and from the King Air platform, flying north to south along the Western Slope. Altogether, the sampled aerosols were characteristic of a rural continental environment and the cloud-active portion varied slowly in time, and little in space. Estimates of the is hygroscopicity parameter indicated consistently low aerosol hygroscopicity typical of organic aerosol species. The modeling approach included the addition of prognostic CCN to the Regional Atmospheric Modeling System (RAMS). The RAMS droplet activation scheme was altered using parcel model simulations to include variations in aerosol hygroscopicity, represented by K. Analysis of the parcel model output and a supplemental sensitivity study showed that model CCN will be sensitive to changes in aerosol hygroscopicity, but only for conditions of low supersaturation or small particle sizes. Aerosol number, size distribution median radius, and hygroscopicity (represented by the K parameter) in RAMS were constrained by nudging to forecasts of these quantities from the Weather Research and Forecasting with Chemistry (WRF/Chem) model. The new system was validated against observations from SPL and research flights along the Colorado Front Range, and used to test the sensitivity of CCN in western Colorado to various anthropogenic emissions of aerosols and aerosol precursor gases. Results showed complex interactions between gas and aerosol species that could lead to an increase in CCN even when some emissions are eliminated. Both observations and modeling suggest that, although several large anthropogenic aerosol sources are located within the study region, these sources have a minor impact on the local CCN population.

Cloud condensation nucleation activities of calcium carbonate and its atmospheric ageing products.

PubMed

Tang, M J; Whitehead, J; Davidson, N M; Pope, F D; Alfarra, M R; McFiggans, G; Kalberer, M

2015-12-28

Aerosol particles can serve as cloud condensation nuclei (CCN) to form cloud droplets, and its composition is a main factor governing whether an aerosol particle is an effective CCN. Pure mineral dust particles are poor CCN; however, changes in chemical composition of mineral dust aerosol particles, due to heterogeneous reactions with reactive trace gases in the troposphere, can modify their CCN properties. In this study we investigated the CCN activities of CaCO3 (as a surrogate for mineral dust) and its six atmospheric ageing products: Ca(NO3)2, CaCl2, CaSO4, Ca(CH3SO3)2, Ca(HCOO)2, and Ca(CH3COO)2. CaCO3 has a very low CCN activity with a hygroscopicity parameter (κ) of 0.001-0.003. The CCN activities of its potential atmospheric ageing products are significantly higher. For example, we determined that Ca(NO3)2, CaCl2 and Ca(HCOO)2 have κ values of ∼0.50, similar to that of (NH4)2SO4. Ca(CH3COO)2 has slightly lower CCN activity with a κ value of ∼0.40, and the κ value of CaSO4 is around 0.02. We further show that exposure of CaCO3 particles to N2O5 at 0% relative humidity (RH) significantly enhances their CCN activity, with κ values increasing to around 0.02-0.04. Within the experimental uncertainties, it appears that the variation in exposure to N2O5 from ∼550 to 15,000 ppbv s does not change the CCN activities of aged CaCO3 particles. This observation indicates that the CaCO3 surface may be already saturated at the shortest exposure. We also discussed the atmospheric implications of our study, and suggested that the rate of change in CCN activities of mineral dust particles in the troposphere is important to determine their roles in cloud formation.

Applying super-droplets as a compact representation of warm-rain microphysics for aerosol-cloud-aerosol interactions

NASA Astrophysics Data System (ADS)

Arabas, S.; Jaruga, A.; Pawlowska, H.; Grabowski, W. W.

2012-12-01

Clouds may influence aerosol characteristics of their environment. The relevant processes include wet deposition (rainout or washout) and cloud condensation nuclei (CCN) recycling through evaporation of cloud droplets and drizzle drops. Recycled CCN physicochemical properties may be altered if the evaporated droplets go through collisional growth or irreversible chemical reactions (e.g. SO2 oxidation). The key challenge of representing these processes in a numerical cloud model stems from the need to track properties of activated CCN throughout the cloud lifecycle. Lack of such "memory" characterises the so-called bulk, multi-moment as well as bin representations of cloud microphysics. In this study we apply the particle-based scheme of Shima et al. 2009. Each modelled particle (aka super-droplet) is a numerical proxy for a multiplicity of real-world CCN, cloud, drizzle or rain particles of the same size, nucleus type,and position. Tracking cloud nucleus properties is an inherent feature of the particle-based frameworks, making them suitable for studying aerosol-cloud-aerosol interactions. The super-droplet scheme is furthermore characterized by linear scalability in the number of computational particles, and no numerical diffusion in the condensational and in the Monte-Carlo type collisional growth schemes. The presentation will focus on processing of aerosol by a drizzling stratocumulus deck. The simulations are carried out using a 2D kinematic framework and a VOCALS experiment inspired set-up (see http://www.rap.ucar.edu/~gthompsn/workshop2012/case1/).

The Impact of Aerosols on Cloud and Precipitation Processes: Cloud-Resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Khain, A.; Simpson, S.; Johnson, D.; Li, X.; Remer, L.

2003-01-01

Cloud microphysics are inevitably affected by the smoke particle (CCN, cloud condensation nuclei) size distributions below the clouds. Therefore, size distributions parameterized as spectral bin microphysics are needed to explicitly study the effects of atmospheric aerosol concentration on cloud development, rainfall production, and rainfall rates for convective clouds. Recently, two detailed spectral-bin microphysical schemes were implemented into the Goddard Cumulus Ensemble (GCE) model. The formulation for the explicit spectral-bin microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (i.e., cloud droplets and raindrops), and several types of ice particles [i.e.,pristine ice crystals (columnar and plate-like), snow (dendrites and aggregates), graupel and frozen drops/hail]. Each type is described by a special size distribution function containing many categories (i.e. 33 bins). Atmospheric aerosols are also described using number density size-distribution functions.A spectral-bin microphysical model is very expensive from a from a computational point of view and has only been implemented into the 2D version of the GCE at the present time. The model is tested by studying the evolution of deep tropical clouds in the west Pacific warm pool region using identical thermodynamic conditions but with different concentrations of CCN: a low "clean" concentration and a high "dirty" concentration. Besides the initial differences in aerosol concentration, preliminary results indicate that the low CCN concentration case produces rainfall at the surface sooner than the high CCN case but has less cloud water mass aloft. Because the spectral-bin model explicitly calculates and allows for the examination of both the mass and number concentration of species in each size categor, a detailed analysis of the instantaneous size spectrum can be obtained for the two cases. It is shown that since the low CCN case produces fewer droplets, larger sized develop due to the greater condensational and collectional growth, leading to a broader size spectrum in comparison to the high CCN case.

Plume-exit modeling to determine cloud condensation nuclei activity of aerosols from residential biofuel combustion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mena, Francisco; Bond, Tami C.; Riemer, Nicole

Residential biofuel combustion is an important source of aerosols and gases in the atmosphere. The change in cloud characteristics due to biofuel burning aerosols is uncertain, in part, due to the uncertainty in the added number of cloud condensation nuclei (CCN) from biofuel burning. We provide estimates of the CCN activity of biofuel burning aerosols by explicitly modeling plume dynamics (coagulation, condensation, chemical reactions, and dilution) in a young biofuel burning plume from emission until plume exit, defined here as the condition when the plume reaches ambient temperature and specific humidity through entrainment. We found that aerosol-scale dynamics affect CCNmore » activity only during the first few seconds of evolution, after which the CCN efficiency reaches a constant value. Homogenizing factors in a plume are co-emission of semi-volatile organic compounds (SVOCs) or emission at small particle sizes; SVOC co-emission can be the main factor determining plume-exit CCN for hydrophobic or small particles. Coagulation limits emission of CCN to about 10 16 per kilogram of fuel. Depending on emission factor, particle size, and composition, some of these particles may not activate at low supersaturation ( s sat). Hygroscopic Aitken-mode particles can contribute to CCN through self-coagulation but have a small effect on the CCN activity of accumulation-mode particles, regardless of composition differences. Simple models (monodisperse coagulation and average hygroscopicity) can be used to estimate plume-exit CCN within about 20 % if particles are unimodal and have homogeneous composition, or when particles are emitted in the Aitken mode even if they are not homogeneous. On the other hand, if externally mixed particles are emitted in the accumulation mode without SVOCs, an average hygroscopicity overestimates emitted CCN by up to a factor of 2. This work has identified conditions under which particle populations become more homogeneous during plume processes. This homogenizing effect requires the components to be truly co-emitted, rather than sequentially emitted.« less

Plume-exit modeling to determine cloud condensation nuclei activity of aerosols from residential biofuel combustion

DOE PAGES

Mena, Francisco; Bond, Tami C.; Riemer, Nicole

2017-08-07

Residential biofuel combustion is an important source of aerosols and gases in the atmosphere. The change in cloud characteristics due to biofuel burning aerosols is uncertain, in part, due to the uncertainty in the added number of cloud condensation nuclei (CCN) from biofuel burning. We provide estimates of the CCN activity of biofuel burning aerosols by explicitly modeling plume dynamics (coagulation, condensation, chemical reactions, and dilution) in a young biofuel burning plume from emission until plume exit, defined here as the condition when the plume reaches ambient temperature and specific humidity through entrainment. We found that aerosol-scale dynamics affect CCNmore » activity only during the first few seconds of evolution, after which the CCN efficiency reaches a constant value. Homogenizing factors in a plume are co-emission of semi-volatile organic compounds (SVOCs) or emission at small particle sizes; SVOC co-emission can be the main factor determining plume-exit CCN for hydrophobic or small particles. Coagulation limits emission of CCN to about 10 16 per kilogram of fuel. Depending on emission factor, particle size, and composition, some of these particles may not activate at low supersaturation ( s sat). Hygroscopic Aitken-mode particles can contribute to CCN through self-coagulation but have a small effect on the CCN activity of accumulation-mode particles, regardless of composition differences. Simple models (monodisperse coagulation and average hygroscopicity) can be used to estimate plume-exit CCN within about 20 % if particles are unimodal and have homogeneous composition, or when particles are emitted in the Aitken mode even if they are not homogeneous. On the other hand, if externally mixed particles are emitted in the accumulation mode without SVOCs, an average hygroscopicity overestimates emitted CCN by up to a factor of 2. This work has identified conditions under which particle populations become more homogeneous during plume processes. This homogenizing effect requires the components to be truly co-emitted, rather than sequentially emitted.« less

Collocated observations of cloud condensation nuclei, particle size distributions, and chemical composition

PubMed Central

Schmale, Julia; Henning, Silvia; Henzing, Bas; Keskinen, Helmi; Sellegri, Karine; Ovadnevaite, Jurgita; Bougiatioti, Aikaterini; Kalivitis, Nikos; Stavroulas, Iasonas; Jefferson, Anne; Park, Minsu; Schlag, Patrick; Kristensson, Adam; Iwamoto, Yoko; Pringle, Kirsty; Reddington, Carly; Aalto, Pasi; Äijälä, Mikko; Baltensperger, Urs; Bialek, Jakub; Birmili, Wolfram; Bukowiecki, Nicolas; Ehn, Mikael; Fjæraa, Ann Mari; Fiebig, Markus; Frank, Göran; Fröhlich, Roman; Frumau, Arnoud; Furuya, Masaki; Hammer, Emanuel; Heikkinen, Liine; Herrmann, Erik; Holzinger, Rupert; Hyono, Hiroyuki; Kanakidou, Maria; Kiendler-Scharr, Astrid; Kinouchi, Kento; Kos, Gerard; Kulmala, Markku; Mihalopoulos, Nikolaos; Motos, Ghislain; Nenes, Athanasios; O’Dowd, Colin; Paramonov, Mikhail; Petäjä, Tuukka; Picard, David; Poulain, Laurent; Prévôt, André Stephan Henry; Slowik, Jay; Sonntag, Andre; Swietlicki, Erik; Svenningsson, Birgitta; Tsurumaru, Hiroshi; Wiedensohler, Alfred; Wittbom, Cerina; Ogren, John A.; Matsuki, Atsushi; Yum, Seong Soo; Myhre, Cathrine Lund; Carslaw, Ken; Stratmann, Frank; Gysel, Martin

2017-01-01

Cloud condensation nuclei (CCN) number concentrations alongside with submicrometer particle number size distributions and particle chemical composition have been measured at atmospheric observatories of the Aerosols, Clouds, and Trace gases Research InfraStructure (ACTRIS) as well as other international sites over multiple years. Here, harmonized data records from 11 observatories are summarized, spanning 98,677 instrument hours for CCN data, 157,880 for particle number size distributions, and 70,817 for chemical composition data. The observatories represent nine different environments, e.g., Arctic, Atlantic, Pacific and Mediterranean maritime, boreal forest, or high alpine atmospheric conditions. This is a unique collection of aerosol particle properties most relevant for studying aerosol-cloud interactions which constitute the largest uncertainty in anthropogenic radiative forcing of the climate. The dataset is appropriate for comprehensive aerosol characterization (e.g., closure studies of CCN), model-measurement intercomparison and satellite retrieval method evaluation, among others. Data have been acquired and processed following international recommendations for quality assurance and have undergone multiple stages of quality assessment. PMID:28291234

Collocated observations of cloud condensation nuclei, particle size distributions, and chemical composition

NASA Astrophysics Data System (ADS)

Schmale, Julia; Henning, Silvia; Henzing, Bas; Keskinen, Helmi; Sellegri, Karine; Ovadnevaite, Jurgita; Bougiatioti, Aikaterini; Kalivitis, Nikos; Stavroulas, Iasonas; Jefferson, Anne; Park, Minsu; Schlag, Patrick; Kristensson, Adam; Iwamoto, Yoko; Pringle, Kirsty; Reddington, Carly; Aalto, Pasi; Äijälä, Mikko; Baltensperger, Urs; Bialek, Jakub; Birmili, Wolfram; Bukowiecki, Nicolas; Ehn, Mikael; Fjæraa, Ann Mari; Fiebig, Markus; Frank, Göran; Fröhlich, Roman; Frumau, Arnoud; Furuya, Masaki; Hammer, Emanuel; Heikkinen, Liine; Herrmann, Erik; Holzinger, Rupert; Hyono, Hiroyuki; Kanakidou, Maria; Kiendler-Scharr, Astrid; Kinouchi, Kento; Kos, Gerard; Kulmala, Markku; Mihalopoulos, Nikolaos; Motos, Ghislain; Nenes, Athanasios; O'Dowd, Colin; Paramonov, Mikhail; Petäjä, Tuukka; Picard, David; Poulain, Laurent; Prévôt, André Stephan Henry; Slowik, Jay; Sonntag, Andre; Swietlicki, Erik; Svenningsson, Birgitta; Tsurumaru, Hiroshi; Wiedensohler, Alfred; Wittbom, Cerina; Ogren, John A.; Matsuki, Atsushi; Yum, Seong Soo; Myhre, Cathrine Lund; Carslaw, Ken; Stratmann, Frank; Gysel, Martin

2017-03-01

Cloud condensation nuclei (CCN) number concentrations alongside with submicrometer particle number size distributions and particle chemical composition have been measured at atmospheric observatories of the Aerosols, Clouds, and Trace gases Research InfraStructure (ACTRIS) as well as other international sites over multiple years. Here, harmonized data records from 11 observatories are summarized, spanning 98,677 instrument hours for CCN data, 157,880 for particle number size distributions, and 70,817 for chemical composition data. The observatories represent nine different environments, e.g., Arctic, Atlantic, Pacific and Mediterranean maritime, boreal forest, or high alpine atmospheric conditions. This is a unique collection of aerosol particle properties most relevant for studying aerosol-cloud interactions which constitute the largest uncertainty in anthropogenic radiative forcing of the climate. The dataset is appropriate for comprehensive aerosol characterization (e.g., closure studies of CCN), model-measurement intercomparison and satellite retrieval method evaluation, among others. Data have been acquired and processed following international recommendations for quality assurance and have undergone multiple stages of quality assessment.

Surfactants from the gas phase may promote cloud droplet formation.

PubMed

Sareen, Neha; Schwier, Allison N; Lathem, Terry L; Nenes, Athanasios; McNeill, V Faye

2013-02-19

Clouds, a key component of the climate system, form when water vapor condenses upon atmospheric particulates termed cloud condensation nuclei (CCN). Variations in CCN concentrations can profoundly impact cloud properties, with important effects on local and global climate. Organic matter constitutes a significant fraction of tropospheric aerosol mass, and can influence CCN activity by depressing surface tension, contributing solute, and influencing droplet activation kinetics by forming a barrier to water uptake. We present direct evidence that two ubiquitous atmospheric trace gases, methylglyoxal (MG) and acetaldehyde, known to be surface-active, can enhance aerosol CCN activity upon uptake. This effect is demonstrated by exposing acidified ammonium sulfate particles to 250 parts per billion (ppb) or 8 ppb gas-phase MG and/or acetaldehyde in an aerosol reaction chamber for up to 5 h. For the more atmospherically relevant experiments, i.e., the 8-ppb organic precursor concentrations, significant enhancements in CCN activity, up to 7.5% reduction in critical dry diameter for activation, are observed over a timescale of hours, without any detectable limitation in activation kinetics. This reduction in critical diameter enhances the apparent particle hygroscopicity up to 26%, which for ambient aerosol would lead to cloud droplet number concentration increases of 8-10% on average. The observed enhancements exceed what would be expected based on Köhler theory and bulk properties. Therefore, the effect may be attributed to the adsorption of MG and acetaldehyde to the gas-aerosol interface, leading to surface tension depression of the aerosol. We conclude that gas-phase surfactants may enhance CCN activity in the atmosphere.

Corona discharge induced snow formation in a cloud chamber.

PubMed

Ju, Jingjing; Wang, Tie-Jun; Li, Ruxin; Du, Shengzhe; Sun, Haiyi; Liu, Yonghong; Tian, Ye; Bai, Yafeng; Liu, Yaoxiang; Chen, Na; Wang, Jingwei; Wang, Cheng; Liu, Jiansheng; Chin, S L; Xu, Zhizhan

2017-09-18

Artificial rainmaking is in strong demand especially in arid regions. Traditional methods of seeding various Cloud Condensation Nuclei (CCN) into the clouds are costly and not environment friendly. Possible solutions based on ionization were proposed more than 100 years ago but there is still a lack of convincing verification or evidence. In this report, we demonstrated for the first time the condensation and precipitation (or snowfall) induced by a corona discharge inside a cloud chamber. Ionic wind was found to have played a more significant role than ions as extra CCN. In comparison with another newly emerging femtosecond laser filamentation ionization method, the snow precipitation induced by the corona discharge has about 4 orders of magnitude higher wall-plug efficiency under similar conditions.

North American and Asian aerosols over the eastern Pacific Ocean and their role in regulating cloud condensation nuclei

NASA Astrophysics Data System (ADS)

Roberts, G.; Mauger, G.; Hadley, O.; Ramanathan, V.

2006-07-01

Measurements of aerosol and cloud properties in the Eastern Pacific Ocean were taken during an airborne experiment on the University of Wyoming's King Air during April 2004 as part of the Cloud Indirect Forcing Experiment (CIFEX). We observed a wide variety of aerosols, including those of long-range transport from Asia, clean marine boundary layer, and North American emissions. These aerosols, classified by their size distribution and history, were found in stratified layers between 500 to 7500 m above sea level and thicknesses from 100 to 3000 m. A comparison of the aerosol size distributions to measurements of cloud condensation nuclei (CCN) provides insight to the CCN activity of the different aerosol types. The overall ratio of measured to predicted CCN concentration (NCCN) is 0.56 ± 0.41 with a relationship of NCCN,measured = NCCN,predicted0.846±0.002 for 23 research flights and 1884 comparisons. Such a relationship does not accurately describe a CCN closure; however, it is consistent with our measurements that high CCN concentrations are more influenced by anthropogenic sources, which are less CCN active. While other CCN closures have obtained results closer to the expected 1:1 relationship, the different aerosol types (and presumably differences in aerosol chemistry) are responsible for the discrepancy. The measured NCCN at 0.3% supersaturation (Sc) ranged from 20 cm-3 (pristine) to 350 cm-3 (anthropogenic) with an average of 106 ± 54 cm-3 over the experiment. The inferred supersaturation in the clouds sampled during this experiment is ˜0.3%. CCN concentrations of cloud-processed aerosol were well predicted using an ammonium sulfate approximation for Sc ≤ 0.4%. Predicted NCCN for other aerosol types (i.e., Asian and North American aerosols) were high compared to measured values indicating a less CCN active aerosol. This study highlights the importance of chemical effects on CCN measurements and introduces a CCN activation index as a method of classifying the efficiency of an aerosol to serve as CCN relative to an ammonium sulfate particle. This index ranged from close to unity for cloud processed aerosols to as low as 0.31 for aged aerosols transported from Asia. We also compare the performance of two CCN instruments (static thermal diffusion chamber and streamwise continuous flow chamber) on a 45 minute level leg where we observe an aged layer and a nucleation event. More than 50% of the aged aerosol served as CCN at 0.2% Sc, primarily owing to their large size, while CCN concentrations during the nucleation event were close to 0 cm-3. CCN concentrations from both instruments agreed within instrument errors; however, the continuous flow chamber effectively captured the rapid transition in aerosol properties.

Process-model simulations of cloud albedo enhancement by aerosols in the Arctic.

PubMed

Kravitz, Ben; Wang, Hailong; Rasch, Philip J; Morrison, Hugh; Solomon, Amy B

2014-12-28

A cloud-resolving model is used to simulate the effectiveness of Arctic marine cloud brightening via injection of cloud condensation nuclei (CCN), either through geoengineering or other increased sources of Arctic aerosols. An updated cloud microphysical scheme is employed, with prognostic CCN and cloud particle numbers in both liquid and mixed-phase marine low clouds. Injection of CCN into the marine boundary layer can delay the collapse of the boundary layer and increase low-cloud albedo. Albedo increases are stronger for pure liquid clouds than mixed-phase clouds. Liquid precipitation can be suppressed by CCN injection, whereas ice precipitation (snow) is affected less; thus, the effectiveness of brightening mixed-phase clouds is lower than for liquid-only clouds. CCN injection into a clean regime results in a greater albedo increase than injection into a polluted regime, consistent with current knowledge about aerosol-cloud interactions. Unlike previous studies investigating warm clouds, dynamical changes in circulation owing to precipitation changes are small. According to these results, which are dependent upon the representation of ice nucleation processes in the employed microphysical scheme, Arctic geoengineering is unlikely to be effective as the sole means of altering the global radiation budget but could have substantial local radiative effects. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Process-model simulations of cloud albedo enhancement by aerosols in the Arctic

PubMed Central

Kravitz, Ben; Wang, Hailong; Rasch, Philip J.; Morrison, Hugh; Solomon, Amy B.

2014-01-01

A cloud-resolving model is used to simulate the effectiveness of Arctic marine cloud brightening via injection of cloud condensation nuclei (CCN), either through geoengineering or other increased sources of Arctic aerosols. An updated cloud microphysical scheme is employed, with prognostic CCN and cloud particle numbers in both liquid and mixed-phase marine low clouds. Injection of CCN into the marine boundary layer can delay the collapse of the boundary layer and increase low-cloud albedo. Albedo increases are stronger for pure liquid clouds than mixed-phase clouds. Liquid precipitation can be suppressed by CCN injection, whereas ice precipitation (snow) is affected less; thus, the effectiveness of brightening mixed-phase clouds is lower than for liquid-only clouds. CCN injection into a clean regime results in a greater albedo increase than injection into a polluted regime, consistent with current knowledge about aerosol–cloud interactions. Unlike previous studies investigating warm clouds, dynamical changes in circulation owing to precipitation changes are small. According to these results, which are dependent upon the representation of ice nucleation processes in the employed microphysical scheme, Arctic geoengineering is unlikely to be effective as the sole means of altering the global radiation budget but could have substantial local radiative effects. PMID:25404677

Aerosol and cloud microphysics covariability in the northeast Pacific boundary layer estimated with ship-based and satellite remote sensing observations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Painemal, David; Chiu, J. -Y. Christine; Minnis, Patrick

We utilized ship measurements collected over the northeast Pacific along transects between the port of Los Angeles (33.7°N, 118.2°W) and Honolulu (21.3°N, 157.8°W) during May to August 2013 in order to investigate the covariability between marine low cloud microphysical and aerosol properties. Ship-based retrievals of cloud optical depth (τ) from a Sun photometer and liquid water path (LWP) from a microwave radiometer were combined to derive cloud droplet number concentration N d and compute a cloud-aerosol interaction (ACI) metric defined as ACI CCN=∂ ln(N d)/∂ ln(CCN), with CCN denoting the cloud condensation nuclei concentration measured at 0.4% (CCN 0.4) andmore » 0.3% (CCN 0.3) supersaturation. Analysis of CCN 0.4, accumulation mode aerosol concentration (N a), and extinction coefficient (σ ext) indicates that N a and σ ext can be used as CCN 0.4 proxies for estimating ACI. ACI CCN derived from 10 min averaged N d and CCN 0.4 and CCN 0.3, and CCN 0.4 regressions using N a and σ ext, produce high ACI CCN: near 1.0, that is, a fractional change in aerosols is associated with an equivalent fractional change in Nd. ACI CCN computed in deep boundary layers was small (ACI CCN=0.60), indicating that surface aerosol measurements inadequately represent the aerosol variability below clouds. Satellite cloud retrievals from MODerate-resolution Imaging Spectroradiometer and GOES-15 data were compared against ship-based retrievals and further analyzed to compute a satellite-based ACI CCN. We found that the satellite data correlated well with their ship-based counterparts with linear correlation coefficients equal to or greater than 0.78. Combined satellite Nd and ship-based CCN 0.4 and Na yielded a maximum ACI CCN=0.88–0.92, a value slightly less than the ship-based ACI CCN, but still consistent with aircraft-based studies in the eastern Pacific.« less

Aerosol and cloud microphysics covariability in the northeast Pacific boundary layer estimated with ship-based and satellite remote sensing observations

DOE PAGES

Painemal, David; Chiu, J. -Y. Christine; Minnis, Patrick; ...

2017-02-27

We utilized ship measurements collected over the northeast Pacific along transects between the port of Los Angeles (33.7°N, 118.2°W) and Honolulu (21.3°N, 157.8°W) during May to August 2013 in order to investigate the covariability between marine low cloud microphysical and aerosol properties. Ship-based retrievals of cloud optical depth (τ) from a Sun photometer and liquid water path (LWP) from a microwave radiometer were combined to derive cloud droplet number concentration N d and compute a cloud-aerosol interaction (ACI) metric defined as ACI CCN=∂ ln(N d)/∂ ln(CCN), with CCN denoting the cloud condensation nuclei concentration measured at 0.4% (CCN 0.4) andmore » 0.3% (CCN 0.3) supersaturation. Analysis of CCN 0.4, accumulation mode aerosol concentration (N a), and extinction coefficient (σ ext) indicates that N a and σ ext can be used as CCN 0.4 proxies for estimating ACI. ACI CCN derived from 10 min averaged N d and CCN 0.4 and CCN 0.3, and CCN 0.4 regressions using N a and σ ext, produce high ACI CCN: near 1.0, that is, a fractional change in aerosols is associated with an equivalent fractional change in Nd. ACI CCN computed in deep boundary layers was small (ACI CCN=0.60), indicating that surface aerosol measurements inadequately represent the aerosol variability below clouds. Satellite cloud retrievals from MODerate-resolution Imaging Spectroradiometer and GOES-15 data were compared against ship-based retrievals and further analyzed to compute a satellite-based ACI CCN. We found that the satellite data correlated well with their ship-based counterparts with linear correlation coefficients equal to or greater than 0.78. Combined satellite Nd and ship-based CCN 0.4 and Na yielded a maximum ACI CCN=0.88–0.92, a value slightly less than the ship-based ACI CCN, but still consistent with aircraft-based studies in the eastern Pacific.« less

Effect of the secondary organic aerosol coatings on black carbon water uptake, cloud condensation nuclei activity, and particle collapse

EPA Science Inventory

The ability of black carbon aerosols to absorb water and act as a cloud condensation nuclei (CCN) directly controls their lifetime in the atmosphere as well as their impact on cloud formation, thus impacting the earth’s climate. Black carbon emitted from most combustion pro...

Prediction of cloud condensation nuclei activity for organic compounds using functional group contribution methods

DOE PAGES

Petters, M. D.; Kreidenweis, S. M.; Ziemann, P. J.

2016-01-19

A wealth of recent laboratory and field experiments demonstrate that organic aerosol composition evolves with time in the atmosphere, leading to changes in the influence of the organic fraction to cloud condensation nuclei (CCN) spectra. There is a need for tools that can realistically represent the evolution of CCN activity to better predict indirect effects of organic aerosol on clouds and climate. This work describes a model to predict the CCN activity of organic compounds from functional group composition. Following previous methods in the literature, we test the ability of semi-empirical group contribution methods in Kohler theory to predict themore » effective hygroscopicity parameter, kappa. However, in our approach we also account for liquid–liquid phase boundaries to simulate phase-limited activation behavior. Model evaluation against a selected database of published laboratory measurements demonstrates that kappa can be predicted within a factor of 2. Simulation of homologous series is used to identify the relative effectiveness of different functional groups in increasing the CCN activity of weakly functionalized organic compounds. Hydroxyl, carboxyl, aldehyde, hydroperoxide, carbonyl, and ether moieties promote CCN activity while methylene and nitrate moieties inhibit CCN activity. Furthermore, the model can be incorporated into scale-bridging test beds such as the Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A) to evaluate the evolution of kappa for a complex mix of organic compounds and to develop suitable parameterizations of CCN evolution for larger-scale models.« less

Relations Between Cloud Condensation Nuclei And Aerosol Optical Properties Relevant to Remote Sensing: Airborne Measurements in Biomass Burning, Pollution and Dust Aerosol Over North America

NASA Astrophysics Data System (ADS)

Shinozuka, Y.; Clarke, A.; Howell, S.; Kapustin, V.; McNaughton, C.; Zhou, J.; Decarlo, P.; Jimenez, J.; Roberts, G.; Tomlinson, J.; Collins, D.

2008-12-01

Remote sensing of the concentration of cloud condensation nuclei (CCN) would help investigate the indirect effect of tropospheric aerosols on clouds and climate. In order to assess its feasibility, this paper evaluates the spectral-based retrieval technique for aerosol number and seeks one for aerosol solubility, using in-situ aircraft measurements of aerosol size distribution, chemical composition, hygroscopicity, CCN activity and optical properties. Our statistical analysis reveals that the CCN concentration over Mexico can be optically determined to a relative error of <20%, smaller than that for the mainland US and the surrounding oceans (~a factor of 2). Mexico's advantage is four-fold. Firstly, many particles originating from the lightly regulated industrial combustion and biomass burning are large enough to significantly affect light extinction, elevating the correlation between extinction and CCN number in absence of substantial dust. Secondly, the generally low ambient humidity near the major aerosol sources limits the error in the estimated response of particle extinction to humidity changes. Thirdly, because many CCN contain black carbon, light absorption also provides a measure of the CCN concentration. Fourthly, the organic fraction of volatile mass of submicron particles (OMF) is anti-correlated with the wavelength dependence of extinction due to preferential anion uptake by coarse dust, which provides a potential tool for remote-sensing OMF and the particle solubility.

In situ measurements of ship tracks

NASA Technical Reports Server (NTRS)

Radke, Lawrence F.; Lyons, Jamie H.; Hobbs, Peter V.; Coakley, James E.

1990-01-01

It has long been known that cloud droplet concentrations are strongly influenced by cloud condensation nuclei (CCN) and that anthropogenic sources of pollution can affect CCN concentrations. More recently it has been suggested that CCN may play an important role in climate through their effect on cloud albedo. A interesting example of the effect of anthropogenic CCN on cloud albedo is the so-called 'ship track' phenomenon. Ship tracks were first observed in satellite imagery when the ship's emissions were evidently needed for the formation of a visible cloud. However, they appear more frequently in satellite imagery as modifications to existing stratus and stratocumulus clouds. The tracks are seen most clearly in satellite imagery by comparing the radiance at 3.7 microns with that at 0.63 and 11 microns. To account for the observed change in radiance, droplet concentrations must be high, and the mean size of the droplets small, in ship tracks. Researchers describe what they believe to be the first in situ measurements in what appears to have been a ship track.

Cloud condensation nucleus counter by impactor sampling technique

NASA Technical Reports Server (NTRS)

Ohtake, T.

1981-01-01

Unlike typical CCN counters, this device counts the numbers of water droplets condensed on aerosol particles sampled on a microcover glass at various different relative humidities. The relative humidities ranged from 75 percent to a calculated value of 110 percent. A schematic of the apparatus is shown. The individual CCN can be identified in an optical micrograph and scanning electron micrograph and may be inspected for their chemical composition later.

Dimethylsulfide/cloud condensation nuclei/climate system - Relevant size-resolved measurements of the chemical and physical properties of atmospheric aerosol particles

NASA Technical Reports Server (NTRS)

Quinn, P. K.; Covert, D. S.; Bates, T. S.; Kapustin, V. N.; Ramsey-Bell, D. C.; Mcinnes, L. M.

1993-01-01

The mass and number relationships occurring within the atmospheric dimethylsulfide/cloud condensation nuclei (CCN)/climate system, using simultaneous measurements of particulate phase mass size distributions of nss SO4(2-), methanesulfonic acid (MSA), and NH4(+); number size distributions of particles having diameters between 0.02 and 9.6 microns; CCN concentrations at a supersaturation of 0.3 percent; relative humidity; and temperature, obtained for the northeastern Pacific Ocean in April and May 1991. Based on these measurements, particulate nss SO4(2-), MSA, and NH4(+) mass appeared to be correlated with both particle effective surface area and number in the accumulation mode size range (0.16 to 0.5 micron). No correlations were found in the size range below 0.16 micron. A correlation was also found between nss SO4(2-) mass and the CCN number concentration, such that a doubling of the SO4(2-) mass corresponded to a 40 percent increase in the CCN number concentration. However, no correlation was found between MSA mass and CCN concentration.

A physically-based approach of treating dust-water cloud interactions in climate models

NASA Astrophysics Data System (ADS)

Kumar, P.; Karydis, V.; Barahona, D.; Sokolik, I. N.; Nenes, A.

2011-12-01

All aerosol-cloud-climate assessment studies to date assume that the ability of dust (and other insoluble species) to act as a Cloud Condensation Nuclei (CCN) is determined solely by their dry size and amount of soluble material. Recent evidence however clearly shows that dust can act as efficient CCN (even if lacking appreciable amounts of soluble material) through adsorption of water vapor onto the surface of the particle. This "inherent" CCN activity is augmented as the dust accumulates soluble material through atmospheric aging. A comprehensive treatment of dust-cloud interactions therefore requires including both of these sources of CCN activity in atmospheric models. This study presents a "unified" theory of CCN activity that considers both effects of adsorption and solute. The theory is corroborated and constrained with experiments of CCN activity of mineral aerosols generated from clays, calcite, quartz, dry lake beds and desert soil samples from Northern Africa, East Asia/China, and Northern America. The unified activation theory then is included within the mechanistic droplet activation parameterization of Kumar et al. (2009) (including the giant CCN correction of Barahona et al., 2010), for a comprehensive treatment of dust impacts on global CCN and cloud droplet number. The parameterization is demonstrated with the NASA Global Modeling Initiative (GMI) Chemical Transport Model using wind fields computed with the Goddard Institute for Space Studies (GISS) general circulation model. References Barahona, D. et al. (2010) Comprehensively Accounting for the Effect of Giant CCN in Cloud Activation Parameterizations, Atmos.Chem.Phys., 10, 2467-2473 Kumar, P., I.N. Sokolik, and A. Nenes (2009), Parameterization of cloud droplet formation for global and regional models: including adsorption activation from insoluble CCN, Atmos.Chem.Phys., 9, 2517- 2532

New particle formation and growth in biomass burning plumes: An important source of cloud condensation nuclei

NASA Astrophysics Data System (ADS)

Hennigan, Christopher J.; Westervelt, Daniel M.; Riipinen, Ilona; Engelhart, Gabriella J.; Lee, Taehyoung; Collett, Jeffrey L., Jr.; Pandis, Spyros N.; Adams, Peter J.; Robinson, Allen L.

2012-05-01

Experiments were performed in an environmental chamber to characterize the effects of photo-chemical aging on biomass burning emissions. Photo-oxidation of dilute exhaust from combustion of 12 different North American fuels induced significant new particle formation that increased the particle number concentration by a factor of four (median value). The production of secondary organic aerosol caused these new particles to grow rapidly, significantly enhancing cloud condensation nuclei (CCN) concentrations. Using inputs derived from these new data, global model simulations predict that nucleation in photo-chemically aging fire plumes produces dramatically higher CCN concentrations over widespread areas of the southern hemisphere during the dry, burning season (Sept.-Oct.), improving model predictions of surface CCN concentrations. The annual indirect forcing from CCN resulting from nucleation and growth in biomass burning plumes is predicted to be -0.2 W m-2, demonstrating that this effect has a significant impact on climate that has not been previously considered.

RACORO aerosol data processing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elisabeth Andrews

2011-10-31

The RACORO aerosol data (cloud condensation nuclei (CCN), condensation nuclei (CN) and aerosol size distributions) need further processing to be useful for model evaluation (e.g., GCM droplet nucleation parameterizations) and other investigations. These tasks include: (1) Identification and flagging of 'splash' contaminated Twin Otter aerosol data. (2) Calculation of actual supersaturation (SS) values in the two CCN columns flown on the Twin Otter. (3) Interpolation of CCN spectra from SGP and Twin Otter to 0.2% SS. (4) Process data for spatial variability studies. (5) Provide calculated light scattering from measured aerosol size distributions. Below we first briefly describe the measurementsmore » and then describe the results of several data processing tasks that which have been completed, paving the way for the scientific analyses for which the campaign was designed. The end result of this research will be several aerosol data sets which can be used to achieve some of the goals of the RACORO mission including the enhanced understanding of cloud-aerosol interactions and improved cloud simulations in climate models.« less

Aerosol and cloud microphysics covariability in the northeast Pacific boundary layer estimated with ship-based and satellite remote sensing observations: NE Pacific Aerosol-Cloud Interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Painemal, David; Chiu, J. -Y. Christine; Minnis, Patrick

Ship measurements collected over the northeast Pacific along transects between the port of Los Angeles (33.7°N, 118.2°W) and Honolulu (21.3°N, 157.8°W) during May to August 2013 were utilized to investigate the covariability between marine low cloud microphysical and aerosol properties. Ship-based retrievals of cloud optical depth (τ) from a Sun photometer and liquid water path (LWP) from a microwave radiometer were combined to derive cloud droplet number concentration Nd and compute a cloud-aerosol interaction (ACI) metric defined as ACICCN = ∂ ln(Nd)/∂ ln(CCN), with CCN denoting the cloud condensation nuclei concentration measured at 0.4% (CCN0.4) and 0.3% (CCN0.3) supersaturation. Analysismore » of CCN0.4, accumulation mode aerosol concentration (Na), and extinction coefficient (σext) indicates that Na and σext can be used as CCN0.4 proxies for estimating ACI. ACICCN derived from 10 min averaged Nd and CCN0.4 and CCN0.3, and CCN0.4 regressions using Na and σext, produce high ACICCN: near 1.0, that is, a fractional change in aerosols is associated with an equivalent fractional change in Nd. ACICCN computed in deep boundary layers was small (ACICCN = 0.60), indicating that surface aerosol measurements inadequately represent the aerosol variability below clouds. Satellite cloud retrievals from MODerate-resolution Imaging Spectroradiometer and GOES-15 data were compared against ship-based retrievals and further analyzed to compute a satellite-based ACICCN. Satellite data correlated well with their ship-based counterparts with linear correlation coefficients equal to or greater than 0.78. Combined satellite Nd and ship-based CCN0.4 and Na yielded a maximum ACICCN = 0.88–0.92, a value slightly less than the ship-based ACICCN, but still consistent with aircraft-based studies in the eastern Pacific.« less

Partially soluble organics as cloud condensation nuclei: Role of trace soluble and surface active species

NASA Astrophysics Data System (ADS)

Broekhuizen, K.; Kumar, P. Pradeep; Abbatt, J. P. D.

2004-01-01

The ability of partially soluble organic species to act as cloud condensation nuclei (CCN) has been studied. A Köhler model incorporating solute solubility and droplet surface tension describes the behavior of solid adipic and succinic acid particles, whereas solid azelaic acid activates much more efficiently that predicted. In addition, it was shown that trace levels of either sulfate or surface active species have a dramatic effect on the activation of adipic acid, a moderately soluble organic, as predicted by the full Köhler model. For internally mixed particles in the atmosphere, these effects will greatly enhance the role of organic aerosols as CCN.

Airborne cloud condensation nuclei measurements during the 2006 Texas Air Quality Study

NASA Astrophysics Data System (ADS)

Asa-Awuku, Akua; Moore, Richard H.; Nenes, Athanasios; Bahreini, Roya; Holloway, John S.; Brock, Charles A.; Middlebrook, Ann M.; Ryerson, Thomas B.; Jimenez, Jose L.; Decarlo, Peter F.; Hecobian, Arsineh; Weber, Rodney J.; Stickel, Robert; Tanner, Dave J.; Huey, Lewis G.

2011-06-01

Airborne measurements of aerosol and cloud condensation nuclei (CCN) were conducted aboard the National Oceanic and Atmospheric Administration WP-3D platform during the 2006 Texas Air Quality Study/Gulf of Mexico Atmospheric Composition and Climate Study (TexAQS/GoMACCS). The measurements were conducted in regions influenced by industrial and urban sources. Observations show significant local variability of CCN activity (CCN/CN from 0.1 to 0.5 at s = 0.43%), while variability is less significant across regional scales (˜100 km × 100 km; CCN/CN is ˜0.1 at s = 0.43%). CCN activity can increase with increasing plume age and oxygenated organic fraction. CCN measurements are compared to predictions for a number of mixing state and composition assumptions. Mixing state assumptions that assumed internally mixed aerosol predict CCN concentrations well. Assuming organics are as hygroscopic as ammonium sulfate consistently overpredicted CCN concentrations. On average, the water-soluble organic carbon (WSOC) fraction is 60 ± 14% of the organic aerosol. We show that CCN closure can be significantly improved by incorporating knowledge of the WSOC fraction with a prescribed organic hygroscopicity parameter (κ = 0.16 or effective κ ˜ 0.3). This implies that the hygroscopicity of organic mass is primarily a function of the WSOC fraction. The overall aerosol hygroscopicity parameter varies between 0.08 and 0.88. Furthermore, droplet activation kinetics are variable and 60% of particles are smaller than the size characteristic of rapid droplet growth.

Cloud condensation nuclei closure study on summer arctic aerosol

NASA Astrophysics Data System (ADS)

Martin, M.; Chang, R. Y.-W.; Sierau, B.; Sjogren, S.; Swietlicki, E.; Abbatt, J. P. D.; Leck, C.; Lohmann, U.

2011-03-01

We present an aerosol - cloud condensation nuclei CCN) closure study on summer high Arctic aerosol based on measurements that were carried out in summer 2008 during the Arctic Summer Cloud Ocean Study (ASCOS) on board the Swedish ice breaker Oden. The data presented here were collected during a three-week time period in the pack ice (>85° N) when the icebreaker Oden was moored to an ice floe and drifted passively during the most biological active period into autumn freeze up conditions. CCN number concentrations were obtained using two CCN counters measuring at different supersaturations. The directly measured CCN number concentration is then compared with a CCN number concentration calculated using both bulk aerosol mass composition data from an aerosol mass spectrometer and aerosol number size distributions obtained from a differential mobility particle sizer, assuming κ-Köhler theory and an internally mixed aerosol. For the two highest measured supersaturations, 0.73 and 0.41%, closure could not be achieved with the investigated settings concerning hygroscopicity and density. The calculated CCN number concentration was always higher than the measured one. One possible explanation is that the smaller particles that activate at these supersaturations have a relative larger insoluble organic mass fraction and thus are less good CCN than the larger particles. At 0.20, 0.15 and 0.10% supersaturation, the measured CCN number can be represented with different parameters for the hygroscopicity and density of the particles. For the best agreement of the calculated CCNnumber concentration with the measured one the organic fraction of the aerosol needs to be nearly insoluble (қorg=0.02). However, this is not unambigious and қorg=0.2 is found as an upper limit at 0.1% supersaturation.

Vertical microphysical profiles of convective clouds as a tool for obtaining aerosol cloud-mediated climate forcings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rosenfeld, Daniel

Quantifying the aerosol/cloud-mediated radiative effect at a global scale requires simultaneous satellite retrievals of cloud condensation nuclei (CCN) concentrations and cloud base updraft velocities (Wb). Hitherto, the inability to do so has been a major cause of high uncertainty regarding anthropogenic aerosol/cloud-mediated radiative forcing. This can be addressed by the emerging capability of estimating CCN and Wb of boundary layer convective clouds from an operational polar orbiting weather satellite. Our methodology uses such clouds as an effective analog for CCN chambers. The cloud base supersaturation (S) is determined by Wb and the satellite-retrieved cloud base drop concentrations (Ndb), which ismore » the same as CCN(S). Developing and validating this methodology was possible thanks to the ASR/ARM measurements of CCN and vertical updraft profiles. Validation against ground-based CCN instruments at the ARM sites in Oklahoma, Manaus, and onboard a ship in the northeast Pacific showed a retrieval accuracy of ±25% to ±30% for individual satellite overpasses. The methodology is presently limited to boundary layer not raining convective clouds of at least 1 km depth that are not obscured by upper layer clouds, including semitransparent cirrus. The limitation for small solar backscattering angles of <25º restricts the satellite coverage to ~25% of the world area in a single day. This methodology will likely allow overcoming the challenge of quantifying the aerosol indirect effect and facilitate a substantial reduction of the uncertainty in anthropogenic climate forcing.« less

Role of molecular size in cloud droplet activation

NASA Astrophysics Data System (ADS)

Petters, M. D.; Kreidenweis, S. M.; Prenni, A. J.; Sullivan, R. C.; Carrico, C. M.; Koehler, K. A.; Ziemann, P. J.

2009-11-01

We examine the observed relationships between molar volume (the ratio of molar mass and density) and cloud condensation nuclei (CCN) activity for sufficiently soluble organic compounds found in atmospheric particulate matter. Our data compilation includes new CCN data for certain carbohydrates and oligoethylene glycols, as well as published data for organic compounds. We compare predictions of CCN activity using water activities based on Raoult's law and Flory-Huggins theory to observations. The Flory-Huggins water activity expression, with an assumed surface tension of pure water, generally predicts CCN activity within a factor of two over the full range of molar volumes considered. CCN activity is only weakly dependent on molar volume for values exceeding 600 cm3 mol-1, and the diminishing sensitivity to molar volume, combined with the significant scatter in the data, limits the accuracy with which molar volume can be inferred from CCN measurements.

Aerosol properties and their influences on surface cloud condensation nuclei during CAP-MBL and MC3E

NASA Astrophysics Data System (ADS)

Logan, T.; Dong, X.; Xi, B.

2016-12-01

Aerosol particles are of particular importance because of their influences on cloud development and precipitation processes over land and ocean. Aerosol physical and chemical properties and their ability to activate as cloud condensation nuclei (CCN) as well as influence CCN number concentration (NCCN) during the 2011 Midlatitude Continental Convective Clouds Experiment (MC3E) over the Southern Great Plains (SGP) region and the 2009-2010 Clouds, Aerosol, and Precipitation in the Marine Boundary Layer (CAP-MBL) over the Azores are presented in this study. Both regions periodically observe increases in NCCN when sulfate pollution and biomass burning smoke are present but over ocean, mineral dust diminishes NCCN. During clean conditions over the ocean, sea salt is the main contributor to CCN production, and strong (weak) surface winds and turbulent conditions can enhance (diminish) NCCN. Over the SGP, there were moderate to high correlations (R > 0.5) between increased magnitudes of aerosol loading (ssp), NCCN, chemical species, and PWV suggesting a shared common transport mechanism via the Gulf of Mexico further indicating the strong dependence on air mass type (e.g., marine vs. continental). Further investigations will greatly help to understand the seasonal influences of air masses on aerosol, NCCN, and cloud properties.

Measurements of cloud condensation nuclei activity and droplet activation kinetics of fresh unprocessed regional dust samples and minerals

NASA Astrophysics Data System (ADS)

Kumar, P.; Sokolik, I. N.; Nenes, A.

2011-04-01

This study reports laboratory measurements of cloud condensation nuclei (CCN) activity and droplet activation kinetics of aerosols dry generated from clays, calcite, quartz, and desert soil samples from Northern Africa, East Asia/China, and Northern America. Based on the observed dependence of critical supersaturation, sc, with particle dry diameter, Ddry, we found that FHH (Frenkel, Halsey and Hill) adsorption activation theory is a far more suitable framework for describing fresh dust CCN activity than Köhler theory. One set of FHH parameters (AFHH ∼ 2.25 ± 0.75, BFHH ∼ 1.20 ± 0.10) can adequately reproduce the measured CCN activity for all species considered, and also explains the large range of hygroscopicities reported in the literature. Based on a threshold droplet growth analysis, mineral dust aerosols were found to display retarded activation kinetics compared to ammonium sulfate. Comprehensive simulations of mineral dust activation and growth in the CCN instrument suggest that this retardation is equivalent to a reduction of the water vapor uptake coefficient (relative to that for calibration ammonium sulfate aerosol) by 30-80%. These results suggest that dust particles do not require deliquescent material to act as CCN in the atmosphere.

Measurements of cloud condensation nuclei activity and droplet activation kinetics of fresh unprocessed regional dust samples and minerals

NASA Astrophysics Data System (ADS)

Kumar, P.; Sokolik, I. N.; Nenes, A.

2010-12-01

This study reports laboratory measurements of cloud condensation nuclei (CCN) activity and droplet activation kinetics of aerosols dry-generated from clays, calcite, quartz, and desert soil samples from Northern Africa, East Asia/China, and Northern America. Based on the observed dependence of critical supersaturation, sc, with particle dry diameter, Ddry, we find that FHH adsorption activation theory is a far more suitable framework for describing fresh dust CCN activity than Köhler theory. One set of FHH parameters (AFFH ~ 2.25 ± 0.75, BFFH ~ 1.20 ± 0.10) can adequately reproduce the measured CCN activity for all species considered, and also explains the large range of hygroscopicities reported in the literature. Based on threshold droplet growth analysis, mineral dust aerosols were found to display retarded activation kinetics compared to ammonium sulfate. Comprehensive simulations of mineral dust activation and growth in the CCN instrument suggest that this retardation is equivalent to a reduction of the water vapor uptake coefficient (relative to that for calibration ammonium sulfate aerosol) by 30-80%. These results suggest that dust particles do not require deliquescent material to act as CCN in the atmosphere.

Cloud Condensation Nuclei Measurements in Tropical Cyclones

NASA Technical Reports Server (NTRS)

Hudson, J. G.; Simpson, J.

2002-01-01

The first measurements of cloud condensation nuclei (CCN) within and around tropical cyclones were made with the Desert Research Institute (DRI) CCN spectrometer (Hudson 1909) from a NOAA P-3 Hurricane Hunter aircraft throughout the 2001 season. Two penetrations of the closed eye of Hurricane Erin off the northeast US coast on Sept. 10 showed concentrations consistently well in excess of 1000 per cubic cm at approximately 1.4% supersaturation. Simultaneous condensation nuclei (CN--total particle) concentrations were consistently well in excess of 2000 per cubic cm throughout these closed eye penetrations. These within eye measurements at 4 km altitude for exceeded CCN and CN measurements just outside of the storm at similar altitudes--300 and 600 per cubic cm respectively. These CCN and CN concentrations within this closed eye were far above concentrations in maritime air masses; they are characteristic of continental or polluted air masses. Although there was a possibility that Saharan duct may have gotten into this storm these sub tenth micrometer particles are much too small and much too numerous to be dust. Such high concentrations may have originated from European air pollution, which may have been transported by similar airflow patterns to those that carry Saharan dust across the Atlantic. These high concentrations may be a manifestation of descending air that brings higher concentrations that are often characteristic of the upper troposphere (Clarke and Kapustin 2002). Later in the month measurements in Humberto showed highly variable CCN and CN concentrations that ranged from lots than 5 per cubic cm to more than 1000 per Cubic cm over km scale distances within and around the open eye of this tropical storm/hurricane. These very low concentrations suggest strong cloud scavenging.

Deployment of ARM Aerial Facility Scanning Mobility Particle Sizer Field Campaign Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jian

2016-09-01

Atmospheric aerosols influence global climate by scattering and absorbing sunlight (direct effects) and by changing the microphysical structure, lifetime, and coverage of clouds (indirect effects). While it is widely accepted that aerosol indirect effects cool the Earth-atmosphere system by increasing cloud reflectivity and coverage, the magnitudes of the indirect effects are poorly quantified. One key aerosol property for understanding aerosol indirect effects is the ability of aerosol particles to form cloud droplets at atmospheric relevant supersaturations—i.e., cloud condensation Nuclei (CCN) activity. For particles consisting of typical atmospheric inorganic compounds, their CCN activity is well understood and can be effectively predictedmore » using Köhler theory based on physicochemical properties of the solute, such as its mass, molar volume, and activity coefficient. However, atmospheric aerosols often consist of hundreds of organic species, which can contribute ~20-90% to the total fine aerosol mass. Depending on their properties, organic species can significantly influence the ability of aerosol particles to act as CCN and form cloud droplets. This project focuses on the CCN activity of secondary organic aerosol (SOA) compounds formed from key biogenic volatile organic compounds (VOCs) under representative conditions, and the relationship between the hygroscopicity and composition of organic aerosols. The U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility Aerial Facility (AAF) scanning mobility particles sizer (SMPS) was deployed during a ~ 2-week intensive measurement campaign, taking place February 10-February 23, 2016 at the Pacific Northwest National Laboratory (PNNL) Environmental Simulation Chamber. The SMPS was operated with a CCN counter (CCNc). Aerosol particles were first classified by the differential mobility analyzer inside the SMPS; the classified aerosol will then be simultaneously characterized by a condensation particle counter (CPC) (part of the SMPS) and the CCNc.« less

Spatial Variability of CCN Sized Aerosol Particles

NASA Astrophysics Data System (ADS)

Asmi, A.; Väänänen, R.

2014-12-01

The computational limitations restrict the grid size used in GCM models, and for many cloud types they are too large when compared to the scale of the cloud formation processes. Several parameterizations for e.g. convective cloud formation exist, but information on spatial subgrid variation of the cloud condensation nuclei (CCNs) sized aerosol concentration is not known. We quantify this variation as a function of the spatial scale by using datasets from airborne aerosol measurement campaigns around the world including EUCAARI LONGREX, ATAR, INCA, INDOEX, CLAIRE, PEGASOS and several regional airborne campaigns in Finland. The typical shapes of the distributions are analyzed. When possible, we use information obtained by CCN counters. In some other cases, we use particle size distribution measured by for example SMPS to get approximated CCN concentration. Other instruments used include optical particle counters or condensational particle counters. When using the GCM models, the CCN concentration used for each the grid-box is often considered to be either flat, or as an arithmetic mean of the concentration inside the grid-box. However, the aircraft data shows that the concentration values are often lognormal distributed. This, combined with the subgrid variations in the land use and atmospheric properties, might cause that the aerosol-cloud interactions calculated by using mean values to vary significantly from the true effects both temporary and spatially. This, in turn, can cause non-linear bias into the GCMs. We calculate the CCN aerosol concentration distribution as a function of different spatial scales. The measurements allow us to study the variation of these distributions within from hundreds of meters up to hundreds of kilometers. This is used to quantify the potential error when mean values are used in GCMs.

Substantial Seasonal Contribution of Observed Biogenic Sulfate Particles to Cloud Condensation Nuclei.

PubMed

Sanchez, Kevin J; Chen, Chia-Li; Russell, Lynn M; Betha, Raghu; Liu, Jun; Price, Derek J; Massoli, Paola; Ziemba, Luke D; Crosbie, Ewan C; Moore, Richard H; Müller, Markus; Schiller, Sven A; Wisthaler, Armin; Lee, Alex K Y; Quinn, Patricia K; Bates, Timothy S; Porter, Jack; Bell, Thomas G; Saltzman, Eric S; Vaillancourt, Robert D; Behrenfeld, Mike J

2018-02-19

Biogenic sources contribute to cloud condensation nuclei (CCN) in the clean marine atmosphere, but few measurements exist to constrain climate model simulations of their importance. The chemical composition of individual atmospheric aerosol particles showed two types of sulfate-containing particles in clean marine air masses in addition to mass-based Estimated Salt particles. Both types of sulfate particles lack combustion tracers and correlate, for some conditions, to atmospheric or seawater dimethyl sulfide (DMS) concentrations, which means their source was largely biogenic. The first type is identified as New Sulfate because their large sulfate mass fraction (63% sulfate) and association with entrainment conditions means they could have formed by nucleation in the free troposphere. The second type is Added Sulfate particles (38% sulfate), because they are preexisting particles onto which additional sulfate condensed. New Sulfate particles accounted for 31% (7 cm -3 ) and 33% (36 cm -3 ) CCN at 0.1% supersaturation in late-autumn and late-spring, respectively, whereas sea spray provided 55% (13 cm -3 ) in late-autumn but only 4% (4 cm -3 ) in late-spring. Our results show a clear seasonal difference in the marine CCN budget, which illustrates how important phytoplankton-produced DMS emissions are for CCN in the North Atlantic.

Classifying organic materials by oxygen-to-carbon elemental ratio to predict the activation regime of Cloud Condensation Nuclei (CCN)

NASA Astrophysics Data System (ADS)

Kuwata, M.; Shao, W.; Lebouteiller, R.; Martin, S. T.

2013-05-01

The governing highly soluble, slightly soluble, or insoluble activation regime of organic compounds as cloud condensation nuclei (CCN) was examined as a function of oxygen-to-carbon elemental ratio (O : C). New data were collected for adipic, pimelic, suberic, azelaic, and pinonic acids. Secondary organic materials (SOMs) produced by α-pinene ozonolysis and isoprene photo-oxidation were also included in the analysis. The saturation concentrations C of the organic compounds in aqueous solutions served as the key parameter for delineating regimes of CCN activation, and the values of C were tightly correlated to the O : C ratios. The highly soluble, slightly soluble, and insoluble regimes of CCN activation were found to correspond to ranges of [O : C] > 0.6, 0.2 < [O : C] < 0.6, and [O : C] < 0.2, respectively. These classifications were evaluated against CCN activation data of isoprene-derived SOM (O : C = 0.69-0.72) and α-pinene-derived SOM (O : C = 0.38-0.48). Isoprene-derived SOM had highly soluble activation behavior, consistent with its high O : C ratio. For α-pinene-derived SOM, although CCN activation can be modeled as a highly soluble mechanism, this behavior was not predicted by the O : C ratio, for which a slightly soluble mechanism was anticipated. Complexity in chemical composition, resulting in continuous water uptake and the absence of a deliquescence transition that can thermodynamically limit CCN activation, might explain the difference in the behavior of α-pinene-derived SOM compared to that of pure organic compounds. The present results suggest that atmospheric particles dominated by hydrocarbon-like organic components do not activate (i.e., insoluble regime) whereas those dominated by oxygenated organic components activate (i.e., highly soluble regime) for typical atmospheric cloud life cycles.

An interfacial mechanism for cloud droplet formation on organic aerosols

DOE PAGES

Ruehl, C. R.; Davies, J. F.; Wilson, K. R.

2016-03-25

Accurate predictions of aerosol/cloud interactions require simple, physically accurate parameterizations of the cloud condensation nuclei (CCN) activity of aerosols. Current models assume that organic aerosol species contribute to CCN activity by lowering water activity. We measured droplet diameters at the point of CCN activation for particles composed of dicarboxylic acids or secondary organic aerosol and ammonium sulfate. Droplet activation diameters were 40 to 60% larger than predicted if the organic was assumed to be dissolved within the bulk droplet, suggesting that a new mechanism is needed to explain cloud droplet formation. A compressed film model explains how surface tension depressionmore » by interfacial organic molecules can alter the relationship between water vapor supersaturation and droplet size (i.e., the Köhler curve), leading to the larger diameters observed at activation.« less

An interfacial mechanism for cloud droplet formation on organic aerosols

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruehl, C. R.; Davies, J. F.; Wilson, K. R.

Accurate predictions of aerosol/cloud interactions require simple, physically accurate parameterizations of the cloud condensation nuclei (CCN) activity of aerosols. Current models assume that organic aerosol species contribute to CCN activity by lowering water activity. We measured droplet diameters at the point of CCN activation for particles composed of dicarboxylic acids or secondary organic aerosol and ammonium sulfate. Droplet activation diameters were 40 to 60% larger than predicted if the organic was assumed to be dissolved within the bulk droplet, suggesting that a new mechanism is needed to explain cloud droplet formation. A compressed film model explains how surface tension depressionmore » by interfacial organic molecules can alter the relationship between water vapor supersaturation and droplet size (i.e., the Köhler curve), leading to the larger diameters observed at activation.« less

An interfacial mechanism for cloud droplet formation on organic aerosols.

PubMed

Ruehl, Christopher R; Davies, James F; Wilson, Kevin R

2016-03-25

Accurate predictions of aerosol/cloud interactions require simple, physically accurate parameterizations of the cloud condensation nuclei (CCN) activity of aerosols. Current models assume that organic aerosol species contribute to CCN activity by lowering water activity. We measured droplet diameters at the point of CCN activation for particles composed of dicarboxylic acids or secondary organic aerosol and ammonium sulfate. Droplet activation diameters were 40 to 60% larger than predicted if the organic was assumed to be dissolved within the bulk droplet, suggesting that a new mechanism is needed to explain cloud droplet formation. A compressed film model explains how surface tension depression by interfacial organic molecules can alter the relationship between water vapor supersaturation and droplet size (i.e., the Köhler curve), leading to the larger diameters observed at activation. Copyright © 2016, American Association for the Advancement of Science.

Cloud condensation nuclei over the Bay of Bengal during the Indian summer monsoon

NASA Astrophysics Data System (ADS)

Chate, D. M.; Waghmare, R. T.; Jena, C. K.; Gopalakrishnan, V.; Murugavel, P.; Ghude, Sachin D.; Kulkarni, Rachana; Devara, P. C. S.

2018-02-01

The first measurements of cloud condensation nuclei (CCN) at five supersaturations were carried out onboard the research vessel "Sagar Kanya" (cruise SK-296) from the south to the head-bay of the Bay of Bengal as part of the Continental Tropical Convergence Zone (CTCZ) Project during the Indian summer monsoon of 2012. In this paper, we assess the diurnal variation in CCN distributions at supersaturations from 0.2% to 1% (in steps of 0.2%) and the power-law fit at supersaturation of 1%. The diurnal pattern shows peaks in CCN concentration (NCCN) at supersaturations from 0.2% to 1% between 0600 and 0700 LST (local standard time, UTC+0530), with relatively low concentrations between 1200 and 1400 LST, followed by a peak at around 1800 LST. The power-law fit for the CCN distribution at different supersaturation levels relates the empirical exponent ( k) of supersaturation (%) and the N CCN at a supersaturation of 1%. The N CCN at a supersaturation of 0.4% is observed to vary from 702 cm-3 to 1289 cm-3, with a mean of 961±161 cm-3 (95% confidence interval), representing the CCN activity of marine air masses. Whereas, the mean N CCN of 1628±193 cm-3 at a supersaturation of 1% is higher than anticipated for the marine background. When the number of CCN spectra is 1293, the value of k is 0.57±0.03 (99% confidence interval) and its probability distribution shows cumulative counts significant at k ≈ 0.55±0.25. The results are found to be better at representing the features of the marine environment (103 cm-3 and k ≈ 0.5) and useful for validating CCN closure studies for Indian sea regions.

Global variability of cloud condensation nuclei concentrations

NASA Astrophysics Data System (ADS)

Makkonen, Risto; Krüger, Olaf

2017-04-01

Atmospheric aerosols can influence cloud optical and dynamical processes by acting as cloud condensation nuclei (CCN). Globally, these indirect aerosol effects are significant to the radiative budget as well as a source of high uncertainty in anthropogenic radiative forcing. While historically many global climate models have fixed CCN concentrations to a certain level, most state-of-the-art models calculate aerosol-cloud interactions with sophisticated methodologies based on interactively simulated aerosol size distributions. However, due to scarcity of atmospheric observations simulated global CCN concentrations remain poorly constrained. Here we assess global CCN variability with a climate model, and attribute potential trends during 2000-2010 to changes in emissions and meteorological fields. Here we have used ECHAM5.5-HAM2 with model M7 microphysical aerosol model. The model has been upgraded with a secondary organic aerosol (SOA) scheme including ELVOCs. Dust and sea salt emissions are calculated online, based on wind speed and hydrology. Each experiment is 11 years, analysed after a 6-month spin-up period. The MODIS CCN product (Terra platform) is used to evaluate model performance throughout 2000-2010. While optical remote observation of CCN column includes several deficiencies, the products serves as a proxy for changes during the simulation period. In our analysis we utilize the observed and simulated vertical column integrated CCN concentration, and limit our analysis only over marine regions. Simulated annual CCN column densities reach 2ṡ108 cm-2 near strong source regions in central Africa, Arabian Sea, Bay of Bengal and China sea. The spatial concentration gradient in CCN(0.2%) is steep, and column densities drop to <50% a few hundred kilometers away from the coasts. While the spatial distribution of CCN at 0.2% supersaturation is closer to that of MODIS proxy, as opposed to 1.0% supersaturation, the overall column integrated CCN are too low. Still, we can compare the relative response of CCN to emission and meteorological variability. Most evident pattern of high temporal correlation is found over North Atlantic ocean, extending throughout Europe and up to Gulf of Mexico. All of these regions show a generally decreasing trend throughout the decade in control simulations and MODIS CCN, and the simulations including the emission trends clearly improve the simulations with climatological emissions. In regions where the observed intra-annual cycle correlates well with sea-spray emissions, the long-term annual correlation usually remains poor. This could indicate that the model is unable to capture the natural variability in marine aerosol emissions.

Evidence of Chemical Cloud Processing from In Situ Measurements in the Polluted Marine Environment

NASA Astrophysics Data System (ADS)

Hudson, J. G.; Noble, S. R., Jr.

2017-12-01

Chemical cloud processing alters activated cloud condensation nuclei (CCN). Aqueous oxidation of trace gases dissolved within cloud droplets adds soluble material. As most cloud droplets evaporate, the residual material produces CCN that are larger and with a different hygroscopicity (κ). This improves the CCN, lowering the critical supersaturation (Sc), making it more easily activated. This process separates the processed (accumulation) and unprocessed (Aitken) modes creating bimodal CCN distributions (Hudson et al., 2015). Various measurements made during the MArine Stratus/stratocumulus Experiment (MASE), including CCN, exhibited aqueous processing signals. Particle size distributions; measured by a differential mobility analyzer; were compared with CCN distributions; measured by the Desert Research Institute CCN spectrometer; by converting size to Sc using κ to overlay concurrent distributions. By tuning each mode to the best agreement, κ for each mode is determined; processed κ (κp), unprocessed κ (κu). In MASE, 59% of bimodal distributions had different κ for the two modes indicating dominance of chemical processing via aqueous oxidation. This is consistent with Hudson et al. (2015). Figure 1A also indicates chemical processing with larger κp between 0.35-0.75. Processed CCN had an influx of soluble material from aqueous oxidation which increased κp versus κu. Above 0.75 κp is lower than κu (Fig. 1A). When κu is high and sulfate material is added, κp tends towards κ of the added material. Thus, κp is reduced by additional material that is less soluble than the original material. Chemistry measurements in MASE also indicate in-cloud aqueous oxidation (Fig. 1B and 1C). Higher fraction of CCN concentrations in the processed mode are also associated with larger amounts of sulfates (Fig. 1B, red) and nitrates (Fig. 1C, orange) while SO2 (Fig. 1B, black) and O3 (Fig. 1C, blue) have lower amounts. This larger amount of sulfate is at the expense of SO2, indicating aqueous oxidation within cloud as associated with larger concentrations in the processed mode. Thus, in situ measurements indicate that chemical cloud processing alters size, Sc and κ of activated CCN. Hudson et al. (2015), JGRA, 120, 3436-3452.

Cloud condensation nuclei activation of limited solubility organic aerosol

NASA Astrophysics Data System (ADS)

Huff Hartz, Kara E.; Tischuk, Joshua E.; Chan, Man Nin; Chan, Chak K.; Donahue, Neil M.; Pandis, Spyros N.

The cloud condensation nuclei (CCN) activation of 19 organic species with water solubilities ( Csat) ranging from 10 -4 to 10 2 g solute 100 g -1 H 2O was measured. The organic particles were generated by nebulization of an aqueous or an alcohol solution. Use of alcohols as solvents enables the measurement of low solubility, non-volatile organic CCN activity and reduces the likelihood of residual water in the aerosol. The activation diameter of organic species with very low solubility in water ( Csat<0.3 g 100 g -1 H 2O) is in agreement with Köhler theory using the bulk solubility (limited solubility case) of the organic in water. Many species, including 2-acetylbenzoic acid, aspartic acid, azelaic acid, glutamic acid, homophthalic acid, phthalic acid, cis-pinonic acid, and salicylic acid are highly CCN active in spite of their low solubility (0.3 g 100 g -1 H 2O< Csat<1 g 100 g -1 H 2O), and activate almost as if completely water soluble. The CCN activity of most species is reduced, if the particles are produced using non-aqueous solvents. The existence of the particles in a metastable state at low RH can explain the observed enhancement in CCN activity beyond the levels suggested by their solubility.

Measurements of cloud condensation nuclei activity and droplet activation kinetics of wet processed regional dust samples and minerals

NASA Astrophysics Data System (ADS)

Kumar, P.; Sokolik, I. N.; Nenes, A.

2011-04-01

This study reports laboratory measurements of particle size distributions, cloud condensation nuclei (CCN) activity, and droplet activation kinetics of wet generated aerosols from clays, calcite, quartz, and desert soil samples from Northern Africa, East Asia/China, and Northern America. The dependence of critical supersaturation, sc, on particle dry diameter, Ddry, is used to characterize particle-water interactions and assess the ability of Frenkel-Halsey-Hill adsorption activation theory (FHH-AT) and Köhler theory (KT) to describe the CCN activity of the considered samples. Regional dust samples produce unimodal size distributions with particle sizes as small as 40 nm, CCN activation consistent with KT, and exhibit hygroscopicity similar to inorganic salts. Clays and minerals produce a bimodal size distribution; the CCN activity of the smaller mode is consistent with KT, while the larger mode is less hydrophilic, follows activation by FHH-AT, and displays almost identical CCN activity to dry generated dust. Ion Chromatography (IC) analysis performed on regional dust samples indicates a soluble fraction that cannot explain the CCN activity of dry or wet generated dust. A mass balance and hygroscopicity closure suggests that the small amount of ions (of low solubility compounds like calcite) present in the dry dust dissolve in the aqueous suspension during the wet generation process and give rise to the observed small hygroscopic mode. Overall these results identify an artifact that may question the atmospheric relevance of dust CCN activity studies using the wet generation method. Based on a threshold droplet growth analysis, wet generated mineral aerosols display similar activation kinetics compared to ammonium sulfate calibration aerosol. Finally, a unified CCN activity framework that accounts for concurrent effects of solute and adsorption is developed to describe the CCN activity of aged or hygroscopic dusts.

Global synthesis of long-term cloud condensation nuclei observations

NASA Astrophysics Data System (ADS)

Schmale, Julia; Henning, Silvia; Stratmann, Frank; Henzing, Bas; Schlag, Patrick; Aalto, Pasi; Keskinen, Helmi; Sellegri, Karine; Ovadnevaite, Jurgita; Krüger, Mira; Jefferson, Anne; Whitehead, James; Carslaw, Ken; Yum, Seong Soo; Kristensson, Adam; Baltensperger, Urs; Gysel, Martin

2016-04-01

Cloud condensation nuclei (CCN) are aerosol particles with the ability to activate into droplets at a given super saturation and therefore influence the microphysical and optical properties of clouds. To predict cloud radiative properties understanding the spatial and temporal variability of CCN concentrations in different environments is important. However, currently, the effects of atmospheric particles on changes in cloud radiative forcing are still the largest contribution of uncertainty in climate forcing prediction (IPCC, 2013). Numerous intensive field campaigns have already explored detailed characteristics of CCN in many locations around the world. However, these rather short-term observations can generally not address seasonal or inter-annual variations and a comparison between campaign sites is difficult due to the higher influence of specific environmental circumstances on short-term measurements results. Here, we present results of more long-term CCN and aerosol number concentrations as well as size distribution data covering at least one full year between 2006 and 2014. The 12 locations include ACTRIS stations (http://www.actris.net/) in Europe, and further sites in North America, Brazil and Korea. The sites are located in different environments allowing for temporal and spatial characterization of CCN variability in different atmospheric regimes. Those include marine, remote-continental, boreal forest, rain forest, Arctic and monsoon-influenced environments, as well as boundary layer and free tropospheric conditions. The aerosol populations and their activation behavior show significant differences across the stations. While peak concentrations of CCN are observed in summer at the high altitude sites, in the Arctic the highest concentrations occur during the Haze period in spring. The rural-marine and rural-continental sites exhibit similar CCN concentration characteristics with a relatively flat annual cycle. At some stations, e.g. in the boreal environment, the annual cycle is more pronounced for higher SS. Geometric mean diameters of aerosol populations as well as the activation ratios on the basis of particles > 50 nm vary strongly among sites and throughout the seasons. Additionally, autocorrelation analysis is performed to investigate the persistence of variables over different timescales and to explore meaningful averaging periods for global modelling of CCN. In terms of CCN persistence, we find three different regimes: (1) CCN concentrations persist for a week or longer showing also seasonal patterns. (2) CCN concentrations persist for less than one week and there is little seasonal pattern. And (3) CCN concentrations are highly variable and do not persist longer than 2 days but show seasonal cycles. Several but not all sites show diurnal cycles. These different behaviors are influenced by environmental factors such as rainy seasons in the Amazon or Korea (monsoon) but also by anthropogenic pollution episodes such as during the Arctic Haze period.

Organic cloud condensation nuclei: the effect of phase, surface tension, trace soluble species, and oxidative processing on particle activation.

NASA Astrophysics Data System (ADS)

Broekhuizen, K. E.; Thornberry, T.; Abbatt, J. P.

2003-12-01

The ability of organic aerosols to act as cloud condensation nuclei (CCN) will be discussed. A variety of laboratory experiments will be presented which address several key questions concerning organic particle activation. Does the particle phase impact activation? How does surface tension play a role and can a trace amount of a surface active species impact activation? Does a trace amount of a highly soluble species impact the activation of organic particles of moderate to low solubility? Can the activation properties of organic aerosols be enhanced through oxidative processing? To systematically address these issues, the CCN activity of various diacids such as oxalic, malonic, succinic, adipic and azelaic acid have been studied, as well as the addition of trace amounts of nonanoic acid and ammonium sulfate to examine the roles of surface active and soluble species, respectively. The first examination of the role of oxidative processing on CCN activity has involved investigating the effect of ozone oxidation on the activity of oleic acid particles.

Optical properties and CCN activity of aerosols in a high-altitude Himalayan environment: Results from RAWEX-GVAX: CCN activity of aerosols over Himalayas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gogoi, Mukunda M.; Babu, S. Suresh; Jayachandran, V.

2015-03-27

The seasonality and mutual dependence of aerosol optical properties and cloud condensation nuclei (CCN) activity under varying meteorological conditions at the high-altitude Nainital site (~2 km) in the Indo-Gangetic Plains were examined using nearly year-round measurements (June 2011 to March 2012) at the Atmospheric Radiation Measurement (ARM) mobile facility as part of the RAWEX-GVAX experiment of the Indian Space Research Organization and the U.S. Department of Energy. The results from collocated measurements provided enhanced aerosol scattering and absorption coefficients, CCN concentrations and total condensation nuclei (CN) concentrations during the dry autumn and winter months. The CCN concentration (at a supersaturationmore » of 0.46) was higher during periods of high aerosol absorption (single-scattering albedo (SSA) < 0.80) than during periods of high aerosol scattering (SSA > 0.85), indicating that the aerosol composition seasonally changes and influences the CCN activity. The monthly mean CCN activation ratio (at a supersaturation of 0.46) was highest (> 0.7) in late autumn (November); this finding is attributed to the contribution of biomass-burning aerosols to CCN formation at high supersaturation conditions.« less

CHASER: An Innovative Satellite Mission Concept to Measure the Effects of Aerosols on Clouds and Climate

NASA Astrophysics Data System (ADS)

Renno, N.; Williams, E.; Rosenfeld, D.; Fischer, D.; Fischer, J.; Kremic, T.; Agrawal, A.; Andreae, M.; Bierbaum, R.; Blakeslee, R.; Boerner, A.; Bowles, N.; Christian, H.; Dunion, J.; Horvath, A.; Huang, X.; Khain, A.; Kinne, S.; Lemos, M.-C.; Penner, J.

2012-04-01

The formation of cloud droplets on aerosol particles, technically known as the activation of cloud condensation nuclei (CCN), is the fundamental process driving the interactions of aerosols with clouds and precipitation. Knowledge of these interactions is foundational to our understanding of weather and climate. The Intergovernmental Panel on Climate Change (IPCC) and the Decadal Survey (NRC 2007) indicate that the uncertainty in how clouds adjust to aerosol perturbations dominates the uncertainty in the overall quantification of the radiative forcing attributable to human activities. The Clouds, Hazards, and Aerosols Survey for Earth Researchers (CHASER) mission concept responds to the IPCC and Decadal Survey concerns by studying the activation of CCN and their interactions with clouds and storms. CHASER proposes to revolutionize our understanding of the interactions of aerosols with clouds by making the first global measurements of the fundamental physical entity linking them: activated cloud condensation nuclei. The CHASER mission was conceptualized to measure all quantities necessary for determining the interactions of aerosols with clouds and storms. Measurements by current satellites allow the determination of crude profiles of cloud particle size but not of the activated CCN that seed them. CHASER uses a new technique (Freud et al. 2011; Rosenfeld et al. 2012) and high-heritage instruments to produce the first global maps of activated CCN and the properties of the clouds associated with them. CHASER measures the CCN concentration and cloud thermodynamic forcing simultaneously, allowing their effects to be distinguished. Changes in the behavior of a group of weather systems in which only one of the quantities varies (a partial derivative of the intensity with the desirable quantity) allow the determination of each effect statistically. The high uncertainties of current climate predictions limit their much-needed use in decision-making. CHASER mitigates this problem by establishing a Data Application Center for conducting social science research focused on understanding the best ways to use, transfer, and communicate mission data to decision-makers. The CHASER Data Application Center supports the visions of the National Research Council and the Decadal Survey for an integrated program of observations from space that secures practical benefits for humankind by developing data products for assessing risks due to severe weather and climate change.

Cloud droplet activation through oxidation of organic aerosol influenced by temperature and particle phase state: CLOUD ACTIVATION BY AGED ORGANIC AEROSOL

DOE PAGES

Slade, Jonathan H.; Shiraiwa, Manabu; Arangio, Andrea; ...

2017-02-04

Chemical aging of organic aerosol (OA) through multiphase oxidation reactions can alter their cloud condensation nuclei (CCN) activity and hygroscopicity. However, the oxidation kinetics and OA reactivity depend strongly on the particle phase state, potentially influencing the hydrophobic-to-hydrophilic conversion rate of carbonaceous aerosol. Here, amorphous Suwannee River fulvic acid (SRFA) aerosol particles, a surrogate humic-like substance (HULIS) that contributes substantially to global OA mass, are oxidized by OH radicals at different temperatures and phase states. When oxidized at low temperature in a glassy solid state, the hygroscopicity of SRFA particles increased by almost a factor of two, whereas oxidation ofmore » liquid-like SRFA particles at higher temperatures did not affect CCN activity. Low-temperature oxidation appears to promote the formation of highly-oxygenated particle-bound fragmentation products with lower molar mass and greater CCN activity, underscoring the importance of chemical aging in the free troposphere and its influence on the CCN activity of OA.« less

The Dominant Snow-forming Process in Warm and Cold Mixed-phase Orographic Clouds: Effects of Cloud Condensation Nuclei and Ice Nuclei

NASA Astrophysics Data System (ADS)

Fan, J.; Rosenfeld, D.; Leung, L. R.; DeMott, P. J.

2014-12-01

Mineral dust aerosols often observed over California in winter and spring from long-range transport can be efficient ice nuclei (IN) and enhance snow precipitation in mixed-phase orographic clouds. On the other hand, local pollution particles can serve as good CCN and suppress warm rain, but their impacts on cold rain processes are uncertain. The main snow-forming mechanism in warm and cold mixed-phase orographic clouds (refer to as WMOC and CMOC, respectively) could be very different, leading to different precipitation response to CCN and IN. We have conducted 1-km resolution model simulations using the Weather Research and Forecasting (WRF) model coupled with a spectral-bin cloud microphysical model for WMOC and CMOC cases from CalWater2011. We investigated the response of cloud microphysical processes and precipitation to CCN and IN with extremely low to extremely high concentrations using ice nucleation parameterizations that connect with dust and implemented based on observational evidences. We find that riming is the dominant process for producing snow in WMOC while deposition plays a more important role than riming in CMOC. Increasing IN leads to much more snow precipitation mainly due to an increase of deposition in CMOC and increased rimming in WMOC. Increasing CCN decreases precipitation in WMOC by efficiently suppressing warm rain, although snow is increased. In CMOC where cold rain dominates, increasing CCN significantly increases snow, leading to a net increase in precipitation. The sensitivity of supercooled liquid to CCN and IN has also been analyzed. The mechanism for the increased snow by CCN and caveats due to uncertainties in ice nucleation parameterizations will be discussed.

Global observations of aerosol-cloud-precipitation-climate interactions

NASA Astrophysics Data System (ADS)

Rosenfeld, Daniel; Andreae, Meinrat O.; Asmi, Ari; Chin, Mian; de Leeuw, Gerrit; Donovan, David P.; Kahn, Ralph; Kinne, Stefan; Kivekäs, Niku; Kulmala, Markku; Lau, William; Schmidt, K. Sebastian; Suni, Tanja; Wagner, Thomas; Wild, Martin; Quaas, Johannes

2014-12-01

Cloud drop condensation nuclei (CCN) and ice nuclei (IN) particles determine to a large extent cloud microstructure and, consequently, cloud albedo and the dynamic response of clouds to aerosol-induced changes to precipitation. This can modify the reflected solar radiation and the thermal radiation emitted to space. Measurements of tropospheric CCN and IN over large areas have not been possible and can be only roughly approximated from satellite-sensor-based estimates of optical properties of aerosols. Our lack of ability to measure both CCN and cloud updrafts precludes disentangling the effects of meteorology from those of aerosols and represents the largest component in our uncertainty in anthropogenic climate forcing. Ways to improve the retrieval accuracy include multiangle and multipolarimetric passive measurements of the optical signal and multispectral lidar polarimetric measurements. Indirect methods include proxies of trace gases, as retrieved by hyperspectral sensors. Perhaps the most promising emerging direction is retrieving the CCN properties by simultaneously retrieving convective cloud drop number concentrations and updraft speeds, which amounts to using clouds as natural CCN chambers. These satellite observations have to be constrained by in situ observations of aerosol-cloud-precipitation-climate (ACPC) interactions, which in turn constrain a hierarchy of model simulations of ACPC. Since the essence of a general circulation model is an accurate quantification of the energy and mass fluxes in all forms between the surface, atmosphere and outer space, a route to progress is proposed here in the form of a series of box flux closure experiments in the various climate regimes. A roadmap is provided for quantifying the ACPC interactions and thereby reducing the uncertainty in anthropogenic climate forcing.

CCN production by new particle formation in the free troposphere

NASA Astrophysics Data System (ADS)

Rose, Clémence; Sellegri, Karine; Moreno, Isabel; Velarde, Fernando; Ramonet, Michel; Weinhold, Kay; Krejci, Radovan; Andrade, Marcos; Wiedensohler, Alfred; Ginot, Patrick; Laj, Paolo

2017-01-01

Global models predict that new particle formation (NPF) is, in some environments, responsible for a substantial fraction of the total atmospheric particle number concentration and subsequently contributes significantly to cloud condensation nuclei (CCN) concentrations. NPF events were frequently observed at the highest atmospheric observatory in the world, on Chacaltaya (5240 m a.s.l.), Bolivia. The present study focuses on the impact of NPF on CCN population. Neutral cluster and Air Ion Spectrometer and mobility particle size spectrometer measurements were simultaneously used to follow the growth of particles from cluster sizes down to ˜ 2 nm up to CCN threshold sizes set to 50, 80 and 100 nm. Using measurements performed between 1 January and 31 December 2012, we found that 61 % of the 94 analysed events showed a clear particle growth and significant enhancement of the CCN-relevant particle number concentration. We evaluated the contribution of NPF, relative to the transport and growth of pre-existing particles, to CCN size. The averaged production of 50 nm particles during those events was 5072, and 1481 cm-3 for 100 nm particles, with a larger contribution of NPF compared to transport, especially during the wet season. The data set was further segregated into boundary layer (BL) and free troposphere (FT) conditions at the site. The NPF frequency of occurrence was higher in the BL (48 %) compared to the FT (39 %). Particle condensational growth was more frequently observed for events initiated in the FT, but on average faster for those initiated in the BL, when the amount of condensable species was most probably larger. As a result, the potential to form new CCN was higher for events initiated in the BL (67 % against 53 % in the FT). In contrast, higher CCN number concentration increases were found when the NPF process initially occurred in the FT, under less polluted conditions. This work highlights the competition between particle growth and the removal of freshly nucleated particles by coagulation processes. The results support model predictions which suggest that NPF is an effective source of CCN in some environments, and thus may influence regional climate through cloud-related radiative processes.

Organic Condensation and Particle Growth to CCN Sizes in the Summertime Marine Arctic Is Driven by Materials More Semivolatile Than at Continental Sites

NASA Astrophysics Data System (ADS)

Burkart, Julia; Hodshire, Anna L.; Mungall, Emma L.; Pierce, Jeffrey R.; Collins, Douglas B.; Ladino, Luis A.; Lee, Alex K. Y.; Irish, Victoria; Wentzell, Jeremy J. B.; Liggio, John; Papakyriakou, Tim; Murphy, Jennifer; Abbatt, Jonathan

2017-10-01

Ship-based aerosol measurements in the summertime Arctic indicate elevated concentrations of ultrafine particles with occasional growth to cloud condensation nuclei (CCN) sizes. Focusing on one episode with two continuously growing modes, growth occurs faster for a large, preexisting mode (dp ≈ 90 nm) than for a smaller nucleation mode (dp ≈ 20 nm). We use microphysical modeling to show that growth is largely via organic condensation. Unlike results for midlatitude forested regions, most of these condensing species behave as semivolatile organics, as lower volatility organics would lead to faster growth of the smaller mode. The magnitude of the CCN hygroscopicity parameter for the growing particles, 0.1, is also consistent with organic species constituting a large fraction of the particle composition. Mixing ratios of common aerosol growth precursors, such as isoprene and sulfur dioxide, are not elevated during the episode, indicating that an unidentified aerosol growth precursor is present in this high-latitude marine environment.

Cold and transition season cloud condensation nuclei measurements in western Colorado

NASA Astrophysics Data System (ADS)

Ward, D. S.; Cotton, W. R.

2011-05-01

Recent studies have shown that orographic precipitation and the water resources that depend on it in the Colorado Rocky Mountains are sensitive to the variability of the region's aerosols, whether emitted locally or from distant sources. However, observations of cloud droplet nucleating aerosols in western Colorado, climatologically upwind of the Colorado Rocky Mountains, have been limited to a few studies at a single, northern site. To address this knowledge gap, atmospheric aerosols were sampled at a ground site in southwestern Colorado and in low-level north to south transects of the Colorado Western Slope as part of the Inhibition of Snowfall by Pollution Aerosols (ISPA-III) field campaign. Total particle and cloud condensation nuclei (CCN) number concentrations were measured for a 24-day period in Mesa Verde National Park, in September and October 2009. Regression analysis showed a positive relationship between mid-troposphere atmospheric pressure to the west of the site and the total particle count at the ground site, but no similar statistically significant relationship was found for the observed CCN. These data were supplemented with particle and CCN number concentration, as well as particle size distribution measurements collected aboard the King Air platform during December 2009. A CCN closure attempt was performed and suggested that the sampled aerosol may have had a low hygroscopicity that changed little with the large-scale wind direction. Together, the sampled aerosols from these field programs were characteristic of a rural continental environment with CCN number concentrations that varied slowly in time, and little in space along the Western Slope.

Calibration Uncertainties in the Droplet Measurement Technologies Cloud Condensation Nuclei Counter

NASA Astrophysics Data System (ADS)

Hibert, Kurt James

Cloud condensation nuclei (CCN) serve as the nucleation sites for the condensation of water vapor in Earth's atmosphere and are important for their effect on climate and weather. The influence of CCN on cloud radiative properties (aerosol indirect effect) is the most uncertain of quantified radiative forcing changes that have occurred since pre-industrial times. CCN influence the weather because intrinsic and extrinsic aerosol properties affect cloud formation and precipitation development. To quantify these effects, it is necessary to accurately measure CCN, which requires accurate calibrations using a consistent methodology. Furthermore, the calibration uncertainties are required to compare measurements from different field projects. CCN uncertainties also aid the integration of CCN measurements with atmospheric models. The commercially available Droplet Measurement Technologies (DMT) CCN Counter is used by many research groups, so it is important to quantify its calibration uncertainty. Uncertainties in the calibration of the DMT CCN counter exist in the flow rate and supersaturation values. The concentration depends on the accuracy of the flow rate calibration, which does not have a large (4.3 %) uncertainty. The supersaturation depends on chamber pressure, temperature, and flow rate. The supersaturation calibration is a complex process since the chamber's supersaturation must be inferred from a temperature difference measurement. Additionally, calibration errors can result from the Kohler theory assumptions, fitting methods utilized, the influence of multiply-charged particles, and calibration points used. In order to determine the calibration uncertainties and the pressure dependence of the supersaturation calibration, three calibrations are done at each pressure level: 700, 840, and 980 hPa. Typically 700 hPa is the pressure used for aircraft measurements in the boundary layer, 840 hPa is the calibration pressure at DMT in Boulder, CO, and 980 hPa is the average surface pressure at Grand Forks, ND. The supersaturation calibration uncertainty is 2.3, 3.1, and 4.4 % for calibrations done at 700, 840, and 980 hPa respectively. The supersaturation calibration change with pressure is on average 0.047 % supersaturation per 100 hPa. The supersaturation calibrations done at UND are 42-45 % lower than supersaturation calibrations done at DMT approximately 1 year previously. Performance checks confirmed that all major leaks developed during shipping were fixed before conducting the supersaturation calibrations. Multiply-charged particles passing through the Electrostatic Classifier may have influenced DMT's activation curves, which is likely part of the supersaturation calibration difference. Furthermore, the fitting method used to calculate the activation size and the limited calibration points are likely significant sources of error in DMT's supersaturation calibration. While the DMT CCN counter's calibration uncertainties are relatively small, and the pressure dependence is easily accounted for, the calibration methodology used by different groups can be very important. The insights gained from the careful calibration of the DMT CCN counter indicate that calibration of scientific instruments using complex methodology is not trivial.

CCN numerical simulations for the GoAmazon with the OLAM model

NASA Astrophysics Data System (ADS)

Ramos-da-Silva, R.; Haas, R.; Barbosa, H. M.; Machado, L.

2015-12-01

Manaus is a large city in the center of the Amazon rainforest. The GoAmazon field project is exploring the region through various data collection and modeling to investigate in impacts of the urban polluted plume on the surrounding pristine areas. In this study a numerical model was applied to simulate the atmospheric dynamics and the Cloud Condensation Nucleai (CCN) concentrations evolution. Simulations with and without the urban plume was performed to identify its dynamics and local impacts. The results show that the land surface characteristics has important hole on the CCN distribution and rainfall over the region. At the south of Manaus the atmospheric dynamics is dominated by the cloud streets that are aligned with the trade winds and the Amazon River. At the north of Manaus, the Negro River produces the advection of a more stable atmosphere causing a higher CCN concentration on the boundary layer. Assuming a local high CCN concentration at the Manaus boundary layer region, the simulations show that the land-atmosphere interaction sets important dynamics on the plume. The model shows that the CCN plume moves along with the flow towards southwest of Manaus following the cloud streets and the river direction having the highest concentrations over the most stable water surface regions.

Cold and transition season cloud condensation nuclei measurements in western Colorado

NASA Astrophysics Data System (ADS)

Ward, D. S.; Cotton, W. R.

2010-11-01

Recent research has shown that orographic precipitation and the water resources that depend on it in the Colorado Rocky Mountains are sensitive to the variability of the region's aerosols, whether emitted locally or from distant sources. However, observations of cloud-active aerosols in western Colorado, climatologically upwind of the Colorado Rocky Mountains, have been limited to a few studies at a single, northern site. To address this knowledge gap, atmospheric aerosols were sampled at a ground site in southwestern Colorado and in low-level north to south transects of the Colorado Western Slope as part of the Inhibition of Snowfall by Pollution Aerosols (ISPA-III) field campaign. Total particle and cloud condensation nuclei (CCN) number concentration were measured for a 24-day period in Mesa Verde National Park, climatologically upwind of the San Juan Mountains, in Sept. and Oct. 2009. Regression analysis showed a positive relationship between mid-troposphere atmospheric pressure to the west of the site and the total particle count at the ground site, but no similar statistically significant relationship for the observed CCN. These data were supplemented with particle and CCN number concentration, as well as particle size distribution measurements aboard the KingAir platform during December 2009. A CCN closure attempt was performed using the size distribution information and suggested that the sampled aerosol in general had low hygroscopicity that changed slightly with the large-scale wind direction. Together, the sampled aerosols from these field programs were characteristic of a rural continental environment with a cloud active portion that varied slowly in time, and little in space along the Western Slope.

Fluorescent pseudomonads isolated from Hebridean cloud and rain water produce biosurfactants but do not cause ice nucleation

NASA Astrophysics Data System (ADS)

Ahern, H. E.; Walsh, K. A.; Hill, T. C. J.; Moffett, B. F.

2007-02-01

Microorganisms were discovered in clouds over 100 years ago but information on bacterial community structure and function is limited. Clouds may not only be a niche within which bacteria could thrive but they might also influence dynamic processes using ice nucleating and cloud condensing abilities. Cloud and rain samples were collected from two mountains in the Outer Hebrides, NW Scotland, UK. Community composition was determined using a combination of amplified 16S ribosomal DNA restriction analysis and sequencing. 256 clones yielded 100 operational taxonomic units (OTUs) of which half were related to bacteria from terrestrial psychrophilic environments. Cloud samples were dominated by a mixture of fluorescent Pseudomonas spp., some of which have been reported to be ice nucleators. It was therefore possible that these bacteria were using the ice nucleation (IN) gene to trigger the Bergeron-Findeisen process of raindrop formation as a mechanism for dispersal. In this study the IN gene was not detected in any of the isolates using both polymerase chain reaction (PCR) and differential scanning calorimetry (DSC). Instead 55% of the total isolates from both cloud and rain samples displayed significant biosurfactant activity when analyzed using the drop-collapse technique. All isolates were characterised as fluorescent pseudomonads. Surfactants have been found to be very important in lowering atmospheric critical supersaturations required for the activation of aerosols into cloud condensation nuclei (CCN). It is also known that surfactants influence cloud droplet size and increase cloud lifetime and albedo. Some bacteria are known to act as CCN and so it is conceivable that these fluorescent pseudomonads are using surfactants to facilitate their activation from aerosols into CCN. This would allow water scavenging,~countering desiccation, and assist in their widespread dispersal.

Ice-nucleation negative fluorescent pseudomonads isolated from Hebridean cloud and rain water produce biosurfactants

NASA Astrophysics Data System (ADS)

Ahern, H. E.; Walsh, K. A.; Hill, T. C. J.; Moffett, B. F.

2006-10-01

Microorganisms were discovered in clouds over 100 years ago but information on bacterial community structure and function is limited. Clouds may not only be a niche within which bacteria could thrive but they might also influence dynamic processes using ice nucleating and cloud condensing abilities. Cloud and rain samples were collected from two mountains in the Outer Hebrides, NW Scotland, UK. Community composition was determined using a combination of amplified 16S ribosomal DNA restriction analysis and sequencing. 256 clones yielded 100 operational taxonomic units (OTUs) of which half were related to bacteria from terrestrial psychrophilic environments. Cloud samples were dominated by a mixture of fluorescent Pseudomonas spp., some of which have been reported to be ice nucleators. It was therefore possible that these bacteria were using the ice nucleation (IN) gene to trigger the Bergeron-Findeisen process of raindrop formation as a mechanism for dispersal. In this study the IN gene was not detected in any of the isolates using both polymerase chain reaction (PCR) and differential scanning calorimetry (DSC). Instead 55% of the total isolates from both cloud and rain samples displayed significant biosurfactant activity when analyzed using the drop-collapse technique. All were characterised as fluorescent pseudomonads. Surfactants have been found to be very important in lowering atmospheric critical supersaturations required for the activation of aerosols into cloud condensation nuclei (CCN). It is also known that surfactants influence cloud droplet size and increase cloud lifetime and albedo. Some bacteria are known to act as CCN and so it is conceivable that these fluorescent pseudomonads are using surfactants to facilitate their activation from aerosols into CCN. This would allow water scavenging, countering desiccation, and assist in their widespread dispersal.

Analysis of CCN activity of Remote and Combustion Aerosol over the South East Pacific during autumn 2008 and links to Sc cloud properties

NASA Astrophysics Data System (ADS)

Freitag, S.; Clarke, A. D.; Howell, S. G.; Twohy, C. H.; Snider, J. R.; Toohey, D. W.; Shank, L.; McNaughton, C. S.; Brekhovskikh, V.; Kapustin, V.

2013-12-01

The earth's most extensive Stratocumulus (Sc) deck, situated off the coast of Northern Chile and Southern Peru, strongly influences the radiation budget and climate over the South East Pacific (SEP) by enhancing solar reflection. This feature makes Sc clouds an important constituent for climate modeling, yet these clouds are poorly represented in models. A large uncertainty in understanding the variability in these low cloud fields arises from our deficit in understanding the role of aerosol. Hence, a major goal of the VOCALS (www.eol.ucar.edu/projects/vocals) campaign in 2008 was to further explore and assess interactions of natural and anthropogenic aerosol with Sc clouds in both the more polluted coastal environment and west of 80W where we encountered nearly pristine boundary layer clouds often exposed to cloud-top entrainment of pollution aerosol from the free troposphere. Extensive airborne measurements of size-resolved aerosol volatility and chemical composition collected aboard the NCAR C-130 were analyzed with an aerosol mass spectrometer (AMS) and a single particle soot photometer (SP2) to calculate aerosol hygroscopicity (κ) and predict cloud condensation nuclei (CCN) concentration for all observed air mass types above and below cloud utilizing estimated Sc cloud supersaturations deduced from cloud-processed aerosol size distribution information. The predicted CCN agree to within 10% to measured CCN. Results from this analysis are presented here and CCN variability observed along VOCALS flight tracks is discussed in conjunction with size-resolved cloud droplet information. This includes assessing the impact of aerosol perturbations on the shape of the cloud droplet size distribution parameterized in models and satellite algorithms such as cloud top effective radius retrievals. We will further discuss cloud droplet residual composition collected using a counterflow virtual impactor (CVI) and analyzed with the AMS and SP2. Size resolved variations in residual composition and its relation to CCN composition measured outside the cloud will be examined in terms of the influence of aerosol concentration, size, and chemical composition on Sc clouds.

Airborne observations of cloud condensation nuclei spectra and aerosols over East Inner Mongolia

NASA Astrophysics Data System (ADS)

Yang, Jiefan; Lei, Hengchi; Lü, Yuhuan

2017-08-01

A set of vertical profiles of aerosol number concentrations, size distributions and cloud condensation nuclei (CCN) spectra was observed using a passive cloud and aerosol spectrometer (PCASP) and cloud condensation nuclei counter, over the Tongliao area, East Inner Mongolia, China. The results showed that the average aerosol number concentration in this region was much lower than that in heavily polluted areas. Monthly average aerosol number concentrations within the boundary layer reached a maximum in May and a minimum in September, and the variations in CCN number concentrations at different supersaturations showed the same trend. The parameters c and k of the empirical function N = cS k were 539 and 1.477 under clean conditions, and their counterparts under polluted conditions were 1615 and 1.42. Measurements from the airborne probe mounted on a Yun-12 (Y12) aircraft, together with Hybrid Single-Particle Lagrangian Integrated Trajectory model backward trajectories indicated that the air mass from the south of Tongliao contained a high concentration of aerosol particles (1000-2500 cm-3) in the middle and lower parts of the troposphere. Moreover, detailed intercomparison of data obtained on two days in 2010 indicated that the activation efficiency in terms of the ratio of N CCN to N a (aerosols measured from PCASP) was 0.74 (0.4 supersaturations) when the air mass mainly came from south of Tongliao, and this value increased to 0.83 on the relatively cleaner day. Thus, long-range transport of anthropogenic pollutants from heavily polluted mega cities, such as Beijing and Tianjin, may result in slightly decreasing activation efficiencies.

The Impact of Aerosols on Cloud and Precipitation Processes: Cloud-Resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Khain, A.; Simpson, S.; Johnson, D.; Li, X.; Remer, L.

2003-01-01

Cloud microphysics are inevitable affected by the smoke particle (CCN, cloud condensation nuclei) size distributions below the clouds. Therefore, size distribution parameterized as spectral bin microphysics are needed to explicitly study the effect of atmospheric aerosol concentration on cloud development, rainfall production, and rainfall rates convective clouds. Recently, two detailed spectral-bin microphysical schemes were implemented into the Goddard Cumulus Ensembel (GCE) model. The formulation for the explicit spectral-bim microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (i.e., cloud droplets and raindrops), and several types of ice particles [i.e., pristine ice crystals (columnar and plate-like), snow (dendrites and aggregates), groupel and frozen drops/hall] Each type is described by a special size distribution function containing many categories (i.e., 33 bins). Atmospheric aerosols are also described using number density size-distribution functions.A spectral-bin microphysical model is very expensive from a computational point of view and has only been implemented into the 2D version of the GCE at the present time. The model is tested by studying the evolution of deep cloud systems in the west Pacific warm pool region and in the mid-latitude using identical thermodynamic conditions but with different concentrations of CCN: a low "clean" concentration and a high "dirty" concentration. Besides the initial differences in aerosol concentration, preliminary results indicate that the low CCN concentration case produces rainfall at the surface sooner than the high CCN case but has less cloud water mass aloft. Because the spectral-bim model explicitly calculates and allows for the examination of both the mass and number concentration of cpecies in each size category, a detailed analysis of the instantaneous size spectrum can be obtained for the two cases. It is shown that since the low CCN case produces fever droplets, larger size develop due to greater condencational and collectional growth, leading to a broader size spectrum in comparison to the high CCN case.

Stratospheric CCN sampling program. [volcanology, Mount Saint Helens

NASA Technical Reports Server (NTRS)

Rogers, C. F.; Hudson, J. G.

1982-01-01

Two one liter grab samples of stratospheric aerosol were returned from each of six U-2 sampling missions. Cloud condensation nuclei (CCN) spectra from each sample were obtained. Interest was centered on the effects of volcanic activity. Spurious particle generation was found to be a serious problem in container 9 LFT and a much smaller problem in container 9 RT. Initial studies of an option for improved sample containers and values were completed. A CCN spectrometer, able to operate at an internal pressure of 300 mb, was designed.

The Role of Aerosols on Precipitation Processes: Cloud Resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Li, X.; Matsui, T.

2012-01-01

Cloud microphysics is inevitably affected by the smoke particle (CCN, cloud condensation nuclei) size distributions below the clouds. Therefore, size distributions parameterized as spectral bin microphysics are needed to explicitly study the effects of atmospheric aerosol concentration on cloud development, rainfall production, and rainfall rates for convective clouds. Recently, a detailed spectral-bin microphysical scheme was implemented into the Goddard Cumulus Ensemble (GCE) model. The formulation for the explicit spectral bin microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (i.e., cloud droplets and raindrops), and several types of ice particles [i.e. pristine ice crystals (columnar and plate-like), snow (dendrites and aggregates), graupel and frozen drops/hail]. Each type is described by a special size distribution function containing many categories (i.e., 33 bins). Atmospheric aerosols are also described using number density size-distribution functions. The model is tested by studying the evolution of deep cloud systems in the west Pacific warm pool region, the sub-tropics (Florida) and midlatitudes using identical thermodynamic conditions but with different concentrations of CCN: a low "clean" concentration and a high "dirty" concentration. Results indicate that the low CCN concentration case produces rainfall at the surface sooner than the high CeN case but has less cloud water mass aloft. Because the spectral-bin model explicitly calculates and allows for the examination of both the mass and number concentration of species in each size category, a detailed analysis of the instantaneous size spectrum can be obtained for these cases. It is shown that since the low (CN case produces fewer droplets, larger sizes develop due to greater condensational and collection growth, leading to a broader size spectrum in comparison to the high CCN case. Sensitivity tests were performed to identify the impact of ice processes, radiation and large-scale influence on cloud-aerosol interactive processes, especially regarding surface rainfall amounts and characteristics (i.e., heavy or convective versus light or stratiform types). In addition, an inert tracer was included to follow the vertical redistribution of aerosols by cloud processes. We will also give a brief review from observational evidence on the role of aerosol on precipitation processes.

How quickly do cloud droplets form on atmospheric particles?

NASA Astrophysics Data System (ADS)

Ruehl, C. R.; Chuang, P. Y.; Nenes, A.

2007-10-01

The influence of aerosols on cloud properties is an important modulator of the climate system. Traditional Köhler theory predicts the equilibrium concentration of cloud condensation nuclei (CCN); however, it is not known to what extent particles exist in the atmosphere that may be prevented from acting as CCN by kinetic limitations. We measured the rate of cloud droplet formation on atmospheric particles sampled at four sites across the United States during the summer of 2006: Great Smoky Mountain National Park, TN; Bondville, IL; Houston, TX; and the Atmospheric Radiation Measurement Program Southern Great Plains site near Lamont, OK. We express droplet growth rates with the mass accommodation coefficient (α), and report values of α measured in the field normalized to the mean α measured for lab-generated ammonium sulfate (AS) particles (i.e., α'=α/αAS). Overall, 61% of ambient CCN grew at a rate similar to AS. We report the fraction of CCN that were "low-α'" (α'<10-0.33). Of the 16 days during which these measurements were made, 7 had relatively few low-α'CCN (<16%), 7 had moderate low-α' fractions (31% to 62%), and 2 had large low-α' fractions (>77% during at least one ~30 min period). Day to day variability was greatest in Tennessee and Illinois, and low-α' CCN were most prevalent on days when back trajectories suggested that air was arriving from aloft. The highest fractions of low-α' CCN in Houston and Illinois occurred around local noon, and decreased later in the day. These results suggest that for some air masses, accurate quantification of CCN concentrations may need to account for kinetic limitations.

Investigation of cloud condensation nuclei properties and droplet growth kinetics of the water-soluble aerosol fraction in Mexico City

NASA Astrophysics Data System (ADS)

Padró, Luz T.; Tkacik, Daniel; Lathem, Terry; Hennigan, Chris J.; Sullivan, Amy P.; Weber, Rodney J.; Huey, L. Greg; Nenes, Athanasios

2010-05-01

We present hygroscopic and cloud condensation nuclei (CCN) relevant properties of the water-soluble fraction of Mexico City aerosol collected upon filters during the 2006 Megacity Initiative: Local and Global Research Observations (MILAGRO) campaign. Application of κ-Köhler theory to the observed CCN activity gave a fairly constant hygroscopicity parameter (κ = 0.28 ± 0.06) regardless of location and organic fraction. Köhler theory analysis was used to understand this invariance by separating the molar volume and surfactant contributions to the CCN activity. Organics were found to depress surface tension (10-15%) from that of pure water. Daytime samples exhibited lower molar mass (˜200 amu) and surface tension depression than nighttime samples (˜400 amu); this is consistent with fresh hygroscopic secondary organic aerosol (SOA) condensing onto particles during peak photochemical hours, subsequently aging during nighttime periods of high relative humidity. Changes in surface tension partially compensate for shifts in average molar volume to give the constant hygroscopicity observed, which implies the amount (volume fraction) of soluble material in the parent aerosol is the key composition parameter required for CCN predictions. This finding, if applicable elsewhere, may explain why CCN predictions are often found to be insensitive to assumptions of chemical composition and provides a very simple way to parameterize organic hygroscopicity in atmospheric models (i.e., κorg = 0.28ɛWSOC). Special care should be given, however, to surface tension depression from organic surfactants, as its nonlinear dependence with organic fraction may introduce biases in observed (and predicted) hygroscopicity. Finally, threshold droplet growth analysis suggests the water-soluble organics do not affect activation kinetics.

Aerosol properties and their impacts on surface CCN at the ARM Southern Great Plains site during the 2011 Midlatitude Continental Convective Clouds Experiment

NASA Astrophysics Data System (ADS)

Logan, Timothy; Dong, Xiquan; Xi, Baike

2018-02-01

Aerosol particles are of particular importance because of their impacts on cloud development and precipitation processes over land and ocean. Aerosol properties as well as meteorological observations from the Department of Energy Atmospheric Radiation Measurement (ARM) platform situated in the Southern Great Plains (SGP) are utilized in this study to illustrate the dependence of continental cloud condensation nuclei (CCN) number concentration ( N CCN) on aerosol type and transport pathways. ARM-SGP observations from the 2011 Midlatitude Continental Convective Clouds Experiment field campaign are presented in this study and compared with our previous work during the 2009-10 Clouds, Aerosol, and Precipitation in the Marine Boundary Layer field campaign over the current ARM Eastern North Atlantic site. Northerly winds over the SGP reflect clean, continental conditions with aerosol scattering coefficient ( σ sp) values less than 20 Mm-1 and N CCN values less than 100 cm-3. However, southerly winds over the SGP are responsible for the observed moderate to high correlation ( R) among aerosol loading ( σ sp < 60 Mm-1) and N CCN, carbonaceous chemical species (biomass burning smoke), and precipitable water vapor. This suggests a common transport mechanism for smoke aerosols and moisture via the Gulf of Mexico, indicating a strong dependence on air mass type. NASA MERRA-2 reanalysis aerosol and chemical data are moderately to highly correlated with surface ARM-SGP data, suggesting that this facility can represent surface aerosol conditions in the SGP, especially during strong aerosol loading events that transport via the Gulf of Mexico. Future long-term investigations will help to understand the seasonal influences of air masses on aerosol, CCN, and cloud properties over land in comparison to over ocean.

Investigation of the marine boundary layer cloud and CCN properties under coupled and decoupled conditions over the Azores

DOE PAGES

Dong, Xiquan; Schwantes, Adam C.; Xi, Baike; ...

2015-06-10

Here, six coupled and decoupled marine boundary layer (MBL) clouds were chosen from the 19 month Atmospheric Radiation Measurement Mobile Facility data set over the Azores. Thresholds of liquid water potential temperature difference Δθ L < 0.5 K (>0.5 K) and total water mixing ratio difference Δq t < 0.5 g/kg (>0.5 g/kg) below the cloud base were used for selecting the coupled (decoupled) cases. A schematic diagram was given to demonstrate the coupled and decoupled MBL vertical structures and how they associate with nondrizzle, virga, and rain drizzle events. Out of a total of 2676 5 min samples, 34.5%more » were classified as coupled and 65.5% as decoupled, 36.2% as nondrizzle and 63.8% as drizzle (47.7% as virga and 16.1% as rain), and 33.4% as daytime and 66.6% as nighttime. The decoupled cloud layer is deeper (0.406 km) than coupled cloud layer (0.304 km), and its liquid water path and cloud droplet effective radius (r e) values (122.1 gm -2 and 13.0 µm) are higher than coupled ones (83.7 gm -2 and 10.4 µm). Conversely, decoupled stratocumuli have lower cloud droplet number concentration (N d) and surface cloud condensation nucleus (CCN) concentration (N CCN) (74.5 cm -3 and 150.9 cm -3) than coupled stratocumuli (111.7 cm -3 and 216.4 cm -3). The linear regressions between r e and N d with N CCN have demonstrated that coupled r e and N d strongly depend on N CCN and have higher correlations (-0.56 and 0.59) with N CCN than decoupled results (-0.14 and 0.25). The MBL cloud properties under nondrizzle and virga drizzle conditions are similar to each other but significantly different to those of rain drizzle.« less

Impacts of New Particle Formation on Midwestern Climate and Air Quality as Determined by the NPF-explicit WRF-Chem

NASA Astrophysics Data System (ADS)

Dong, C.; Stanier, C. O.; Bullard, R.; Singh, A.

2016-12-01

A one month simulation has been performed using the New particle formation (NPF)-explicit WRF-Chem (Matsui et al, Journal of Geophysical Research, 116(D19208), 2011). The simulation was run for a domain of the continental United States, with analysis focused on the Midwestern and eastern portions of the U.S. Analysis focused on quantification and explanation of planetary boundary layer (PBL) NPF in the model on variables beyond condensation nuclei (CN), cloud condensation nuclei (CCN), and cloud droplet size distributions. The model was evaluated against meteorology, chemical species and aerosol physical property observations. Comparison shows the model performance was comparable to that of other studies. Nucleation enhanced the concentration of condensation nuclei (CN). Cloud condensation nuclei (CCN) concentrations were enhanced and suppressed at high and low supersaturations, respectively. For air pollutants, the most pronounced influence of PBL nucleation was PM2.5 reduction, which was mainly caused by SO4 decreases (62.7%). For shortwave radiation, changes due to indirect effects of NPF were larger than direct effects. Shortwave radiation and cloud droplet concentration typically changed in the same way. Similar change patterns were found for T2 and PBL height. PBL nucleation led to a net increase of precipitation during the simulation period. Sensitivity tests showed that the combination of PBL NPF together with aqueous chemistry was the predominant cause of SO4 reduction.

Effect of vehicular traffic, remote sources and new particle formation on the activation properties of cloud condensation nuclei in the megacity of São Paulo, Brazil

NASA Astrophysics Data System (ADS)

Souto-Oliveira, Carlos Eduardo; de Fátima Andrade, Maria; Kumar, Prashant; Juliano da Silva Lopes, Fábio; Babinski, Marly; Landulfo, Eduardo

2016-11-01

Atmospheric aerosol is the primary source of cloud condensation nuclei (CCN). The microphysics and chemical composition of aerosols can affect cloud development and the precipitation process. Among studies conducted in Latin America, only a handful have reported the impact of urban aerosol on CCN activation parameters such as activation ratio (AR) and activation diameter (Dact). With over 20 million inhabitants, the Metropolitan Area of São Paulo (MASP) is the largest megacity in South America. To our knowledge, this is the first study to assess the impact that remote sources and new particle formation (NPF) events have on CCN activation properties in a South American megacity. The measurements were conducted in the MASP between August and September 2014. We measured the CCN within the 0.2-1.0 % range of supersaturation, together with particle number concentration (PNC) and particle number distribution (PND), as well as trace-element concentrations and black carbon (BC). NPF events were identified on 35 % of the sampling days. Combining multivariate analysis in the form of positive matrix factorization (PMF) with an aerosol profile from lidar and HYSPLIT model analyses allowed us to identify the main contribution of vehicular traffic on all days and sea salt and biomass burning from remote regions on 28 and 21 % of the sampling days, respectively. The AR and Dact parameters showed distinct patterns for daytime with intense vehicular traffic and nighttime periods. For example, CCN activation was lower during the daytime than during the nighttime periods, a pattern that was found to be associated mainly with local road-traffic emissions. A decrease in CCN activation was observed on the NPF event days, mainly due to high concentrations of particles with smaller diameters. We also found that aerosols from sea salt, industrial emissions, and biomass burning had minor effects on Dact. For example, nights with biomass burning and vehicular emissions showed slightly lower CCN activation properties than sea-salt, industrial and non-event nights. Our results show that particulate matter from local vehicular emissions during the daytime has a greater effect on CCN activation parameters than that from remote sources.

Classifying organic materials by oxygen-to-carbon elemental ratio to predict the activation regime of cloud condensation nuclei (CCN)

NASA Astrophysics Data System (ADS)

Kuwata, M.; Shao, W.; Lebouteiller, R.; Martin, S. T.

2012-12-01

The governing highly soluble, slightly soluble, or insoluble activation regime of organic compounds as cloud condensation nuclei (CCN) was examined as a function of oxygen-to-carbon elemental ratio (O : C). New data were collected for adipic, pimelic, suberic, azelaic and pinonic acids. Secondary organic materials (SOMs) produced by α-pinene ozonolysis and isoprene photo-oxidation were also included in the analysis. The saturation concentrations C of the organic compounds in aqueous solutions served as the key parameter for delineating regimes of CCN activation, and the values of C were tightly correlated to the O : C ratios. The highly soluble, slightly soluble, and insoluble regimes of CCN activation were found to correspond to ranges of [O : C] > 0.6, 0.2 < [O : C] < 0.6, and [O : C] < 0.2, respectively. These classifications were evaluated against CCN activation data of isoprene-derived SOM (O : C = 0.69-0.72) and α-pinene-derived SOM (O : C = 0.38-0.48). Isoprene-derived SOM had highly soluble activation behavior, consistent with its high O : C ratio. For α-pinene-derived SOM, although CCN activation can be modeled as a highly soluble mechanism, this behavior was not predicted by the O : C ratio, for which a slightly soluble mechanism was anticipated. Complexity in chemical composition, resulting in continuous water uptake and the absence of a deliquescence transition that can thermodynamically limit CCN activation, might explain the differences of α-pinene-derived SOM compared to the behavior of pure organic compounds. The present results suggest that atmospheric particles dominated by hydrocarbon-like organic components do not activate (i.e. insoluble regime) whereas those dominated by oxygenated organic components activate (i.e. highly soluble regime).

Long-term observations of cloud condensation nuclei in the Amazon rain forest – Part 1: Aerosol size distribution, hygroscopicity, and new model parametrizations for CCN prediction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pöhlker, Mira L.; Pöhlker, Christopher; Ditas, Florian

Size-resolved long-term measurements of atmospheric aerosol and cloud condensation nuclei (CCN) concentrations and hygroscopicity were conducted at the remote Amazon Tall Tower Observatory (ATTO) in the central Amazon Basin over a 1-year period and full seasonal cycle (March 2014–February 2015). Our measurements provide a climatology of CCN properties characteristic of a remote central Amazonian rain forest site.The CCN measurements were continuously cycled through 10 levels of supersaturation ( S=0.11 to 1.10 %) and span the aerosol particle size range from 20 to 245 nm. The mean critical diameters of CCN activation range from 43 nm at S = 1.10 % to 172more » nm at S = 0.11 %. Furthermore, the particle hygroscopicity exhibits a pronounced size dependence with lower values for the Aitken mode ( κ Ait = 0.14 ± 0.03), higher values for the accumulation mode ( κ Acc = 0.22 ± 0.05), and an overall mean value of κ mean = 0.17 ± 0.06, consistent with high fractions of organic aerosol.The hygroscopicity parameter, κ, exhibits remarkably little temporal variability: no pronounced diurnal cycles, only weak seasonal trends, and few short-term variations during long-range transport events. In contrast, the CCN number concentrations exhibit a pronounced seasonal cycle, tracking the pollution-related seasonality in total aerosol concentration. Here, we find that the variability in the CCN concentrations in the central Amazon is mostly driven by aerosol particle number concentration and size distribution, while variations in aerosol hygroscopicity and chemical composition matter only during a few episodes.For modeling purposes, we compare different approaches of predicting CCN number concentration and present a novel parametrization, which allows accurate CCN predictions based on a small set of input data.« less

Long-term observations of cloud condensation nuclei in the Amazon rain forest – Part 1: Aerosol size distribution, hygroscopicity, and new model parametrizations for CCN prediction

DOE PAGES

Pöhlker, Mira L.; Pöhlker, Christopher; Ditas, Florian; ...

2016-12-20

Size-resolved long-term measurements of atmospheric aerosol and cloud condensation nuclei (CCN) concentrations and hygroscopicity were conducted at the remote Amazon Tall Tower Observatory (ATTO) in the central Amazon Basin over a 1-year period and full seasonal cycle (March 2014–February 2015). Our measurements provide a climatology of CCN properties characteristic of a remote central Amazonian rain forest site.The CCN measurements were continuously cycled through 10 levels of supersaturation ( S=0.11 to 1.10 %) and span the aerosol particle size range from 20 to 245 nm. The mean critical diameters of CCN activation range from 43 nm at S = 1.10 % to 172more » nm at S = 0.11 %. Furthermore, the particle hygroscopicity exhibits a pronounced size dependence with lower values for the Aitken mode ( κ Ait = 0.14 ± 0.03), higher values for the accumulation mode ( κ Acc = 0.22 ± 0.05), and an overall mean value of κ mean = 0.17 ± 0.06, consistent with high fractions of organic aerosol.The hygroscopicity parameter, κ, exhibits remarkably little temporal variability: no pronounced diurnal cycles, only weak seasonal trends, and few short-term variations during long-range transport events. In contrast, the CCN number concentrations exhibit a pronounced seasonal cycle, tracking the pollution-related seasonality in total aerosol concentration. Here, we find that the variability in the CCN concentrations in the central Amazon is mostly driven by aerosol particle number concentration and size distribution, while variations in aerosol hygroscopicity and chemical composition matter only during a few episodes.For modeling purposes, we compare different approaches of predicting CCN number concentration and present a novel parametrization, which allows accurate CCN predictions based on a small set of input data.« less

Long-term observations of cloud condensation nuclei in the Amazon rain forest

NASA Astrophysics Data System (ADS)

Pöhlker, Mira L.; Pöhlker, Christopher; Ditas, Florian; Klimach, Thomas; Hrabe de Angelis, Isabella; Brito, Joel; Carbone, Samara; Cheng, Yafang; Martin, Scot T.; Moran-Zuloaga, Daniel; Rose, Diana; Saturno, Jorge; Su, Hang; Thalman, Ryan; Walter, David; Wang, Jian; Barbosa, Henrique; Artaxo, Paulo; Andreae, Meinrat O.; Pöschl, Ulrich

2017-04-01

Size-resolved long-term measurements of atmospheric aerosol and cloud condensation nuclei (CCN) concentrations and hygroscopicity were conducted at the remote Amazon Tall Tower Observatory (ATTO) in the central Amazon Basin over a full seasonal cycle (Mar 2014 - Feb 2015). The measurements provide a climatology of CCN properties characteristic of a remote central Amazonian rain forest site [1,2]. The CCN measurements were continuously cycled through 10 levels of supersaturation (S = 0.11 to 1.10 %) and span the aerosol particle size range from 20 to 245 nm. The particle hygroscopicity exhibits a pronounced size dependence with lower values for the Aitken mode (κAit = 0.14 ± 0.03), higher values for the accumulation mode (κAcc = 0.22 ± 0.05), and an overall mean value of κmean = 0.17 ± 0.06, consistent with high fractions of organic aerosol. The hygroscopicity parameter, κ, exhibits remarkably little temporal variability: no pronounced diurnal cycles, only weak seasonal trends, and few short-term variations during long-range transport events. In contrast, the CCN number concentrations exhibit a pronounced seasonal cycle, tracking the pollution-related seasonality in total aerosol concentration. We find that the variability in the CCN concentrations in the central Amazon is mostly driven by aerosol particle number concentration and size distribution, while variations in aerosol hygroscopicity and chemical composition matter only during a few episodes. For modelling purposes, we compare different approaches of predicting CCN number concentration and present a novel parameterization, which allows accurate CCN predictions based on a small set of input data. In addition, we analyzed the CCN short-term variability in relation to air mass changes as well as aerosol emission and transformation processes. The CCN short term variability is presented for selected case studies, which analyze particularly interesting and characteristic events/conditions in the Amazon region. References: [1] Andreae, M. O., et al. (2015), Atmos. Chem. Phys., 15, 10723-10776. [2] Pöhlker, M. L.., et al. (2016), Atmos. Chem. Phys., 16, 15709-15740.

Cloud condensation nuclei activity and droplet activation kinetics of wet processed regional dust samples and minerals

NASA Astrophysics Data System (ADS)

Kumar, P.; Sokolik, I. N.; Nenes, A.

2011-08-01

This study reports laboratory measurements of particle size distributions, cloud condensation nuclei (CCN) activity, and droplet activation kinetics of wet generated aerosols from clays, calcite, quartz, and desert soil samples from Northern Africa, East Asia/China, and Northern America. The dependence of critical supersaturation, sc, on particle dry diameter, Ddry, is used to characterize particle-water interactions and assess the ability of Frenkel-Halsey-Hill adsorption activation theory (FHH-AT) and Köhler theory (KT) to describe the CCN activity of the considered samples. Wet generated regional dust samples produce unimodal size distributions with particle sizes as small as 40 nm, CCN activation consistent with KT, and exhibit hygroscopicity similar to inorganic salts. Wet generated clays and minerals produce a bimodal size distribution; the CCN activity of the smaller mode is consistent with KT, while the larger mode is less hydrophilic, follows activation by FHH-AT, and displays almost identical CCN activity to dry generated dust. Ion Chromatography (IC) analysis performed on regional dust samples indicates a soluble fraction that cannot explain the CCN activity of dry or wet generated dust. A mass balance and hygroscopicity closure suggests that the small amount of ions (from low solubility compounds like calcite) present in the dry dust dissolve in the aqueous suspension during the wet generation process and give rise to the observed small hygroscopic mode. Overall these results identify an artifact that may question the atmospheric relevance of dust CCN activity studies using the wet generation method. Based on the method of threshold droplet growth analysis, wet generated mineral aerosols display similar activation kinetics compared to ammonium sulfate calibration aerosol. Finally, a unified CCN activity framework that accounts for concurrent effects of solute and adsorption is developed to describe the CCN activity of aged or hygroscopic dusts.

Laboratory study of the effect of oxalic acid on the cloud condensation nuclei activity of mineral dust aerosol

NASA Astrophysics Data System (ADS)

Gierlus, Kelly M.; Laskina, Olga; Abernathy, Tricia L.; Grassian, Vicki H.

2012-01-01

Dicarboxylic acids, which make up a significant portion of the atmospheric organic aerosol, are emitted directly through biomass burning as well as produced through the oxidation of volatile organic compounds. Oxalic acid, the most abundant of the dicarboxylic acids, has been shown by recent field studies to be present in mineral dust aerosol particles. The presence of these internally mixed organic compounds can alter the water absorption and cloud condensation nuclei (CCN) abilities of mineral particles in the Earth's atmosphere. The University of Iowa's Multi-Analysis Aerosol Reactor System ( MAARS) was used to measure the CCN activity of internally mixed particles that were generated from a mixture of either calcite or polystyrene latex spheres (PSLs) in an aqueous solution of oxalic acid. Although PSL is not a mineral dust component, it is used here as a non-reactive, insoluble particle. CCN measurements indicate that the internally mixed oxalate/calcite particles showed nearly identical CCN activity compared to the original calcite particles whereas oxalic acid/PSL internally mixed particles showed much greater CCN activity compared to PSL particles alone. This difference is due to the reaction of calcite with oxalic acid, which produces a relatively insoluble calcium oxalate coating on the particle surface and not a soluble coating as it does on the PSL particle. Our results suggest that atmospheric processing of mineral dust aerosol through heterogeneous processes will likely depend on the mineralogy and the specific chemistry involved. Increase in the CCN activity by incorporation of oxalic acid are only expected for unreactive insoluble dust particles that form a soluble coating.

New particle formation events as a source for cloud condensation nuclei in an urban environment

NASA Astrophysics Data System (ADS)

Wonaschütz, Anna; Burkart, Julia; Wagner, Robert; Reischl, Georg; Steiner, Gerhard; Hitzenberger, Regina

2014-05-01

Nucleation and growth events have been observed in many remote, urban and rural environments. The new particles can contribute significantly to cloud condensation nuclei concentrations, after growing into the appropriate size range (Kerminen et al., 2012). Several studies have attempted to quantify this contribution (e.g. Asmi et al., 2011, Matsui et al., 2013), but only a limited number of them to date have used simultaneous measurements of CCN concentrations and particle size distributions for this purpose (e.g. Levin et al., 2012). In this study, a data set from an urban background station, consisting of 22 months of size distribution and 12 months of CCN concentration measurements (Burkart et al., 2011, Burkart et al., 2012) with 10 months of overlapping measurements is combined to explore the variability of CCN concentrations, their possible causes, and the contribution of nucleation and growth events to CCN concentrations. Consistent with observations in many other locations, nucleation and growth events occur on 30% of all days in spring and summer, on 11% of days in fall and on 4% of days in winter. This suggests a potentially large source of CCN from nucleation and growth events, particularly in the warm season. We acknowledge funding from FWF (Austrian Science Fund) P19515-N20 References: Asmi E., Kivekas, N., Kerminen, V. M., Komppula, M., Hyvarinen, A. P., Hatakka, J., Viisanen, Y., and Lihavainen, H.: Secondary new particle formation in Northern Finland Pallas site between the years 2000 and 2010, Atmos. Chem. Phys., 11, 12959-12972, doi: 10.5194/acp-11-12959-2011, 2011 Burkart J., Steiner, G., Reischl, G., and Hitzenberger, R.: Long-term study of cloud condensation nuclei (CCN) acticvation of the atmospheric aerosol in Vienna, Atmos. Environ., 45, 5751-5759, doi: 10.1016/j.atmosenv.2011.07.022, 2011. Burkart J., Hitzenberger, R., Reischl, G., Bauer, H., Leder, K., and Puxbaum, H.: Activation of "synthetic ambient" aerosols - relation to chemical composition of particles < 100 nm, Atmos. Environ., 54, 583-591, doi: 10.1016/j.atmosenv.2012.01.063, 2012. Kerminen V.-M., Paramonov, M., Anttila, T., Riipinen, I., Fountoukis, C., Korhonen, H., Asmi, E., Laakso, L., Lihavainen, H., Swietlicki, E., Svenningsson, B., Asmi, A., Pandis, S. N., Kulmala, M., and Petäjä, T.: Cloud condensation nuclei production associated with atmospheric nucleation: a synthesis based on existing literature and new results, Atmos. Chem. Phys., 12, 12037-12059, doi: 10.5194/acp-12-12037-2012, 2012. Levin, E. J. T., Prenni, A. J., Petters, M. D., Kreidenweis, S. M., Sullivan, R. C., Atwood, S. A., Ortega, J., DeMott, P. J., and Smith, J. N.: An annual cycle of size-resolved aerosol hygroscopicity at a forested site in Colorado, J. Geophys. Res., 117, 06201, doi:10.1029/2011JD016854, 2012. Matsui, H., Koike, M., Kondo, Y., Takegawa, N., Wiedensohler, A., Fast, J. D., and Zaveri, R. A.: Impact of new particle formation on the concentrations of aerosols and cloud condensation nuclei around Beijing, J. Geophys. Res., 116, 19208, doi:10.1029/2011JD016025, 2011.

Project Fog Drops. Part 2: Laboratory investigations

NASA Technical Reports Server (NTRS)

Kocmond, W. C.; Mack, E. J.; Katz, U.; Pilie, R. J.

1972-01-01

Measurements of the total nucleus concentration and cloud condensation nuclei (CCN) were acquired for several conditions representing both high normal and severe pollution levels for the Los Angeles Basin as well as clean filtered air. The data show that in filtered air there is a large photochemically induced increase in the total particle content within a few minutes after starting the lamp. The concentration of CCN remains near zero, until sufficient coagulation and condensation occurs on the smaller Aitken particles. The addition of gaseous pollutants to filtered air results in large increases in the photochemical production of both the cloud and Aitken nucleus concentration. Fogs were also generated under controlled, reproducible conditions in the cloud chamber and seeded with aerosols of various compounds which form monomolecular surface films at air-water interfaces. Visibility characteristics and droplet data were obtained. The data suggest that droplet growth on treated nuclei can be retarded but fog formation was not significantly altered by the chemical seeding.

The impact of organic vapours on warm cloud formation; characterisation of chamber setup and first experimental results

NASA Astrophysics Data System (ADS)

Frey, Wiebke; Connolly, Paul; Dorsey, James; Hu, Dawei; Alfarra, Rami; McFiggans, Gordon

2016-04-01

The Manchester Ice Cloud Chamber (MICC), consisting of a 10m high stainless steel tube and 1m in diameter, can be used to study cloud processes. MICC is housed in three separate cold rooms stacked on top of each other and warm pseudo-adiabatic expansion from controlled initial temperature and pressure is possible through chamber evacuation. Further details about the facility can be found at http://www.cas.manchester.ac.uk/restools/cloudchamber/index.html. MICC can be connected to the Manchester Aerosol Chamber (MAC, http://www.cas.manchester.ac.uk/restools/aerosolchamber/), which allows to inject specified aerosol particles into the cloud chamber for nucleation studies. The combination of MAC and MICC will be used in the CCN-Vol project, which seeks to bring the experimental evidence for co-condensation of organic and water vapour in cloud formation which leads to an increase in cloud particle numbers (see Topping et al., 2013, Nature Geoscience Letters, for details). Here, we will show a characterisation of the cloud and aerosol chamber coupling in regard to background aerosol particles and nucleation. Furthermore, we will show preliminary results from the warm CCN-Vol experiment, investigating the impact of co-condensation of organic vapours and water vapour on warm cloud droplet formation.

Nucleation and condensational growth to CCN sizes during a sustained pristine biogenic SOA event in a forested mountain valley

NASA Astrophysics Data System (ADS)

Liggio, J.; Pierce, J. R.; Leaitch, R.; Macdonald, A.; Whistler Aerosol; Cloud Study (WACS2010) Team

2011-12-01

The Whistler Aerosol and Cloud Study (WACS 2010), included intensive measurements of trace gases and particles at two sites on Whistler Mountain. Between July 6-11, 2010 there was a sustained high-pressure system over the region with cloud-free and higher-temperature conditions. During this period, the organic aerosol concentrations rose from <1 to 6 μ g m-3. Precursor gas and aerosol composition measurements show that these organics were almost entirely of secondary biogenic nature. Throughout July 6-11, the anthropogenic influence was minimal with sulfate concentrations < 0.2 μ g m-3 and SO2 mixing ratios ≈ 0.5 ppbv. Although SO2 mixing ratios were relatively low, companion box-model simulations show that nucleation and growth may be modeled accurately if Jnuc=3x10-7[H2SO4] and the organics are treated as effectively non-volatile. Due to the low condensation sink and the fast rate of condensing organics, the nucleated particles grew rapidly (2-5 nm hr-1) with a high probability of growing to CCN sizes before being scavenged by coagulation with larger particles (>10% growing to 100 nm in the first two days). The particles were observed to ultimately grow to ~200 nm after three days. Comparisons of SMPS with DMT CCN data show that particle hygroscopicity was generally around 0.1-0.11. The concentration of particles with diameters larger than 100 nm as well as CCN at 3% supersaturation rise from about 300 cm-3 to 1200 cm-3 during the 5 days due entirely to nucleation and growth. Relatively little SO2 is necessary to generate nucleation and growth to CCN sizes when biogenic SOA is abundant. This case offers a unique look at processes that may have controlled CCN formation in the pristine pre-industrial forested continental atmosphere.

Combustion Aerosol over Marine Stratus: Long Range Transport, Subsidence and Aerosol-Cloud Interactions over the South East Pacific

NASA Astrophysics Data System (ADS)

Clarke, A. D.; Snider, J.; Freitag, S.; Feingold, G.; Campos, T. L.; Breckhovskikh, V.; Kazil, J.

2011-12-01

The worlds largest stratus deck over the South East Pacific (SEP) was a study target for the VOCALS (http://www.eol.ucar.edu/projects/vocals/) experiment in October 2008. Aerosol-cloud interactions were one major goal of several ship and aircraft studies including results from 14 flights of the NCAR C-130 aircraft reported here. Each flight covered about a 1000 km range with multiple profiles and legs below, in and above the Sc deck. Strong aerosol sources along the coast of Chile were expected and found to influence cloud condensation nuclei (CCN) in coastal clouds. However; "rivers" of elevated CO, black carbon (BC) associated with combustion aerosol effective as CCN at <0.3%S were also common in subsiding FT air overlying the extensive Sc deck for over 1000km offshore. This subsidence, linked to the Hadley circulation, brought in aerosol from sources over the western Pacific as well as South America. Observed entrainment of this aerosol appeared linked to cloud related turbulence. When present, this combustion aerosol increased available CCN and decreased effective radius compared to clouds in "clean" MBL air advected from the South Pacific. We hypothesize that this entrainment can help buffer MBL clouds over the SEP against depletion of CCN by drizzle. This may delay transition of closed cell to open cell convection, potentially leading to increased lifetimes of Sc clouds that entrain such aerosol.

Aerosol effect on cloud droplet size as monitored from surface-based remote sensing over East China Sea region

NASA Astrophysics Data System (ADS)

Pandithurai, G.; Takamura, T.; Yamaguchi, J.; Miyagi, K.; Takano, T.; Ishizaka, Y.; Dipu, S.; Shimizu, A.

2009-07-01

The effect of increased aerosol concentrations on the low-level, non-precipitating, ice-free stratus clouds is examined using a suite of surface-based remote sensing systems. Cloud droplet effective radius and liquid water path are retrieved using cloud radar and microwave radiometer. Collocated measurements of aerosol scattering coefficient, size distribution and cloud condensation nuclei (CCN) concentrations were used to examine the response of cloud droplet size and optical thickness to increased CCN proxies. During the episodic events of increase in aerosol accumulation-mode volume distribution, the decrease in droplet size and increase in cloud optical thickness is observed. The indirect effect estimates are made for both droplet effective radius and cloud optical thickness for different liquid water path ranges and they range 0.02-0.18 and 0.005-0.154, respectively. Data are also categorized into thin and thick clouds based on cloud geometric thickness (Δz) and estimates show IE values are relatively higher for thicker clouds.

CCN and IN concentration measurements during the Antarctic Circumnavigation Expedition

NASA Astrophysics Data System (ADS)

Stratmann, F.; Henning, S.; Löffler, M.; Welti, A.; Hartmann, M.; Wernli, H.; Baccarini, A.; Schmale, J.

2017-12-01

Cloud condensation nuclei (CCN) and ice nuclei (IN) concentrations measured during the Antarctic Circumnavigation Expedition (ACE) within the Study of Preindustrial-like Aerosol-Climate Effects (SPACE) are presented. The measurements give a circumpolar transect through the Sub Antarctic Ocean, where existing measurements are scarce. ACE took place during the austral summer 2016/17 and included exploration of different environments from pristine open Ocean to Antarctic islands and the southernmost ports of the 3 surrounding continents. CCN concentrations are measured over the entire range of expected in-cloud supersaturations from 0.1 to 1% using a CCNc instrument from DMT. IN concentrations are determined from filter samples at water saturated conditions from -5°C to -25°C, covering common temperatures of mixed-phase cloud glaciation. The sensitivity of measured IN and CCN concentrations to meteorological parameters, activity of marine biology and location is assessed to gain insight into potential sources of CCN and IN. Back trajectory modelling is used to allocate regional variations to aerosol sources originating in the marine boundary layer or long-range transport. The gained datasets constrain CCN and IN concentrations in the marine boundary layer along the cruise track. The comprehensive set of parallel measured parameters during ACE allow to evaluate contributions of local ocean-surface sources versus long-range transport to Sub-Antarctic CCN and IN. The measurements can be used as input to climate models, e.g. pristine Sub Antarctic conditions can provide an approximation for a pre-industrial environment.

Stratospheric CCN sampling program

NASA Technical Reports Server (NTRS)

Rogers, C. F.

1981-01-01

When Mt. St. Helens produced several major eruptions in the late spring of 1980, there was a strong interest in the characterization of the cloud condensation nuclei (CCN) activity of the material that was injected into the troposphere and stratosphere. The scientific value of CCN measurements is two fold: CCN counts may be directly applied to calculations of the interaction of the aerosol (enlargement) at atmospherically-realistic relative humidities or supersaturations; and if the chemical constituency of the aerosol can be assumed, the number-versus-critical supersaturation spectrum may be converted into a dry aerosol size spectrum covering a size region not readily measured by other methods. The sampling method is described along with the instrumentation used in the experiments.

Toward Aerosol/Cloud Condensation Nuclei (CCN) Closure during CRYSTAL-FACE

NASA Technical Reports Server (NTRS)

VanReken, Timothy M.; Rissman, Tracey, A.; Roberts, Gregory C.; Varutbangkul, Varuntida; Jonsson, Haflidi H.; Flagan, Richard C.; Seinfeld, John H.

2003-01-01

During July 2002, measurements of cloud condensation nuclei were made in the vicinity of southwest Florida as part of the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE) field campaign. These observations, at supersaturations of 0.2 and 0.85%, are presented here. The performance of each of the two CCN counters was validated through laboratory calibration and an in situ intercomparison. The measurements indicate that the aerosol sampled during the campaign was predominantly marine in character: the median concentrations were 233 cm-3 (at S = 0.2%) and 371 cm(sup -3) (at S = 0.85%). Three flights during the experiment differed from this general trend; the aerosol sampled during the two flights on 18 July was more continental in character, and the observations on 28 July indicate high spatial variability and periods of very high aerosol concentrations. This study also includes a simplified aerosol/CCN closure analysis. Aerosol size distributions were measured simultaneously with the CCN observations, and these data are used to predict a CCN concentration using Kohler theory. For the purpose of this analysis, an idealized composition of pure ammonium sulfate was assumed. The analysis indicates that in this case, there was good general agreement between the predicted and observed CCN concentrations: at S = 0.2%, N(sub predicted)/N(sub observed)= 1.047 (R(sup 2)= 0.911)); at S = 0.85%, N(sub predicted)/N(sub observed)=1.201 (R(sup 2)= 0.835)). The impacts of the compositional assumption and of including in-cloud data in the analysis are addressed. The effect of removing the data from the 28 July flight is also examined; doing so improves the result of the closure analysis at S = 0.85%. When omitting that atypical flight, N(sub predicted)/N(sub observed) = 1.085 (R(sup 2) = 0.770) at S = 0.85%.

Macroscopic impacts of cloud and precipitation processes on maritime shallow convection as simulated by a large eddy simulation model with bin microphysics

DOE PAGES

Grabowski, W. W.; Wang, L. -P.; Prabha, T. V.

2015-01-27

This paper discusses impacts of cloud and precipitation processes on macrophysical properties of shallow convective clouds as simulated by a large eddy model applying warm-rain bin microphysics. Simulations with and without collision–coalescence are considered with cloud condensation nuclei (CCN) concentrations of 30, 60, 120, and 240 mg -1. Simulations with collision–coalescence include either the standard gravitational collision kernel or a novel kernel that includes enhancements due to the small-scale cloud turbulence. Simulations with droplet collisions were discussed in Wyszogrodzki et al. (2013) focusing on the impact of the turbulent collision kernel. The current paper expands that analysis and puts modelmore » results in the context of previous studies. Despite a significant increase of the drizzle/rain with the decrease of CCN concentration, enhanced by the effects of the small-scale turbulence, impacts on the macroscopic cloud field characteristics are relatively minor. Model results show a systematic shift in the cloud-top height distributions, with an increasing contribution of deeper clouds for stronger precipitating cases. We show that this is consistent with the explanation suggested in Wyszogrodzki et al. (2013); namely, the increase of drizzle/rain leads to a more efficient condensate offloading in the upper parts of the cloud field. A second effect involves suppression of the cloud droplet evaporation near cloud edges in low-CCN simulations, as documented in previous studies (e.g., Xue and Feingold, 2006). We pose the question whether the effects of cloud turbulence on drizzle/rain formation in shallow cumuli can be corroborated by remote sensing observations, for instance, from space. Although a clear signal is extracted from model results, we argue that the answer is negative due to uncertainties caused by the temporal variability of the shallow convective cloud field, sampling and spatial resolution of the satellite data, and overall accuracy of remote sensing retrievals.« less

Comparison of aerosol effects on simulated spring and summer hailstorm clouds

NASA Astrophysics Data System (ADS)

Yang, Huiling; Xiao, Hui; Guo, Chunwei; Wen, Guang; Tang, Qi; Sun, Yue

2017-07-01

Numerical simulations are carried out to investigate the effect of cloud condensation nuclei (CCN) concentrations on microphysical processes and precipitation characteristics of hailstorms. Two hailstorm cases are simulated, a spring case and a summer case, in a semiarid region of northern China, with the Regional Atmospheric Modeling System. The results are used to investigate the differences and similarities of the CCN effects between spring and summer hailstorms. The similarities are: (1) The total hydrometeor mixing ratio decreases, while the total ice-phase mixing ratio enhances, with increasing CCN concentration; (2) Enhancement of the CCN concentration results in the production of a greater amount of small-sized hydrometeor particles, but a lessening of large-sized hydrometeor particles; (3) As the CCN concentration increases, the supercooled cloud water and rainwater make a lesser contribution to hail, while the ice-phase hydrometeors take on active roles in the growth of hail; (4) When the CCN concentration increases, the amount of total precipitation lessens, while the role played by liquid-phase rainfall in the amount of total precipitation reduces, relatively, compared to that of ice-phase precipitation. The differences between the two storms include: (1) An increase in the CCN concentration tends to reduce pristine ice mixing ratios in the spring case but enhance them in the summer case; (2) Ice-phase hydrometeor particles contribute more to hail growth in the spring case, while liquid water contributes more in the summer case; (3) An increase in the CCN concentration has different effects on surface hail precipitation in different seasons.

How quickly do cloud droplets form on atmospheric particles?

NASA Astrophysics Data System (ADS)

Ruehl, C. R.; Chuang, P. Y.; Nenes, A.

2008-02-01

The influence of aerosols on cloud properties is an important modulator of the climate system. Traditional Köhler theory predicts the equilibrium concentration of cloud condensation nuclei (CCN); however, it is not known to what extent particles exist in the atmosphere that may be prevented from acting as CCN by kinetic limitations. We measured the rate of cloud droplet formation on atmospheric particles sampled at four sites across the United States during the summer of 2006: Great Smoky Mountain National Park, TN; Bondville, IL; Houston, TX; and the Atmospheric Radiation Measurement Program Southern Great Plains site near Lamont, OK. We express droplet growth rates with the mass accommodation coefficient (α), and report values of α measured in the field normalized to the mean α measured for lab-generated ammonium sulfate (AS) particles (i.e., α'=α/αAS). Overall, 59% of ambient CCN grew at a rate similar to AS. We report the fraction of CCN that were "low-α' " (α'<10-1, corresponding to α<1.5×10-2). Of the 16 days during which these measurements were made, 8 had relatively few low-α' CCN (<16%), 6 had moderate low-α' fractions (27% to 59%), and 2 had large low-α' fractions (>82% during at least one ~30 min period). Day to day variability was greatest in Tennessee and Illinois, and low-α' particles were most prevalent on days when back trajectories suggested that air was arriving from aloft. The highest fractions of low-α' CCN in Houston and Illinois occurred around local noon, and decreased later in the day. These results suggest that for some air masses, accurate quantification of CCN concentrations may need to account for kinetic limitations.

STORMVEX. Ice Nuclei and Cloud Condensation Nuclei Characterization Field Campaign Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cziczo, D.

2016-03-01

The relationship between aerosol particles and the formation of clouds is among the most uncertain aspects in our current understanding of climate change. Warm clouds have been the most extensively studied, in large part because they are normally close to the Earth’s surface and only contain large concentrations of liquid droplets. Ice and mixed-phase clouds have been less studied even though they have extensive global coverage and dominate precipitation formation. Because they require low temperatures to form, both cloud types are infrequently found at ground level, resulting in more difficult field studies. Complex mixtures of liquid and ice elements, normallymore » at much lower concentrations than found in warm clouds, require precise separation techniques and accurate identification of phase. Because they have proved so difficult to study, the climatic impact of ice-containing clouds remains unresolved. In this study, cloud condensation nuclei (CCN) concentrations and associated single particles’ composition and size were measured at a high-elevation research site—Storm Peak Lab, east of Steamboat Springs, Colorado, operated by the Desert Research Institute. Detailed composition analyses were presented to compare CCN activation with single-particle composition. In collaboration with the scientists of the Storm Peak Lab Cloud Property Validation Experiment (STORMVEX), our goal was to relate these findings to the cloud characteristics and the effect of anthropogenic activities.« less

Hygroscopicity of organic compounds as a function of carbon chain length, carboxyl, hydroperoxy, and carbonyl functional groups

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petters, Sarah Suda; Pagonis, Demetrios; Claflin, Megan Suzanne

The albedo and microphysical properties of clouds are controlled in part by the hygroscopicity of particles serving as cloud condensation nuclei (CCN). Hygroscopicity of complex organic mixtures in the atmosphere varies widely and remains challenging to predict. Here we present new measurements characterizing the CCN activity of pure compounds in which carbon chain length and the number of hydroperoxy, carboxyl, and carbonyl functional groups were systematically varied to establish the contributions of these groups to organic aerosol apparent hygroscopicity. Apparent hygroscopicity decreased with carbon chain length and increased with polar functional groups in the order carboxyl > hydroperoxy > carbonyl.more » Activation diameters at different supersaturations deviated from the -3/2 slope in log-log space predicted by Köhler theory, suggesting that water solubility limits CCN activity of particles composed of weakly functionalized organic compounds. Results are compared to a functional group contribution model that predicts CCN activity of organic compounds. The model performed well for most compounds but under-predicted the CCN activity of hydroperoxy groups. New best-fit hydroperoxy group/water interaction parameters were derived from the available CCN data. Lastly, these results may help improve estimates of the CCN activity of ambient organic aerosols from composition data.« less

Hygroscopicity of organic compounds as a function of carbon chain length, carboxyl, hydroperoxy, and carbonyl functional groups

DOE PAGES

Petters, Sarah Suda; Pagonis, Demetrios; Claflin, Megan Suzanne; ...

2017-06-16

The albedo and microphysical properties of clouds are controlled in part by the hygroscopicity of particles serving as cloud condensation nuclei (CCN). Hygroscopicity of complex organic mixtures in the atmosphere varies widely and remains challenging to predict. Here we present new measurements characterizing the CCN activity of pure compounds in which carbon chain length and the number of hydroperoxy, carboxyl, and carbonyl functional groups were systematically varied to establish the contributions of these groups to organic aerosol apparent hygroscopicity. Apparent hygroscopicity decreased with carbon chain length and increased with polar functional groups in the order carboxyl > hydroperoxy > carbonyl.more » Activation diameters at different supersaturations deviated from the -3/2 slope in log-log space predicted by Köhler theory, suggesting that water solubility limits CCN activity of particles composed of weakly functionalized organic compounds. Results are compared to a functional group contribution model that predicts CCN activity of organic compounds. The model performed well for most compounds but under-predicted the CCN activity of hydroperoxy groups. New best-fit hydroperoxy group/water interaction parameters were derived from the available CCN data. Lastly, these results may help improve estimates of the CCN activity of ambient organic aerosols from composition data.« less

Mass extinctions, atmospheric sulphur and climatic warming at the K/T boundary

NASA Technical Reports Server (NTRS)

Rampino, Michael R.; Volk, Tyler

1988-01-01

The possible climatic effects of a drastic decrease in cloud condensation nuclei (CCN) associated with a severe reduction in the global marine phytoplankton abundance are investigated. Calculations suggest that a reduction in CCN of more than 80 percent and the resulting decrease in marine cloud albedo could have produced a rapid global warming of 6 C or more. Oxygen isotope analyses of marine sediments from many parts of the world have been interpreted as indicating a marked warming coincident with the demise of calcareous nannoplankton at the K/T boundary. Decreased marine cloud albedo and resulting high sea surface temperatures could have been a factor in the maintenance of low productivity in the 'Strangelove Ocean' period following the K/T extinctions.

Cloud forming potential of oligomers relevant to secondary organic aerosols

NASA Astrophysics Data System (ADS)

Xu, Wen; Guo, Song; Gomez-Hernandez, Mario; Zamora, Misti L.; Secrest, Jeremiah; Marrero-Ortiz, Wilmarie; Zhang, Annie L.; Collins, Don R.; Zhang, Renyi

2014-09-01

The hygroscopic growth factor (HGF) and cloud condensation nuclei (CCN) activity are measured for surrogates that mimic atmospherically relevant oligomers, including glyoxal trimer dihydrate, methyl glyoxal trimer dihydrate, sucrose, methyl glyoxal mixtures with sulfuric acid and glycolic acid, and 2,4-hexandienal mixtures with sulfuric acid and glycolic acid. For the single-component aerosols, the measured HGF ranges from 1.3 to 1.4 at a relative humidity of 90%, and the hygroscopicity parameter (κ) is in the range of 0.06 to 0.19 on the basis of the measured CCN activity and 0.13 to 0.22 on the basis of the measured HGF, compared to the calculated values of 0.08 to 0.16. Large differences exist in the κ values derived using the measured HGF and CCN data for the multi-component aerosols. Our results reveal that, in contrast to the oxidation process, oligomerization decreases particle hygroscopicity and CCN activity and provides guidance for analyzing the organic species in ambient aerosols.

A new method for calculating number concentrations of cloud condensation nuclei based on measurements of a three-wavelength humidified nephelometer system

NASA Astrophysics Data System (ADS)

Tao, Jiangchuan; Zhao, Chunsheng; Kuang, Ye; Zhao, Gang; Shen, Chuanyang; Yu, Yingli; Bian, Yuxuan; Xu, Wanyun

2018-02-01

The number concentration of cloud condensation nuclei (CCN) plays a fundamental role in cloud physics. Instrumentations of direct measurements of CCN number concentration (NCCN) based on chamber technology are complex and costly; thus a simple way for measuring NCCN is needed. In this study, a new method for NCCN calculation based on measurements of a three-wavelength humidified nephelometer system is proposed. A three-wavelength humidified nephelometer system can measure the aerosol light-scattering coefficient (σsp) at three wavelengths and the light-scattering enhancement factor (fRH). The Ångström exponent (Å) inferred from σsp at three wavelengths provides information on mean predominate aerosol size, and hygroscopicity parameter (κ) can be calculated from the combination of fRH and Å. Given this, a lookup table that includes σsp, κ and Å is established to predict NCCN. Due to the precondition for the application, this new method is not suitable for externally mixed particles, large particles (e.g., dust and sea salt) or fresh aerosol particles. This method is validated with direct measurements of NCCN using a CCN counter on the North China Plain. Results show that relative deviations between calculated NCCN and measured NCCN are within 30 % and confirm the robustness of this method. This method enables simplerNCCN measurements because the humidified nephelometer system is easily operated and stable. Compared with the method using a CCN counter, another advantage of this newly proposed method is that it can obtain NCCN at lower supersaturations in the ambient atmosphere.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bae, Soo Ya; Jeong, Jaein I.; Park, R.

We examine the effect of anthropogenic aerosols on the weekly variability of precipitation in Korea in summer 2004 by using Weather Research and Forecasting (WRF) and Community Multiscale Air Quality (CMAQ) models. We con-duct two WRF simulations including a baseline simulation with empirically based cloud condensation nuclei (CCN) number concentrations and a sensitivity simulation with our implementation to account for the effect of aerosols on CCN number concentrations. The first simulation underestimates observed precipitation amounts, particularly in northeastern coastal areas of Korea, whereas the latter shows higher precipitation amounts that are in better agree-ment with the observations. In addition, themore » sensitivity model with the aerosol effects reproduces the observed weekly variability, particularly for precipitation frequency with a high R at 0.85, showing 20% increase of precipita-tion events during the weekend than those during weekdays. We find that the aerosol effect results in higher CCN number concentrations during the weekdays and a three-fold increase of the cloud water mixing ratio through en-hanced condensation. As a result, the amount of warm rain is generally suppressed because of the low auto-conversion process from cloud water to rain water under high aerosol conditions. The inefficient conversion, how-ever, leads to higher vertical development of clouds in the mid-atmosphere with stronger updrafts in the sensitivity model, which increases by 21% cold-phase hydrometeors including ice, snow, and graupel relative to the baseline model and ultimately results in higher precipitation amounts in summer.« less

Competition for water vapour results in suppression of ice formation in mixed-phase clouds

NASA Astrophysics Data System (ADS)

Simpson, Emma L.; Connolly, Paul J.; McFiggans, Gordon

2018-05-01

The formation of ice in clouds can initiate precipitation and influence a cloud's reflectivity and lifetime, affecting climate to a highly uncertain degree. Nucleation of ice at elevated temperatures requires an ice nucleating particle (INP), which results in so-called heterogeneous freezing. Previously reported measurements for the ability of a particle to nucleate ice have been made in the absence of other aerosol which will act as cloud condensation nuclei (CCN) and are ubiquitous in the atmosphere. Here we show that CCN can outcompete INPs for available water vapour thus suppressing ice formation, which has the potential to significantly affect the Earth's radiation budget. The magnitude of this suppression is shown to be dependent on the mass of condensed water required for freezing. Here we show that ice formation in a state-of-the-art cloud parcel model is strongly dependent on the criteria for heterogeneous freezing selected from those previously hypothesised. We have developed an alternative criteria which agrees well with observations from cloud chamber experiments. This study demonstrates the dominant role that competition for water vapour can play in ice formation, highlighting both a need for clarity in the requirements for heterogeneous freezing and for measurements under atmospherically appropriate conditions.

Real-time characterization of the mixing state and droplet growth kinetics of CCN sampled during ICARTT

NASA Astrophysics Data System (ADS)

Nenes, A.; Medina, J.; Cottrell, L.; Griffin, R.

2005-12-01

Ground measurements of cloud condensation nuclei (CCN) were made during July and August of 2004 as part of the NEAQS ITCT-2K4 (New England Air Quality Study - Intercontinental Transport and Chemical Transformation 2004) mission at the Thompson Farm sampling site maintained by the University of New Hampshire. Over the duration of the field campaign, the two CCN instruments (built by Droplet Measurement Technologies, Inc.) were used to measure the concentration of CCN at 0.1, 0.2, 0.3, 0.37, 0.4, 0.5 and 0.6% supersaturation continuously over extended periods of time. One of the CCN instruments sampled unclassified ambient aerosol and the other was operated in our newly developed "Scanning Mobility CCN Analysis" technique (in which classified ambient aerosol obtained from a scanning DMA is introduced into the CCN counter), which allows the rapid characterization of the activation properties of classified ambient aerosol. Aerosol size distributions were measured using a TSI scanning mobility particle sizer (SMPS 3080). Finally, an Aerodyne Aerosol Mass Spectrometer (AMS) operated by the University of New Hampshire was used to measure the size-resolved chemical composition of the aerosol. We analyze the measurements using detailed numerical models of the CCN instrumentation. By close integration of measurements and theory, CCN closure can be assessed and real-time observations of CCN mixing state, ageing and droplet growth kinetics can be obtained. Finally, we derive characteristic aggregate properties for the carbonaceous component of the CCN, and discuss how this information can be introduced into aerosol-cloud interaction modules for GCM assessments of the aerosol indirect effect.

Organic condensation: a vital link connecting aerosol formation to cloud condensation nuclei (CCN) concentrations

NASA Astrophysics Data System (ADS)

Riipinen, I.; Pierce, J. R.; Yli-Juuti, T.; Nieminen, T.; Häkkinen, S.; Ehn, M.; Junninen, H.; Lehtipalo, K.; Petäjä, T.; Slowik, J.; Chang, R.; Shantz, N. C.; Abbatt, J.; Leaitch, W. R.; Kerminen, V.-M.; Worsnop, D. R.; Pandis, S. N.; Donahue, N. M.; Kulmala, M.

2011-04-01

Atmospheric aerosol particles influence global climate as well as impair air quality through their effects on atmospheric visibility and human health. Ultrafine (<100 nm) particles often dominate aerosol numbers, and nucleation of atmospheric vapors is an important source of these particles. To have climatic relevance, however, the freshly nucleated particles need to grow in size. We combine observations from two continental sites (Egbert, Canada and Hyytiälä, Finland) to show that condensation of organic vapors is a crucial factor governing the lifetimes and climatic importance of the smallest atmospheric particles. We model the observed ultrafine aerosol growth with a simplified scheme approximating the condensing species as a mixture of effectively non-volatile and semi-volatile species, demonstrate that state-of-the-art organic gas-particle partitioning models fail to reproduce the observations, and propose a modeling approach that is consistent with the measurements. We find that roughly half of the mass of the condensing mass needs to be distributed proportional to the aerosol surface area (thus implying that the condensation is governed by gas-phase concentration rather than the equilibrium vapour pressure) to explain the observed aerosol growth. We demonstrate the large sensitivity of predicted number concentrations of cloud condensation nuclei (CCN) to these interactions between organic vapors and the smallest atmospheric nanoparticles - highlighting the need for representing this process in global climate models.

Cloud condensation nuclei activity and hygroscopicity of fresh and aged cooking organic aerosol

NASA Astrophysics Data System (ADS)

Li, Yanwei; Tasoglou, Antonios; Liangou, Aikaterini; Cain, Kerrigan P.; Jahn, Leif; Gu, Peishi; Kostenidou, Evangelia; Pandis, Spyros N.

2018-03-01

Cooking organic aerosol (COA) is potentially a significant fraction of organic particulate matter in urban areas. COA chemical aging experiments, using aerosol produced by grilling hamburgers, took place in a smog chamber in the presence of UV light or excess ozone. The water solubility distributions, cloud condensation nuclei (CCN) activity, and corresponding hygroscopicity of fresh and aged COA were measured. The average mobility equivalent activation diameter of the fresh particles at 0.4% supersaturation ranged from 87 to 126 nm and decreased for aged particles, ranging from 65 to 88 nm. Most of the fresh COA had water solubility less than 0.1 g L-1, even though the corresponding particles were quite CCN active. After aging, the COA fraction with water solubility greater than 0.1 g L-1 increased more than 2 times. Using the extended Köhler theory for multiple partially soluble components in order to predict the measured activation diameters, the COA solubility distribution alone could not explain the CCN activity. Surface tensions less than 30 dyn cm-1 were required to explain the measured activation diameters. In addition, COA particles appear to not be spherical, which can introduce uncertainties into the corresponding calculations.

Characterization and parameterization of aerosol cloud condensation nuclei activation under different pollution conditions

PubMed Central

Che, H. C.; Zhang, X. Y.; Wang, Y. Q.; Zhang, L.; Shen, X. J.; Zhang, Y. M.; Ma, Q. L.; Sun, J. Y.; Zhang, Y. W.; Wang, T. T.

2016-01-01

To better understand the cloud condensation nuclei (CCN) activation capacity of aerosol particles in different pollution conditions, a long-term field experiment was carried out at a regional GAW (Global Atmosphere Watch) station in the Yangtze River Delta area of China. The homogeneity of aerosol particles was the highest in clean weather, with the highest active fraction of all the weather types. For pollution with the same visibility, the residual aerosol particles in higher relative humidity weather conditions were more externally mixed and heterogeneous, with a lower hygroscopic capacity. The hygroscopic capacity (κ) of organic aerosols can be classified into 0.1 and 0.2 in different weather types. The particles at ~150 nm were easily activated in haze weather conditions. For CCN predictions, the bulk chemical composition method was closer to observations at low supersaturations (≤0.1%), whereas when the supersaturation was ≥0.2%, the size-resolved chemical composition method was more accurate. As for the mixing state of the aerosol particles, in haze, heavy haze, and severe haze weather conditions CCN predictions based on the internal mixing assumption were robust, whereas for other weather conditions, predictions based on the external mixing assumption were more accurate. PMID:27075947

Droplet Size Distributions as a function of rainy system type and Cloud Condensation Nuclei concentrations

NASA Astrophysics Data System (ADS)

Cecchini, Micael A.; Machado, Luiz A. T.; Artaxo, Paulo

2014-06-01

This work aims to study typical Droplet Size Distributions (DSDs) for different types of precipitation systems and Cloud Condensation Nuclei concentrations over the Vale do Paraíba region in southeastern Brazil. Numerous instruments were deployed during the CHUVA (Cloud processes of tHe main precipitation systems in Brazil: a contribUtion to cloud resolVing modeling and to the GPM) Project in Vale do Paraíba campaign, from November 22, 2011 through January 10, 2012. Measurements of CCN (Cloud Condensation Nuclei) and total particle concentrations, along with measurements of rain DSDs and standard atmospheric properties, including temperature, pressure and wind intensity and direction, were specifically made in this study. The measured DSDs were parameterized with a gamma function using the moment method. The three gamma parameters were disposed in a 3-dimensional space, and subclasses were classified using cluster analysis. Seven DSD categories were chosen to represent the different types of DSDs. The DSD classes were useful in characterizing precipitation events both individually and as a group of systems with similar properties. The rainfall regime classification system was employed to categorize rainy events as local convective rainfall, organized convection rainfall and stratiform rainfall. Furthermore, the frequencies of the seven DSD classes were associated to each type of rainy event. The rainfall categories were also employed to evaluate the impact of the CCN concentration on the DSDs. In the stratiform rain events, the polluted cases had a statistically significant increase in the total rain droplet concentrations (TDCs) compared to cleaner events. An average concentration increase from 668 cm- 3 to 2012 cm- 3 for CCN at 1% supersaturation was found to be associated with an increase of approximately 87 m- 3 in TDC for those events. For the local convection cases, polluted events presented a 10% higher mass weighted mean diameter (Dm) on average. For the organized convection events, no significant results were found.

Marine CCN Activation: A Battle Between Primary and Secondary Sources

NASA Astrophysics Data System (ADS)

Fossum, K. N.; Ovadnevaite, J.; Ceburnis, D.; Preissler, J.; O'Dowd, C. D. D.

2017-12-01

Low-altitude marine clouds are cooling components of the Earth's radiative budget, and the direct measurements of the properties of these cloud forming particles, called cloud condensation nuclei (CCN), helps modellers reconstruct aerosol-to-cloud droplet processes, improving climate predictions. In this study, CCN are directly measured (CCNC commercially available from Droplet Measurement Technologies, Inc.), resolving activation efficiency at varying supersaturated conditions. Previous studies show that sub-micron sea salt particulates activate competitively, reducing the cloud peak supersaturation and inhibiting the activation of sulphate particulates into cloud droplets, making chemical composition an important component in determining cloud droplet number concentration (CDNC). This effect and the sea salt numbers needed to induce it have not been previously studied long-term in the natural environment. As part of this work, data was analysed from a two month marine research ship campaign during the Antarctic Austral summer, in 2015. Ambient aerosol in the Scotia Sea region was sampled continuously, and through the use of multiple aerosol in-situ instruments, this study shows that CCN number in both the open ocean and ice-pack influenced air masses are largely proportionate to secondary aerosol. However, open ocean air masses show a significant primary aerosol influence which changes the aerosol characteristics. Higher sea salt mass concentrations in the open ocean lead to better CCN activation efficiencies. Coupled with high wind speeds and sea surface turbulence, open ocean air masses show a repression of the CDNC number compared with the theoretical values that should be expected with the sub-cloud aerosol number concentration. This is not seen in the ice-pack air masses. Work is ongoing, looking into a long-term North Atlantic marine aerosol data set, but it would appear that chemical composition plays a large role in aerosol to cloud droplet processes, and can initially restrict CDNC when sea salt is abundant and updraft velocities are relatively low.

Long-term cloud condensation nuclei number concentration, particle number size distribution and chemical composition measurements at regionally representative observatories

NASA Astrophysics Data System (ADS)

Schmale, Julia; Henning, Silvia; Decesari, Stefano; Henzing, Bas; Keskinen, Helmi; Sellegri, Karine; Ovadnevaite, Jurgita; Pöhlker, Mira L.; Brito, Joel; Bougiatioti, Aikaterini; Kristensson, Adam; Kalivitis, Nikos; Stavroulas, Iasonas; Carbone, Samara; Jefferson, Anne; Park, Minsu; Schlag, Patrick; Iwamoto, Yoko; Aalto, Pasi; Äijälä, Mikko; Bukowiecki, Nicolas; Ehn, Mikael; Frank, Göran; Fröhlich, Roman; Frumau, Arnoud; Herrmann, Erik; Herrmann, Hartmut; Holzinger, Rupert; Kos, Gerard; Kulmala, Markku; Mihalopoulos, Nikolaos; Nenes, Athanasios; O'Dowd, Colin; Petäjä, Tuukka; Picard, David; Pöhlker, Christopher; Pöschl, Ulrich; Poulain, Laurent; Prévôt, André Stephan Henry; Swietlicki, Erik; Andreae, Meinrat O.; Artaxo, Paulo; Wiedensohler, Alfred; Ogren, John; Matsuki, Atsushi; Yum, Seong Soo; Stratmann, Frank; Baltensperger, Urs; Gysel, Martin

2018-02-01

Aerosol-cloud interactions (ACI) constitute the single largest uncertainty in anthropogenic radiative forcing. To reduce the uncertainties and gain more confidence in the simulation of ACI, models need to be evaluated against observations, in particular against measurements of cloud condensation nuclei (CCN). Here we present a data set - ready to be used for model validation - of long-term observations of CCN number concentrations, particle number size distributions and chemical composition from 12 sites on 3 continents. Studied environments include coastal background, rural background, alpine sites, remote forests and an urban surrounding. Expectedly, CCN characteristics are highly variable across site categories. However, they also vary within them, most strongly in the coastal background group, where CCN number concentrations can vary by up to a factor of 30 within one season. In terms of particle activation behaviour, most continental stations exhibit very similar activation ratios (relative to particles > 20 nm) across the range of 0.1 to 1.0 % supersaturation. At the coastal sites the transition from particles being CCN inactive to becoming CCN active occurs over a wider range of the supersaturation spectrum. Several stations show strong seasonal cycles of CCN number concentrations and particle number size distributions, e.g. at Barrow (Arctic haze in spring), at the alpine stations (stronger influence of polluted boundary layer air masses in summer), the rain forest (wet and dry season) or Finokalia (wildfire influence in autumn). The rural background and urban sites exhibit relatively little variability throughout the year, while short-term variability can be high especially at the urban site. The average hygroscopicity parameter, κ, calculated from the chemical composition of submicron particles was highest at the coastal site of Mace Head (0.6) and lowest at the rain forest station ATTO (0.2-0.3). We performed closure studies based on κ-Köhler theory to predict CCN number concentrations. The ratio of predicted to measured CCN concentrations is between 0.87 and 1.4 for five different types of κ. The temporal variability is also well captured, with Pearson correlation coefficients exceeding 0.87. Information on CCN number concentrations at many locations is important to better characterise ACI and their radiative forcing. But long-term comprehensive aerosol particle characterisations are labour intensive and costly. Hence, we recommend operating migrating-CCNCs to conduct collocated CCN number concentration and particle number size distribution measurements at individual locations throughout one year at least to derive a seasonally resolved hygroscopicity parameter. This way, CCN number concentrations can only be calculated based on continued particle number size distribution information and greater spatial coverage of long-term measurements can be achieved.

Aerosol-Cloud Interactions and Cloud Microphysical Properties in the Asir Region of Saudi Arabia

NASA Astrophysics Data System (ADS)

Kucera, P. A.; Axisa, D.; Burger, R. P.; Li, R.; Collins, D. R.; Freney, E. J.; Buseck, P. R.

2009-12-01

In recent advertent and inadvertent weather modification studies, a considerable effort has been made to understand the impact of varying aerosol properties and concentration on cloud properties. Significant uncertainties exist with aerosol-cloud interactions for which complex microphysical processes link the aerosol and cloud properties. Under almost all environmental conditions, increased aerosol concentrations within polluted air masses will enhance cloud droplet concentration relative to that in unperturbed regions. The interaction between dust particles and clouds are significant, yet the conditions in which dust particles become cloud condensation nuclei (CCN) are uncertain. In order to quantify this aerosol effect on clouds and precipitation, a field campaign was launched in the Asir region, located adjacent to the Red Sea in the southwest region of Saudi Arabia. Ground measurements of aerosol size distributions, hygroscopic growth factors, CCN concentrations as well as aircraft measurements of cloud hydrometeor size distributions were observed in the Asir region in August 2009. The presentation will include a summary of the analysis and results with a focus on aerosol-cloud interactions and cloud microphysical properties observed during the convective season in the Asir region.

Model Intercomparison of CCN-Limited Arctic Clouds During ASCOS

NASA Astrophysics Data System (ADS)

Stevens, Robin; Dearden, Chris; Dimetrelos, Antonios; Eirund, Gesa; Possner, Anna; Raatikainen, Tomi; Loewe, Katharina; Hill, Adrian; Shipway, Ben; Connolly, Paul; Ekman, Annica; Hoose, Corinna; Laaksonen, Ari; de Leeuw, Gerrit; Kolmonen, Pekka; Saponaro, Giulia; Field, Paul; Carlsaw, Ken

2017-04-01

Future decreases in Arctic sea ice are expected to increase fluxes of aerosol and precursor gases from the open ocean surface within the Arctic. The resulting increase in cloud condensation nuclei (CCN) concentrations would be expected to result in increased cloud albedo (Struthers et al, 2011), leading to potentially large changes in radiative forcings. However, Browse et al. (2014) have shown that these increases in condensable material could also result in the growth of existing particles to sizes where they are more efficiently removed by wet deposition in drizzling stratocumulus clouds, ultimately decreasing CCN concentrations in the high Arctic. Their study was limited in that it did not simulate alterations of dynamics or cloud properties due to either changes in heat and moisture fluxes following sea­-ice loss or changing aerosol concentrations. Taken together, these results show that significant uncertainties remain in trying to quantify aerosol­-cloud processes in the Arctic system. The current representation of these processes in global climate models is most likely insufficient to realistically simulate long­-term changes. In order to better understand the microphysical processes currently governing Arctic clouds, we perform a model intercomparison of summertime high Arctic (>80N) clouds observed during the 2008 ASCOS campaign. The intercomparison includes results from three large eddy simulation models (UCLALES-SALSA, COSMO-LES, and MIMICA) and three numerical weather prediction models (COSMO-NWP, WRF, and UM-CASIM). The results of these experiments will be used as a basis for sensitivity studies on the impact of sea-ice loss on Arctic clouds through changes in aerosol and precursor emissions as well as changes in latent and sensible heat fluxes. Browse, J., et al., Atmos. Chem. Phys., 14(14), 7543-7557, doi:10.5194/acp-14-7543-2014, 2014. Struthers, H., et al., Atmos. Chem. Phys., 11(7), 3459-3477, doi:10.5194/acp-11-3459-2011, 2011.

Hemispheric aerosol vertical profiles: anthropogenic impacts on optical depth and cloud nuclei.

PubMed

Clarke, Antony; Kapustin, Vladimir

2010-09-17

Understanding the effect of anthropogenic combustion upon aerosol optical depth (AOD), clouds, and their radiative forcing requires regionally representative aerosol profiles. In this work, we examine more than 1000 vertical profiles from 11 major airborne campaigns in the Pacific hemisphere and confirm that regional enhancements in aerosol light scattering, mass, and number are associated with carbon monoxide from combustion and can exceed values in unperturbed regions by more than one order of magnitude. Related regional increases in a proxy for cloud condensation nuclei (CCN) and AOD imply that direct and indirect aerosol radiative effects are coupled issues linked globally to aged combustion. These profiles constrain the influence of combustion on regional AOD and CCN suitable for challenging climate model performance and informing satellite retrievals.

Effects of Ocean Ecosystem on Marine Aerosol-Cloud Interaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meskhidze, Nicholas; Nenes, Athanasios

Using smore » atellite data for the surface ocean, aerosol optical depth (AOD), and cloud microphysical parameters, we show that statistically significant positive correlations exist between ocean ecosystem productivity, the abundance of submicron aerosols, and cloud microphysical properties over different parts of the remote oceans. The correlation coefficient for remotely sensed surface chlorophyll a concentration ([Chl- a ]) and liquid cloud effective radii over productive areas of the oceans varies between − 0.2 and − 0.6 . Special attention is given to identifying (and addressing) problems from correlation analysis used in the previous studies that can lead to erroneous conclusions. A new approach (using the difference between retrieved AOD and predicted sea salt aerosol optical depth, AOD diff ) is developed to explore causal links between ocean physical and biological systems and the abundance of cloud condensation nuclei (CCN) in the remote marine atmosphere. We have found that over multiple time periods, 550 nm AOD diff (sensitive to accumulation mode aerosol, which is the prime contributor to CCN) correlates well with [Chl- a ] over the productive waters of the Southern Ocean. Since [Chl- a ] can be used as a proxy of ocean biological productivity, our analysis demonstrates the role of ocean ecology in contributing CCN, thus shaping the microphysical properties of low-level marine clouds.« less

Effects of Ocean Ecosystem on Marine Aerosol-Cloud Interaction

DOE PAGES

Meskhidze, Nicholas; Nenes, Athanasios

2010-01-01

Using smore » atellite data for the surface ocean, aerosol optical depth (AOD), and cloud microphysical parameters, we show that statistically significant positive correlations exist between ocean ecosystem productivity, the abundance of submicron aerosols, and cloud microphysical properties over different parts of the remote oceans. The correlation coefficient for remotely sensed surface chlorophyll a concentration ([Chl- a ]) and liquid cloud effective radii over productive areas of the oceans varies between − 0.2 and − 0.6 . Special attention is given to identifying (and addressing) problems from correlation analysis used in the previous studies that can lead to erroneous conclusions. A new approach (using the difference between retrieved AOD and predicted sea salt aerosol optical depth, AOD diff ) is developed to explore causal links between ocean physical and biological systems and the abundance of cloud condensation nuclei (CCN) in the remote marine atmosphere. We have found that over multiple time periods, 550 nm AOD diff (sensitive to accumulation mode aerosol, which is the prime contributor to CCN) correlates well with [Chl- a ] over the productive waters of the Southern Ocean. Since [Chl- a ] can be used as a proxy of ocean biological productivity, our analysis demonstrates the role of ocean ecology in contributing CCN, thus shaping the microphysical properties of low-level marine clouds.« less

CCN in the marine environment: Results from two intensive measurement campaigns - The Eastern North Atlantic (Mace Head) and The Southern Ocean (PEGASO cruise)

NASA Astrophysics Data System (ADS)

Ovadnevaite, Jurgita; Fossum, Kirsten; Ceburnis, Darius; Dall'Osto, Manuel; Simo, Rafel; O'Dowd, Colin

2016-04-01

Marine aerosol occurring in cloud condensation nucleus (CCN) sizes suggest that it may contribute notably to the CCN population [1, 2], but further cloud droplet number concentration would strongly depend on the ambient (cloud) conditions, such as available water content, supersaturation and competition between the CCN of different composition [3]. Since the global importance of marine aerosol particles to the cloud formation was postulated several decades ago [4], it has progressed from the evaluation of the nss-sulphate and sea salt effects to an acknowledgement of the significant role of organic aerosol [5]. It was demonstrated that primary marine organics, despite its hydrophobic nature, can possess the high CCN activation efficiency, resulting in the efficient cloud formation [6]. Results from two intensive measurement campaigns in The Eastern North Atlantic (Mace Head) and The Southern Ocean (PEGASO cruise) is presented here with the main focus on ssCCN dependence on aerosol chemical composition and, especially, origin and sources of marine organic. We investigate the activation of sea spray composed of the sea salt and externally mixed with nss-sulphate as well as the sea spray highly enriched in organics, stressing the importance of the latter to the formation of the cloud droplets. We also explore the suitability of existing theories to explain the marine aerosol activation to CCN. Acknowledgments The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) project BACCHUS under grant agreement n° 603445; Spanish Ministry of Economy and Competitiveness (MINECO) as part of the PEGASO (Ref.: CTM2012-37615) and BIO-NUC (Ref.: CGL2013-49020-R); HEA-PRTLI4;EC ACTRIS. [1] Meskhidze & Nenes (2006) Science 314, 1419-1423. [2] Sorooshian et al. (2009) Global Biogeochemical Cycles 23, GB4007. [3] O'Dowd et al. (1999) Quarterly Journal of the Royal Meteorological Society 125, 1295-1313. [4] Charlson et al. (1987) Nature 326, 655-661. [5] O'Dowd et al. (2004) Nature 431, 676-680. [6] Ovadnevaite et al. (2011) Geophysical Research Letters 38, L21806.

Vertical Profiles of Cloud Condensation Nuclei, Condensation Nuclei, Optical Aerosol, Aerosol Optical Properties, and Aerosol Volatility Measured from Balloons

NASA Technical Reports Server (NTRS)

Deshler, T.; Snider, J. R.; Vali, G.

1998-01-01

Under the support of this grant a balloon-borne gondola containing a variety of aerosol instruments was developed and flown from Laramie, Wyoming, (41 deg N, 105 deg W) and from Lauder, New Zealand (45 deg S, 170 deg E). The gondola includes instruments to measure the concentrations of condensation nuclei (CN), cloud condensation nuclei (CCN), optically detectable aerosol (OA.) (r greater than or equal to 0.15 - 2.0 microns), and optical scattering properties using a nephelometer (lambda = 530 microns). All instruments sampled from a common inlet which was heated to 40 C on ascent and to 160 C on descent. Flights with the CN counter, OA counter, and nephelometer began in July 1994. The CCN counter was added in November 1994, and the engineering problems were solved by June 1995. Since then the flights have included all four instruments, and were completed in January 1998. Altogether there were 20 flights from Laramie, approximately 5 per year, and 2 from Lauder. Of these there were one or more engineering problems on 6 of the flights from Laramie, hence the data are somewhat limited on those 6 flights, while a complete data set was obtained from the other 14 flights. Good CCN data are available from 12 of the Laramie flights. The two flights from Lauder in January 1998 were successful for all measurements. The results from these flights, and the development of the balloon-bome CCN counter have formed the basis for five conference presentations. The heated and unheated CN and OA measurements have been used to estimate the mass fraction of the aerosol volatile, while comparisons of the nephelometer measurements were used to estimate the light scattering, associated with the volatile aerosol. These estimates were calculated for 0.5 km averages of the ascent and descent data between 2.5 km and the tropopause, near 11.5 km.

Biomass-burning impact on CCN number, hygroscopicity and cloud formation during summertime in the eastern Mediterranean

NASA Astrophysics Data System (ADS)

Bougiatioti, Aikaterini; Bezantakos, Spiros; Stavroulas, Iasonas; Kalivitis, Nikos; Kokkalis, Panagiotis; Biskos, George; Mihalopoulos, Nikolaos; Papayannis, Alexandros; Nenes, Athanasios

2016-06-01

This study investigates the concentration, cloud condensation nuclei (CCN) activity and hygroscopic properties of particles influenced by biomass burning in the eastern Mediterranean and their impacts on cloud droplet formation. Air masses sampled were subject to a range of atmospheric processing (several hours up to 3 days). Values of the hygroscopicity parameter, κ, were derived from CCN measurements and a Hygroscopic Tandem Differential Mobility Analyzer (HTDMA). An Aerosol Chemical Speciation Monitor (ACSM) was also used to determine the chemical composition and mass concentration of non-refractory components of the submicron aerosol fraction. During fire events, the increased organic content (and lower inorganic fraction) of the aerosol decreases the values of κ, for all particle sizes. Particle sizes smaller than 80 nm exhibited considerable chemical dispersion (where hygroscopicity varied up to 100 % for particles of same size); larger particles, however, exhibited considerably less dispersion owing to the effects of condensational growth and cloud processing. ACSM measurements indicate that the bulk composition reflects the hygroscopicity and chemical nature of the largest particles (having a diameter of ˜ 100 nm at dry conditions) sampled. Based on positive matrix factorization (PMF) analysis of the organic ACSM spectra, CCN concentrations follow a similar trend as the biomass-burning organic aerosol (BBOA) component, with the former being enhanced between 65 and 150 % (for supersaturations ranging between 0.2 and 0.7 %) with the arrival of the smoke plumes. Using multilinear regression of the PMF factors (BBOA, OOA-BB and OOA) and the observed hygroscopicity parameter, the inferred hygroscopicity of the oxygenated organic aerosol components is determined. We find that the transformation of freshly emitted biomass burning (BBOA) to more oxidized organic aerosol (OOA-BB) can result in a 2-fold increase of the inferred organic hygroscopicity; about 10 % of the total aerosol hygroscopicity is related to the two biomass-burning components (BBOA and OOA-BB), which in turn contribute almost 35 % to the fine-particle organic water of the aerosol. Observation-derived calculations of the cloud droplet concentrations that develop for typical boundary layer cloud conditions suggest that biomass burning increases droplet number, on average by 8.5 %. The strongly sublinear response of clouds to biomass-burning (BB) influences is a result of strong competition of CCN for water vapor, which results in very low maximum supersaturation (0.08 % on average). Attributing droplet number variations to the total aerosol number and the chemical composition variations shows that the importance of chemical composition increases with distance, contributing up to 25 % of the total droplet variability. Therefore, although BB may strongly elevate CCN numbers, the impact on droplet number is limited by water vapor availability and depends on the aerosol particle concentration levels associated with the background.

Cloud condensation nuclei closure study on summer arctic aerosol

NASA Astrophysics Data System (ADS)

Martin, M.; Chang, R. Y.-W.; Sierau, B.; Sjogren, S.; Swietlicki, E.; Abbatt, J. P. D.; Leck, C.; Lohmann, U.

2011-11-01

We present an aerosol - cloud condensation nuclei (CCN) closure study on summer high Arctic aerosol based on measurements that were carried out in 2008 during the Arctic Summer Cloud Ocean Study (ASCOS) on board the Swedish ice breaker Oden. The data presented here were collected during a three-week time period in the pack ice (>85° N) when the icebreaker Oden was moored to an ice floe and drifted passively during the most biological active period into autumn freeze up conditions. CCN number concentrations were obtained using two CCN counters measuring at different supersaturations. The directly measured CCN number concentration was then compared with a CCN number concentration calculated using both bulk aerosol mass composition data from an aerosol mass spectrometer (AMS) and aerosol number size distributions obtained from a differential mobility particle sizer, assuming κ-Köhler theory, surface tension of water and an internally mixed aerosol. The last assumption was supported by measurements made with a hygroscopic tandem differential mobility analyzer (HTDMA) for particles >70 nm. For the two highest measured supersaturations, 0.73 and 0.41%, closure could not be achieved with the investigated settings concerning hygroscopicity and density. The calculated CCN number concentration was always higher than the measured one for those two supersaturations. This might be caused by a relative larger insoluble organic mass fraction of the smaller particles that activate at these supersaturations, which are thus less good CCN than the larger particles. On average, 36% of the mass measured with the AMS was organic mass. At 0.20, 0.15 and 0.10% supersaturation, closure could be achieved with different combinations of hygroscopic parameters and densities within the uncertainty range of the fit. The best agreement of the calculated CCN number concentration with the observed one was achieved when the organic fraction of the aerosol was treated as nearly water insoluble (κorg=0.02), leading to a mean total κ, κtot, of 0.33 ± 0.13. However, several settings led to closure and κorg=0.2 is found to be an upper limit at 0.1% supersaturation. κorg≤0.2 leads to a κtot range of 0.33 ± 013 to 0.50 ± 0.11. Thus, the organic material ranges from being sparingly soluble to effectively insoluble. These results suggest that an increase in organic mass fraction in particles of a certain size would lead to a suppression of the Arctic CCN activity.

Cloud Condensation Nuclei and Chemical Composition of size-resolved particles in a Brazilian megacity: Effect of NPF event, biomass burning and sea salt from remote regions on the CCN properties

NASA Astrophysics Data System (ADS)

Souto-Oliveira, Carlos; de Fátima Andrade, Maria; Kumar, Prashant; Lopes, Fabio; Babinski, Marly; Landulfo, Eduado; Vara-Vela, Angel

2016-04-01

Atmospheric aerosol particles are an important source of cloud condensation nuclei (CCN). Their microphysics and chemical composition can directly affect development of clouds and precipitation process1,2. Only a few studies in Latin American have reported the impact of urban aerosol on the formation of CCN and their contribution to global climate change3. In this study, we simultaneously measured size distributed particle number concentration (PNC), CCN, black carbon (BC) and elemental concentrations (EC) in aerosol samples from São Paulo city. The PNC was measured by DMPS (model 3936) operated with a DMA (model 3080) and CPC (TSI, model 3010). The CCN was measuredby a single-column continuous-flow stream-wise thermal gradient CCN chamber (DMT CCNC-100). The BC and EC were determined in polycarbonate filter collected by Cascade Impactor (MOUDI-MSP), using a smoke stain reflectometer and an ED-XRF (EDX 700; Shimadzu), respectively. During the study period, which was August to September 2014, four events of new particle formation (NPF), characterizing secondary process of aerosol formation were noted. The total PNC varied between 1106 and 29168 cm-3, while CCN presented concentrations of 206 to 12761 cm-3for SS=1.0%. The PNC showed different concentrations during diurnal and nocturnal periods with average of 16392±7811 cm-3 and 6874±3444cm-3, respectively. The activated ratio (CCN/CN) presented diurnal and nocturnal values of 0.19±0.10 and 0.41±0.18, while apparent activation diameter (Dact,a) was estimated to be 110±29 and 71±28 nm (SS=0.6%), respectively. Combining EC and BC results with air mass trajectory analysis (Lidar aerosol profiles and Hysplit air trajectories), apportionment events were identified for sea salt and biomass burning from coastal and continental regions, respectively. The nocturnal AR and Dact,apresented values of 0.46±0.11 and 49±15 nm (SS=0.6%) for sea salt events as opposed to 0.33±0.14 and 64±30 nm (SS=0.6%) during biomass burning events. Although statistically not robust, it was observed diurnal and nocturnal tendencies for CCN properties (AR, Dact,a), which were accompanied by small variability for sea salt and biomass burning events. References [1] Andreae et al. (2004). Science, 303, 1337-1342. [2] Andreae, M. O., and Rosenfeld, D. (2008). Earth-Science Reviews, 89, 13-41. [3] Almeida et al. Atmospheric Chemistry and Physics, 14, 7559-7572.

Applying the WRF Double-Moment Six-Class Microphysics Scheme in the GRAPES_Meso Model: A Case Study

NASA Astrophysics Data System (ADS)

Zhang, Meng; Wang, Hong; Zhang, Xiaoye; Peng, Yue; Che, Huizheng

2018-04-01

This study incorporated the Weather Research and Forecasting (WRF) model double-moment 6-class (WDM6) microphysics scheme into the mesoscale version of the Global/Regional Assimilation and PrEdiction System (GRAPES_Meso). A rainfall event that occurred during 3-5 June 2015 around Beijing was simulated by using the WDM6, the WRF single-moment 6-class scheme (WSM6), and the NCEP 5-class scheme, respectively. The results show that both the distribution and magnitude of the rainfall simulated with WDM6 were more consistent with the observation. Compared with WDM6, WSM6 simulated larger cloud liquid water content, which provided more water vapor for graupel growth, leading to increased precipitation in the cold-rain processes. For areas with the warmrain processes, the sensitivity experiments using WDM6 showed that an increase in cloud condensation nuclei (CCN) number concentration led to enhanced CCN activation ratio and larger cloud droplet number concentration ( N c) but decreased cloud droplet effective diameter. The formation of more small-size cloud droplets resulted in a decrease in raindrop number concentration ( N r), inhibiting the warm-rain processes, thus gradually decreasing the amount of precipitation. For areas mainly with the cold-rain processes, the overall amount of precipitation increased; however, it gradually decreased when the CCN number concentration reached a certain magnitude. Hence, the effect of CCN number concentration on precipitation exhibits significant differences in different rainfall areas of the same precipitation event.

CCN characteristics over a tropical coastal station during south-west monsoon: observations and closure studies

NASA Astrophysics Data System (ADS)

Jayachandran, V.; Nair, Vijayakumar S.; Babu, S. Suresh

2017-09-01

Number concentration measurements of cloud condensation nuclei (CCN) at five supersaturation values between 0.2 and 1.0% were made from a coastal site (Thiruvananthapuram) of peninsular India using a single column CCN counter during the summer monsoon period (June-September) of 2013 and 2014. The CCN concentration over this site showed diurnal variations of high values during nighttime and low values during daytime in association with the change in mesoscale circulation patterns. The inter-annual variations of CCN (CCN0.4% = 2,232 ± 672 cm-3 during August 2013 and CCN0.4% = 941 ± 325 cm-3 during August 2014) are mostly associated with the varying intensity of monsoon rainfall. The variation of CCN number concentration with supersaturation is found to be steeper during nighttime (indicating a less CCN active aerosol system) than during daytime (CCN active system). The CCN activation ratio estimated using simultaneous measurements of CCN and aerosol number (CN) concentration clearly depict the role of land-sea breeze circulations with higher values during daytime than the nighttime. The CCN number concentration predicted for different supersaturations, from measured aerosol number size distribution using Kohler theory, indicate the importance of the change in aerosol composition associated with different airmasses in a coastal environment.

Surface tension prevails over solute effect in organic-influenced cloud droplet activation.

PubMed

Ovadnevaite, Jurgita; Zuend, Andreas; Laaksonen, Ari; Sanchez, Kevin J; Roberts, Greg; Ceburnis, Darius; Decesari, Stefano; Rinaldi, Matteo; Hodas, Natasha; Facchini, Maria Cristina; Seinfeld, John H; O' Dowd, Colin

2017-06-29

The spontaneous growth of cloud condensation nuclei (CCN) into cloud droplets under supersaturated water vapour conditions is described by classic Köhler theory. This spontaneous activation of CCN depends on the interplay between the Raoult effect, whereby activation potential increases with decreasing water activity or increasing solute concentration, and the Kelvin effect, whereby activation potential decreases with decreasing droplet size or increases with decreasing surface tension, which is sensitive to surfactants. Surface tension lowering caused by organic surfactants, which diminishes the Kelvin effect, is expected to be negated by a concomitant reduction in the Raoult effect, driven by the displacement of surfactant molecules from the droplet bulk to the droplet-vapour interface. Here we present observational and theoretical evidence illustrating that, in ambient air, surface tension lowering can prevail over the reduction in the Raoult effect, leading to substantial increases in cloud droplet concentrations. We suggest that consideration of liquid-liquid phase separation, leading to complete or partial engulfing of a hygroscopic particle core by a hydrophobic organic-rich phase, can explain the lack of concomitant reduction of the Raoult effect, while maintaining substantial lowering of surface tension, even for partial surface coverage. Apart from the importance of particle size and composition in droplet activation, we show by observation and modelling that incorporation of phase-separation effects into activation thermodynamics can lead to a CCN number concentration that is up to ten times what is predicted by climate models, changing the properties of clouds. An adequate representation of the CCN activation process is essential to the prediction of clouds in climate models, and given the effect of clouds on the Earth's energy balance, improved prediction of aerosol-cloud-climate interactions is likely to result in improved assessments of future climate change.

A Condensation-coalescence Cloud Model for Exoplanetary Atmospheres: Formulation and Test Applications to Terrestrial and Jovian Clouds

NASA Astrophysics Data System (ADS)

Ohno, Kazumasa; Okuzumi, Satoshi

2017-02-01

A number of transiting exoplanets have featureless transmission spectra that might suggest the presence of clouds at high altitudes. A realistic cloud model is necessary to understand the atmospheric conditions under which such high-altitude clouds can form. In this study, we present a new cloud model that takes into account the microphysics of both condensation and coalescence. Our model provides the vertical profiles of the size and density of cloud and rain particles in an updraft for a given set of physical parameters, including the updraft velocity and the number density of cloud condensation nuclei (CCNs). We test our model by comparing with observations of trade-wind cumuli on Earth and ammonia ice clouds in Jupiter. For trade-wind cumuli, the model including both condensation and coalescence gives predictions that are consistent with observations, while the model including only condensation overestimates the mass density of cloud droplets by up to an order of magnitude. For Jovian ammonia clouds, the condensation-coalescence model simultaneously reproduces the effective particle radius, cloud optical thickness, and cloud geometric thickness inferred from Voyager observations if the updraft velocity and CCN number density are taken to be consistent with the results of moist convection simulations and Galileo probe measurements, respectively. These results suggest that the coalescence of condensate particles is important not only in terrestrial water clouds but also in Jovian ice clouds. Our model will be useful to understand how the dynamics, compositions, and nucleation processes in exoplanetary atmospheres affect the vertical extent and optical thickness of exoplanetary clouds via cloud microphysics.

Biogenic influence on cloud microphysics in the 'clean' oceanic atmosphere

NASA Astrophysics Data System (ADS)

Lana, A.; Simó, R.; Vallina, S. M.; Jurado, E.; Dachs, J.

2009-12-01

A 20 years old hypothesis postulates a feedback relationship between marine biota and climate through the emission of dimethylsulfide (DMS) as the principal natural source of Sulfate Secondary Aerosols (S-DMS) that are very efficient as cloud condensation nuclei (CCN). In recent years, the biological influence on cloud microphysics have been expanded to other potential biogenic cloud precursors: (i) volatile organic compounds produced by plankton and emitted to the atmosphere to form Secondary Organic Aerosols (SOA); (ii) biological particles and biogenic polymers, lifted with the seaspray by wind friction and bubble-bursting processes, that act as Primary Organic Aerosols (POA). Besides these biogenic aerosols, also seaspray-associated Sea Salt (SS) emissions, which are the dominant contribution to aerosol mass in the remote mixed boundary layer, also contribute to cloud condensation. All these aerosols affect cloud microphysics by providing new CCN, reducing the size of cloud droplets, and increasing cloud albedo. We have compared the seasonalities of the parameterized source functions of these natural cloud precursors with that of the satellite-derived cloud droplet effective radius (CLEFRA) over large regions of the ocean. Regions where big loads of continental aerosols (including anthropogenic -industrial, urban, and biomass burning) dominate during a significant part of the year were identified by use of remote sensing aerosol optical properties and excluded from our analysis. Our results show that the seasonality of cloud droplet effective radius matches those of S-DMS and SOA in the clean marine atmosphere, whereas SS and chlorophyll-associated POA on their own do not seem to play a major role in driving cloud droplet size.

Measurements of the hygroscopic and deliquescence properties of organic compounds of different solubilities in water and their relationship with cloud condensation nuclei activities.

PubMed

Chan, Man Nin; Kreidenweis, Sonia M; Chan, Chak K

2008-05-15

The initial phase (solid or aqueous droplet) of aerosol particles prior to activation is among the critical factors in determining their cloud condensation nuclei (CCN) activity. Single-particle levitation in an electrodynamic balance (EDB)was used to measure the phase transitions and hygroscopic properties of aerosol particles of 11 organic compounds with different solubilities (10(-1) to 102 g solute/100 g water). We use these data and other literature data to relate the CCN activity and hygroscopicity of organic compounds with different solubilities. The EDB data show that glyoxylic acid, 4-methylphthalic acid, monosaccharides (fructose and mannose), and disaccharides (maltose and lactose) did not crystallize and existed as metastable droplets at low relative humidity (RH). Hygroscopic data from this work and in the literature support earlier studies showing that the CCN activities of compounds with solubilities down to the order of 10(-1) g solute/100 g water can be predicted by standard Köhler theory with the assumption of complete dissolution of the solute at activation. We also demonstrate the use of evaporation data (or efflorescence data), which provides information on the water contents of metastable solutions below the compound deliquescence RH that can be extrapolated to higher dilutions, to predict the CCN activity of organic particles, particularly for sparingly soluble organic compounds that do not deliquesce at RH achievable in the EDB and in the hygroscopic tandem differential mobility analyzer.

Multivariate quadrature for representing cloud condensation nuclei activity of aerosol populations

DOE PAGES

Fierce, Laura; McGraw, Robert L.

2017-07-26

Here, sparse representations of atmospheric aerosols are needed for efficient regional- and global-scale chemical transport models. Here we introduce a new framework for representing aerosol distributions, based on the quadrature method of moments. Given a set of moment constraints, we show how linear programming, combined with an entropy-inspired cost function, can be used to construct optimized quadrature representations of aerosol distributions. The sparse representations derived from this approach accurately reproduce cloud condensation nuclei (CCN) activity for realistically complex distributions simulated by a particleresolved model. Additionally, the linear programming techniques described in this study can be used to bound key aerosolmore » properties, such as the number concentration of CCN. Unlike the commonly used sparse representations, such as modal and sectional schemes, the maximum-entropy approach described here is not constrained to pre-determined size bins or assumed distribution shapes. This study is a first step toward a particle-based aerosol scheme that will track multivariate aerosol distributions with sufficient computational efficiency for large-scale simulations.« less

Multivariate quadrature for representing cloud condensation nuclei activity of aerosol populations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fierce, Laura; McGraw, Robert L.

Here, sparse representations of atmospheric aerosols are needed for efficient regional- and global-scale chemical transport models. Here we introduce a new framework for representing aerosol distributions, based on the quadrature method of moments. Given a set of moment constraints, we show how linear programming, combined with an entropy-inspired cost function, can be used to construct optimized quadrature representations of aerosol distributions. The sparse representations derived from this approach accurately reproduce cloud condensation nuclei (CCN) activity for realistically complex distributions simulated by a particleresolved model. Additionally, the linear programming techniques described in this study can be used to bound key aerosolmore » properties, such as the number concentration of CCN. Unlike the commonly used sparse representations, such as modal and sectional schemes, the maximum-entropy approach described here is not constrained to pre-determined size bins or assumed distribution shapes. This study is a first step toward a particle-based aerosol scheme that will track multivariate aerosol distributions with sufficient computational efficiency for large-scale simulations.« less

Integrated approach towards understanding interactions of mineral dust aerosol with warm clouds

NASA Astrophysics Data System (ADS)

Kumar, Prashant

2011-12-01

Mineral dust is ubiquitous in the atmosphere and represents a dominant type of particulate matter by mass. Dust particles can serve as cloud condensation nuclei (CCN), giant CCN (GCCN), or ice nuclei (IN), thereby, affecting cloud microphysics, albedo, and lifetime. Despite its well-recognized importance, assessments of dust impacts on clouds and climate remain highly uncertain. This thesis addresses the role of dust as CCN and GCCN with the goal of improving our understanding of dust-warm cloud interactions and their representation in climate models. Most studies to date focus on the soluble fraction of aerosol particles when describing cloud droplet nucleation, and overlook the interactions of the hydrophilic insoluble fraction with water vapor. A new approach to include such interactions (expressed by the process of water vapor adsorption) is explored, by combining multilayer Frenkel-Halsey-Hill (FHH) physical adsorption isotherm and curvature (Kelvin) effects. The importance of adsorption activation theory (FHH-AT) is corroborated by measurements of CCN activity of mineral aerosols generated from clays, calcite, quartz, and desert soil samples from Northern Africa, East Asia/China, and Northern America. A new aerosol generation setup for CCN measurements was developed based on a dry generation technique capable of reproducing natural dust aerosol emission. Based on the dependence of critical supersaturation with particle dry diameter, it is found that the FHH-AT is a better framework for describing fresh (and unprocessed) dust CCN activity than the classical Kohler theory (KT). Ion Chromatography (IC) measurements performed on fresh regional dust samples indicate negligible soluble fraction, and support that water vapor adsorption is the prime source of CCN activity in the dust. CCN measurements with the commonly used wet generated mineral aerosol (from atomization of a dust aqueous suspension) are also carried out. Results indicate that the method is subject to biases as it generates a bimodal size distribution with a broad range of hygroscopicity. It is found that smaller particles generated in the more hygroscopic peak follow CCN activation by KT, while the larger peak is less hydrophilic with activation similar to dry generated dust that follow FHH-AT. Droplet activation kinetics measurements demonstrate that dry generated mineral aerosol display retarded activation kinetics with an equivalent water vapor uptake coefficient that is 30 - 80% lower relative to ammonium sulfate aerosol. Wet generated mineral aerosols, however, display similar activation kinetics to ammonium sulfate. These results suggest that at least a monolayer of water vapor (the rate-limiting step for adsorption) persists during the timescale of aerosol generation in the experiment, and questions the atmospheric relevance of studies on mineral aerosol generated from wet atomization method. A new parameterization of cloud droplet formation from insoluble dust CCN for regional and global climate models is also developed. The parameterization framework considers cloud droplet formation from dust CCN activating via FHH-AT, and soluble aerosol with activation described through KT. The parameterization is validated against a numerical parcel model, agreeing with predictions to within 10% (R2 ˜ 0.98). The potential role of dust GCCN activating by FHH-AT within warm stratocumulus and convective clouds is also evaluated. It is found that under pristine aerosol conditions, dust GCCN can act as collector drops with implications to dust-cloud-precipitation linkages. Biases introduced from describing dust GCCN activation by KT are also addressed. The results demonstrate that dust particles do not require deliquescent material to act as CCN in the atmosphere. Furthermore, the impact of dust particles as giant CCN on warm cloud and precipitation must be considered. Finally, the new parameterization of cloud droplet formation can be implemented in regional and global models providing an improved treatment of mineral aerosol on clouds and precipitation. The new framework is uniquely placed to address dust aerosol indirect effects on climate.

Organic Aerosols as Cloud Condensation Nuclei

NASA Astrophysics Data System (ADS)

Hudson, J. G.

2002-05-01

The large organic component of the atmospheric aerosol contributes to both natural and anthropogenic cloud condensation nuclei (CCN). Moreover, some organic substances may reduce droplet surface tension (Facchini et al. 1999), while others may be partially soluble (Laaksonen et al. 1998), and others may inhibit water condensation. The interaction of organics with water need to be understood in order to better understand the indirect aerosol effect. Therefore, laboratory CCN spectral measurements of organic aerosols are presented. These are measurements of the critical supersaturation (Sc), the supersaturation needed to produce an activated cloud droplet, as a function of the size of the organic particles. Substances include sodium lauryl (dodecyl) sulfate, oxalic, adipic, pinonic, hexadecanedioic, glutaric, stearic, succinic, phthalic, and benzoic acids. These size-Sc relationships are compared with theoretical and measured size-Sc relationships of common inorganic compounds (e.g., NaCl, KI, ammonium and calcium sulfate). Unlike most inorganics some organics display variations in solubility per unit mass as a function of particle size. Those showing relatively greater solubility at smaller sizes may be attributable to surface tension reduction, which is greater for less water dilution, as is the case for smaller particles, which are less diluted at the critical sizes. This was the case for sodium dodecyl sulfate, which does reduce surface tension. Relatively greater solubility for larger particles may be caused by greater dissolution at the higher dilutions that occur with larger particles; this is partial solubility. Measurements are also presented of internal mixtures of various organic and inorganic substances. These measurements were done with two CCN spectrometers (Hudson 1989) operating simultaneously. These two instruments usually displayed similar results in spite of the fact that they have different flow rates and supersaturation profiles. The degree of agreement between these cloud chambers then tests and defines the limits of possible alterations of conventional Kohler theory (e.g., Kulmala et al. 1993).

Aircraft measurements of aerosol properties during GoAmazon - G1 and HALO inter-comparison

NASA Astrophysics Data System (ADS)

Mei, F.; Cecchini, M. A.; Wang, J.; Tomlinson, J. M.; Comstock, J. M.; Hubbe, J. M.; Pekour, M. S.; Machado, L.; Wendisch, M.; Longo, K.; Martin, S. T.; Schmid, B.; Weinzierl, B.; Krüger, M. L.; Zöger, M.

2015-12-01

Currently, the indirect effects of atmospheric aerosols remain the most uncertain components in forcing of climate change over the industrial period (IPCC, 2013). This large uncertainty is partially a result of our incomplete understanding of the ability of particles to form cloud droplets under atmospherically relevant supersaturations. One objective of the US Department of Energy (DOE) Green Ocean Amazon Project (GoAmazon2014/5) is to understand the influence of the emission from Manaus, a tropical megacity, on aerosol size, concentration, and chemical composition, and their impact on cloud condensation nuclei (CCN) spectrum. The GoAmazon2014/5 study was an international campaign with the collaboration efforts from US, Brazil and Germany. During the intensive operation period, in the dry season (Sep. 1st - Oct. 10th, 2014), aerosol concentration, size distributions, and CCN spectra, both under pristine conditions and inside the Manaus plume, were characterized in-situ from the DOE Gulfstream-1 (G-1) research aircraft and German HALO aircraft during 4 coordinated flights on Sep. 9th, Sep. 16th, Sep 21st and Oct. 1st, 2014. During those four flights, aerosol number concentrations and CCN concentrations at two supersaturations (0.25% and 0.5%) were measured by condensation particle counters (CPCs) and a DMT dual column CCN counter onboard both G-1 and HALO. Aerosol size distribution was also measured by a Fast Integrated Mobility Spectrometer (FIMS) aboard the G-1 and is compared with the size distribution from Ultra High Sensitivity Aerosol Spectrometer - Airborne (UHSAS-A, DMT), which were deployed both on the G-1 and the HALO. Good agreement between the aerosol properties measured from the two aircraft has been achieved. The vertical profiles of aerosol size distribution and CCN spectrum will be discussed.

CCN activity of thermodenuded aerosol particles downwind of the Sacramento area urban plume

NASA Astrophysics Data System (ADS)

Hiranuma, N.; Cziczo, D. J.; Nelson, D.; Zhang, Q.; Setyan, A.; Song, C.; Shrivastava, M.; Shilling, J. E.

2010-12-01

This study focuses on the characterization of cloud condensation nuclei (CCN) properties of aerosol particles measured during the Carbonaceous Aerosols and Radiative Effects Study (CARES) near Sacramento, CA in June 2010. Supersaturation-dependant CCN activity (0.07 - 0.5% supersaturation) was measured with DMT CCN counters at two locations; one near the city center (T0) and the other in Cool, CA, a small town located ~40 kilometers downwind of the urban plume in the Sierra Nevada foothills (T1). The T1 CCN counter was operated behind a thermodenuder to study volatility-dependant CCN activity of the urban aerosol plume as it was transported into the biogenically influenced foothills. Preliminary analysis indicated that activated fraction was inversely proportional to the thermodenuder temperature, suggesting that the more-volatile fraction of the aerosol might have played an important role in the CCN activity of the aerosol. The relationship between the chemical composition and CCN activity of the aerosol will be discussed. The physical and chemical transformations of particles aged in the foothills as well as the diurnal profiles of CCN both at T0 and T1 will also be discussed for the transport event of 15 June 2010.

Measurements of cloud condensation nuclei spectra within maritime cumulus cloud droplets: Implications for mixing processes

NASA Technical Reports Server (NTRS)

Twohy, Cynthia H.; Hudson, James G.

1995-01-01

In a cloud formed during adiabatic expansion, the droplet size distribution will be systematically related to the critical supersaturation of the cloud condensation nuclei (CNN), but this relationship can be complicated in entraining clouds. Useful information about cloud processes, such as mixing, can be obtained from direct measurements of the CNN involved in droplet nucleation. This was accomplished by interfacing two instruments for a series of flights in maritime cumulus clouds. One instrument, the counterflow virtual impactor, collected cloud droplets, and the nonvolatile residual nuclei of the droplets was then passed to a CCN spectrometer, which measured the critical supersaturation (S(sub c)) spectrum of the droplet nuclei. The measured S(sub c) spectra of the droplet nuclei were compared with the S(sub c) spectra of ambient aerosol particles in order to identify which CCN were actually incorporated into droplets and to determine when mixing processes were active at different cloud levels. The droplet nuclei nearly always exhibited lower median S(sub c)'s than the ambient aerosol, as expected since droplets nucleate perferentially on particles with lower critical supersaturations. Critical supersaturation spectra from nuclei of droplets near cloud base were similar to those predicted for cloud regions formed adiabatically, but spectra of droplet nuclei from middle cloud levels showed some evidence that mixing had occurred. Near cloud top, the greatest variation in the spectra of the droplet nuclei was observed, and nuclei with high S(sub c)'s were sometimes present even within relatively large droplets. This suggests that the extent of mixing increases with height in cumulus clouds and that inhomogeneous mixing may be important near cloud top. These promising initial results suggest improvements to the experimental technique that will permit more quantitative results in future experiments.

Investigation of the CCN Activity, BC and UVBC Mass Concentrations of Biomass Burning Aerosols during the 2013 BASELInE Campaign

NASA Technical Reports Server (NTRS)

Hsiao, Ta-Chih; Ye, Wei-Cheng; Wang, Sheng-Hsiang; Tsay, Si-Chee; Chen, Wei-Nai; Lin, Neng-Huei; Lee, Chung-Te; Hung, Hui-Ming; Chuang, Ming-Tung; Chantara, Somporn

2015-01-01

Biomass-burning (BB) aerosols, acting as cloud condensation nuclei (CCN), can influence cloud microphysical and radiative properties. In this study, we present CCN measured near the BB source regions over northern Southeast Asia (Doi Ang Khang, Thailand) and at downwind receptor areas (Lulin Atmospheric Background Station, Taiwan), focusing exclusively on 13-20 March 2013 as part of 2013 spring campaign of the Seven SouthEast Asian Studies (7-SEAS) intensive observation. One of the campaigns objectives is to characterize BB aerosols serving as CCN in SouthEast Asia (SEA). CCN concentrations were measured by a CCN counter at 5 supersaturation (SS) levels: 0.15%, 0.30%, 0.45%, 0.60%, and 0.75%. In addition, PM2.5 and black carbon mass concentrations were analyzed by using a tapered element oscillating microbalance and an aethalometer. It was found the number-size distributions and the characteristics of hygroscopicity (e.g., activation ratio and k) of BB aerosols in SEA have a strong diurnal pattern, and different behaviors of patterns were characterized under two distinct weather systems. The overall average value was low (0.05-0.1) but comparable with previous CCN studies in other BB source regions. Furthermore, a large fraction of UV-absorbing organic material (UVBC) and high Delta-C among BB aerosols were also observed, which suggest the existence of substantial particulate organic matter in fresh BB aerosols. These data provide the most extensive characterization of BB aerosols in SEA until now.

Chemical aging of single and multicomponent biomass burning aerosol surrogate-particles by OH: Implications for cloud condensation nucleus activity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thalman, R.; Thalman, R.; Wang, J.

Multiphase OH and O₃ oxidation reactions with atmospheric organic aerosol (OA) can influence particle physicochemical properties including composition, morphology, and lifetime. Chemical aging of initially insoluble or low soluble single-component OA by OH and O₃ can increase their water-solubility and hygroscopicity, making them more active as cloud condensation nuclei (CCN) and susceptible to wet deposition. However, an outstanding problem is whether the effects of chemical aging on their CCN activity are preserved when mixed with other organic or inorganic compounds exhibiting greater water-solubility. In this work, the CCN activity of laboratory-generated biomass burning aerosol (BBA) surrogate-particles exposed to OH andmore » O₃ is evaluated by determining the hygroscopicity parameter, κ, as a function of particle type, mixing state, and OH/O₃ exposure applying a CCN counter (CCNc) coupled to an aerosol flow reactor (AFR). Levoglucosan (LEV), 4-methyl-5-nitrocatechol (MNC), and potassium sulfate (KS) serve as representative BBA compounds that exhibit different hygroscopicity, water solubility, chemical functionalities, and reactivity with OH radicals, and thus exemplify the complexity of mixed inorganic/organic aerosol in the atmosphere. The CCN activities of all of the particles were unaffected by O₃ exposure. Following exposure to OH, κ of MNC was enhanced by an order of magnitude, from 0.009 to ~0.1, indicating that chemically-aged MNC particles are better CCN and more prone to wet deposition than pure MNC particles. No significant enhancement in κ was observed for pure LEV particles following OH exposure. κ of the internally-mixed particles was not affected by OH oxidation. Furthermore, the CCN activity of OH exposed MNC-coated KS particles is similar to the OH unexposed atomized 1:1 by mass MNC: KS binary-component particles. Our results strongly suggest that when OA is dominated by water-soluble organic carbon (WSOC) or inorganic ions, chemical aging has no significant impact on OA hygroscopicity. The organic compounds exhibiting low solubility behave as if they are infinitely soluble when mixed with a sufficient amount of water-soluble compounds. At and beyond this point, the particles' CCN activity is governed entirely by the water-soluble fraction and not influenced by the oxidized organic fraction. Our results have important implications for heterogeneous oxidation and its impact on cloud formation given that atmospheric aerosol is a complex mixture of organic and inorganic compounds exhibiting a wide-range of solubilities.« less

Chemical aging of single and multicomponent biomass burning aerosol surrogate particles by OH: implications for cloud condensation nucleus activity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Slade, J. H.; Thalman, R.; Wang, J.

Multiphase OH and O 3 oxidation reactions with atmospheric organic aerosol (OA) can influence particle physicochemical properties including composition, morphology, and lifetime. Chemical aging of initially insoluble or low-soluble single-component OA by OH and O 3 can increase their water solubility and hygroscopicity, making them more active as cloud condensation nuclei (CCN) and susceptible to wet deposition. However, an outstanding problem is whether the effects of chemical aging on their CCN activity are preserved when mixed with other organic or inorganic compounds exhibiting greater water solubility. In this work, the CCN activity of laboratory-generated biomass burning aerosol (BBA) surrogate particlesmore » exposed to OH and O 3 is evaluated by determining the hygroscopicity parameter, κ, as a function of particle type, mixing state, and OH and O 3 exposure applying a CCN counter (CCNc) coupled to an aerosol flow reactor (AFR). Levoglucosan (LEV), 4-methyl-5-nitrocatechol (MNC), and potassium sulfate (KS) serve as representative BBA compounds that exhibit different hygroscopicity, water solubility, chemical functionalities, and reactivity with OH radicals, and thus exemplify the complexity of mixed inorganic/organic aerosol in the atmosphere. The CCN activities of all of the particles were unaffected by O 3 exposure. Following exposure to OH, κ of MNC was enhanced by an order of magnitude, from 0.009 to ~ 0.1, indicating that chemically aged MNC particles are better CCN and more prone to wet deposition than pure MNC particles. No significant enhancement in κ was observed for pure LEV particles following OH exposure. κ of the internally mixed particles was not affected by OH oxidation. Furthermore, the CCN activity of OH-exposed MNC-coated KS particles is similar to the OH unexposed atomized 1 : 1 by mass MNC : KS binary-component particles. Our results strongly suggest that when OA is dominated by water-soluble organic carbon (WSOC) or inorganic ions, chemical aging has no significant impact on OA hygroscopicity. The organic compounds exhibiting low solubility behave as if they are infinitely soluble when mixed with a sufficient number of water-soluble compounds. At and beyond this point, the particles' CCN activity is governed entirely by the water-soluble fraction and is not influenced by the oxidized organic fraction. Our results have important implications for heterogeneous oxidation and its impact on cloud formation given that atmospheric aerosol is a complex mixture of organic and inorganic compounds exhibiting a wide range of solubilities.« less

Chemical aging of single and multicomponent biomass burning aerosol surrogate particles by OH: implications for cloud condensation nucleus activity

DOE PAGES

Slade, J. H.; Thalman, R.; Wang, J.; ...

2015-09-14

Multiphase OH and O 3 oxidation reactions with atmospheric organic aerosol (OA) can influence particle physicochemical properties including composition, morphology, and lifetime. Chemical aging of initially insoluble or low-soluble single-component OA by OH and O 3 can increase their water solubility and hygroscopicity, making them more active as cloud condensation nuclei (CCN) and susceptible to wet deposition. However, an outstanding problem is whether the effects of chemical aging on their CCN activity are preserved when mixed with other organic or inorganic compounds exhibiting greater water solubility. In this work, the CCN activity of laboratory-generated biomass burning aerosol (BBA) surrogate particlesmore » exposed to OH and O 3 is evaluated by determining the hygroscopicity parameter, κ, as a function of particle type, mixing state, and OH and O 3 exposure applying a CCN counter (CCNc) coupled to an aerosol flow reactor (AFR). Levoglucosan (LEV), 4-methyl-5-nitrocatechol (MNC), and potassium sulfate (KS) serve as representative BBA compounds that exhibit different hygroscopicity, water solubility, chemical functionalities, and reactivity with OH radicals, and thus exemplify the complexity of mixed inorganic/organic aerosol in the atmosphere. The CCN activities of all of the particles were unaffected by O 3 exposure. Following exposure to OH, κ of MNC was enhanced by an order of magnitude, from 0.009 to ~ 0.1, indicating that chemically aged MNC particles are better CCN and more prone to wet deposition than pure MNC particles. No significant enhancement in κ was observed for pure LEV particles following OH exposure. κ of the internally mixed particles was not affected by OH oxidation. Furthermore, the CCN activity of OH-exposed MNC-coated KS particles is similar to the OH unexposed atomized 1 : 1 by mass MNC : KS binary-component particles. Our results strongly suggest that when OA is dominated by water-soluble organic carbon (WSOC) or inorganic ions, chemical aging has no significant impact on OA hygroscopicity. The organic compounds exhibiting low solubility behave as if they are infinitely soluble when mixed with a sufficient number of water-soluble compounds. At and beyond this point, the particles' CCN activity is governed entirely by the water-soluble fraction and is not influenced by the oxidized organic fraction. Our results have important implications for heterogeneous oxidation and its impact on cloud formation given that atmospheric aerosol is a complex mixture of organic and inorganic compounds exhibiting a wide range of solubilities.« less

Chemical aging of single and multicomponent biomass burning aerosol surrogate-particles by OH: Implications for cloud condensation nucleus activity

DOE PAGES

Thalman, R.; Thalman, R.; Wang, J.; ...

2015-03-06

Multiphase OH and O₃ oxidation reactions with atmospheric organic aerosol (OA) can influence particle physicochemical properties including composition, morphology, and lifetime. Chemical aging of initially insoluble or low soluble single-component OA by OH and O₃ can increase their water-solubility and hygroscopicity, making them more active as cloud condensation nuclei (CCN) and susceptible to wet deposition. However, an outstanding problem is whether the effects of chemical aging on their CCN activity are preserved when mixed with other organic or inorganic compounds exhibiting greater water-solubility. In this work, the CCN activity of laboratory-generated biomass burning aerosol (BBA) surrogate-particles exposed to OH andmore » O₃ is evaluated by determining the hygroscopicity parameter, κ, as a function of particle type, mixing state, and OH/O₃ exposure applying a CCN counter (CCNc) coupled to an aerosol flow reactor (AFR). Levoglucosan (LEV), 4-methyl-5-nitrocatechol (MNC), and potassium sulfate (KS) serve as representative BBA compounds that exhibit different hygroscopicity, water solubility, chemical functionalities, and reactivity with OH radicals, and thus exemplify the complexity of mixed inorganic/organic aerosol in the atmosphere. The CCN activities of all of the particles were unaffected by O₃ exposure. Following exposure to OH, κ of MNC was enhanced by an order of magnitude, from 0.009 to ~0.1, indicating that chemically-aged MNC particles are better CCN and more prone to wet deposition than pure MNC particles. No significant enhancement in κ was observed for pure LEV particles following OH exposure. κ of the internally-mixed particles was not affected by OH oxidation. Furthermore, the CCN activity of OH exposed MNC-coated KS particles is similar to the OH unexposed atomized 1:1 by mass MNC: KS binary-component particles. Our results strongly suggest that when OA is dominated by water-soluble organic carbon (WSOC) or inorganic ions, chemical aging has no significant impact on OA hygroscopicity. The organic compounds exhibiting low solubility behave as if they are infinitely soluble when mixed with a sufficient amount of water-soluble compounds. At and beyond this point, the particles' CCN activity is governed entirely by the water-soluble fraction and not influenced by the oxidized organic fraction. Our results have important implications for heterogeneous oxidation and its impact on cloud formation given that atmospheric aerosol is a complex mixture of organic and inorganic compounds exhibiting a wide-range of solubilities.« less

Long-term observations of aerosol and cloud condensation nuclei concentrations in Barbados

NASA Astrophysics Data System (ADS)

Pöhlker, Mira L.; Klimach, Thomas; Krüger, Ovid O.; Hrabe de Angelis, Isabella; Ditas, Florian; Praß, Maria; Holanda, Bruna; Su, Hang; Weber, Bettina; Pöhlker, Christopher; Farrell, David A.; Stevens, Bjorn; Prospero, Joseph M.; Andreae, Meinrat O.; Pöschl, Ulrich

2017-04-01

Long-term observation of atmospheric aerosol and cloud condensation nuclei (CCN) concentrations has been conducted at the Ragged Point site in Barbados since August 2016. Ragged Point is a well-established station to monitor the transatlantic transport of Saharan dust outbreaks [1]. In the absence of dust plumes, it represents an ideal site to analyze the maritime boundary layer aerosol that is transported with the trade winds over the Atlantic towards Barbados [2,3]. Broad aerosol size distribution (10 nm to 10 µm) as well as size-resolved CCN measurements at 10 different supersaturations from 0.05 % to 0.84 % have been conducted. The continuous online analyses are supplemented by intensive sampling periods to probe specific aerosol properties with various offline techniques (i.e., microscopy and spectroscopy). Aerosol key properties from our measurements are compared with the continuous and in depth observation of cloud properties at Deebles Point, which is in close neighborhood to the Ragged Point site [2]. Moreover, our activities have been synchronized with the HALO-NARVAL-2 aircraft campaign in August 2016 that added further detailed information on shallow cumulus clouds, which are characteristic for the Atlantic trade winds and represent a crucial factor in the Earth climate system. Our measurements have the following two focal points: (i) We aim to obtain a detailed CCN climatology for the alternation of maritime and dust-impacted episodes at this unique coastal location. This study will complement our recent in-depth analysis for the long-term CCN variability at a remote rain forest location [4]. (ii) Furthermore, we aim to collect detailed information on the role of different aerosol populations on the properties of the climatically important shallow cumulus clouds. References: [1] Prospero, J. M., Collard, F. X., Molinie, J., Jeannot, A. (2014), Global Biogeochemical Cycles, 28, 757-773. [2] Stevens, B., et al. (2016), Bulletin of the American Meteorological Society, 97, 787-801. [3] Wex, H., et al., (2016), Atmos. Chem. Phys., 16, 14107-14130. [4] Pöhlker, M. L.., et al. (2016), Atmos. Chem. Phys., 16, 15709-15740.

Aerosol and CCN properties at Princess Elisabeth station, East Antarctica: seasonality, new particle formation events and properties around precipitation events

NASA Astrophysics Data System (ADS)

Mangold, Alexander; Laffineur, Quentin; De Backer, Hugo; Herenz, Paul; Wex, Heike; Gossart, Alexandra; Souverijns, Niels; Gorodetskaya, Irina; Van Lipzig, Nicole

2016-04-01

Since 2010, several complementary ground-based instruments for measuring the aerosol composition of the Antarctic atmosphere have been operated at the Belgian Antarctic research station Princess Elisabeth, in Dronning Maud Land, East Antarctica (71.95° S, 23.35° E, 1390 m asl.). In addition, three ground-based remote sensing instruments for cloud and precipitation observations have been installed for continuous operation, including a ceilometer (cloud base height, type, vertical extent), a 24 Ghz micro-rain radar (vertical profiles of radar effective reflectivity and Doppler velocity), and a pyrometer (cloud base temperature). The station is inhabited from November to end of February and operates under remote control during the other months. In this contribution, the general aerosol and cloud condensation nuclei (CCN) properties will be described with a special focus on new particle formation events and around precipitation events. New particle formation events are important for the atmospheric aerosol budget and they also show that aerosols are not only transported to Antarctica but are also produced there, also inland. Aerosols are essential for cloud formation and therefore also for precipitation, which is the only source for mass gain of the Antarctic ice sheet. Measured aerosol properties comprise size distribution, total number, total mass concentration, mass concentration of light-absorbing aerosol and absorption coefficient and total scattering coefficient. In addition, a CCN counter has been operated during austral summers 2013/14, 2014/15 and 2015/16. The baseline total number concentration N-total was around some hundreds of particles/cm3. During new particle formation events N-total increased to some thousands of particles/cm3. Simultaneous measurements of N-total, size distribution and CCN number revealed that mostly the number of particles smaller than 100 nm increased and that the concentration of cloud condensation nuclei increased only very weakly, respectively. Further analysis of the CCN data indicate that the aerosol measured at Princess Elisabeth station consisted mainly of material with a hygroscopicity close to that of sulfate. The measured wavelength-dependent aerosol absorption and scattering coefficients give further insight on the aerosol type, showing that mainly strongly scattering aerosol dominates. However, the fraction of light-absorbing aerosol increased during the passage of some extra-tropical cyclones or frontal systems, indicating the presence of aged, long-range transported aerosol. The characterisation of the atmospheric aerosol at Princess Elisabeth station will be used in this contribution to compare it with simultaneously measured precipitation observations.

The Hygroscopicity Parameter of Marine Organics in Sea Spray Aerosols

NASA Astrophysics Data System (ADS)

Boyer, M.; Chang, R. Y. W.

2015-12-01

The effects of aerosols on climate are poorly understood, specifically with respect to their influence on cloud properties. Since oceans cover >70% of Earth's surface, sea spray aerosols (SSA), which act efficiently as cloud condensation nuclei (CCN), may have important implications on Earth's radiation budget. Surface active organic species readily accumulate in the sea surface microlayer (SML), located at the ocean-atmosphere interface, and transfer onto nascent SSA. While it is understood that SSA are commonly enriched with organics, the resulting effect of the organic content on CCN activation remains unresolved. The hygroscopicity parameter, kappa (k), allows for the cloud nucleating properties of individual components to be predicted in particles of mixed composition; however, most studies typically infer k from ambient measurements without assessing the contribution of the individual components to the overall k. In this study, a method for quantifying the cloud nucleating properties of the organic species in surface seawater using k-Kohler theory is proposed. Ambient SML and bulk water samples will be collected and atomized to generate particles such that the overall k can be inferred from CCN measurements. The inorganic and organic components will be quantified, and the organic component will be separated so that the hygroscopicity of only the organic constituents can be determined. By comparing the inferred k values for the samples before and after removal of the inorganic component, the hygroscopicity of the organic constituents alone can be calculated, providing insight on the effect of organic species on CCN activation in SSA.

Aerosol and CCN over the Southern Ocean: Sources, Sinks and Processes

NASA Astrophysics Data System (ADS)

Clarke, A. D.; Freitag, S.; Howell, S. G.; Snider, J. R.; Kazil, J.; Feingold, G.; McNaughton, C. S.; Brekhovskikh, V.; Kapustin, V.; Campos, T. L.; Shank, L.

2013-12-01

Aerosol able to activate as cloud condensation nuclei (CCN) in marine stratus play an important role in cloud properties and processes. The 2008 VOCALS experiment (http://www.eol.ucar.edu/projects/vocals/) explored the aerosol cloud system over the South East Pacific (SEP). There, marine boundary layer (MBL) air from the Southern Ocean is directed north parallel to the South American coast and exposed to continental emissions. During this transport the initial clean MBL aerosol is modified in response to production, processing, entrainment, mixing, and removal. Here we discuss how the aerosol, the CCN and the clouds over the SEP are coupled by these processes. VOCALS data along 20S indicated cleanest air offshore and west of about 78W. However, some of the cleanest air (lowest CO concentrations) over the SEP were present in pockets of open cells (POC's). This suggests POC's are favored in places where remnants of Southern Ocean MBL air experienced the least mixing with higher CO sources during transport, either coastal or via entrainment of free troposphere air. Entrainment from the free troposphere (FT) was found to be an important source of marine boundary layer (MBL) aerosol in both near-shore and off-shore regions while direct advection of continental aerosol tended to influence aerosol and CCN closer to the coast. Entrainment from the FT included diverse sources from South America as well as long range transport from the western Pacific. Entrainment of FT aerosol can resupply the MBL with CCN and this process appears greatly enhanced when patchy 'rivers' of pollution lie directly above the inversion. This process was evident both offshore and near the coast. Production of CCN from sea spray aerosol (SSA) were found to increase with wind speed but atmospheric concentrations did not generally increase in the higher wind offshore regions because these regions had greater drizzle removal that compensated for increased production. Generally SSA larger than 60 nm were effective as marine cloud CCN but were only about 20% of the total. Elevated organic aerosol was usually associated with biomass burning sources and a natural marine organic aerosol source was weak. Although nucleation in clean scavenged air layers near the top of the boundary layer were observed under certain conditions, the resulting small aerosol sizes did not appear to provide an effective source of CCN sizes compared to other processes.

Water adsorption constrained Frenkel-Halsey-Hill adsorption activation theory: Montmorillonite and illite

NASA Astrophysics Data System (ADS)

Hatch, Courtney D.; Greenaway, Ann L.; Christie, Matthew J.; Baltrusaitis, Jonas

2014-04-01

Fresh mineral aerosol has recently been found to be effective cloud condensation nuclei (CCN) and contribute to the number of cloud droplets in the atmosphere due to the effect of water adsorption on CCN activation. The work described here uses experimental water adsorption measurements on Na-montmorillonite and illite clay to determine empirical adsorption parameters that can be used in a recently derived theoretical framework (Frenkel-Halsey-Hill Activation Theory, FHH-AT) that accounts for the effect of water adsorption on CCN activation. Upon fitting the Frenkel-Halsey-Hill (FHH) adsorption model to water adsorption measurements, we find FHH adsorption parameters, AFHH and BFHH, to be 98 ± 22 and 1.79 ± 0.11 for montmorillonite and 75 ± 17 and 1.77 ± 0.11 for illite, respectively. The AFHH and BFHH values obtained from water adsorption measurements differ from values reported previously determined by applying FHH-AT to CCN activation measurements. Differences in FHH adsorption parameters were attributed to different methods used to obtain them and the hydratable nature of the clays. FHH adsorption parameters determined from water adsorption measurements were then used to calculate the critical super-saturation (sc) for CCN activation using FHH-AT. The relationship between sc and the dry particle diameter (Ddry) gave CCN activation curve exponents (xFHH) of -0.61 and -0.64 for montmorillonite and illite, respectively. The xFHH values were slightly lower than reported previously for mineral aerosol. The lower exponent suggests that the CCN activity of hydratable clays is less sensitive to changes in Ddry and the hygroscopicity parameter exhibits a broader variability with Ddry compared to more soluble aerosols. Despite the differences in AFHH, BFHH and xFHH, the FHH-AT derived CCN activities of montmorillonite and illite are quite similar to each other and in excellent agreement with experimental CCN measurements resulting from wet-generated clay aerosol. This study illustrates that FHH-AT using adsorption parameters constrained by water adsorption is a simple, valid method for predicting CCN activation of fresh clay minerals and provides parameters that can be used in atmospheric models to study the effect of mineral dust aerosol on cloud formation and climate.

Particle growth kinetics over the Amazon rainforest

NASA Astrophysics Data System (ADS)

Pinterich, T.; Andreae, M. O.; Artaxo, P.; Kuang, C.; Longo, K.; Machado, L.; Manzi, A. O.; Martin, S. T.; Mei, F.; Pöhlker, C.; Pöhlker, M. L.; Poeschl, U.; Shilling, J. E.; Shiraiwa, M.; Tomlinson, J. M.; Zaveri, R. A.; Wang, J.

2016-12-01

Aerosol particles larger than 100 nm play a key role in global climate by acting as cloud condensation nuclei (CCN). Most of these particles, originated from new particle formation or directly emitted into the atmospheric, are initially too small to serve as CCN. These small particles grow to CCN size mainly through condensation of secondary species. In one extreme, the growth is dictated by kinetic condensation of very low-volatility compounds, favoring the growth of the smallest particles; in the other extreme, the process is driven by Raoult's law-based equilibrium partitioning of semi-volatile organic compound, favoring the growth of larger particles. These two mechanisms can lead to very different production rates of CCN. The growth of particles depends on a number of parameters, including the volatility of condensing species, particle phase, and diffusivity inside the particles, and this process is not well understood in part due to lack of ambient data. Here we examine atmospheric particle growth using high-resolution size distributions measured onboard the DOE G-1 aircraft during GoAmazon campaign, which took place from January 2014 to December 2015 near Manaus, Brazil, a city surrounded by natural forest for over 1000 km in every direction. City plumes are clearly identified by the strong enhancement of nucleation and Aitken mode particle concentrations over the clean background. As the plume traveled downwind, particle growth was observed, and is attributed to condensation of secondary species and coagulation (Fig.1). Observed aerosol growth is modeled using MOSAIC (Model for Simulating Aerosol Interactions and Chemistry), which dynamically partitions multiple compounds to all particle size bins by taking into account compound volatility, gas-phase diffusion, interfacial mass accommodation, particle-phase diffusion, and particle-phase reaction. The results from both wet and dry seasons will be discussed.

Measuring the CCN and IN ability of bacterial isolates: implications for the southeastern United States and Puerto Rico

NASA Astrophysics Data System (ADS)

Purdue, S.; Waters, S.; Konstantinidis, K.; Nenes, A.; DeLeon-Rodriguez, N.

2015-12-01

Ice nucleation is an important process in the climate system as it influences global precipitation processes, and can affect the vertical distribution of clouds with effects that both cool and warm the atmosphere. Of the pathways to ice nucleation, immersion mode, which occurs when ice nuclei (IN) particles are surrounded by an aqueous phase that subsequently freezes, dominates primary ice production in mixed-phase clouds. A simple but effective method to study immersion freezing is to utilize a droplet freezing assay (DFA) that consists of an aluminum plate, precisely cooled by a continuous flow of an ethylene glycol-water mixture. Using such a system we study the immersion IN characteristics of bacterial isolates (for temperatures ranging from -15oC to 0oC) isolated from rainwater and air collected in Atlanta, GA and Puerto Rico, over storms throughout the year. Despite their relatively large size and the presence of hydrophilic groups on the outer membranes of many bacteria, it is unclear if bacteria possess an inherent ability to nucleate an aqueous phase (a requirement for immersion freezing) for the wide range of supersaturations found in clouds. For this, we measure the cloud condensation nucleation (CCN) activity of each isolate (over the 0.05% to 0.6% supersaturation range) using a Continuous Flow Streamwise Thermal Gradient CCN Counter. Initial results have shown certain isolates to be very efficient CCN, allowing them to form droplets even for the very low supersaturations found in radiation fogs. In combination, these experiments provide insight into the potential dual-ability of some bacteria, isolated from the southeastern United States and Puerto Rico, to act as both efficient CCN and IN.

Correlation Of Giant Nuclei With Cloud Droplet Concentration

NASA Astrophysics Data System (ADS)

Jha, V.; Hudson, J. G.; Noble, S.

2011-12-01

The effect of giant nuclei (GN; larger than 1 micrometer particles produced by wind on the ocean surface) on warm rain has been debated for decades. During RICO (Rain in Cumulus over the Ocean) Hudson et al. (2011) found a negative correlation (R) between CCN concentrations at 1% supersaturation (S) and large cloud droplet concentrations (Fig. 1A). This reversal from positive R for CCN with total (or small) cloud droplet concentrations (left side of Fig. 1A) was explained by the greater competition for condensate, which thus limits droplet sizes when CCN concentrations are higher. The negative R increased in magnitude with altitude, and the droplet size where the maximum negative R occurred increased with altitude (Fig. 1A). However, at all altitudes this negative R decreased in magnitude for even larger cloud and drizzle drops (right side of Fig. 1A except highest altitude). The decrease in magnitude of the negative R was greater for increasing drop sizes at higher altitudes. Thus, at the higher altitudes, R for CCN with large drizzle drops was of low negative magnitude and even positive at the highest RICO altitudes. The disparity between CCN and drizzle drop concentrations precluded a causal relationship. But the high R between GN and drizzle drop concentrations at the highest altitudes (Fig. 1B) and the comparable concentrations indicated that GN were engendering drizzle. This is supported by the increasing R with altitude of the GN-drizzle drop R (right side of Fig. 1B). The conclusion of a GN-drizzle connection is also supported by the fact that CCN concentrations should inhibit drizzle. This analysis of Hudson et al. (2011) is here expanded to include correlations of CCN concentrations at lower S with cloud and drizzle drop concentrations to investigate intermediate relationships; i.e., between large nuclei (i.e., 0.1-1 micrometer; critical S 0.1-0.01%) and drizzle drop concentrations. A shortcoming of Hudson et al. (2011) was the small number of high altitude flights, which limited the significance of the R values. The very recent (July 2011) ICE-T project was a similar study in the same region (Caribbean). The greater number of high altitude cloud measurements during the summer season should provide better statistics to test the GN warm rain hypothesis.

On the CCN (de)activation nonlinearities

NASA Astrophysics Data System (ADS)

Arabas, Sylwester; Shima, Shin-ichiro

2017-09-01

We take into consideration the evolution of particle size in a monodisperse aerosol population during activation and deactivation of cloud condensation nuclei (CCN). Our analysis reveals that the system undergoes a saddle-node bifurcation and a cusp catastrophe. The control parameters chosen for the analysis are the relative humidity and the particle concentration. An analytical estimate of the activation timescale is derived through estimation of the time spent in the saddle-node bifurcation bottleneck. Numerical integration of the system coupled with a simple air-parcel cloud model portrays two types of activation/deactivation hystereses: one associated with the kinetic limitations on droplet growth when the system is far from equilibrium, and one occurring close to equilibrium and associated with the cusp catastrophe. We discuss the presented analyses in context of the development of particle-based models of aerosol-cloud interactions in which activation and deactivation impose stringent time-resolution constraints on numerical integration.

Properties of jet engine combustion particles during the PartEmis experiment. Hygroscopic growth at supersaturated conditions

NASA Astrophysics Data System (ADS)

Hitzenberger, R.; Giebl, H.; Petzold, A.; Gysel, M.; Nyeki, S.; Weingartner, E.; Baltensperger, U.; Wilson, C. W.

2003-07-01

During the EU Project PartEmis, the microphysical properties of aircraft combustion aerosol were investigated. This study is focused on the ability of exhaust aerosols to act as cloud condensation nuclei (CCN). The combustor was operated at two different conditions representing old and modern aircraft engine technology. CCN concentrations were measured with the University of Vienna CCN counter [ Giebl et al., 2002] at supersaturations around 0.7%. The activation ratio (fraction of CCN in total aerosol) depended on the fuel sulphur content (FSC) and also on the operation conditions. CCN/CN ratios increased from 0.93 through 1.43 to 5.15 . 10-3 (old cruise conditions) and 0.67 through 3.04 to 7.94 . 10-3 (modern cruise conditions) when FSC increased from 50 through 410 to1270 μg/g. The activation behaviour was modelled using classical theories and with a semi-empirical model [ Gysel et al., 2003] based on measured hygroscopicity of the aerosol under subsaturated conditions, which gave the best agreement.

Impact of new particle formation on the concentrations of aerosol number and cloud condensation nuclei around Beijing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsui, H.; Koike, Makoto; Kondo, Yutaka

New particle formation (NPF) is one of the most important processes in controlling the concentrations of aerosol number (condensation nuclei, CN) and cloud condensation nuclei (CCN) in the atmosphere. In this study, we introduced a new aerosol model representation with 20 size bins between 1 nm and 10 {mu}m and activation-type and kinetic nucleation parameterizations into the WRF-chem model (called NPF-explicit WRF-chem). Model calculations were conducted in the Beijing region in China for the periods during the CARE-Beijing 2006 campaign conducted in August and September 2006. Model calculations successfully reproduced the timing of NPF and no-NPF days in the measurementsmore » (21 of 26 days). Model calculations also reproduced the subsequent rapid growth of new particles with a time scale of half a day. These results suggest that once a reasonable nucleation rate at a diameter of 1 nm is given, explicit calculations of condensation and coagulation processes can reproduce the clear contrast between NPF and no-NPF days as well as further growth up to several tens nanometers. With this reasonable representation of the NPF process, we show that NPF contributed 20-30% of CN concentrations (> 10 nm in diameter) in and around Beijing on average. We also show that NPF increases CCN concentrations at higher supersaturations (S > 0.2%), while it decreases them at lower supersaturations (S < 0.1%). This is likely because NPF suppresses the increases in both the size and hygroscopicity of pre-existing particles through the competition of condensable gases between new particles and pre-existing particles. Sensitivity calculations show that a reduction of primary aerosol emissions, such as black carbon (BC), would not necessarily decrease CCN concentrations because of an increase in NPF. Sensitivity calculations also suggest that the reduction ratio of primary aerosol and SO2 emissions will be key in enhancing or damping the BC mitigation effect.« less

Impact of new particle formation on the concentrations of aerosols and cloud condensation nuclei around Beijing

NASA Astrophysics Data System (ADS)

Matsui, H.; Koike, M.; Kondo, Y.; Takegawa, N.; Wiedensohler, A.; Fast, J. D.; Zaveri, R. A.

2011-10-01

New particle formation (NPF) is one of the most important processes in controlling the concentrations of aerosols (condensation nuclei, CN) and cloud condensation nuclei (CCN) in the atmosphere. In this study, we introduce a new aerosol model representation with 20 size bins between 1 nm and 10 μm and activation-type and kinetic nucleation parameterizations into the WRF-chem model (called NPF-explicit WRF-chem). Model calculations were conducted in the Beijing region in China for the periods during the Campaign of Air Quality Research in Beijing and Surrounding Region 2006 (CARE-Beijing 2006) campaign conducted in August and September 2006. Model calculations successfully reproduced the timing of NPF and no-NPF days in the measurements (21 of 26 days). Model calculations also reproduced the subsequent rapid growth of new particles with a time scale of half a day. These results suggest that once a reasonable nucleation rate at a diameter of 1 nm is given, explicit calculations of condensation and coagulation processes can reproduce the clear contrast between NPF and no-NPF days as well as further growth up to several tens of nanometers. With this reasonable representation of the NPF process, we show that NPF contributed 20%-30% of the CN concentrations (>10 nm in diameter) in and around Beijing on average. We also show that NPF increases CCN concentrations at higher supersaturations (S > 0.2%), while it decreases them at lower supersaturations (S < 0.1%). This is likely because NPF suppresses the increases in both the size and hygroscopicity of preexisting particles through the competition of condensable gases between new particles and preexisting particles. Sensitivity calculations show that a reduction of primary aerosol emissions, such as black carbon (BC), would not necessarily decrease CCN concentrations because of an increase in NPF. Sensitivity calculations also suggest that the reduction ratio of primary aerosol and SO2 emissions will be key in enhancing or damping the BC mitigation effect.

Biomass Burning Organic Aerosol as a Modulator of Droplet Number in the Southern Atlantic

NASA Astrophysics Data System (ADS)

Kacarab, M.; Howell, S. G.; Small Griswold, J. D.; Thornhill, K. L., II; Wood, R.; Redemann, J.; Nenes, A.

2017-12-01

Aerosols play a significant yet highly variable role in local and global air quality and climate. They act as cloud condensation nuclei (CCN) and both scatter and absorb radiation, lending a large source of uncertainty to climate predictions. Biomass burning organic aerosol (BBOA) can drastically elevate CCN concentrations, but the response in cloud droplet number may be suppressed or even reversed due to low supersaturations that develop from strong competition for water vapor. Constraining droplet response to BBOA is a key factor to understanding aerosol-cloud interactions. The southeastern Atlantic (SEA) cloud deck off the west coast of central Africa is a prime opportunity to study these cloud-BBOA interactions for marine stratocumulus as during winter in the southern hemisphere the SEA cloud deck is overlain by a large, optically thick BBOA plume. The NASA ObseRvations of Aerosols above Clouds and their intEractionS (ORACLES) study focuses on increasing the understanding of how these BBOA affect the SEA cloud deck. Measurements of CCN concentration, aerosol size distribution and composition, updraft velocities, and cloud droplet number in and around the SEA cloud deck and associated BBOA plume were taken aboard the NASA P-3 aircraft during the first two years of the ORACLES campaign in September 2016 and August 2017. Here we evaluate the predicted and observed droplet number sensitivity to the aerosol fluctuations and quantify, using the data, the drivers of droplet number variability (vertical velocity or aerosol properties) as a function of biomass burning plume characteristics. Over the course of the campaign, different levels of BBOA influence in the marine boundary layer (MBL) were observed, allowing for comparison of cloud droplet number, hygroscopicity parameter (κ), and maximum in-cloud supersaturation over a range of "clean" and "dirty" conditions. Droplet number sensitivity to aerosol concentration, κ, and vertical updraft velocities are also evaluated. Generally, an increase in BBOA led to increased droplet number along with decreased κ and maximum in-cloud supersaturation (leading to an increase in competition for water vapor). This work seeks to contribute to an increased understanding of how CCN and aerosol properties affect the radiative and hydrological properties and impact of the cloud.

Intercomparison between Individual Particles Scavenged as CCN and Those Collected at Ground-based Site on West Coast of Japan During Asian Dust Storm

NASA Astrophysics Data System (ADS)

Ma, C. J.; Tohno, S.; Kasahara, M.; Hayakawa, S.

2002-12-01

Asian dust storm particles can affect precipitation composition because they are either incorporated into cloud via condensation of water vapour (nucleation) or due to the uptake of particles by existing droplets. And subsequently they affect aquatic and terrestrial ecosystems. In order to study the intercorrelation between the chemical natures of both the particles collected at ground-based site and those scavenged as CCN, the intensive field measurement was carried out on west coast of Japan (Yasaka, Tango Peninsula, 35.62°N; 135.07°E) during dense Asian dust storm event on March 22, 2002. Due to the size dependence of the chemical composition of aerosol particle, size-segregated aerosol particles were collect using Low pressure Andersen impactor sampler. Also, to collect cloud droplets individually, a particular method for the cloud droplet replication was newly applied using collodion (nitrocellulose) film. Sampling of cloud droplets was performed at summit of a mountain (680 m) in Yasaka. To analyze the ambient individual aerosol particles and individual retained particles in cloud droplet, X-ray fluorescence (XRF) analytical method set at SPring-8 on BL39XU was applied. Analytical result enables us not only to compare the characteristics of individual particles scavenged as CCN and those collected at ground-based site, but also to estimate the influence of long-range transport.

Aerosol Activation Properties within and above Mixing Layer in the North China Plain

NASA Astrophysics Data System (ADS)

Deng, Z.; Ran, L.

2013-12-01

Aerosol particles, serving as cloud condensation nuclei (CCN), may modify the properties of clouds and have an impact on climate. The vertical distribution of aerosols and their activation properties is critical to quantify the effect of aerosols on clouds. An intensive field campaign, Vertical Observations of trace Gases and Aerosols in the North China Plain (VOGA-NCP 2013), was conducted in the North China Plain during the late July and early August 2013 to measure the vertical profiles of atmospheric components in this polluted region and estimate their effects on atmospheric environment and climate. Aerosols were measured with in-situ instruments and Lidar. Particularly, the aerosols were collected at 1000 m height with a 1 m3 bag sampler attached to a tethered balloon, and subsequently measured with combined scanning mobility particle sizer (SMPS) and CCN counter. Comparisons of size-resolved activation ratios at ground level and 1000 m height showed that aerosols in upper atmosphere were not only less concentrated, but also less CCN-active than those at the surface. The difference in aerosol properties between upper atmosphere and the ground indicates that the analysis of impacts of aerosols on cloud might be misleading in heavily polluted region based on the relationship of cloud properties and surface aerosols or column without considering the vertical distribution of aerosol activation abilities.

Urban aerosol hygroscopicity and CCN activity measured during the MAPS-Seoul 2016 campaign

NASA Astrophysics Data System (ADS)

Kim, N.; Park, M.; Yum, S. S.; Kim, D. S.

2016-12-01

While submicron aerosols in atmosphere and their effects on air quality and climate are a rising issue in atmospheric sciences, scientific understanding of them is still limited due to the lack of comprehensive observations. In particular, studies for hygroscopic properties of aerosols, closely related to cloud condensation nuclei (CCN) activity, are essential to aerosol-cloud-interaction study as aerosols can act as CCN, which crucially influence cloud microphysical and radiative properties. Urban aerosol properties were measured at Olympic Park in Seoul, a typical megacity with various anthropogenic sources, during the Megacity Air Pollution Studies (MAPS-Seoul 2016) campaign (9 May- 12 June 2016) for understanding diverse aspects of air quality problem in Korea. Physical properties of aerosols, including aerosol and CCN number concentration, aerosol size distribution and growth factor were measured by CPC, CCNC, SMPS and H-TDMA, respectively. Simultaneously, size-resolved chemical component of aerosol and water-soluble aerosol mass concentration were measured by AMS and PILS-IC. These measurement data are used for comprehensive analysis. A main focus will be on the relationship between overall properties of aerosols and their CCN activity in urban area. Results from MAPS-Seoul 2015 will also be used as reference for comparison with measurements in 2016 campaign. For example, aerosol number concentrations peaked at 0800, 1500 and 2000 LT due to traffic at rush hours and photochemical reaction in the afternoon. This is slightly different from the results of MAPS-Seoul 2015 campaign that showed two dominant peaks in the morning and afternoon.

Production of extremely low volatile organic compounds from biogenic emissions: Measured yields and atmospheric implications

PubMed Central

Jokinen, Tuija; Berndt, Torsten; Makkonen, Risto; Kerminen, Veli-Matti; Junninen, Heikki; Stratmann, Frank; Herrmann, Hartmut; Guenther, Alex B.; Worsnop, Douglas R.; Kulmala, Markku; Ehn, Mikael; Sipilä, Mikko

2015-01-01

Oxidation products of monoterpenes and isoprene have a major influence on the global secondary organic aerosol (SOA) burden and the production of atmospheric nanoparticles and cloud condensation nuclei (CCN). Here, we investigate the formation of extremely low volatility organic compounds (ELVOC) from O3 and OH radical oxidation of several monoterpenes and isoprene in a series of laboratory experiments. We show that ELVOC from all precursors are formed within the first minute after the initial attack of an oxidant. We demonstrate that under atmospherically relevant concentrations, species with an endocyclic double bond efficiently produce ELVOC from ozonolysis, whereas the yields from OH radical-initiated reactions are smaller. If the double bond is exocyclic or the compound itself is acyclic, ozonolysis produces less ELVOC and the role of the OH radical-initiated ELVOC formation is increased. Isoprene oxidation produces marginal quantities of ELVOC regardless of the oxidant. Implementing our laboratory findings into a global modeling framework shows that biogenic SOA formation in general, and ELVOC in particular, play crucial roles in atmospheric CCN production. Monoterpene oxidation products enhance atmospheric new particle formation and growth in most continental regions, thereby increasing CCN concentrations, especially at high values of cloud supersaturation. Isoprene-derived SOA tends to suppress atmospheric new particle formation, yet it assists the growth of sub-CCN-size primary particles to CCN. Taking into account compound specific monoterpene emissions has a moderate effect on the modeled global CCN budget. PMID:26015574

Production of extremely low volatile organic compounds from biogenic emissions: Measured yields and atmospheric implications.

PubMed

Jokinen, Tuija; Berndt, Torsten; Makkonen, Risto; Kerminen, Veli-Matti; Junninen, Heikki; Paasonen, Pauli; Stratmann, Frank; Herrmann, Hartmut; Guenther, Alex B; Worsnop, Douglas R; Kulmala, Markku; Ehn, Mikael; Sipilä, Mikko

2015-06-09

Oxidation products of monoterpenes and isoprene have a major influence on the global secondary organic aerosol (SOA) burden and the production of atmospheric nanoparticles and cloud condensation nuclei (CCN). Here, we investigate the formation of extremely low volatility organic compounds (ELVOC) from O3 and OH radical oxidation of several monoterpenes and isoprene in a series of laboratory experiments. We show that ELVOC from all precursors are formed within the first minute after the initial attack of an oxidant. We demonstrate that under atmospherically relevant concentrations, species with an endocyclic double bond efficiently produce ELVOC from ozonolysis, whereas the yields from OH radical-initiated reactions are smaller. If the double bond is exocyclic or the compound itself is acyclic, ozonolysis produces less ELVOC and the role of the OH radical-initiated ELVOC formation is increased. Isoprene oxidation produces marginal quantities of ELVOC regardless of the oxidant. Implementing our laboratory findings into a global modeling framework shows that biogenic SOA formation in general, and ELVOC in particular, play crucial roles in atmospheric CCN production. Monoterpene oxidation products enhance atmospheric new particle formation and growth in most continental regions, thereby increasing CCN concentrations, especially at high values of cloud supersaturation. Isoprene-derived SOA tends to suppress atmospheric new particle formation, yet it assists the growth of sub-CCN-size primary particles to CCN. Taking into account compound specific monoterpene emissions has a moderate effect on the modeled global CCN budget.

Aerosol measurements during COPE: composition, size, and sources of CCN and INPs at the interface between marine and terrestrial influences

NASA Astrophysics Data System (ADS)

Taylor, Jonathan W.; Choularton, Thomas W.; Blyth, Alan M.; Flynn, Michael J.; Williams, Paul I.; Young, Gillian; Bower, Keith N.; Crosier, Jonathan; Gallagher, Martin W.; Dorsey, James R.; Liu, Zixia; Rosenberg, Philip D.

2016-09-01

Heavy rainfall from convective clouds can lead to devastating flash flooding, and observations of aerosols and clouds are required to improve cloud parameterisations used in precipitation forecasts. We present measurements of boundary layer aerosol concentration, size, and composition from a series of research flights performed over the southwest peninsula of the UK during the COnvective Precipitation Experiment (COPE) of summer 2013. We place emphasis on periods of southwesterly winds, which locally are most conducive to convective cloud formation, when marine air from the Atlantic reached the peninsula. Accumulation-mode aerosol mass loadings were typically 2-3 µg m-3 (corrected to standard cubic metres at 1013.25 hPa and 273.15 K), the majority of which was sulfuric acid over the sea, or ammonium sulfate inland, as terrestrial ammonia sources neutralised the aerosol. The cloud condensation nuclei (CCN) concentrations in these conditions were ˜ 150-280 cm-3 at 0.1 % and 400-500 cm-3 at 0.9 % supersaturation (SST), which are in good agreement with previous Atlantic measurements, and the cloud drop concentrations at cloud base ranged from 100 to 500 cm-3. The concentration of CCN at 0.1 % SST was well correlated with non-sea-salt sulfate, meaning marine sulfate formation was likely the main source of CCN. Marine organic aerosol (OA) had a similar mass spectrum to previous measurements of sea spray OA and was poorly correlated with CCN. In one case study that was significantly different to the rest, polluted anthropogenic emissions from the southern and central UK advected to the peninsula, with significant enhancements of OA, ammonium nitrate and sulfate, and black carbon. The CCN concentrations here were around 6 times higher than in the clean cases, and the cloud drop number concentrations were 3-4 times higher. Sources of ice-nucleating particles (INPs) were assessed by comparing different parameterisations used to predict INP concentrations, using measured aerosol concentrations as input. The parameterisations based on total aerosol produced INP concentrations that agreed within an order of magnitude with measured first ice concentrations at cloud temperatures as low as -12 °C. Composition-specific parameterisations for mineral dust, fluorescent particles, and sea spray OA were 3-4 orders of magnitude lower than the measured first ice concentrations, meaning a source of INPs was present that was not characterised by our measurements and/or one or more of the composition-specific parameterisations greatly underestimated INPs in this environment.

Cloud Condensation Nuclei in Cumulus Humilis - Selected Case Study During the CHAPS Campaign

NASA Astrophysics Data System (ADS)

Yu, X.; Berg, L. K.; Berkowitz, C. M.; Alexander, M. L.; Lee, Y.; Laskin, A.; Ogren, J. A.; Andrews, B.

2009-12-01

The Cumulus Humilis Aerosol Processing Study (CHAPS) provided a unique opportunity to study aerosol and cloud processing. Clouds play an active role in the processing and cycling of atmospheric constituents. Gases and particles can partition to cloud droplets by absorption and condensation as well as activation and pact scavenging. The Department of Energy (DOE) G-1 aircraft was used as one of the main platforms in CHAPS. Flight tracks were designed and implemented to characterize freshly emitted aerosols on cloud top and cloud base as well as with cloud, i.e., cumulus humilis (or fair-weather cumulus), in the vicinity of Oklahoma City. Measurements of interstitial aerosols and residuals of activated condensation cloud nuclei were conducted simultaneously. The interstitial aerosols were determined downstream of an isokinetic inlet; and the activated particles downstream of a counter-flow virtual impactor (CVI). The sampling line to the Aerodyne Aerosol Mass Spectrometer was switched between the isokinetic inlet and the CVI to allow characterization of interstitial particles out of clouds in contrast to particles activated in clouds. Trace gases including ozone, carbon monoxide, sulfur dioxide, and a series of volatile organic compounds (VOCs) were also measured as were key meteorological state parameters including liquid water content, cloud drop size, and dew point temperature were measured. This work will focus on studying CCN properties in cumulus humilis. Several approaches will be taken. The first is single particle analysis of particles collected by the Time-Resolved Aerosol Sampler (TRAC) by SEM/TEM coupled with EDX. We will specifically look into differences in particle properties such as chemical composition and morphology between activated and interstitial ones. The second analysis will link in situ measurements with the snap shots observations by TRAC. For instance, by looking into the characteristic m/z obtained by AMS vs. CO or isoprene, one can gain more insight into the role of primary and secondary organic aerosols in CCNs and background aerosols. Combined with observations of cloud properties, an improved picture of CCN activation in cumulus humilis can be made.

Examination of the potential impacts of dust and pollution aerosol acting as cloud nucleating aerosol on water resources in the Colorado River Basin

NASA Astrophysics Data System (ADS)

Jha, Vandana

In this study we examine the cumulative effect of dust acting as cloud nucleating aerosol (cloud condensation nuclei (CCN), giant cloud condensation nuclei (GCCN), and ice nuclei (IN)) along with anthropogenic aerosol pollution acting primarily as CCN, over the entire Colorado Rocky Mountains from the months of October to April in the year 2004-2005; the snow year. This ˜6.5 months analysis provides a range of snowfall totals and variability in dust and anthropogenic aerosol pollution. The specific objectives of this research is to quantify the impacts of both dust and pollution aerosols on wintertime precipitation in the Colorado Mountains using the Regional Atmospheric Modeling System (RAMS). In general, dust enhances precipitation primarily by acting as IN, while aerosol pollution reduces water resources in the CRB via the so-called "spill-over" effect, by enhancing cloud droplet concentrations and reducing riming rates. Dust is more episodic and aerosol pollution is more pervasive throughout the winter season. Combined response to dust and aerosol pollution is a net reduction of water resources in the CRB. The question is by how much are those water resources affected? Our best estimate is that total winter-season precipitation loss for for the CRB the 2004-2005 winter season due to the combined influence of aerosol pollution and dust is 5,380,00 acre-feet of water. Sensitivity studies for different cases have also been run for the specific cases in 2004-2005 winter season to analyze the impact of changing dust and aerosol ratios on precipitation in the Colorado River Basin. The dust is varied from 3 to 10 times in the experiments and the response is found to be non monotonic and depends on various environmental factors. The sensitivity studies show that adding dust in a wet system increases precipitation when IN affects are dominant. For a relatively dry system high concentrations of dust can result in over-seeding the clouds and reductions in precipitation. However, when adding dust to a system with warmer cloud bases, the response is non-monotonical, and when CCN affects are dominant, reductions in precipitation are found.

Individual aerosol particles in ambient and updraft conditions below convective cloud bases in the Oman mountain region

NASA Astrophysics Data System (ADS)

Semeniuk, T. A.; Bruintjes, R. T.; Salazar, V.; Breed, D. W.; Jensen, T. L.; Buseck, P. R.

2014-03-01

An airborne study of cloud microphysics provided an opportunity to collect aerosol particles in ambient and updraft conditions of natural convection systems for transmission electron microscopy (TEM). Particles were collected simultaneously on lacey carbon and calcium-coated carbon (Ca-C) TEM grids, providing information on particle morphology and chemistry and a unique record of the particle's physical state on impact. In total, 22 particle categories were identified, including single, coated, aggregate, and droplet types. The fine fraction comprised up to 90% mixed cation sulfate (MCS) droplets, while the coarse fraction comprised up to 80% mineral-containing aggregates. Insoluble (dry), partially soluble (wet), and fully soluble particles (droplets) were recorded on Ca-C grids. Dry particles were typically silicate grains; wet particles were mineral aggregates with chloride, nitrate, or sulfate components; and droplets were mainly aqueous NaCl and MCS. Higher numbers of droplets were present in updrafts (80% relative humidity (RH)) compared with ambient conditions (60% RH), and almost all particles activated at cloud base (100% RH). Greatest changes in size and shape were observed in NaCl-containing aggregates (>0.3 µm diameter) along updraft trajectories. Their abundance was associated with high numbers of cloud condensation nuclei (CCN) and cloud droplets, as well as large droplet sizes in updrafts. Thus, compositional dependence was observed in activation behavior recorded for coarse and fine fractions. Soluble salts from local pollution and natural sources clearly affected aerosol-cloud interactions, enhancing the spectrum of particles forming CCN and by forming giant CCN from aggregates, thus, making cloud seeding with hygroscopic flares ineffective in this region.

Potential origin of organic CNN observed at a marine site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andrews, E.; Kreidenweis, S.M.; Penner, J.E.

1995-12-31

Observations by Novakov and Penner (1993) suggest that organic aerosol particles may make up a significant portion of cloud condensation nuclei (CCN) comparable, perhaps, to the sulfate aerosol contribution to CCN. Because organic CCN would influence the albedo and radiative properties of clouds and play a role in climate change, it is important to identify the sources of these aerosols. In their research Novakov and Penner assumed that particles larger than 0.05 {mu}m could act as CCN. Therefore the origins of nucleation mode aerosol (0.03 < dp < 0.1 {mu}m) are the focus of our research. In our research, wemore » apply a dynamic aerosol model (MAEROS) to explore potential sources of the nucleation mode organic aerosol observed at a marine site in Puerto Rico. Novakov and Penner measured the size segregated mass and composition of the atmospheric aerosol at this site and found that organic aerosol mass dominated the sulfate mass in the nucleation size range. The presence of organics in this size range suggests that these organic aerosol particles were generated by nucleation of a gas phase organic followed by condensational processes, i.e., identifying sources of the gas phase precursors is important to determining the organic CCN origins. Back trajectory analysis shows that the air mass was without continental contact for 12 days prior to being sampled. This implicates two possible sources for the gas phase organic: biogenic emissions from the Puerto Rican forest and emissions from the ocean surface. In this research we explore both the forest and ocean source scenarios, showing that the forest is more likely to be the ultimate source of the observed organic aerosol particles. Using MAEROS (modified to include nucleation) and reasonable input parameters taken from the literature we were able to show that an organic vapor flux very similar to the measured biogenic fluxes reported by Zimmerman et al. generated size distributions similar to the observed aerosol.« less

Size-resolved aerosol and cloud condensation nuclei (CCN) properties in the remote marine South China Sea - Part 1: Observations and source classification

NASA Astrophysics Data System (ADS)

Atwood, Samuel A.; Reid, Jeffrey S.; Kreidenweis, Sonia M.; Blake, Donald R.; Jonsson, Haflidi H.; Lagrosas, Nofel D.; Xian, Peng; Reid, Elizabeth A.; Sessions, Walter R.; Simpas, James B.

2017-01-01

Ship-based measurements of aerosol and cloud condensation nuclei (CCN) properties are presented for 2 weeks of observations in remote marine regions of the South China Sea/East Sea during the southwestern monsoon (SWM) season. Smoke from extensive biomass burning throughout the Maritime Continent advected into this region during the SWM, where it was mixed with anthropogenic continental pollution and emissions from heavy shipping activities. Eight aerosol types were identified using a k-means cluster analysis with data from a size-resolved CCN characterization system. Interpretation of the clusters was supplemented by additional onboard aerosol and meteorological measurements, satellite, and model products for the region. A typical bimodal marine boundary layer background aerosol population was identified and observed mixing with accumulation mode aerosol from other sources, primarily smoke from fires in Borneo and Sumatra. Hygroscopicity was assessed using the κ parameter and was found to average 0.40 for samples dominated by aged accumulation mode smoke; 0.65 for accumulation mode marine aerosol; 0.60 in an anthropogenic aerosol plume; and 0.22 during a short period that was characterized by elevated levels of volatile organic compounds not associated with biomass burning impacts. As a special subset of the background marine aerosol, clean air masses substantially scrubbed of particles were observed following heavy precipitation or the passage of squall lines, with changes in observed aerosol properties occurring on the order of minutes. Average CN number concentrations, size distributions, and κ values are reported for each population type, along with CCN number concentrations for particles that activated at supersaturations between 0.14 and 0.85 %.

A Condensation–coalescence Cloud Model for Exoplanetary Atmospheres: Formulation and Test Applications to Terrestrial and Jovian Clouds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ohno, Kazumasa; Okuzumi, Satoshi

A number of transiting exoplanets have featureless transmission spectra that might suggest the presence of clouds at high altitudes. A realistic cloud model is necessary to understand the atmospheric conditions under which such high-altitude clouds can form. In this study, we present a new cloud model that takes into account the microphysics of both condensation and coalescence. Our model provides the vertical profiles of the size and density of cloud and rain particles in an updraft for a given set of physical parameters, including the updraft velocity and the number density of cloud condensation nuclei (CCNs). We test our modelmore » by comparing with observations of trade-wind cumuli on Earth and ammonia ice clouds in Jupiter. For trade-wind cumuli, the model including both condensation and coalescence gives predictions that are consistent with observations, while the model including only condensation overestimates the mass density of cloud droplets by up to an order of magnitude. For Jovian ammonia clouds, the condensation–coalescence model simultaneously reproduces the effective particle radius, cloud optical thickness, and cloud geometric thickness inferred from Voyager observations if the updraft velocity and CCN number density are taken to be consistent with the results of moist convection simulations and Galileo probe measurements, respectively. These results suggest that the coalescence of condensate particles is important not only in terrestrial water clouds but also in Jovian ice clouds. Our model will be useful to understand how the dynamics, compositions, and nucleation processes in exoplanetary atmospheres affect the vertical extent and optical thickness of exoplanetary clouds via cloud microphysics.« less

Particles from a Diesel ship engine: Mixing state on the nano scale and cloud condensation abilities

NASA Astrophysics Data System (ADS)

Lieke, K. I.; Rosenørn, T.; Fuglsang, K.; Frederiksen, T.; Butcher, A. C.; King, S. M.; Bilde, M.

2012-04-01

Transport by ship plays an important role in global logistics. Current international policy initiatives by the International Maritime Organization (IMO) are taken to reduce emissions from ship propulsion systems (NO and SO, primarily). However, particulate emissions (e.g. soot) from ships are yet not regulated by legislations. To date, there is still a lack of knowledge regarding the global and local effects of the particulate matter emitted from ships at sea. Particles may influence the climate through their direct effects (scattering and absorption of long and shortwave radiation) and indirectly through formation of clouds. Many studies have been carried out estimating the mass and particle number from ship emissions (e.g. Petzold et al. 2008), many of them in test rig studies (e.g. Kasper et al. 2007). It is shown that particulate emissions vary with engine load and chemical composition of fuels. Only a few studies have been carried out to characterize the chemical composition and cloud-nucleating ability of the particulate matter (e.g. Corbett et al. 1997). In most cases, the cloud-nucleating ability of emission particles is estimated from number size distribution. We applied measurements to characterize particulate emissions from a MAN B&W Low Speed engine on test bed. A unique data set was obtained through the use of a scanning mobility particle sizing system (SMPS), combined with a cloud condensation nucleus (CCN) counter and a thermodenuder - all behind a dilution system. In addition, impactor samples were taken on nickel grids with carbon foil for use in an electron microscope (EM) to characterize the mineral phase and mixing state of the particles. The engine was operated at a series of different load conditions and an exhaust gas recirculation (EGR) system was applied. Measurements were carried out before and after the EGR system respectively. Our observations show significant changes in number size distribution and CCN activity with varying conditions. Results of transmission electron microscopy revealed salt condensates of nanometer size attached to soot particles. High resolution structural analysis of single particles shows that three different phases (graphitic soot, crystalline salt and amorphous condensed organic matter) may be present in the same particle volume. A closure between CCN activation curves, EM samples, and SMPS size distribution will be presented and used to identify climate active parts in single particles. ACKNOWLEDGEMENTS We thank the Danish Agency for Science, Technology and Innovation for support through the NaKIM project (www.nakim.dk).

Analysis of African Biomass Burning Over the South East Atlantic and its Interaction with Stratocumulus Clouds during ORACLES 2016/17

NASA Astrophysics Data System (ADS)

Freitag, S.; Howell, S. G.; Dobracki, A. N.; Smirnow, N.; Winchester, C.; Sedlacek, A. J., III; Podolske, J. R.; Noone, D.; McFarquhar, G. M.; Poellot, M.; Delene, D. J.

2017-12-01

During NASA ORACLES 2016/17 airborne missions, biomass burning (BB) advected from the African continent out over the South East Atlantic was intensively studied to better understand the role of BB aerosol in the regional radiation budget but also to discern its effect from natural aerosol on underlying Stratocumulus (Sc) clouds in the marine boundary layer (MBL). Because of its particle size and vast quantities BB aerosol once entrained into the MBL are highly effective as cloud condensation nuclei (CCN) impacting cloud microphysical properties and as such the Sc deck's radiative budget. This work identifies characteristic in-plume size resolved aerosol physiochemistry observed during the campaign with focus on absorbing aerosol measurements retrieved with a Single Particle Soot Photometer (SP2). The results are compared to MBL aerosol obervations and adjacent Sc cloud properties such as the cloud droplet number concentration. Additionally, size resolved aerosol physiochemistry and black carbon concentration were measured in the cloud occasionally using a Counterflow Virtual Impactor (CVI) inlet sampling exclusively cloud droplet residuals. Employing the CVI cloud droplets are inertially separated from the air and dried in-situ en-route to the aerosol instrumentation. This allows us to study natural and combustion-influenced aerosol that were actually activated as CCN in the Sc deck.

Size-resolved measurements of mixing state and cloud-nucleating ability of aerosols in Nanjing, China

NASA Astrophysics Data System (ADS)

Ma, Yan; Li, Shizheng; Zheng, Jun; Khalizov, Alexei; Wang, Xing; Wang, Zhen; Zhou, Yaoyao

2017-09-01

An integrated aerosol analytical system was deployed in Nanjing, a megacity in the Yangtze River Delta, to measure size-resolved aerosol mixing states, effective densities, cloud condensation nucleus (CCN) activities, and chemical composition in August 2013. It was found that aerosols were predominantly internally mixed. The average effective densities were 1.38 ± 0.09, 1.48 ± 0.08, and 1.53 ± 0.07 g cm-3 for 50, 80, and 120 nm particles, respectively. Although black carbon (BC) represented only 0.3%, 1.6%, and 3.3% of the particle mass, on average, it was present in 7%, 38%, and 47% of the total particle number concentration at 50, 80, and 120 nm, respectively, indicating that BC particles may contribute significantly to the total atmospheric aerosol population. Externally mixed BC was only occasionally observed with an effective density of 0.67-0.97 g cm-3. Aerosols sampled generally exhibited a relatively high CCN activity and hygroscopicity (κ = 0.35 ± 0.13). Both newly formed particles and freshly emitted BC particles were observed to age rapidly from photochemical processes, with a significant enhancement in the particle CCN activity and an increase in the effective density. Aerosols influenced by four different air masses presented similar CCN activation, indicating that CCN activation would be primarily dependent on the particle size rather than the particle origin (and hence original composition). Our results suggest that under highly active photochemical conditions as encountered in this study, particles from both local sources and regional transport can be rapidly converted into efficient CCN by photochemical aging, thereby making important contributions to the atmospheric CCN budget and exerting profound implications on aerosol indirect climate forcing.

Study to perform preliminary experiments to evaluate particle generation and characterization techniques for zero-gravity cloud physics experiments

NASA Technical Reports Server (NTRS)

Katz, U.

1982-01-01

Methods of particle generation and characterization with regard to their applicability for experiments requiring cloud condensation nuclei (CCN) of specified properties were investigated. Since aerosol characterization is a prerequisite to assessing performance of particle generation equipment, techniques for characterizing aerosol were evaluated. Aerosol generation is discussed, and atomizer and photolytic generators including preparation of hydrosols (used with atomizers) and the evaluation of a flight version of an atomizer are studied.

A global lightning parameterization based on statistical relationships among environmental factors, aerosols, and convective clouds in the TRMM climatology

NASA Astrophysics Data System (ADS)

Stolz, Douglas C.; Rutledge, Steven A.; Pierce, Jeffrey R.; van den Heever, Susan C.

2017-07-01

The objective of this study is to determine the relative contributions of normalized convective available potential energy (NCAPE), cloud condensation nuclei (CCN) concentrations, warm cloud depth (WCD), vertical wind shear (SHEAR), and environmental relative humidity (RH) to the variability of lightning and radar reflectivity within convective features (CFs) observed by the Tropical Rainfall Measuring Mission (TRMM) satellite. Our approach incorporates multidimensional binned representations of observations of CFs and modeled thermodynamics, kinematics, and CCN as inputs to develop approximations for total lightning density (TLD) and the average height of 30 dBZ radar reflectivity (AVGHT30). The results suggest that TLD and AVGHT30 increase with increasing NCAPE, increasing CCN, decreasing WCD, increasing SHEAR, and decreasing RH. Multiple-linear approximations for lightning and radar quantities using the aforementioned predictors account for significant portions of the variance in the binned data set (R2 ≈ 0.69-0.81). The standardized weights attributed to CCN, NCAPE, and WCD are largest, the standardized weight of RH varies relative to other predictors, while the standardized weight for SHEAR is comparatively small. We investigate these statistical relationships for collections of CFs within various geographic areas and compare the aerosol (CCN) and thermodynamic (NCAPE and WCD) contributions to variations in the CF population in a partial sensitivity analysis based on multiple-linear regression approximations computed herein. A global lightning parameterization is developed; the average difference between predicted and observed TLD decreases from +21.6 to +11.6% when using a hybrid approach to combine separate approximations over continents and oceans, thus highlighting the need for regionally targeted investigations in the future.

A three-dimensional sectional representation of aerosol mixing state for simulating optical properties and cloud condensation nuclei

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ching, Ping Pui; Zaveri, Rahul A.; Easter, Richard C.

2016-05-27

Light absorption by black carbon (BC) particles emitted from fossil fuel combustion depends on the how thickly they are coated with non-refractory species such as ammonium, sulfate, nitrate, organics, and water. The cloud condensation nuclei (CCN) activation property of a particle depends on its dry size and the hygroscopicities of all the individual species mixed together. It is therefore necessary to represent both size and mixing state of aerosols to reliably predict their climate-relevant properties in atmospheric models. Here we describe and evaluate a novel sectional framework in the Model for Simulating Aerosol Interactions and Chemistry, referred to as MOSAIC-mix,more » that represents the mixing state by resolving aerosol dry size (Ddry), BC dry mass fraction (wBC), and hygroscopicity (κ). Using ten idealized urban plume scenarios in which different types of aerosols evolve over 24 hours under a range of atmospherically relevant environmental conditions, we examine errors in CCN concentrations and optical properties with respect to a more explicit aerosol mixing state representation. We find that only a small number of wBC and κ bins are needed to achieve significant reductions in the errors, and propose a configuration consisting of 24 Ddry bins, 2 wBC bins, and 2 κ bins that gives 24-hour average errors of about 5% or less in CCN concentrations and optical properties, 3-4 times lower than those from size-only-resolved simulations. These results show that MOSAIC-mix is suitable for use in regional and global models to examine the effects of evolving aerosol mixing states on aerosol-radiation-cloud feedbacks.« less

Description and evaluation of GLOMAP-mode: a modal global aerosol microphysics model for the UKCA composition-climate model

NASA Astrophysics Data System (ADS)

Mann, G. W.; Carslaw, K. S.; Spracklen, D. V.; Ridley, D. A.; Manktelow, P. T.; Chipperfield, M. P.; Pickering, S. J.; Johnson, C. E.

2010-10-01

A new version of the Global Model of Aerosol Processes (GLOMAP) is described, which uses a two-moment pseudo-modal aerosol dynamics approach rather than the original two-moment bin scheme. GLOMAP-mode simulates the multi-component global aerosol, resolving sulfate, sea-salt, dust, black carbon (BC) and particulate organic matter (POM), the latter including primary and biogenic secondary POM. Aerosol processes are simulated in a size-resolved manner including primary emissions, secondary particle formation by binary homogeneous nucleation of sulfuric acid and water, particle growth by coagulation, condensation and cloud-processing and removal by dry deposition, in-cloud and below-cloud scavenging. A series of benchmark observational datasets are assembled against which the skill of the model is assessed in terms of normalised mean bias (b) and correlation coefficient (R). Overall, the model performs well against the datasets in simulating concentrations of aerosol precursor gases, chemically speciated particle mass, condensation nuclei (CN) and cloud condensation nuclei (CCN). Surface sulfate, sea-salt and dust mass concentrations are all captured well, while BC and POM are biased low (but correlate well). Surface CN concentrations compare reasonably well in free troposphere and marine sites, but are underestimated at continental and coastal sites related to underestimation of either primary particle emissions or new particle formation. The model compares well against a compilation of CCN observations covering a range of environments and against vertical profiles of size-resolved particle concentrations over Europe. The simulated global burden, lifetime and wet removal of each of the simulated aerosol components is also examined and each lies close to multi-model medians from the AEROCOM model intercomparison exercise.

Description and evaluation of GLOMAP-mode: a modal global aerosol microphysics model for the UKCA composition-climate model

NASA Astrophysics Data System (ADS)

Mann, G. W.; Carslaw, K. S.; Spracklen, D. V.; Ridley, D. A.; Manktelow, P. T.; Chipperfield, M. P.; Pickering, S. J.; Johnson, C. E.

2010-05-01

A new version of the Global Model of Aerosol Processes (GLOMAP) is described, which uses a two-moment modal aerosol scheme rather than the original two-moment bin scheme. GLOMAP-mode simulates the multi-component global aerosol, resolving sulphate, sea-salt, dust, black carbon (BC) and particulate organic matter (POM), the latter including primary and biogenic secondary POM. Aerosol processes are simulated in a size-resolved manner including primary emissions, secondary particle formation by binary homogeneous nucleation of sulphuric acid and water, particle growth by coagulation, condensation and cloud-processing and removal by dry deposition, in-cloud and below-cloud scavenging. A series of benchmark observational datasets are assembled against which the skill of the model is assessed in terms of normalised mean bias (b) and correlation coefficient (R). Overall, the model performs well against the datasets in simulating concentrations of aerosol precursor gases, chemically speciated particle mass, condensation nuclei (CN) and cloud condensation nuclei (CCN). Surface sulphate, sea-salt and dust mass concentrations are all captured well, while BC and POM are biased low (but correlate well). Surface CN concentrations compare reasonably well in free troposphere and marine sites, but are underestimated at continental and coastal sites related to underestimation of either primary particle emissions or new particle formation. The model compares well against a compilation of CCN observations covering a range of environments and against vertical profiles of size-resolved particle concentrations over Europe. The simulated global burden, lifetime and wet removal of each of the simulated aerosol components is also examined and each lies close to multi-model medians from the AEROCOM model intercomparison exercise.

Modeling studying on ice formation by bacteria in warm-based convective cloud

NASA Astrophysics Data System (ADS)

Sun, J.

2005-12-01

Bacteria have been recognized as cloud condensation nuclei (CCN), and certain bacteria, commonly found in plants, have exhibited capacity to act as ice nuclei (IN) at temperatures as warm as -2 °C. These ice nucleating bacteria are readily disseminated into the atmosphere and have been observed in clouds at altitudes of several kilometres. It is noteworthy that over 20 years ago, one assumed the possibility of bacterial transport and their importance into cloud formation process, rain and precipitation, as well as causing disease in plants and animal kingdom. We used a 1-D cumulus cloud model with the CCOPE 19th July 1981 case and the observed field profile of bacterial concentration, to simulate the significance of bacteria as IN through condensation freezing mechanism. In this paper, we will present our results on the role of bacteria as active ice nuclei in the developing stage of cumulus clouds, and their potential significance in atmospheric sciences.

Aerosol Production and Growth in the Upper Troposphere over the Amazon Forest Observed during ACRIDICON-CHUVA

NASA Astrophysics Data System (ADS)

Andreae, M. O.; Afchine, A.; Albrecht, R. I.; Artaxo, P.; Borrmann, S.; Cecchini, M. A.; Costa, A.; Fütterer, D.; Järvinen, E.; Klimach, T.; Konemann, T.; Kraemer, M.; Machado, L.; Mertes, S.; Pöhlker, C.; Pöhlker, M. L.; Poeschl, U.; Sauer, D. N.; Schnaiter, M.; Schneider, J.; Schulz, C.; Spanu, A.; Walser, A.; Wang, J.; Weinzierl, B.; Wendisch, M.

2016-12-01

Observations during ACRIDICON-CHUVA showed high aerosol concentrations in the upper troposphere (UT) over the Amazon Basin, with aerosol number concentrations after normalization to STP often exceeding those in the boundary layer (BL) by one or two orders of magnitude. The measurements were made during the German-Brazilian cooperative aircraft campaign ACRIDICON-CHUVA (Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems) on the German research aircraft HALO. The campaign took place over the Amazon Basin in September/October 2014, with the objective of studying tropical deep convective clouds over the Amazon rainforest and their interactions with trace gases, aerosol particles, and atmospheric radiation. Aerosol enhancements were consistently observed on all flights, using several aerosol metrics, including condensation nuclei (CN), cloud condensation nuclei (CCN), and chemical species mass concentrations. These UT aerosols were different in their composition and size distribution from the aerosol in the BL, making convective transport of particles unlikely as a source. The regions in the immediate outflow of deep convective clouds were depleted in aerosol particles, whereas dramatically enhanced small (<90 nm diameter) aerosol number concentrations were found in UT regions that had experienced outflow from deep convection in the preceding 24-48 hours. We also found elevated concentrations of larger (>90 nm) particles in the UT, which consisted mostly of organic matter and nitrate and were very effective CCN. Our findings suggest that aerosol production takes place in the UT from volatile material brought up by deep convection, which is converted to condensable species in the UT. Subsequently, downward mixing and transport of upper tropospheric aerosol may be a source of particles to the BL, where they increase in size by the condensation of biogenic volatile organic carbon (BVOC) oxidation products. This may be an important source of aerosol particles in the Amazonian BL, where aerosol nucleation and new particle formation has not been observed. We propose that this may have been the dominant process supplying secondary aerosols in the pristine atmosphere, making clouds the dominant control of both removal and production of atmospheric particles.

Cloud Processed CCN Suppress Stratus Cloud Drizzle

NASA Astrophysics Data System (ADS)

Hudson, J. G.; Noble, S. R., Jr.

2017-12-01

Conversion of sulfur dioxide to sulfate within cloud droplets increases the sizes and decreases the critical supersaturation, Sc, of cloud residual particles that had nucleated the droplets. Since other particles remain at the same sizes and Sc a size and Sc gap is often observed. Hudson et al. (2015) showed higher cloud droplet concentrations (Nc) in stratus clouds associated with bimodal high-resolution CCN spectra from the DRI CCN spectrometer compared to clouds associated with unimodal CCN spectra (not cloud processed). Here we show that CCN spectral shape (bimodal or unimodal) affects all aspects of stratus cloud microphysics and drizzle. Panel A shows mean differential cloud droplet spectra that have been divided according to traditional slopes, k, of the 131 measured CCN spectra in the Marine Stratus/Stratocumulus Experiment (MASE) off the Central California coast. K is generally high within the supersaturation, S, range of stratus clouds (< 0.5%). Because cloud processing decreases Sc of some particles, it reduces k. Panel A shows higher concentrations of small cloud droplets apparently grown on lower k CCN than clouds grown on higher k CCN. At small droplet sizes the concentrations follow the k order of the legend, black, red, green, blue (lowest to highest k). Above 13 µm diameter the lines cross and the hierarchy reverses so that blue (highest k) has the highest concentrations followed by green, red and black (lowest k). This reversed hierarchy continues into the drizzle size range (panel B) where the most drizzle drops, Nd, are in clouds grown on the least cloud-processed CCN (blue), while clouds grown on the most processed CCN (black) have the lowest Nd. Suppression of stratus cloud drizzle by cloud processing is an additional 2nd indirect aerosol effect (IAE) that along with the enhancement of 1st IAE by higher Nc (panel A) are above and beyond original IAE. However, further similar analysis is needed in other cloud regimes to determine if MASE was typical. Hudson, J.G., S. Noble, and S. Tabor, 2015: J. Geophys. Res., Atmos., 120, 3436-3452, doi:10.1002/2014JD022669.

Gas-phase kinetics modifies the CCN activity of a biogenic SOA.

PubMed

Vizenor, A E; Asa-Awuku, A A

2018-02-28

Our current knowledge of cloud condensation nuclei (CCN) activity and the hygroscopicity of secondary organic aerosol (SOA) depends on the particle size and composition, explicitly, the thermodynamic properties of the aerosol solute and subsequent interactions with water. Here, we examine the CCN activation of 3 SOA systems (2 biogenic single precursor and 1 mixed precursor SOA system) in relation to gas-phase decay. Specifically, the relationship between time, gas-phase precursor decay and CCN activity of 100 nm SOA is studied. The studied SOA systems exhibit a time-dependent growth of CCN activity at an instrument supersaturation of ∼0.2%. As such, we define a critical activation time, t 50 , above which a 100 nm SOA particle will activate. The critical activation time for isoprene, longifolene and a mixture of the two precursor SOA is 2.01 hours, 2.53 hours and 3.17 hours, respectively. The activation times are then predicted with gas-phase kinetic data inferred from measurements of precursor decay. The gas-phase prediction of t 50 agrees well with CCN measured t 50 (within 0.05 hours of the actual critical times) and suggests that the gas-to-particle phase partitioning may be more significant for SOA CCN prediction than previously thought.

Metrics to quantify the importance of mixing state for CCN activity

DOE PAGES

Ching, Joseph; Fast, Jerome; West, Matthew; ...

2017-06-21

It is commonly assumed that models are more prone to errors in predicted cloud condensation nuclei (CCN) concentrations when the aerosol populations are externally mixed. In this work we investigate this assumption by using the mixing state index ( χ) proposed by Riemer and West (2013) to quantify the degree of external and internal mixing of aerosol populations. We combine this metric with particle-resolved model simulations to quantify error in CCN predictions when mixing state information is neglected, exploring a range of scenarios that cover different conditions of aerosol aging. We show that mixing state information does indeed become unimportantmore » for more internally mixed populations, more precisely for populations with χ larger than 75 %. For more externally mixed populations ( χ below 20 %) the relationship of χ and the error in CCN predictions is not unique and ranges from lower than -40 % to about 150 %, depending on the underlying aerosol population and the environmental supersaturation. We explain the reasons for this behavior with detailed process analyses.« less

Metrics to quantify the importance of mixing state for CCN activity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ching, Joseph; Fast, Jerome; West, Matthew

It is commonly assumed that models are more prone to errors in predicted cloud condensation nuclei (CCN) concentrations when the aerosol populations are externally mixed. In this work we investigate this assumption by using the mixing state index ( χ) proposed by Riemer and West (2013) to quantify the degree of external and internal mixing of aerosol populations. We combine this metric with particle-resolved model simulations to quantify error in CCN predictions when mixing state information is neglected, exploring a range of scenarios that cover different conditions of aerosol aging. We show that mixing state information does indeed become unimportantmore » for more internally mixed populations, more precisely for populations with χ larger than 75 %. For more externally mixed populations ( χ below 20 %) the relationship of χ and the error in CCN predictions is not unique and ranges from lower than -40 % to about 150 %, depending on the underlying aerosol population and the environmental supersaturation. We explain the reasons for this behavior with detailed process analyses.« less

Quantifying compositional impacts of ambient aerosol on cloud droplet formation

NASA Astrophysics Data System (ADS)

Lance, Sara

It has been historically assumed that most of the uncertainty associated with the aerosol indirect effect on climate can be attributed to the unpredictability of updrafts. In Chapter 1, we analyze the sensitivity of cloud droplet number density, to realistic variations in aerosol chemical properties and to variable updraft velocities using a 1-dimensional cloud parcel model in three important environmental cases (continental, polluted and remote marine). The results suggest that aerosol chemical variability may be as important to the aerosol indirect effect as the effect of unresolved cloud dynamics, especially in polluted environments. We next used a continuous flow streamwise thermal gradient Cloud Condensation Nuclei counter (CCNc) to study the water-uptake properties of the ambient aerosol, by exposing an aerosol sample to a controlled water vapor supersaturation and counting the resulting number of droplets. In Chapter 2, we modeled and experimentally characterized the heat transfer properties and droplet growth within the CCNc. Chapter 3 describes results from the MIRAGE field campaign, in which the CCNc and a Hygroscopicity Tandem Differential Mobility Analyzer (HTDMA) were deployed at a ground-based site during March, 2006. Size-resolved CCN activation spectra and growth factor distributions of the ambient aerosol in Mexico City were obtained, and an analytical technique was developed to quantify a probability distribution of solute volume fractions for the CCN in addition to the aerosol mixing-state. The CCN were shown to be much less CCN active than ammonium sulfate, with water uptake properties more consistent with low molecular weight organic compounds. The pollution outflow from Mexico City was shown to have CCN with an even lower fraction of soluble material. "Chemical Closure" was attained for the CCN, by comparing the inferred solute volume fraction with that from direct chemical measurements. A clear diurnal pattern was observed for the CCN solute volume fraction, showing that measurable aging of the aerosol population occurs during the day, on the timescale of a few hours. The mixing state of the aerosol, also showing a consistent diurnal pattern, clearly correlates with a chemical tracer for local combustion sources. Chapter 4 describes results from the GoMACCS field study, in which the CCNc was subsequently deployed on an airborne field campaign in Houston, Texas during August-September, 2006. GoMACCS tested our ability to predict CCN for highly polluted conditions with limited chemical information. Assuming the particles were composed purely of ammonium sulfate, CCN closure was obtained with a 10% overprediction bias on average for CCN concentrations ranging from less than 100 cm-3 to over 10,000 cm-3, but with on average 50% variability. Assuming measured concentrations of organics to be internally mixed and insoluble tended to reduce the overprediction bias for less polluted conditions, but led to underprediction bias in the most polluted conditions. A likely explanation is that the high organic concentrations in the polluted environments depress the surface tension of the droplets, thereby enabling activation at lower soluble fractions.

Cloud condensation nucleus activity of internally mixed ammonium sulfate/organic acid aerosol particles

NASA Astrophysics Data System (ADS)

Abbatt, J. P. D.; Broekhuizen, K.; Pradeep Kumar, P.

The ability of mixed ammonium sulfate/organic acid particles to act as cloud condensation nuclei (CCN) has been studied in the laboratory using a continuous flow, thermal-gradient diffusion chamber operated at supersaturations between 0.3% and 0.6%. The organic acids studied were malonic acid, azelaic acid, hexanoic acid, cis-pinonic acid, oleic acid and stearic acid, and the particles were largely prepared by condensation of the organic vapor onto a dry ammonium sulfate core. For malonic acid and hexanoic acid, the mixed particles activated as predicted by a simple Köhler theory model where both species are assumed to be fully soluble and the droplet has the surface tension of water. Three low-solubility species, cis-pinonic acid, azelaic acid and oleic acid, are well modeled where the acid was assumed to be either partially or fully insoluble. Interestingly, although thin coats of stearic acid behaved in a manner similar to that displayed by oleic and cis-pinonic acid, we observed that thick coats led to a complete deactivation of the ammonium sulfate, presumably because the water vapor could not diffuse through the solid stearic acid. We observed no CCN behavior that could be clearly attributed to a lowering of the surface tension of the growing droplet by the presence of the organic constituents, some of which are highly surface active.

Complex Coupling of Air Quality and Climate-Relevant Aerosols in a Chemistry-Aerosol Microphysics Model

NASA Astrophysics Data System (ADS)

Yoshioka, M.; Carslaw, K. S.; Reddington, C.; Mann, G.

2013-12-01

Controlling emissions of aerosols and their precursors to improve air quality will impact the climate through direct and indirect radiative forcing. We have investigated the impacts of changes in a range of aerosol and gas-phase emission fluxes and changes in temperature on air quality and climate change metrics using a global aerosol microphysics and chemistry model, GLOMAP. We investigate how the responses of PM2.5 and cloud condensation nuclei (CCN) are coupled, and how attempts to improve air quality could have inadvertent effects on CCN, clouds and climate. The parameter perturbations considered are a 5°C increase in global temperature, increased or decreased precursor emissions of anthropogenic SO2, NH3, and NOx, and biogenic monoterpenes, and increased or decreased primary emissions of organic and black carbon aerosols from wildfire, fossil fuel, and biofuel. To quantify the interactions, we define a new sensitivity metric in terms of the response of CCN divided by the response of PM in different regions. .Our results show that the coupled chemistry and aerosol processes cause complex responses that will make any co-benefit policy decision problematic. In particular, we show that reducing SO2 emissions effectively reduces surface-level PM2.5 over continental regions in summer when background PM2.5 is high, with a relatively small reduction in marine CCN (and hence indirect radiative cooling over ocean), which is beneficial for near-term climate. Reducing NOx emissions does not improve summertime air quality very effectively but leads to a relatively high reduction of marine CCN. Reducing NH3 emissions has moderate effects on both PM2.5 and CCN. These three species are strongly coupled chemically and microphysically and the effects of changing emissions of one species on mass and size distributions of aerosols are very complex and spatially and temporally variable. For example, reducing SO2 emissions leads to reductions in sulphate and ammonium mass concentrations and an increase in nitrate aerosol mass due to an increase in available NH3 for NOx to form aerosol. However, the rate of new particle formation increases due to a decrease in the condensation on pre-existing particles, so the effect of reduced SO2 on CCN is partly compensated. Controlling primary or precursor emissions of carbonaceous aerosols appears less effective in improving air quality, although it shows strong effects on marine CCN, which would constitute a detrimental effect on climate. Any policy decisions related to particulate matter, air quality and climate need to account for such couplings.

Organic condensation: A vital link connecting aerosol formation to climate forcing (Invited)

NASA Astrophysics Data System (ADS)

Riipinen, I.; Pierce, J. R.; Yli-Juuti, T.; Nieminen, T.; Häkkinen, S.; Ehn, M.; Junninen, H.; Lehtipalo, K.; Petdjd, T. T.; Slowik, J. G.; Chang, R. Y.; Shantz, N. C.; Abbatt, J.; Leaitch, W. R.; Kerminen, V.; Worsnop, D. R.; Pandis, S. N.; Donahue, N. M.; Kulmala, M. T.

2010-12-01

Aerosol-cloud interactions represent the largest uncertainty in calculations of Earth’s radiative forcing. Number concentrations of atmospheric aerosol particles are in the core of this uncertainty, as they govern the numbers of cloud condensation nuclei (CCN) and influence the albedo and lifetime of clouds. Aerosols also impair air quality through their adverse effects on atmospheric visibility and human health. The ultrafine fraction (<100 nm) of atmospheric aerosol particles often dominates the total aerosol numbers, and nucleation of atmospheric vapours is one of the most important sources of these particles. To have climatic relevance, however, the freshly-nucleated particles need to grow in size, and consequently their climatic importance remains to be quantified (see Fig. 1). We combine observations from two continental sites (Egbert, Canada and Hyytiälä, Finland) to show that condensation of organic vapours is a crucial factor governing the lifetimes and climatic importance of the smallest atmospheric particles. We demonstrate that state-of-the-science organic gas-particle partitioning models fail to reproduce the observations; we propose a new modelling approach that is consistent with the measurements. Finally, we demonstrate the large sensitivity of climatic forcing of atmospheric aerosols to these interactions between organic vapours and the smallest atmospheric nanoparticles - highlighting the need for representing this process in global climate models. Figure 1. Organic emissions and the dynamic processes governing the climatic importance of ultrafine aerosol. Condensable vapours are produced upon oxidation of volatile organic compounds (VOCs) and can 1) nucleate to form new small particles; 2) grow freshly formed particles to larger sizes and increase their probability to serve as CCN; 3) condense on the background aerosol (> 100 nm) and enhance the loss of ultrafine particles. Primary organic aerosol (POA) contributes to the large end of the aerosol size distribution, enhancing the scavenging of the ultrafine particles.

Aerosol and Cloud Microphysical Characteristics of Rifts and Gradients in Maritime Stratocumulus Clouds

NASA Technical Reports Server (NTRS)

Sharon, Tarah M.; Albrecht, Bruce A.; Jonsson, Haflidi H.; Minnis, Patrick; Khaiyer, Mandana M.; Van Reken, Timothy; Seinfeld, John; Flagan, Rick

2008-01-01

A cloud rift is characterized as a large-scale, persistent area of broken, low reflectivity stratocumulus clouds usually surrounded by a solid deck of stratocumulus. A rift observed off the coast of Monterey Bay, California on 16 July 1999 was studied to compare the aerosol and cloud microphysical properties in the rift with those of the surrounding solid stratus deck. Variables measured from an instrumented aircraft included temperature, water vapor, and cloud liquid water. These measurements characterized the thermodynamic properties of the solid deck and rift areas. Microphysical measurements made included aerosol, cloud drop and drizzle drop concentrations and cloud condensation nuclei (CCN) concentrations. The microphysical characteristics in a solid stratus deck differ substantially from those of a broken, cellular rift where cloud droplet concentrations are a factor of 2 lower than those in the solid cloud. Further, CCN concentrations were found to be about 3 times greater in the solid cloud area compared with those in the rift and aerosol concentrations showed a similar difference as well. Although drizzle was observed near cloud top in parts of the solid stratus cloud, the largest drizzle rates were associated with the broken clouds within the rift area. In addition to marked differences in particle concentrations, evidence of a mesoscale circulation near the solid cloud rift boundary is presented. This mesoscale circulation provides a mechanism for maintaining a rift, but further study is required to understand the initiation of a rift and the conditions that may cause it to fill.

Aerosol optical properties relevant to regional remote sensing of CCN activity and links to their organic mass fraction: airborne observations over Central Mexico and the US West Coast during MILAGRO/INTEX-B

NASA Astrophysics Data System (ADS)

Shinozuka, Y.; Clarke, A. D.; Decarlo, P. F.; Jimenez, J. L.; Dunlea, E. J.; Roberts, G. C.; Tomlinson, J. M.; Collins, D. R.; Howell, S. G.; Kapustin, V. N.; McNaughton, C. S.; Zhou, J.

2009-09-01

Remote sensing of cloud condensation nuclei (CCN) would help evaluate the indirect effects of tropospheric aerosols on clouds and climate. To assess its feasibility, we examined relationships of submicron aerosol composition to CCN activity and optical properties observed during the MILAGRO/INTEX-B aircraft campaigns. An indicator of CCN activity, κ, was calculated from hygroscopicity measured under saturation. κ for dry 100 nm particles decreased with increasing organic fraction of non-refractory mass of submicron particles (OMF) as 0.34-0.20×OMF over Central Mexico and 0.47-0.43×OMF over the US West Coast. These fits represent the critical dry diameter, centered near 100 nm for 0.2% supersaturation but varied as κ(-1/3), within measurement uncertainty (~20%). The decreasing trends of CCN activity with the organic content, evident also in our direct CCN counts, were consistent with previous ground and laboratory observations of highly organic particles. The wider range of OMF, 0-0.8, for our research areas means that aerosol composition will be more critical for estimation of CCN concentration than at the fixed sites previously studied. Furthermore, the wavelength dependence of extinction was anti-correlated with OMF as -0.70×OMF+2.0 for Central Mexico's urban and industrial pollution air masses, for unclear reasons. The Angstrom exponent of absorption increased with OMF, more rapidly under higher single scattering albedo, as expected for the interplay between soot and colored weak absorbers (some organic species and dust). Because remote sensing products currently use the wavelength dependence of extinction albeit in the column integral form and may potentially include that of absorption, these regional spectral dependencies are expected to facilitate retrievals of aerosol bulk chemical composition and CCN activity over Central Mexico.

Aerosol optical properties relevant to regional remote sensing of CCN activity and links to their organic mass fraction: airborne observations over Central Mexico and the US West Coast during MILAGRO/INTEX-B

NASA Astrophysics Data System (ADS)

Shinozuka, Y.; Clarke, A. D.; Decarlo, P. F.; Jimenez, J. L.; Dunlea, E. J.; Roberts, G. C.; Tomlinson, J. M.; Collins, D. R.; Howell, S. G.; Kapustin, V. N.; McNaughton, C. S.; Zhou, J.

2009-05-01

Remote sensing of cloud condensation nuclei (CCN) would help evaluate the indirect effects of tropospheric aerosols on clouds and climate. To assess its feasibility, we examined relationships of submicron aerosol composition to CCN activity and optical properties observed during the MILAGRO/INTEX-B aircraft campaigns. An indicator of CCN activity, κ, was calculated from hygroscopicity measured under saturation. κ for dry 100-nm particles decreased with the organic fraction of non-refractory mass of submicron particles (OMF) as 10(-0.43-0.44*OMF) over Central Mexico and 10(-0.29-0.70*OMF) over the US West Coast. These fits represent the critical dry diameter, centered near 100 nm for 0.2% supersaturation but varied as κ(-1/3), within measurement uncertainty (~20%). The decreasing trends of CCN activity with the organic content, evident also in our direct CCN counts, were consistent with previous ground and laboratory observations of highly organic particles. The wider range of OMF, 0-0.8, for our research areas means that aerosol composition will be more critical for estimation of CCN concentration than at the fixed sites previously studied. Furthermore, the wavelength dependence of extinction was anti-correlated with OMF as -0.70*OMF+2.0 for Central Mexico's urban and industrial pollution air masses, for unclear reasons. The Angstrom exponent of absorption increased with OMF, more rapidly under higher single scattering albedo, as expected for the interplay between soot and colored weak absorbers (some organic species and dust). Because remote sensing products currently use the wavelength dependence of extinction albeit in the column integral form and may potentially include that of absorption, these regional spectral dependencies are expected to facilitate retrievals of aerosol bulk chemistry and CCN activity over Central Mexico.

Global and regional modeling of clouds and aerosols in the marine boundary layer during VOCALS: the VOCA intercomparison

DOE PAGES

Wyant, M. C.; Bretherton, Christopher S.; Wood, Robert; ...

2015-01-09

A diverse collection of models are used to simulate the marine boundary layer in the southeast Pacific region during the period of the October–November 2008 VOCALS REx (VAMOS Ocean Cloud Atmosphere Land Study Regional Experiment) field campaign. Regional models simulate the period continuously in boundary-forced free-running mode, while global forecast models and GCMs (general circulation models) are run in forecast mode. The models are compared to extensive observations along a line at 20° S extending westward from the South American coast. Most of the models simulate cloud and aerosol characteristics and gradients across the region that are recognizably similar tomore » observations, despite the complex interaction of processes involved in the problem, many of which are parameterized or poorly resolved. Some models simulate the regional low cloud cover well, though many models underestimate MBL (marine boundary layer) depth near the coast. Most models qualitatively simulate the observed offshore gradients of SO 2, sulfate aerosol, CCN (cloud condensation nuclei) concentration in the MBL as well as differences in concentration between the MBL and the free troposphere. Most models also qualitatively capture the decrease in cloud droplet number away from the coast. However, there are large quantitative intermodel differences in both means and gradients of these quantities. Many models are able to represent episodic offshore increases in cloud droplet number and aerosol concentrations associated with periods of offshore flow. Most models underestimate CCN (at 0.1% supersaturation) in the MBL and free troposphere. The GCMs also have difficulty simulating coastal gradients in CCN and cloud droplet number concentration near the coast. The overall performance of the models demonstrates their potential utility in simulating aerosol–cloud interactions in the MBL, though quantitative estimation of aerosol–cloud interactions and aerosol indirect effects of MBL clouds with these models remains uncertain.« less

The Impact of Aerosols on Cloud and Precipitation Processes: Cloud-Resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Li, X.; Khain, A.; Simpson, S.

2004-01-01

Cloud microphysics are inevitably affected by the smoke particle (CCN, cloud condensation nuclei) size distributions below the clouds. Therefore, size distributions parameterized as spectral bin microphysics are needed to explicitly study the effects of atmospheric aerosol concentration on cloud development, rainfall production, and rainfall rates for convective clouds. Recently, two detailed spectral-bin microphysical schemes were implemented into the Goddard Cumulus Ensemble (GCE) model. The formulation for the explicit spectral-bin microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (i.e., cloud droplets and raindrops), and several types of ice particles (i.e., pristine ice crystals (columnar and plate-like), snow (dendrites and aggregates), graupel and frozen drops/hail). Each type is described by a special size distribution function containing many categories (i.e. 33 bins). Atmospheric aerosols are also described using number density size-distribution functions. A spectral-bin microphysical model is very expensive from a computational point of view and has only been implemented into the 2D version of the GCE at the present time. The model is tested by studying the evolution of deep cloud systems in the west Pacific warm pool region, in the sub-tropics (Florida) and in the mid-latitude using identical thermodynamic conditions but with different concentrations of CCN: a low 'clean' concentration and a high 'dirty' concentration.

Robust relations between CCN and the vertical evolution of cloud drop size distribution in deep convective clouds

NASA Astrophysics Data System (ADS)

Freud, E.; Rosenfeld, D.; Andreae, M. O.; Costa, A. A.; Artaxo, P.

2008-03-01

In-situ measurements in convective clouds (up to the freezing level) over the Amazon basin show that smoke from deforestation fires prevents clouds from precipitating until they acquire a vertical development of at least 4 km, compared to only 1-2 km in clean clouds. The average cloud depth required for the onset of warm rain increased by ~350 m for each additional 100 cloud condensation nuclei per cm3 at a super-saturation of 0.5% (CCN0.5%). In polluted clouds, the diameter of modal liquid water content grows much slower with cloud depth (at least by a factor of ~2), due to the large number of droplets that compete for available water and to the suppressed coalescence processes. Contrary to what other studies have suggested, we did not observe this effect to reach saturation at 3000 or more accumulation mode particles per cm3. The CCN0.5% concentration was found to be a very good predictor for the cloud depth required for the onset of warm precipitation and other microphysical factors, leaving only a secondary role for the updraft velocities in determining the cloud drop size distributions. The effective radius of the cloud droplets (re) was found to be a quite robust parameter for a given environment and cloud depth, showing only a small effect of partial droplet evaporation from the cloud's mixing with its drier environment. This supports one of the basic assumptions of satellite analysis of cloud microphysical processes: the ability to look at different cloud top heights in the same region and regard their re as if they had been measured inside one well developed cloud. The dependence of re on the adiabatic fraction decreased higher in the clouds, especially for cleaner conditions, and disappeared at re≥~10 μm. We propose that droplet coalescence, which is at its peak when warm rain is formed in the cloud at re=~10 μm, continues to be significant during the cloud's mixing with the entrained air, cancelling out the decrease in re due to evaporation.

Robust relations between CCN and the vertical evolution of cloud drop size distribution in deep convective clouds

NASA Astrophysics Data System (ADS)

Freud, E.; Rosenfeld, D.; Andreae, M. O.; Costa, A. A.; Artaxo, P.

2005-10-01

In-situ measurements in convective clouds (up to the freezing level) over the Amazon basin show that smoke from deforestation fires prevents clouds from precipitating until they acquire a vertical development of at least 4 km, compared to only 1-2 km in clean clouds. The average cloud depth required for the onset of warm rain increased by ~350 m for each additional 100 cloud condensation nuclei per cm3 at a super-saturation of 0.5% (CCN0.5%). In polluted clouds, the diameter of modal liquid water content grows much slower with cloud depth (at least by a factor of ~2), due to the large number of droplets that compete for available water and to the suppressed coalescence processes. Contrary to what other studies have suggested, we did not observe this effect to reach saturation at 3000 or more accumulation mode particles per cm3. The CCN0.5% concentration was found to be a very good predictor for the cloud depth required for the onset of warm precipitation and other microphysical factors, leaving only a secondary role for the updraft velocities in determining the cloud drop size distributions. The effective radius of the cloud droplets (re) was found to be a quite robust parameter for a given environment and cloud depth, showing only a small effect of partial droplet evaporation from the cloud's mixing with its drier environment. This supports one of the basic assumptions of satellite analysis of cloud microphysical processes: the ability to look at different cloud top heights in the same region and regard their re as if they had been measured inside one well developed cloud. The dependence of re on the adiabatic fraction decreased higher in the clouds, especially for cleaner conditions, and disappeared at re≥~10 µm. We propose that droplet coalescence, which is at its peak when warm rain is formed in the cloud at re~10 µm, continues to be significant during the cloud's mixing with the entrained air, canceling out the decrease in re due to evaporation.

Reduced anthropogenic aerosol radiative forcing caused by biogenic new particle formation

PubMed Central

Sengupta, Kamalika; Duplissy, Jonathan; Frege, Carla; Williamson, Christina; Heinritzi, Martin; Simon, Mario; Yan, Chao; Almeida, João; Tröstl, Jasmin; Nieminen, Tuomo; Ortega, Ismael K.; Wagner, Robert; Dunne, Eimear M.; Adamov, Alexey; Amorim, Antonio; Bernhammer, Anne-Kathrin; Bianchi, Federico; Breitenlechner, Martin; Brilke, Sophia; Chen, Xuemeng; Craven, Jill S.; Dias, Antonio; Ehrhart, Sebastian; Fischer, Lukas; Flagan, Richard C.; Franchin, Alessandro; Fuchs, Claudia; Guida, Roberto; Hakala, Jani; Hoyle, Christopher R.; Jokinen, Tuija; Junninen, Heikki; Kangasluoma, Juha; Kim, Jaeseok; Krapf, Manuel; Kürten, Andreas; Laaksonen, Ari; Lehtipalo, Katrianne; Makhmutov, Vladimir; Mathot, Serge; Molteni, Ugo; Monks, Sarah A.; Onnela, Antti; Peräkylä, Otso; Piel, Felix; Petäjä, Tuukka; Praplan, Arnaud P.; Pringle, Kirsty J.; Richards, Nigel A. D.; Rissanen, Matti P.; Rondo, Linda; Sarnela, Nina; Scott, Catherine E.; Seinfeld, John H.; Sharma, Sangeeta; Sipilä, Mikko; Steiner, Gerhard; Stozhkov, Yuri; Stratmann, Frank; Tomé, Antonio; Virtanen, Annele; Vogel, Alexander Lucas; Wagner, Andrea C.; Wagner, Paul E.; Weingartner, Ernest; Wimmer, Daniela; Winkler, Paul M.; Ye, Penglin; Zhang, Xuan; Hansel, Armin; Worsnop, Douglas R.; Baltensperger, Urs; Kulmala, Markku; Curtius, Joachim

2016-01-01

The magnitude of aerosol radiative forcing caused by anthropogenic emissions depends on the baseline state of the atmosphere under pristine preindustrial conditions. Measurements show that particle formation in atmospheric conditions can occur solely from biogenic vapors. Here, we evaluate the potential effect of this source of particles on preindustrial cloud condensation nuclei (CCN) concentrations and aerosol–cloud radiative forcing over the industrial period. Model simulations show that the pure biogenic particle formation mechanism has a much larger relative effect on CCN concentrations in the preindustrial atmosphere than in the present atmosphere because of the lower aerosol concentrations. Consequently, preindustrial cloud albedo is increased more than under present day conditions, and therefore the cooling forcing of anthropogenic aerosols is reduced. The mechanism increases CCN concentrations by 20–100% over a large fraction of the preindustrial lower atmosphere, and the magnitude of annual global mean radiative forcing caused by changes of cloud albedo since 1750 is reduced by 0.22 W m−2 (27%) to −0.60 W m−2. Model uncertainties, relatively slow formation rates, and limited available ambient measurements make it difficult to establish the significance of a mechanism that has its dominant effect under preindustrial conditions. Our simulations predict more particle formation in the Amazon than is observed. However, the first observation of pure organic nucleation has now been reported for the free troposphere. Given the potentially significant effect on anthropogenic forcing, effort should be made to better understand such naturally driven aerosol processes. PMID:27790989

Reduced anthropogenic aerosol radiative forcing caused by biogenic new particle formation

NASA Astrophysics Data System (ADS)

Gordon, Hamish; Sengupta, Kamalika; Rap, Alexandru; Duplissy, Jonathan; Frege, Carla; Williamson, Christina; Heinritzi, Martin; Simon, Mario; Yan, Chao; Almeida, João; Tröstl, Jasmin; Nieminen, Tuomo; Ortega, Ismael K.; Wagner, Robert; Dunne, Eimear M.; Adamov, Alexey; Amorim, Antonio; Bernhammer, Anne-Kathrin; Bianchi, Federico; Breitenlechner, Martin; Brilke, Sophia; Chen, Xuemeng; Craven, Jill S.; Dias, Antonio; Ehrhart, Sebastian; Fischer, Lukas; Flagan, Richard C.; Franchin, Alessandro; Fuchs, Claudia; Guida, Roberto; Hakala, Jani; Hoyle, Christopher R.; Jokinen, Tuija; Junninen, Heikki; Kangasluoma, Juha; Kim, Jaeseok; Kirkby, Jasper; Krapf, Manuel; Kürten, Andreas; Laaksonen, Ari; Lehtipalo, Katrianne; Makhmutov, Vladimir; Mathot, Serge; Molteni, Ugo; Monks, Sarah A.; Onnela, Antti; Peräkylä, Otso; Piel, Felix; Petäjä, Tuukka; Praplan, Arnaud P.; Pringle, Kirsty J.; Richards, Nigel A. D.; Rissanen, Matti P.; Rondo, Linda; Sarnela, Nina; Schobesberger, Siegfried; Scott, Catherine E.; Seinfeld, John H.; Sharma, Sangeeta; Sipilä, Mikko; Steiner, Gerhard; Stozhkov, Yuri; Stratmann, Frank; Tomé, Antonio; Virtanen, Annele; Vogel, Alexander Lucas; Wagner, Andrea C.; Wagner, Paul E.; Weingartner, Ernest; Wimmer, Daniela; Winkler, Paul M.; Ye, Penglin; Zhang, Xuan; Hansel, Armin; Dommen, Josef; Donahue, Neil M.; Worsnop, Douglas R.; Baltensperger, Urs; Kulmala, Markku; Curtius, Joachim; Carslaw, Kenneth S.

2016-10-01

The magnitude of aerosol radiative forcing caused by anthropogenic emissions depends on the baseline state of the atmosphere under pristine preindustrial conditions. Measurements show that particle formation in atmospheric conditions can occur solely from biogenic vapors. Here, we evaluate the potential effect of this source of particles on preindustrial cloud condensation nuclei (CCN) concentrations and aerosol-cloud radiative forcing over the industrial period. Model simulations show that the pure biogenic particle formation mechanism has a much larger relative effect on CCN concentrations in the preindustrial atmosphere than in the present atmosphere because of the lower aerosol concentrations. Consequently, preindustrial cloud albedo is increased more than under present day conditions, and therefore the cooling forcing of anthropogenic aerosols is reduced. The mechanism increases CCN concentrations by 20-100% over a large fraction of the preindustrial lower atmosphere, and the magnitude of annual global mean radiative forcing caused by changes of cloud albedo since 1750 is reduced by 0.22 W m-2 (27%) to -0.60 W m-2. Model uncertainties, relatively slow formation rates, and limited available ambient measurements make it difficult to establish the significance of a mechanism that has its dominant effect under preindustrial conditions. Our simulations predict more particle formation in the Amazon than is observed. However, the first observation of pure organic nucleation has now been reported for the free troposphere. Given the potentially significant effect on anthropogenic forcing, effort should be made to better understand such naturally driven aerosol processes.

Mixed Calcium Dust and Carbonaceous Particles from Asia Contributing to Precipitation Changes in California

NASA Astrophysics Data System (ADS)

Kristensen, L.; Cornwell, G.; Sedlacek, A. J., III; Prather, K. A.

2016-12-01

Mineral dust particles can serve as cloud condensation nuclei (CCN), with enhanced CCN activity observed when the dust is mixed with additional soluble species. Long range atmospheric transport can change the composition of dust particles through aging, cloud processing and mixing with other particles. The CalWater2 campaign measured single particles and cloud dynamics to investigate the influence aerosols have on the hydrological cycle in California. An Aircraft Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) was used to characterize and identify single particles within clouds potentially acting as ice and cloud nuclei. Two matching flights over California's mountains in March 2015 detected significantly different particle types that resulted in different precipitation totals. Calcium dust dominated the particle composition during the first flight which had an observed decrease in orographic precipitation. Particle composition and air mass back trajectories indicate an Asian desert origin. The calcium dust particles contained secondary acids, in particular oxalic acid, acquired during transport from Asia to California. This chemical processing likely increased the solubility of the dust, enabling the particles to act as more effective CCN. The chemical composition also showed oligomeric carbonaceous species were mixed with the calcium dust particles, potentially further increasing the solubility the particles. A single particle soot photometer (SP2) measured black carbon concurrently and returned intense incandescence when calcium dust was present, confirming the calcium dust particles were internally mixed with a carbonaceous species. Dust particles were greatly reduced during the second flight with local biomass burning particles the dominant type. Observed precipitation in California were within forecast levels during the second flight. These single particle measurements from CalWater2 show that dust particles from Asia can affect cloud process and thus precipitation in California.

Response of Cloud Condensation Nuclei (> 50 nm) to changes in ion-nucleation

NASA Astrophysics Data System (ADS)

Pedersen, J. O.; Enghoff, M. B.; Svensmark, H.

2012-12-01

The role of ionization in the formation of clouds and aerosols has been debated for many years. A body of evidence exists that correlates cloud properties to galactic cosmic ray ionization; however these results are still contested. In recent years experimental evidence has also been produced showing that ionization can promote the nucleation of small aerosols at atmospheric conditions. The experiments showed that an increase in ionization leads to an increase in the formation of ultrafine aerosols (~3 nm), but in the real atmosphere such small particles have to grow by coagulation and condensation to become cloud condensation nuclei (CCN) in order to have an effect on clouds. However, numerical studies predict that variations in the count of ultra-fine aerosols will lead only to an insignificant change in the count of CCN. This is due to 1) the competition between the additional ultra-fine aerosols for the limited supply of condensable gases leading to a slower growth and 2) the increased loss rates of the additional particles during the longer growth-time. We investigated the growth of aerosols to CCN sizes using an 8 m3 reaction chamber made from electro-polished stainless steel. One side was fitted with a Teflon foil to allow ultraviolet light to illuminate the chamber, which was continuously flushed with dry purified air. Variable concentrations of water vapor, ozone, and sulfur dioxide could be added to the chamber. UV-lamps initiated photochemistry producing sulfuric acid. Ionization could be enhanced with two Cs-137 gamma sources (30 MBq), mounted on each side of the chamber. Figure 1 shows the evolution of the aerosols, following a nucleation event induced by the gamma sources. Previous to the event the aerosols were in steady state. Each curve represents a size bin: 3-10 nm (dark purple), 10-20 nm (purple), 20-30 nm (blue), 30-40 nm (light blue), 40-50 nm (green), 50-60 nm (yellow), and 60-68 nm (red). Black curves show a ~1 hour smoothing. The initial increase in small aerosols persists all the way to the largest size bin. Similar experiments where the aerosol burst was produced with either the ionization source or an aerosol generator (neutralized aerosols) were made and compared with each other and model runs. The runs using neutral aerosol bursts agree with the model predictions, where the initial burst is dampened such that there is little or no change in the largest sizes. Thus there seems to be a fundamental difference between the bursts produced by ionization and those produced by the aerosol generator. Growth of aerosols, nucleated by ionization.

On the competition among aerosol number, size and composition in predicting CCN variability: a multi-annual field study in an urbanized desert.

PubMed

Crosbie, E; Youn, J-S; Balch, B; Wonaschütz, A; Shingler, T; Wang, Z; Conant, W C; Betterton, E A; Sorooshian, A

2015-02-10

A 2-year data set of measured CCN (cloud condensation nuclei) concentrations at 0.2 % supersaturation is combined with aerosol size distribution and aerosol composition data to probe the effects of aerosol number concentrations, size distribution and composition on CCN patterns. Data were collected over a period of 2 years (2012-2014) in central Tucson, Arizona: a significant urban area surrounded by a sparsely populated desert. Average CCN concentrations are typically lowest in spring (233 cm -3 ), highest in winter (430 cm -3 ) and have a secondary peak during the North American monsoon season (July to September; 372 cm -3 ). There is significant variability outside of seasonal patterns, with extreme concentrations (1 and 99 % levels) ranging from 56 to 1945 cm -3 as measured during the winter, the season with highest variability. Modeled CCN concentrations based on fixed chemical composition achieve better closure in winter, with size and number alone able to predict 82% of the variance in CCN concentration. Changes in aerosol chemical composition are typically aligned with changes in size and aerosol number, such that hygroscopicity can be parameterized even though it is still variable. In summer, models based on fixed chemical composition explain at best only 41% (pre-monsoon) and 36% (monsoon) of the variance. This is attributed to the effects of secondary organic aerosol (SOA) production, the competition between new particle formation and condensational growth, the complex interaction of meteorology, regional and local emissions and multi-phase chemistry during the North American monsoon. Chemical composition is found to be an important factor for improving predictability in spring and on longer timescales in winter. Parameterized models typically exhibit improved predictive skill when there are strong relationships between CCN concentrations and the prevailing meteorology and dominant aerosol physicochemical processes, suggesting that similar findings could be possible in other locations with comparable climates and geography.

Impacts of the mixing state and chemical composition on the cloud condensation nuclei (CCN) activity in Beijing during winter, 2016

NASA Astrophysics Data System (ADS)

Ren, J.; Zhang, F.

2017-12-01

Abstract.Understanding aerosol chemical composition and mixing state on CCN activity in polluted urban area is crucial to determine NCCN accurately and thus to quantify aerosol indirect effects. Aerosol hrgroscopicity, size-resolved cloud condensation nuclei (CCN) concentration and chemical composition are measured under polluted and background conditions in Beijing based on the Air Pollution and Human Health (APHH) field campaign in winter 2016. The CCN number concentration (NCCN) is predicted by using κ-Köhler theory from the PNSD and five simplified of the mixing state and chemical composition. The assumption of EIS (sulfate, nitrate and SOA internally mixed, and POA and BC externally mixed with size-resolved chemical composition) shows the best closure to predict NCCN with the ratio of predicted to measured NCCN of 0.96-1.12 both in POL and BG conditions. Under BG conditions, IB (internal mixture with bulk chemical composition) scheme achieves the best CCN closure during any periods of a day. In polluted days, EIS and IS (internal mixture with size-resolved chemical composition) scheme may achieve better closure than IB scheme due to the heterogeneity in particles composition across different size. ES (external mixture with size-resolved chemical composition) and EB (external mixture with bulk chemical composition) scheme markedly underestimate the NCCN with the ratio of predicted to measured NCCN of 0.6-0.8. In addition, we note that assumptions of size-resolved composition (IS or ES) show very limited promotes by comparing with the assumptions of bulk composition (IB or EB), furthermore, the prediction becomes worse by using size-resolved assumption in clean days. The predicted NCCN during eve-rush periods shows the most sensitivity to the five different assumptions, with ratios of the predicted and measured NCCN ranging from 0.5 to 1.4, reflecting great impacts from evening traffic and cooking sources. The result from the sensitivity examination of predict NCCN to particles mixing state and organic volume fractions with the aging of organic particles suggests that the mixing state of particles plays a minor role when the κorg exceeds 0.1. Our study could provide new dataset to evaluate the CCN parameterization in models in those heavily polluted regions with large fraction of POA and BC.

Sensitivity of the Palaeocene-Eocene Thermal Maximum climate to cloud properties.

PubMed

Kiehl, Jeffrey T; Shields, Christine A

2013-10-28

The Palaeocene-Eocene Thermal Maximum (PETM) was a significant global warming event in the Earth's history (approx. 55 Ma). The cause for this warming event has been linked to increases in greenhouse gases, specifically carbon dioxide and methane. This rapid warming took place in the presence of the existing Early Eocene warm climate. Given that projected business-as-usual levels of atmospheric carbon dioxide reach concentrations of 800-1100 ppmv by 2100, it is of interest to study past climates where atmospheric carbon dioxide was higher than present. This is especially the case given the difficulty of climate models in simulating past warm climates. This study explores the sensitivity of the simulated pre-PETM and PETM periods to change in cloud condensation nuclei (CCN) and microphysical properties of liquid water clouds. Assuming lower levels of CCN for both of these periods leads to significant warming, especially at high latitudes. The study indicates that past differences in cloud properties may be an important factor in accurately simulating past warm climates. Importantly, additional shortwave warming from such a mechanism would imply lower required atmospheric CO2 concentrations for simulated surface temperatures to be in reasonable agreement with proxy data for the Eocene.

Radiative Importance of Aerosol-Cloud Interaction

NASA Technical Reports Server (NTRS)

Tsay, Si-Chee

1999-01-01

Aerosol particles are input into the troposphere by biomass burning, among other sources. These aerosol palls cover large expanses of the earth's surface. Aerosols may directly scatter solar radiation back to space, thus increasing the earth's albedo and act to cool the earth's surface and atmosphere. Aerosols also contribute to the earth's energy balance indirectly. Hygroscopic aerosol act as cloud condensation nuclei (CCN) and thus affects cloud properties. In 1977, Twomey theorized that additional available CCN would create smaller but more numerous cloud droplets in a cloud with a given amount of liquid water. This in turn would increase the cloud albedo which would scatter additional radiation back to space and create a similar cooling pattern as the direct aerosol effect. Estimates of the magnitude of the aerosol indirect effect on a global scale range from 0.0 to -4.8 W/sq m. Thus the indirect effect can be of comparable magnitude and opposite in sign to the estimates of global greenhouse gas forcing Aerosol-cloud interaction is not a one-way process. Just as aerosols have an influence on clouds through the cloud microphysics, clouds have an influence on aerosols. Cloud droplets are solutions of liquid water and CCN, now dissolved. When the cloud droplet evaporates it leaves behind an aerosol particle. This new particle does not have to have the same properties as the original CCN. In fact, studies show that aerosol particles that result from cloud processing are larger in size than the original CCN. Optical properties of aerosol particles are dependent on the size of the particles. Larger particles have a smaller backscattering fraction, and thus less incoming solar radiation will be backscattered to space if the aerosol particles are larger. Therefore, we see that aerosols and clouds modify each other to influence the radiative balance of the earth. Understanding and quantifying the spatial and seasonal patterns of the aerosol indirect forcing may have even greater consequences. Presently we know that through the use of fossil fuel and land-use changes we have increased the concentration of greenhouse gases in the atmosphere. In parallel, we have seen a modest increase of global temperature in the last century. These two observations have been linked as cause and effect by climate models, but this connection is still experimentally not verified. The spatial and seasonal distribution of aerosol forcing is different from that of greenhouse gases, thus generating a different spatial fingerprint of climate change. This fingerprint was suggested as a method to identify the response of the climate system to anthropogenic forcing of greenhouse gases and aerosol. The aerosol fingerprint may be the only way to firmly establish the presence (or absence) of human impact on climate. Aerosol-cloud interaction through the indirect effect will be an important component of establishing this fingerprint.

Seasonal inhomogeneity in cloud precursors over Gangetic Himalayan region during GVAX campaign

NASA Astrophysics Data System (ADS)

Dumka, U. C.; Bhattu, Deepika; Tripathi, S. N.; Kaskaoutis, D. G.; Madhavan, B. L.

2015-03-01

Atmospheric aerosols are key elements in cloud microphysics, the hydrological cycle and climate by serving as cloud condensation nuclei (CCN). The present work analyzes simultaneous measurements of number concentration of CCN (NCCN) and condensation nuclei (NCN) obtained at Nainital, in the Gangetic-Himalayan (GH) region, during the frameworks of Ganges Valley Aerosol Experiment (GVAX), June 2011 to March 2012. The NCCN, NCN and activation (AR = NCCN/NCN) at 0.31-0.33% S (supersaturation ratio), exhibit significant daily, monthly and seasonal variations within a range of 684-2065 cm- 3 for NCCN, 1606-4124 cm- 3 for NCN, and 0.38-0.60 for AR, suggesting large inhomogeneity in aerosol properties, types and sources, which control the degree of aerosol potential activation. Thus, transported aerosols from the Ganges valley and abroad, the boundary-layer dynamics and atmospheric modification processes play an important role in aerosol-cloud interactions over the GH region. The NCN and NCCN show monthly-dependent diurnal variations with afternoon maxima due to transported aerosols from the Ganges valley up to the Himalayan foothills, while the AR is lower during these hours implying lower hygroscopicities or smaller sizes of the transported aerosols. The dependence of NCCN on S is highest during Dec-Mar and lowest during monsoon (Jun-Sep), suggesting different aerosol chemical composition. Comparison between Nainital and Kanpur shows that NCN and NCCN are much lower at Nainital, while the similarity in AR suggests aerosols of similar type, source and chemical composition uplifted from the Ganges valley to the Himalayan foothills.

From hygroscopic aerosols to cloud droplets: The HygrA-CD campaign in the Athens basin - An overview.

PubMed

Papayannis, A; Argyrouli, A; Bougiatioti, A; Remoundaki, E; Vratolis, S; Nenes, A; Solomos, S; Komppula, M; Giannakaki, E; Kalogiros, J; Banks, R; Eleftheriadis, K; Mantas, E; Diapouli, E; Tzanis, C G; Kazadzis, S; Binietoglou, I; Labzovskii, L; Vande Hey, J; Zerefos, C S

2017-01-01

The international experimental campaign Hygroscopic Aerosols to Cloud Droplets (HygrA-CD), organized in the Greater Athens Area (GAA), Greece from 15 May to 22 June 2014, aimed to study the physico-chemical properties of aerosols and their impact on the formation of clouds in the convective Planetary Boundary Layer (PBL). We found that under continental (W-NW-N) and Etesian (NE) synoptic wind flow and with a deep moist PBL (~2-2.5km height), mixed hygroscopic (anthropogenic, biomass burning and marine) particles arrive over the GAA, and contribute to the formation of convective non-precipitating PBL clouds (of ~16-20μm mean diameter) with vertical extent up to 500m. Under these conditions, high updraft velocities (1-2ms -1 ) and cloud condensation nuclei (CCN) concentrations (~2000cm -3 at 1% supersaturation), generated clouds with an estimated cloud droplet number of ~600cm -3 . Under Saharan wind flow conditions (S-SW) a shallow PBL (<1-1.2km height) develops, leading to much higher CCN concentrations (~3500-5000cm -3 at 1% supersaturation) near the ground; updraft velocities, however, were significantly lower, with an estimated maximum cloud droplet number of ~200cm -3 and without observed significant PBL cloud formation. The largest contribution to cloud droplet number variance is attributed to the updraft velocity variability, followed by variances in aerosol number concentration. Copyright © 2016 Elsevier B.V. All rights reserved.

Cloud residues and interstitial aerosols from non-precipitating clouds over an industrial and urban area in northern China

NASA Astrophysics Data System (ADS)

Li, Weijun; Li, Peiren; Sun, Guode; Zhou, Shengzhen; Yuan, Qi; Wang, Wenxing

2011-05-01

Most studies of aerosol-cloud interactions have been conducted in remote locations; few have investigated the characterization of cloud condensation nuclei (CCN) over highly polluted urban and industrial areas. The present work, based on samples collected at Mt. Tai, a site in northern China affected by nearby urban and industrial air pollutant emissions, illuminates CCN properties in a polluted atmosphere. High-resolution transmission electron microscopy (TEM) was used to obtain the size, composition, and mixing state of individual cloud residues and interstitial aerosols. Most of the cloud residues displayed distinct rims which were found to consist of soluble organic matter (OM). Nearly all (91.7%) cloud residues were attributed to sulfate-related salts (the remainder was mostly coarse crustal dust particles with nitrate coatings). Half the salt particles were internally mixed with two or more refractory particles (e.g., soot, fly ash, crustal dust, CaSO 4, and OM). A comparison between cloud residues and interstitial particles shows that the former contained more salts and were of larger particle size than the latter. In addition, a somewhat high number scavenging ratio of 0.54 was observed during cloud formation. Therefore, the mixtures of salts with OMs account for most of the cloud-nucleating ability of the entire aerosol population in the polluted air of northern China. We advocate that both size and composition - the two influential, controlling factors for aerosol activation - should be built into all regional climate models of China.

Hygroscopic properties of atmospheric particles emitted during wintertime biomass burning episodes in Athens

NASA Astrophysics Data System (ADS)

Psichoudaki, Magda; Nenes, Athanasios; Florou, Kalliopi; Kaltsonoudis, Christos; Pandis, Spyros N.

2018-04-01

This study explores the Cloud Condensation Nuclei (CCN) activity of atmospheric particles during intense biomass burning periods in an urban environment. During a one-month campaign in the center of Athens, Greece, a CCN counter coupled with a Scanning Mobility Particle Sizer (SMPS) and a high resolution Aerosol Mass Spectrometer (HR-AMS) were used to measure the size-resolved CCN activity and composition of the atmospheric aerosols. During the day, the organic fraction of the particles was more than 50%, reaching almost 80% at night, when the fireplaces were used. Positive Matrix Factorization (PMF) analysis revealed 4 factors with biomass burning being the dominant source after 18:00 until the early morning. The CCN-based overall hygroscopicity parameter κ ranged from 0.15 to 0.25. During the night, when the biomass burning organic aerosol (bbOA) dominated, the hygroscopicity parameter for the mixed organic/inorganic particles was on average 0.16. The hygroscopicity of the biomass-burning organic particles was 0.09, while the corresponding average value for all organic particulate matter during the campaign was 0.12.

New Particle Formation in the Mid-Latitude Upper Troposphere

NASA Astrophysics Data System (ADS)

Axisa, Duncan

Primary aerosol production due to new particle formation (NPF) in the upper troposphere and the impact that this might have on cloud condensation nuclei (CCN) concentration can be of sufficient magnitude to contribute to the uncertainty in radiative forcing. This uncertainty affects our ability to estimate how sensitive the climate is to greenhouse gas emissions. Therefore, new particle formation must be accurately defined, parametrized and accounted for in models. This research involved the deployment of instruments, data analysis and interpretation of particle formation events during the Mid-latitude Airborne Cirrus Properties Experiment (MACPEX) campaign. The approach combined field measurements and observations with extensive data analysis and modeling to study the process of new particle formation and growth to CCN active sizes. Simultaneous measurements of O3, CO, ultrafine aerosol particles and surface area from a high-altitude research aircraft were used to study tropospheric-stratospheric mixing as well as the frequency and location of NPF. It was found that the upper troposphere was an active region in the production of new particles by gas-to-particle conversion, that nucleation was triggered by convective clouds and mixing processes, and that NPF occurred in regions with high relative humidity and low surface area. In certain cases, mesoscale and synoptic features enhanced mixing and facilitated the formation of new particles in the northern mid-latitudes. A modeling study of particle growth and CCN formation was done based on measured aerosol size distributions and modeled growth. The results indicate that when SO2 is of sufficient concentration NPF is a significant source of potential CCN in the upper troposphere. In conditions where convective cloud outflow eject high concentrations of SO2, a large number of new particles can form especially in the instance when the preexisting surface area is low. The fast growth of nucleated clusters produces a particle mode that becomes CCN active within 24-hours.

Cloud condensation nuclei and ice nucleation activity of hydrophobic and hydrophilic soot particles.

PubMed

Koehler, Kirsten A; DeMott, Paul J; Kreidenweis, Sonia M; Popovicheva, Olga B; Petters, Markus D; Carrico, Christian M; Kireeva, Elena D; Khokhlova, Tatiana D; Shonija, Natalia K

2009-09-28

Cloud condensation nuclei (CCN) activity and ice nucleation behavior (for temperatures

Aerosol characteristics and particle production in the upper troposphere over the Amazon Basin

NASA Astrophysics Data System (ADS)

Andreae, Meinrat O.; Afchine, Armin; Albrecht, Rachel; Amorim Holanda, Bruna; Artaxo, Paulo; Barbosa, Henrique M. J.; Borrmann, Stephan; Cecchini, Micael A.; Costa, Anja; Dollner, Maximilian; Fütterer, Daniel; Järvinen, Emma; Jurkat, Tina; Klimach, Thomas; Konemann, Tobias; Knote, Christoph; Krämer, Martina; Krisna, Trismono; Machado, Luiz A. T.; Mertes, Stephan; Minikin, Andreas; Pöhlker, Christopher; Pöhlker, Mira L.; Pöschl, Ulrich; Rosenfeld, Daniel; Sauer, Daniel; Schlager, Hans; Schnaiter, Martin; Schneider, Johannes; Schulz, Christiane; Spanu, Antonio; Sperling, Vinicius B.; Voigt, Christiane; Walser, Adrian; Wang, Jian; Weinzierl, Bernadett; Wendisch, Manfred; Ziereis, Helmut

2018-01-01

Airborne observations over the Amazon Basin showed high aerosol particle concentrations in the upper troposphere (UT) between 8 and 15 km altitude, with number densities (normalized to standard temperature and pressure) often exceeding those in the planetary boundary layer (PBL) by 1 or 2 orders of magnitude. The measurements were made during the German-Brazilian cooperative aircraft campaign ACRIDICON-CHUVA, where ACRIDICON stands for Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems and CHUVA is the acronym for Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (global precipitation measurement), on the German High Altitude and Long Range Research Aircraft (HALO). The campaign took place in September-October 2014, with the objective of studying tropical deep convective clouds over the Amazon rainforest and their interactions with atmospheric trace gases, aerosol particles, and atmospheric radiation. Aerosol enhancements were observed consistently on all flights during which the UT was probed, using several aerosol metrics, including condensation nuclei (CN) and cloud condensation nuclei (CCN) number concentrations and chemical species mass concentrations. The UT particles differed sharply in their chemical composition and size distribution from those in the PBL, ruling out convective transport of combustion-derived particles from the boundary layer (BL) as a source. The air in the immediate outflow of deep convective clouds was depleted of aerosol particles, whereas strongly enhanced number concentrations of small particles (< 90 nm diameter) were found in UT regions that had experienced outflow from deep convection in the preceding 5-72 h. We also found elevated concentrations of larger (> 90 nm) particles in the UT, which consisted mostly of organic matter and nitrate and were very effective CCN. Our findings suggest a conceptual model, where production of new aerosol particles takes place in the continental UT from biogenic volatile organic material brought up by deep convection and converted to condensable species in the UT. Subsequently, downward mixing and transport of upper tropospheric aerosol can be a source of particles to the PBL, where they increase in size by the condensation of biogenic volatile organic compound (BVOC) oxidation products. This may be an important source of aerosol particles for the Amazonian PBL, where aerosol nucleation and new particle formation have not been observed. We propose that this may have been the dominant process supplying secondary aerosol particles in the pristine atmosphere, making clouds the dominant control of both removal and production of atmospheric particles.

Aerosol characteristics and particle production in the upper troposphere over the Amazon Basin

DOE PAGES

Andreae, Meinrat O.; Afchine, Armin; Albrecht, Rachel; ...

2018-01-25

Airborne observations over the Amazon Basin showed high aerosol particle concentrations in the upper troposphere (UT) between 8 and 15 km altitude, with number densities (normalized to standard temperature and pressure) often exceeding those in the planetary boundary layer (PBL) by 1 or 2 orders of magnitude. The measurements were made during the German–Brazilian cooperative aircraft campaign ACRIDICON–CHUVA, where ACRIDICON stands for Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems and CHUVA is the acronym for Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (globalmore » precipitation measurement), on the German High Altitude and Long Range Research Aircraft (HALO). The campaign took place in September–October 2014, with the objective of studying tropical deep convective clouds over the Amazon rainforest and their interactions with atmospheric trace gases, aerosol particles, and atmospheric radiation. Aerosol enhancements were observed consistently on all flights during which the UT was probed, using several aerosol metrics, including condensation nuclei (CN) and cloud condensation nuclei (CCN) number concentrations and chemical species mass concentrations. The UT particles differed sharply in their chemical composition and size distribution from those in the PBL, ruling out convective transport of combustion-derived particles from the boundary layer (BL) as a source. The air in the immediate outflow of deep convective clouds was depleted of aerosol particles, whereas strongly enhanced number concentrations of small particles (< 90 nm diameter) were found in UT regions that had experienced outflow from deep convection in the preceding 5–72 h. We also found elevated concentrations of larger (> 90 nm) particles in the UT, which consisted mostly of organic matter and nitrate and were very effective CCN. Our findings suggest a conceptual model, where production of new aerosol particles takes place in the continental UT from biogenic volatile organic material brought up by deep convection and converted to condensable species in the UT. Subsequently, downward mixing and transport of upper tropospheric aerosol can be a source of particles to the PBL, where they increase in size by the condensation of biogenic volatile organic compound (BVOC) oxidation products. This may be an important source of aerosol particles for the Amazonian PBL, where aerosol nucleation and new particle formation have not been observed. We propose that this may have been the dominant process supplying secondary aerosol particles in the pristine atmosphere, making clouds the dominant control of both removal and production of atmospheric particles.« less

Aerosol characteristics and particle production in the upper troposphere over the Amazon Basin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andreae, Meinrat O.; Afchine, Armin; Albrecht, Rachel

Airborne observations over the Amazon Basin showed high aerosol particle concentrations in the upper troposphere (UT) between 8 and 15 km altitude, with number densities (normalized to standard temperature and pressure) often exceeding those in the planetary boundary layer (PBL) by 1 or 2 orders of magnitude. The measurements were made during the German–Brazilian cooperative aircraft campaign ACRIDICON–CHUVA, where ACRIDICON stands for Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems and CHUVA is the acronym for Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (globalmore » precipitation measurement), on the German High Altitude and Long Range Research Aircraft (HALO). The campaign took place in September–October 2014, with the objective of studying tropical deep convective clouds over the Amazon rainforest and their interactions with atmospheric trace gases, aerosol particles, and atmospheric radiation. Aerosol enhancements were observed consistently on all flights during which the UT was probed, using several aerosol metrics, including condensation nuclei (CN) and cloud condensation nuclei (CCN) number concentrations and chemical species mass concentrations. The UT particles differed sharply in their chemical composition and size distribution from those in the PBL, ruling out convective transport of combustion-derived particles from the boundary layer (BL) as a source. The air in the immediate outflow of deep convective clouds was depleted of aerosol particles, whereas strongly enhanced number concentrations of small particles (< 90 nm diameter) were found in UT regions that had experienced outflow from deep convection in the preceding 5–72 h. We also found elevated concentrations of larger (> 90 nm) particles in the UT, which consisted mostly of organic matter and nitrate and were very effective CCN. Our findings suggest a conceptual model, where production of new aerosol particles takes place in the continental UT from biogenic volatile organic material brought up by deep convection and converted to condensable species in the UT. Subsequently, downward mixing and transport of upper tropospheric aerosol can be a source of particles to the PBL, where they increase in size by the condensation of biogenic volatile organic compound (BVOC) oxidation products. This may be an important source of aerosol particles for the Amazonian PBL, where aerosol nucleation and new particle formation have not been observed. We propose that this may have been the dominant process supplying secondary aerosol particles in the pristine atmosphere, making clouds the dominant control of both removal and production of atmospheric particles.« less

The Impact of Aerosols on Cloud and Precipitation Processes: Cloud-Resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Li, X.; Khain, A.; Simpson, S.; Johnson, D.; Remer, L.

2004-01-01

Cloud microphysics is inevitably affected by the smoke particle (CCN, cloud condensation nuclei) size distributions below the clouds. Therefore, size distributions parameterized as spectral bin microphysics are needed to explicitly study the effects of atmospheric aerosol concentration on cloud development, rainfall production, and rainfall rates for convective clouds. Recently, two detailed spectral-bin microphysical schemes were implemented into the Goddard Cumulus Ensembel (GCE) model. The formulation for the explicit spectral-bin microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (i.e., cloud droplets and raindrops), and several types of ice particles [i.e. pristine ice crystals (columnar and plate-like), snow (dendrites and aggregates), graupel and frozen drops/hail]. Each type is described by a special size distribution function containing many categories (i.e. 33 bins). Atmospheric aerosols are also described using number density size distribution functions. A spectral-bin microphysical model is very expensive from a computational point of view and has only been implemented into the 2D version of the GCE at the present time. The model is tested by studying the evolution of deep tropical clouds in the west Pacific warm pool region and in the mid-latitude continent with different concentrations of CCN: a low "c1ean"concentration and a high "dirty" concentration. In addition, differences and similarities between bulk microphysics and spectral-bin microphysical schemes will be examined and discussed.

The Impact of Aerosols on Cloud and Precipitation Processes: Cloud-resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Li, X.; Khain, A.; Simpson, S.; Johnson, D.; Remer, L.

2004-01-01

Cloud microphysics is inevitably affected by the smoke particle (CCN, cloud condensation nuclei) size distributions below the clouds. Therefore, size distributions parameterized as spectral bin microphysics are needed to explicitly study the effects of atmospheric aerosol concentration on cloud development, r d a U production, and rainfall rates for convective clouds. Recently, two detailed spectral-bin microphysical schemes were implemented into the Goddard Cumulus Ensembe1 (GCE) model. The formulation for the explicit spectral-bin microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (i.e., cloud droplets and raindrops), and several types of ice particles [i.e. pristine ice crystals (columnar and platelike), snow (dendrites and aggregates), graupel and frozen drops/hail]. Each type is described by a special size distribution function containing many categories (i.e. 33 bins). Atmospheric aerosols are also described using number density size-distribution functions. A spectral-bin microphysical model is very expensive from a computational point of view and has only been implemented into the 2D version of the GCE at the present time. The model is tested by studying the evolution of deep tropical clouds in the west Pacific warm pool region and in the mid-latitude continent with different concentrations of CCN: a low "c1ean"concentration and a high "dirty" concentration. In addition, differences and similarities between bulk microphysics and spectral-bin microphysical schemes will be examined and discussed.

Experimental Characterization and Hygroscopicity Determination of Secondary Aerosol from D5 Cyclic Siloxane Oxidation

NASA Astrophysics Data System (ADS)

Stanier, C. O.; Janechek, N. J.; Bryngelson, N.; Marek, R. F.; Lersch, T.; Bunker, K.; Casuccio, G.; Brune, W. H.; Hornbuckle, K. C.

2017-12-01

Cyclic volatile methyl siloxanes are anthropogenic chemicals present in personal care products such as antiperspirants and lotions. These are volatile chemicals that are readily released into the atmosphere by product use. Due to their emission and relatively slow kinetics of their major transformation pathway, reaction with hydroxyl radicals (OH), these compounds are present in high concentrations in indoor environments and widespread in outdoor environments. Cyclic siloxane reaction with OH can lead to secondary organic aerosols, and due to the widespread prevalence of the parent compounds, may be an important source of ambient aerosols. Atmospheric aerosols have important influences to the climate by affecting the radiative balance and by serving as cloud condensation nuclei (CCN) which influence clouds. While the parent compounds have been well-studied, the oxidation products have received much less attention, with almost no ambient measurements or experimental physical property data. We report physical properties of aerosols generated by reacting the cyclic siloxane D5 with OH using a Potential Aerosol Mass (PAM) photochemical chamber. The particles were characterized by SMPS, imaging and elemental analysis using both Transmission Electron Microscopy and Scanning Transmission Electron Microscopy equipped with Energy Dispersive X-ray Spectroscopy systems (TEM-EDS and STEM-EDS), volatility measurements using Volatility Tandem Differential Mobility Analyzer (V-TDMA), and hygroscopicity measurements to determine CCN potential using a Droplet Measurement Technologies Cloud Condensation Nuclei Counter (DMT-CCN). Aerosol yield sensitivity to D5 and OH concentrations, residence time, and seed aerosols were analyzed. TEM-EDS and STEM-EDS analysis show spherical particle morphology with elemental composition consistent with aerosols derived from cyclic siloxane sources. Measured aerosol yields were 20-50% with typical aerosol concentrations 300,000 particles cm-3, up to 200 μg m-3, and diameters of 30-90 nm. Particles experienced little diameter change after heating up to 200°C suggesting low volatility, while particle activation was shifted to higher supersaturations compared to ammonium sulfate suggesting moderate hygroscopicity in line with other secondary organics.

High resolution simulations of aerosol microphysics in a global and regionally nested chemical transport model

NASA Astrophysics Data System (ADS)

Adams, P. J.; Marks, M.

2015-12-01

The aerosol indirect effect is the largest source of forcing uncertainty in current climate models. This effect arises from the influence of aerosols on the reflective properties and lifetimes of clouds, and its magnitude depends on how many particles can serve as cloud droplet formation sites. Assessing levels of this subset of particles (cloud condensation nuclei, or CCN) requires knowledge of aerosol levels and their global distribution, size distributions, and composition. A key tool necessary to advance our understanding of CCN is the use of global aerosol microphysical models, which simulate the processes that control aerosol size distributions: nucleation, condensation/evaporation, and coagulation. Previous studies have found important differences in CO (Chen, D. et al., 2009) and ozone (Jang, J., 1995) modeled at different spatial resolutions, and it is reasonable to believe that short-lived, spatially-variable aerosol species will be similarly - or more - susceptible to model resolution effects. The goal of this study is to determine how CCN levels and spatial distributions change as simulations are run at higher spatial resolution - specifically, to evaluate how sensitive the model is to grid size, and how this affects comparisons against observations. Higher resolution simulations are necessary supports for model/measurement synergy. Simulations were performed using the global chemical transport model GEOS-Chem (v9-02). The years 2008 and 2009 were simulated at 4ox5o and 2ox2.5o globally and at 0.5ox0.667o over Europe and North America. Results were evaluated against surface-based particle size distribution measurements from the European Supersites for Atmospheric Aerosol Research project. The fine-resolution model simulates more spatial and temporal variability in ultrafine levels, and better resolves topography. Results suggest that the coarse model predicts systematically lower ultrafine levels than does the fine-resolution model. Significant differences are also evident with respect to model-measurement comparisons, and will be discussed.

Water uptake of clay and desert dust aerosol particles at sub- and supersaturated water vapor conditions.

PubMed

Herich, Hanna; Tritscher, Torsten; Wiacek, Aldona; Gysel, Martin; Weingartner, Ernest; Lohmann, Ulrike; Baltensperger, Urs; Cziczo, Daniel J

2009-09-28

Airborne mineral dust particles serve as cloud condensation nuclei (CCN), thereby influencing the formation and properties of warm clouds. It is therefore of atmospheric interest how dust aerosols with different mineralogy behave when exposed to high relative humidity (RH) or supersaturation (SS) with respect to liquid water. In this study the subsaturated hygroscopic growth and the supersaturated cloud condensation nucleus activity of pure clays and real desert dust aerosols were determined using a hygroscopicity tandem differential mobility analyzer (HTDMA) and a cloud condensation nuclei counter (CCNC), respectively. Five different illite, montmorillonite and kaolinite clay samples as well as three desert dust samples (Saharan dust (SD), Chinese dust (CD) and Arizona test dust (ATD)) were investigated. Aerosols were generated both with a wet and a dry disperser. The water uptake was parameterized via the hygroscopicity parameter kappa. The hygroscopicity of dry generated dust aerosols was found to be negligible when compared to processed atmospheric aerosols, with CCNC derived kappa values between 0.00 and 0.02 (the latter corresponds to a particle consisting of 96.7% by volume insoluble material and approximately 3.3% ammonium sulfate). Pure clay aerosols were generally found to be less hygroscopic than natural desert dust particles. The illite and montmorillonite samples had kappa approximately 0.003. The kaolinite samples were less hygroscopic and had kappa=0.001. SD (kappa=0.023) was found to be the most hygroscopic dry-generated desert dust followed by CD (kappa=0.007) and ATD (kappa=0.003). Wet-generated dust showed an increased water uptake when compared to dry-generated samples. This is considered to be an artifact introduced by redistribution of soluble material between the particles. Thus, the generation method is critically important when presenting such data. These results indicate any atmospheric processing of a fresh mineral dust particle which leads to the addition of more than approximately 3% soluble material will significantly enhance its hygroscopicity and CCN activity.

Cloud condensation nuclei in pristine tropical rainforest air of Amazonia: size-resolved measurements and modeling of atmospheric aerosol composition and CCN activity

NASA Astrophysics Data System (ADS)

Gunthe, S. S.; King, S. M.; Rose, D.; Chen, Q.; Roldin, P.; Farmer, D. K.; Jimenez, J. L.; Artaxo, P.; Andreae, M. O.; Martin, S. T.; Pöschl, U.

2009-02-01

Atmospheric aerosol particles serving as cloud condensation nuclei (CCN) are key elements of the hydrological cycle and climate. We have measured and characterized CCN at water vapor supersaturations in the range of S=0.10-0.82% in pristine tropical rainforest air during the AMAZE-08 campaign in central Amazonia. The effective hygroscopicity parameters describing the influence of chemical composition on the CCN activity of aerosol particles varied in the range of κ=0.05-0.45. The overall median value of κ≍0.15 was only half of the value typically observed for continental aerosols in other regions of the world. Aitken mode particles were less hygroscopic than accumulation mode particles (κ≍0.1 at D≍50 nm; κ≍0.2 at D≍200 nm). The CCN measurement results were fully consistent with aerosol mass spectrometry (AMS) data, which showed that the organic mass fraction (Xm,org) was on average as high as ~90% in the Aitken mode (D≤100 nm) and decreased with increasing particle diameter in the accumulation mode (~80% at D≍200 nm). The κ values exhibited a close linear correlation with Xm,org and extrapolation yielded the following effective hygroscopicity parameters for organic and inorganic particle components: κorg≍0.1 which is consistent with laboratory measurements of secondary organic aerosols and κinorg≍0.6 which is characteristic for ammonium sulfate and related salts. Both the size-dependence and the temporal variability of effective particle hygroscopicity could be parameterized as a function of AMS-based organic and inorganic mass fractions (κp=0.1 Xm,org+0.6 Xm,inorg), and the CCN number concentrations predicted with κp were in fair agreement with the measurement results. The median CCN number concentrations at S=0.1-0.82% ranged from NCCN,0.10≍30 cm-3 to NCCN,0.82≍150 cm-3, the median concentration of aerosol particles larger than 30 nm was NCN,30≍180 cm-3, and the corresponding integral CCN efficiencies were in the range of NCCN,0.10/NCN,30≍0.1 to NCCN,0.82/NCN,30≍0.8. Although the number concentrations and hygroscopicity parameters were much lower, the integral CCN efficiencies observed in pristine rainforest air were similar to those in highly polluted mega-city air. Moreover, model calculations of NCCN,S with a global average value of κ=0.3 led to systematic overpredictions, but the relative deviations exceeded ~50% only at low water vapor supersaturation (0.1%) and low particle number concentrations (≤100 cm-3). These findings confirm earlier studies suggesting that aerosol particle number and size are the major predictors for the variability of the CCN concentration in continental boundary layer air, followed by particle composition and hygroscopicity as relatively minor modulators. Depending on the required and applicable level of detail, the information and parameterizations presented in this paper should enable efficient description of the CCN properties of pristine tropical rainforest aerosols in detailed process models as well as in large-scale atmospheric and climate models.

Aerosol Effects on Microphysical Processes, Storm Structure, and Cold Pool Strength in Simulated Supercell Thunderstorms from VORTEX-2 and VORTEX-SE

NASA Astrophysics Data System (ADS)

Guo, M.; Dawson, D. T., II; Baldwin, M. E.; Mansell, E. R.

2017-12-01

The cloud condensation nuclei (CCN) concentration has been found to strongly affect microphysical, dynamical and thermodynamical processes in supercells and other deep convective storms. Moreover, recent simulation studies have shown aerosols effects differ between higher- and lower-CAPE environments. Owing to the known sensitivity of severe storms to microphysical differences, studying the impact of aerosols supercell storms different environments is of clear societal importance. Tornadic environments in the southwastern U.S. are generally characterized by lower magnitudes CAPE and deeper tropospheric moisture than those in the Great Plains. These two regions were the focus of Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX)-2 and VORTEX-Southeast (SE) field campaigns, respectively. In our study, we simulate several cases from VORTEX-2 and -SE with the Advanced Regional Prediction System (ARPS) Model at 6 different CCN concentrations (100-3000 cm-3). We use NSSL 3-moment microphysics parameterization schemeto explicitly predict precipitation particle size distributions and microphysirocess rates. Overall, storms under the higher-CAPE VORTEX-2 environments are more sensitiveto the change of CCN than those under the lower-CAPE VORTEX-SE environments. Updraft volume decreases as CCN increases for the VORTEX-2 cases, whereas the opposite is true but with a much weaker trend for the VORTEX-SE cases. Moreover, the cold pool strength drops dramatically as CCN surpasses 1000 cm-3n the VORTEX-2 cases but barely changes for the VORTEX-SE cases. Through a microphysics budget analysis, we show the change of the importance of ice processes is key to the differing sensitivities. in the VORTEX-2 cases, deposition to ice nuclei, cloud drop freezing and rain drop freezing in the upper levels (5-11km) contribute more to latent heating since more rain and cloud drops are lifted above the freezing level due to stronger updrafts. For CCN concentration over 1000cm-3, the drops become too small for efficient accretion by graupel and hail, leading to considerable decrease of latent heating and thus updraft volume. Finally, the decrease in cold pool strength in the VORTEX-2 cases at higher CCN is due to the rapid decrease of graupel melting at lower levels (<2km).

The Impact of Aerosols on Cloud and Precipitation Processes: Cloud-Resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Li, X.; Khain, A.; Simpson, S.

2005-01-01

Cloud microphysics are inevitable affected by the smoke particle (CCN, cloud condensation nuclei) size distributions below the clouds, Therefore, size distributions parameterized as spectral bin microphysics are needed to explicitly study the effect of atmospheric aerosol concentration on cloud development, rainfall production, and rainfall rates for convective clouds. Recently, a detailed spectral-bin microphysical scheme was implemented into the the Goddard Cumulus Ensemble (GCE) model. The formulation for the explicit spectral-bim microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (i.e., cloud droplets and raindrops), and several types of ice particles [i.e., pristine ice crystals (columnar and plate-like), snow (dendrites and aggregates), graupel and frozen drops/hail]. Each type is described by a special size distribution function containing many categories (i.e., 33 bins). Atmospheric aerosols are also described using number density size-distribution functions.

Characterization of distinct Arctic aerosol accumulation modes and their sources

NASA Astrophysics Data System (ADS)

Lange, R.; Dall'Osto, M.; Skov, H.; Nøjgaard, J. K.; Nielsen, I. E.; Beddows, D. C. S.; Simo, R.; Harrison, R. M.; Massling, A.

2018-06-01

In this work we use cluster analysis of long term particle size distribution data to expand an array of different shorter term atmospheric measurements, thereby gaining insights into longer term patterns and properties of Arctic aerosol. Measurements of aerosol number size distributions (9-915 nm) were conducted at Villum Research Station (VRS), Station Nord in North Greenland during a 5 year record (2012-2016). Alongside this, measurements of aerosol composition, meteorological parameters, gaseous compounds and cloud condensation nuclei (CCN) activity were performed during different shorter occasions. K-means clustering analysis of particle number size distributions on daily basis identified several clusters. Clusters of accumulation mode aerosols (main size modes > 100 nm) accounted for 56% of the total aerosol during the sampling period (89-91% during February-April, 1-3% during June-August). By association to chemical composition, cloud condensation nuclei properties, and meteorological variables, three typical accumulation mode aerosol clusters were identified: Haze (32% of the time), Bimodal (14%) and Aged (6%). In brief: (1) Haze accumulation mode aerosol shows a single mode at 150 nm, peaking in February-April, with highest loadings of sulfate and black carbon concentrations. (2) Accumulation mode Bimodal aerosol shows two modes, at 38 nm and 150 nm, peaking in June-August, with the highest ratio of organics to sulfate concentrations. (3) Aged accumulation mode aerosol shows a single mode at 213 nm, peaking in September-October and is associated with cloudy and humid weather conditions during autumn. The three aerosol clusters were considered alongside CCN concentrations. We suggest that organic compounds, that are likely marine biogenic in nature, greatly influence the Bimodal cluster and contribute significantly to its CCN activity. This stresses the importance of better characterizing the marine ecosystem and the aerosol-mediated climate effects in the Arctic.

Challenges in constraining anthropogenic aerosol effects on cloud radiative forcing using present-day spatiotemporal variability.

PubMed

Ghan, Steven; Wang, Minghuai; Zhang, Shipeng; Ferrachat, Sylvaine; Gettelman, Andrew; Griesfeller, Jan; Kipling, Zak; Lohmann, Ulrike; Morrison, Hugh; Neubauer, David; Partridge, Daniel G; Stier, Philip; Takemura, Toshihiko; Wang, Hailong; Zhang, Kai

2016-05-24

A large number of processes are involved in the chain from emissions of aerosol precursor gases and primary particles to impacts on cloud radiative forcing. Those processes are manifest in a number of relationships that can be expressed as factors dlnX/dlnY driving aerosol effects on cloud radiative forcing. These factors include the relationships between cloud condensation nuclei (CCN) concentration and emissions, droplet number and CCN concentration, cloud fraction and droplet number, cloud optical depth and droplet number, and cloud radiative forcing and cloud optical depth. The relationship between cloud optical depth and droplet number can be further decomposed into the sum of two terms involving the relationship of droplet effective radius and cloud liquid water path with droplet number. These relationships can be constrained using observations of recent spatial and temporal variability of these quantities. However, we are most interested in the radiative forcing since the preindustrial era. Because few relevant measurements are available from that era, relationships from recent variability have been assumed to be applicable to the preindustrial to present-day change. Our analysis of Aerosol Comparisons between Observations and Models (AeroCom) model simulations suggests that estimates of relationships from recent variability are poor constraints on relationships from anthropogenic change for some terms, with even the sign of some relationships differing in many regions. Proxies connecting recent spatial/temporal variability to anthropogenic change, or sustained measurements in regions where emissions have changed, are needed to constrain estimates of anthropogenic aerosol impacts on cloud radiative forcing.

Challenges in constraining anthropogenic aerosol effects on cloud radiative forcing using present-day spatiotemporal variability

PubMed Central

Ghan, Steven; Wang, Minghuai; Zhang, Shipeng; Ferrachat, Sylvaine; Gettelman, Andrew; Griesfeller, Jan; Kipling, Zak; Lohmann, Ulrike; Morrison, Hugh; Neubauer, David; Partridge, Daniel G.; Stier, Philip; Takemura, Toshihiko; Wang, Hailong; Zhang, Kai

2016-01-01

A large number of processes are involved in the chain from emissions of aerosol precursor gases and primary particles to impacts on cloud radiative forcing. Those processes are manifest in a number of relationships that can be expressed as factors dlnX/dlnY driving aerosol effects on cloud radiative forcing. These factors include the relationships between cloud condensation nuclei (CCN) concentration and emissions, droplet number and CCN concentration, cloud fraction and droplet number, cloud optical depth and droplet number, and cloud radiative forcing and cloud optical depth. The relationship between cloud optical depth and droplet number can be further decomposed into the sum of two terms involving the relationship of droplet effective radius and cloud liquid water path with droplet number. These relationships can be constrained using observations of recent spatial and temporal variability of these quantities. However, we are most interested in the radiative forcing since the preindustrial era. Because few relevant measurements are available from that era, relationships from recent variability have been assumed to be applicable to the preindustrial to present-day change. Our analysis of Aerosol Comparisons between Observations and Models (AeroCom) model simulations suggests that estimates of relationships from recent variability are poor constraints on relationships from anthropogenic change for some terms, with even the sign of some relationships differing in many regions. Proxies connecting recent spatial/temporal variability to anthropogenic change, or sustained measurements in regions where emissions have changed, are needed to constrain estimates of anthropogenic aerosol impacts on cloud radiative forcing. PMID:26921324

Investigation of aerosol indirect effects on simulated flash-flood heavy rainfall over Korea

NASA Astrophysics Data System (ADS)

Lim, Kyo-Sun Sunny; Hong, Song-You

2012-11-01

This study investigates aerosol indirect effects on the development of heavy rainfall near Seoul, South Korea, on 12 July 2006, focusing on precipitation amount. The impact of the aerosol concentration on simulated precipitation is evaluated by varying the initial cloud condensation nuclei (CCN) number concentration in the Weather Research and Forecasting (WRF) Double-Moment 6-class (WDM6) microphysics scheme. The simulations are performed under clean, semi-polluted, and polluted conditions. Detailed analysis of the physical processes that are responsible for surface precipitation, including moisture and cloud microphysical budgets shows enhanced ice-phase processes to be the primary driver of increased surface precipitation under the semi-polluted condition. Under the polluted condition, suppressed auto-conversion and the enhanced evaporation of rain cause surface precipitation to decrease. To investigate the role of environmental conditions on precipitation response under different aerosol number concentrations, a set of sensitivity experiments are conducted with a 5 % decrease in relative humidity at the initial time, relative to the base simulations. Results show ice-phase processes having small sensitivity to CCN number concentration, compared with the base simulations. Surface precipitation responds differently to CCN number concentration under the lower humidity initial condition, being greatest under the clean condition, followed by the semi-polluted and polluted conditions.

Effect of metal complex formation on the potential of organic aerosols as cloud condensation nuclei

NASA Astrophysics Data System (ADS)

Furukawa, T.; Takahashi, Y.

2010-12-01

Secondary organic aerosols (SOA) play a key role on the solar radiation balance in troposphere, since SOA can act as cloud condensation nuclei (CCN) due to its high hygroscopic nature. Oxalic acid is one of the most dominant components of SOA, which has cooling effects of the earth by acting as CCN. However, it is uncertain whether the oxalic acid can exist as free oxalic acid or metal-oxalate complexes in aerosols, even if there is a largedifference in their solubilities into water. Consequently, XAFS measurement was conducted to demonstrate the presence of metal-oxalate complexes. Size fractionated aerosol samples were collected in Tsukuba (located at northeast about 60 km from Tokyo) using a low-volume Andersen-type air sampler. The sampler had eight stages and a back-up filter. The sampling was conducted during winter and summer in 2002. Calcium oxalate was observed in finer particles in each period from Ca K-edge XANES, and its fractions among total Ca were approximately 20%. Similarly,, Zn oxalate was also detected in finer particles from Zn K-edge XANES and EXAFS. The [Zn-oxalate] / [Zn]total ratio in each period clearly increased with the decrease in the particle diameter. This result revealed that Zn-oxalate was formed in the aqueous phase at particle surfaces or in cloud processing. In other words, Zn-oxalate was abundant at the particle surface, resulting from the increase in the [surface]/[bulk] ratio with decreasing particle size. Based on (i) total concentrations of oxalate, Ca, and Zn determined by ion-chromatography and ICP-AES analyses and (ii) Ca- and Zn- oxalate fractions obtained by XAFS, we determined the fraction of metal-oxalate complexes among total oxalate in aerosols. In winter, Ca- and Zn- oxalate fractions reached about 60% of total oxalate in the ranges of 1.1-2.1 μm and 0.65-1.1 μm, while the value was about 60-80% in the same particle size range in summer. On the other hand, Ca- and Zn- oxalates are highly insoluble, showing that the complexes cannot act as CCN. Therefore, the ability of oxalic acid as CCN is needed to be reconsidered, because most of oxalic acid in aerosols exists as metal-oxalate complexes as shown by XAFS spectroscopy in this study.

Detecting Aerosol Effect on Deep Precipitation Systems: A Modeling Study

NASA Astrophysics Data System (ADS)

Li, X.; Tao, W.; Khain, A.; Kummerow, C.; Simpson, J.

2006-05-01

Urban cities produce high concentrations of anthropogenic aerosols. These aerosols are generally hygroscopic and may serve as Cloud Condensation Nuclei (CCN). This study focuses on the aerosol indirect effect on the deep convective systems over the land. These deep convective systems contribute to the majority of the summer time rainfall and are important for local hydrological cycle and weather forecast. In a companion presentation (Tao et al.) in this session, the mechanisms of aerosol-cloud-precipitation interactions in deep convective systems are explored using cloud-resolving model simulations. Here these model results will be analyzed to provide guidance to the detection of the impact of aerosols as CCN on summer time, deep convections using the currently available observation methods. The two-dimensional Goddard Cumulus Ensemble (GCE) model with an explicit microphysical scheme has been used to simulate the aerosol effect on deep precipitation systems. This model simulates the size distributions of aerosol particles, as well as cloud, rain, ice crystals, snow, graupel, and hail explicitly. Two case studies are analyzed: a midlatitude summer time squall in Oklahoma, and a sea breeze convection in Florida. It is shown that increasing the CCN number concentration does not affect the rainfall structure and rain duration in these two cases. The total surface rainfall rate is reduced in the squall case, but remains essentially the same in the sea breeze case. For the long-lived squall system with a significant portion of the stratiform rain, the surface rainfall PDF (probability density function) distribution is more sensitive to the change of the initial CCN concentrations compared with the total surface rainfall. The possibility of detecting the aerosol indirect effect in deep precipitation systems from the space is also studied in this presentation. The hydrometeors fields from the GCE model simulations are used as inputs to a microwave radiative transfer model. It is found that Tb at higher frequencies (35 GHz and 85 GHz) are quite sensitive to the CCN concentration variations. This is because the higher frequency brightness temperatures are sensitive to large, ice-phase particles. In a clean environment, the deep convections produce larger cloud particles. When these cloud particles are transported above the freezing level by strong updrafts, they form larger precipitable ice particles (snow, graupel and hail) compared with dirty environment simulations. These larger ice particles result in significantly colder brightness temperatures at high frequencies in the clean scenario simulations.

Airborne measurement of submicron aerosol number concentration and CCN activity in and around the Korean Peninsula and their comparison to ground measurement in Seoul

NASA Astrophysics Data System (ADS)

Park, M.; Kim, N.; Yum, S. S.

2016-12-01

Aerosols exert impact not only on human health and visibility but also on climate change directly by scattering or absorbing solar radiation and indirectly by acting as cloud condensation nuclei (CCN) and thus altering cloud radiative and microphysical properties. Aerosol indirect effects on climate has been known to have large uncertainty because of insufficient measurement data on aerosol and CCN activity distribution. Submicron aerosol number concentration (NCN, TSI CPC) and CCN number concentration (NCCN, DMT CCNC) were measured on board the NASA DC-8 research aircraft and at a ground site at Olympic Park in Seoul from May 2nd to June 10th, 2016. CCNC on the airborne platform was operated with the fixed internal supersaturation of 0.6% and CCNC at the ground site was operated with the five different supersaturations (0.2%, 0.4%, 0.6%, 0.8%, and 1.0%). The NASA DC-8 conducted 20 research flights (about 150 hours) in and around the Korean Peninsula and the ground measurement at Olympic Park was continuously made during the measurement period. Both airborne and ground measurements showed spatially and temporally varied aerosol number concentration and CCN activity. Aerosol number concentration in the boundary layer measured on airborne platform was highly affected by pollution sources on the ground. The average diurnal distribution of ground aerosol number concentration showed distinct peaks are located at about 0800, 1500, and 2000. The middle peak indicates that new particle formation events frequently occurred during the measurement period. CCN activation ratio at 0.6% supersaturation (NCCN/NCN) of the airborne measurement ranged from 0.1 to 0.9, indicating that aerosol properties in and around the Korean Peninsula varied so much (e. g. size, hygroscopicity). Comprehensive analysis results will be shown at the conference.

Alterations of Cloud Microphysics Due to Cloud Processed CCN

NASA Astrophysics Data System (ADS)

Hudson, J. G.; Tabor, S. S.; Noble, S. R., Jr.

2015-12-01

High-resolution CCN spectra have revealed bimodality (Hudson et al. 2015) similar to aerosol size spectra (e.g., Hoppel et al. 1985). Bimodality is caused by chemical and physical cloud processes that increase mass or hygroscopicity of only CCN that produced activated cloud droplets. Bimodality is categorized by relative CCN concentrations (NCCN) within the two modes, Nu-Np; i.e., NCCN within the higher critical supersaturation, Sc, mode that did not undergo cloud processing minus NCCN within the lower Sc mode that was cloud processed. Lower, especially negative, Nu-Np designates greater processing. The table shows regressions between Nu-Np and characteristics of clouds nearest the CCN measurements. ICE-T MASE parameter R SL R SL Nc 0.17 93.24 -0.26 98.65 MD -0.31 99.69 0.33 99.78 σ -0.27 99.04 0.48 100.00 Ld -0.31 99.61 0.38 99.96 Table. Correlation coefficients, R, and one-tailed significance levels in percent, SL, for Nu-Np with microphysics of the clouds closest to each CCN measurement, 75 ICE-T and 74 MASE cases. Nc is cloud droplet concentration, MD is cloud droplet mean diameter, σ is standard deviation of cloud droplet spectra, Ldis drizzle drop LWC. Two aircraft field campaigns, Ice in Clouds Experiment-Tropical (ICE-T) and Marine Stratus/Stratocumulus Experiment (MASE) show opposite R signs because coalescence dominated cloud processing in low altitude ICE-T cumuli whereas chemical transformations predominated in MASE low altitude polluted stratus. Coalescence reduces Nc and NCCN, which thus increases MD, and σ, which promote Ld. Chemical transformations, e.g., SO2 to SO4, increase CCN hygroscopicity, thus reducing Sc, but not affecting Nc or NCCN. Lower Sc CCN are capable of producing greater Nc in subsequent cloud cycles, which leads to lower MD and σ which reduce Ld (figure). These observations are consistent with cloud droplet growth models for the higher vertical wind (W) of cumuli and lower W of stratus. Coalescence thus reduces the indirect aerosol effect (IAE) with a positive feedback that further enhances coalescence and drizzle. Chemical cloud processing enhances both components of IAE; 1st IAE by greater droplet surface area, 2ndIAE by suppressing drizzle and thus increasing cloudiness. Hoppel, Fitzgerald and Larson: JGR 90, 2365-79 Hudson, Noble and Tabor: JGRA 120, 3436-52

Potential indirect effects of aerosol on tropical cyclone intensity: convective fluxes and cold-pool activity

NASA Astrophysics Data System (ADS)

Krall, G. M.; Cottom, W. R.

2012-01-01

Observational and model evidence suggest that a 2008 Western Pacific typhoon (NURI) ingested elevated concentrations of aerosol as it neared the Chinese coast. This study uses a regional model with two-moment bin-emulating microphysics to simulate the typhoon as it enters the field of elevated aerosol concentrations. A clean maritime field of cloud condensation nuclei (CCN) was prescribed as marine background CCN concentrations and then based on satellite and global aerosol model output, increased to pollution levels and further enhanced in sensitivity tests. The typhoon was simulated for 96 h beginning 17 August 2008. During the final 60 h CCN concentrations were enhanced as it neared the Philippines and coastal China. The model was initialized with both global reanalysis model data and irregularly spaced dropsonde data from the 2008 T-PARC observational campaign using an objective analysis routine. At 36 h, the internal nudging of the model was switched off and allowed to freely evolve on its own. As the typhoon encountered the elevated CCN in the sensitivity tests, a significant perturbation of windspeed, convective fluxes, and hydrometeor species behavior was simulated. Early during the ingestion of enhanced CCN, precipitation was reduced due to suppressed collision and coalescence, and storm winds increased in strength. Subsequently, owing to reduced fall speeds of the smaller drops, greater amounts of condensate were thrust into supercooled levels where the drops froze releasing greater amounts of latent heat of freezing. Convection thereby intensified which resulted in enhanced rainfall and more vigorous convectively-produced downdrafts. As the convection intensified in the outer rainbands the storm drifted over the developing cold-pools. The enhanced cold-pools blocked the inflow of warm, moist air into the core of the typhoon which led to a weakening of the typhoon with significantly reduced low level wind speeds. The very high amounts of pollution aerosols resulted in large amounts of condensate being thrust into the storm anvil which weakened convective downdrafts and cold-pools, yet the system did show reductions in windspeed (although weaker) compared with the clean control run. This study suggests that ingestion of elevated amounts of CCN into a tropical cyclone (TC) can appreciably alter the intensity of the storm. This implies that intensity prediction of TCs would be improved by including indirect aerosol affects. However, the pollution aerosols have very little impact on the storm track.

Collaborative Research: Quantifying the Uncertainties of Aerosol Indirect Effects and Impacts on Decadal-Scale Climate Variability in NCAR CAM5 and CESM1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nenes, Athanasios

The goal of this proposed project is to assess the climatic importance and sensitivity of aerosol indirect effect (AIE) to cloud and aerosol processes and feedbacks, which include organic aerosol hygroscopicity, cloud condensation nuclei (CCN) activation kinetics, Giant CCN, cloud-scale entrainment, ice nucleation in mixed-phase and cirrus clouds, and treatment of subgrid variability of vertical velocity. A key objective was to link aerosol, cloud microphysics and dynamics feedbacks in CAM5 with a suite of internally consistent and integrated parameterizations that provide the appropriate degrees of freedom to capture the various aspects of the aerosol indirect effect. The proposal integrated newmore » parameterization elements into the cloud microphysics, moist turbulence and aerosol modules used by the NCAR Community Atmospheric Model version 5 (CAM5). The CAM5 model was then used to systematically quantify the uncertainties of aerosol indirect effects through a series of sensitivity tests with present-day and preindustrial aerosol emissions. New parameterization elements were developed as a result of these efforts, and new diagnostic tools & methodologies were also developed to quantify the impacts of aerosols on clouds and climate within fully coupled models. Observations were used to constrain key uncertainties in the aerosol-cloud links. Advanced sensitivity tools were developed and implements to probe the drivers of cloud microphysical variability with unprecedented temporal and spatial scale. All these results have been published in top and high impact journals (or are in the final stages of publication). This proposal has also supported a number of outstanding graduate students.« less

Production of extremely low volatile organic compounds from biogenic emissions: Measured yields and atmospheric implications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jokinen, Tuija; Berndt, Torsten; Makkonen, Risto

2015-06-09

Extremely low volatility organic compounds (ELVOC) are suggested to promote aerosol particle formation and cloud condensation nuclei (CCN) production in the atmosphere. We show that the capability of biogenic VOC (BVOC) to produce ELVOC depends strongly on their chemical structure and relative oxidant levels. BVOC with an endocyclic double bond, representative emissions from, e.g., boreal forests, efficiently produce ELVOC from ozonolysis. Compounds with exocyclic double bonds or acyclic compounds including isoprene, emission representative of the tropics, produce minor quantities of ELVOC, and the role of OH radical oxidation is relatively larger. Implementing these findings into a global modeling framework showsmore » that detailed assessment of ELVOC production pathways is crucial for understanding biogenic secondary organic aerosol and atmospheric CCN formation.« less

Cloud condensation nuclei in pristine tropical rainforest air of Amazonia: size-resolved measurements and modeling of atmospheric aerosol composition and CCN activity

NASA Astrophysics Data System (ADS)

Gunthe, S. S.; King, S. M.; Rose, D.; Chen, Q.; Roldin, P.; Farmer, D. K.; Jimenez, J. L.; Artaxo, P.; Andreae, M. O.; Martin, S. T.; Pöschl, U.

2009-10-01

Atmospheric aerosol particles serving as cloud condensation nuclei (CCN) are key elements of the hydrological cycle and climate. We have measured and characterized CCN at water vapor supersaturations in the range of S=0.10-0.82% in pristine tropical rainforest air during the AMAZE-08 campaign in central Amazonia. The effective hygroscopicity parameters describing the influence of chemical composition on the CCN activity of aerosol particles varied in the range of κ≍0.1-0.4 (0.16±0.06 arithmetic mean and standard deviation). The overall median value of κ≍0.15 was by a factor of two lower than the values typically observed for continental aerosols in other regions of the world. Aitken mode particles were less hygroscopic than accumulation mode particles (κ≍0.1 at D≍50 nm; κ≍0.2 at D≍200 nm), which is in agreement with earlier hygroscopicity tandem differential mobility analyzer (H-TDMA) studies. The CCN measurement results are consistent with aerosol mass spectrometry (AMS) data, showing that the organic mass fraction (forg) was on average as high as ~90% in the Aitken mode (D≤100 nm) and decreased with increasing particle diameter in the accumulation mode (~80% at D≍200 nm). The κ values exhibited a negative linear correlation with forg (R2=0.81), and extrapolation yielded the following effective hygroscopicity parameters for organic and inorganic particle components: κorg≍0.1 which can be regarded as the effective hygroscopicity of biogenic secondary organic aerosol (SOA) and κinorg≍0.6 which is characteristic for ammonium sulfate and related salts. Both the size dependence and the temporal variability of effective particle hygroscopicity could be parameterized as a function of AMS-based organic and inorganic mass fractions (κp=κorg×forg +κinorg×finorg). The CCN number concentrations predicted with κp were in fair agreement with the measurement results (~20% average deviation). The median CCN number concentrations at S=0.1-0.82% ranged from NCCN,0.10≍35 cm-3 to NCCN,0.82≍160 cm-3, the median concentration of aerosol particles larger than 30 nm was NCN,30≍200 cm-3, and the corresponding integral CCN efficiencies were in the range of NCCN,0.10/NCN,30≍0.1 to NCCN,0.82/NCN,30≍0.8. Although the number concentrations and hygroscopicity parameters were much lower in pristine rainforest air, the integral CCN efficiencies observed were similar to those in highly polluted megacity air. Moreover, model calculations of NCCN,S assuming an approximate global average value of κ≍0.3 for continental aerosols led to systematic overpredictions, but the average deviations exceeded ~50% only at low water vapor supersaturation (0.1%) and low particle number concentrations (≤100 cm-3). Model calculations assuming a constant aerosol size distribution led to higher average deviations at all investigated levels of supersaturation: ~60% for the campaign average distribution and ~1600% for a generic remote continental size distribution. These findings confirm earlier studies suggesting that aerosol particle number and size are the major predictors for the variability of the CCN concentration in continental boundary layer air, followed by particle composition and hygroscopicity as relatively minor modulators. Depending on the required and applicable level of detail, the information and parameterizations presented in this paper should enable efficient description of the CCN properties of pristine tropical rainforest aerosols of Amazonia in detailed process models as well as in large-scale atmospheric and climate models.

IN and CCN Measurements on RV Polarstern and Cape Verde

NASA Astrophysics Data System (ADS)

Welti, André; Herenz, Paul; Henning, Silvia; Stratmann, Frank

2016-04-01

Two field campaigns, one situated on RV Polarstern (Oct. - Dec. 2015) and one on the Cape Verde islands (Jan. - Feb. 2016) measuring ice nuclei (IN) and cloud condensation nuclei (CCN) concentrations as a function of supersaturation and temperature are presented. The Polarstern cruise from Bremerhaven to Cape Town yields a cross section of IN and CCN concentrations from 54°N to 35°S and passes the Cape Verde Islands at 15°N. Measurements were conducted using the commercial CCNC and SPIN instruments from DMT. During both campaigns, a comprehensive set of aerosol characterization data including size distribution, optical properties and chemical information were measured in parallel. The ship based measurements provide a measure of variability in IN/CCN concentration with geographic position. As an example a clear influence on IN and CCN number concentration of the Saharan desert dust outflow between the Canary Islands and Cape Verde or the continental aerosol from Europe and South Africa was observed. The measurements on Cape Verde provide information on the temporal variability at a fixed position varying between clean marine and dust influenced conditions. Both datasets are related to auxiliary data of aerosol size distribution and chemical composition. The datasets are used to distinguish the influence of local sources and background concentration of IN/CCN. By combining of the geographically fix measurements with the geographical cross section, typical ranges of IN and CCN concentration are derived. The datasets will be part of the BACCHUS database thereby providing valuable input for future climate modeling activities.

Aerosol Enhancements in the Upper Troposphere Over The Amazon Forest: Do Amazonian Clouds Produce Aerosols?

NASA Astrophysics Data System (ADS)

Andreae, M. O.; Afchine, A.; Albrecht, R. I.; Artaxo, P.; Borrmann, S.; Cecchini, M. A.; Costa, A.; Dollner, M.; Fütterer, D.; Järvinen, E.; Klimach, T.; Konemann, T.; Kraemer, M.; Krüger, M. L.; Machado, L.; Mertes, S.; Pöhlker, C.; Poeschl, U.; Sauer, D. N.; Schnaiter, M.; Schneider, J.; Schulz, C.; Spanu, A.; Walser, A.; Weinzierl, B.; Wendisch, M.

2015-12-01

The German-Brazilian cooperative aircraft campaign ACRIDICON-CHUVA (Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems) on the German research aircraft HALO took place over the Amazon Basin in September/October 2014, with the objective of studying tropical deep convective clouds over the Amazon rainforest and their interactions with trace gases, aerosol particles, and atmospheric radiation. The aircraft was equipped with about 30 remote sensing and in-situ instruments for meteorological, trace gas, aerosol, cloud, precipitation, and solar radiation measurements. Fourteen research flights were conducted during this campaign. Observations during ACRIDICON-CHUVA showed high aerosol concentrations in the upper troposphere (UT) over the Amazon Basin, with concentrations after normalization to standard conditions often exceeding those in the boundary layer (BL). This behavior was consistent between several aerosol metrics, including condensation nuclei (CN), cloud condensation nuclei (CCN), and chemical species mass concentrations. These UT aerosols were different in their composition and size distribution from the aerosol in the BL, making convective transport of particles unlikely as a source. The regions in the immediate outflow of deep convective clouds were found to be depleted in aerosol particles, whereas enhanced aerosol number and mass concentrations were found in UT regions that had experienced outflow from deep convection in the preceding 24-48 hours. This suggests that aerosol production takes place in the UT based on volatile and condensable material brought up by deep convection. Subsequently, downward mixing and transport of upper tropospheric aerosol may be a source of particles to the BL, where they increase in size by the condensation of biogenic volatile organic carbon (BVOC) oxidation products. This may be an important source of aerosol particles in the Amazonian BL, where aerosol nucleation and new particle formation has not been observed.

Effects of biomass smoke from southern Africa on stratocumulus over southeastern Atlantic Ocean based on satellite observations and WRF-Chem model simulations

NASA Astrophysics Data System (ADS)

Lu, Z.; Liu, X.; Zhang, Z.; Zhao, C.; Meyer, K.; Rajapakshe, C.; Wu, C.; Yang, Z.; Penner, J.

2017-12-01

Each year, large amount of biomass burning (BB) aerosols are emitted over southern Africa, and transported by the predominant circulation to the southeastern Atlantic Ocean (SEA), where they overly and potentially interact with the semi-permanent stratocumulus deck in the marine boundary layer (MBL). Many previous studies suggested that the aerosol plumes are well separated from the MBL clouds, and only focused on the radiative effects of BB aerosols (direct + semi-direct radiative effects); however, as shown in several recent satellite observational studies, BB aerosols are able to be frequently entrained into the underlying clouds, function as cloud condensation nuclei (CCN), and potentially cause microphysical effects. Based on satellite observations from CATS, we found that the mixing frequencies between above-cloud aerosols and MBL clouds are very high ( 50%) over both coastal and remote regions, suggesting that BB aerosols may likely contact MBL cloud top and function as CCN quickly after they are transported over SEA. Despite the potential importance of the microphysical effect of BB aerosols over SEA, its magnitude is not fully assessed by modeling studies. In this study, we employ WRF-Chem model to study the impacts of BB aerosols on MBL stratocumulus clouds over SEA during the fire season of 2014. By designing three cases, we are able to quantitatively determine the relative importance of microphysical and radiative effects of BB aerosols. Our modeling results show that, by serving as CCN, BB aerosols are able to alter cloud properties of stratocumulus (e.g. higher cloud droplet number concentration [CDNC], higher cloud liquid water path [LWP], and larger cloud fraction [CF] before noon) and exert significant cooling effect at TOA (-8.05 Wm-2) over SEA. The cooling is primarily caused by higher CDNC (the Twomey effect), and secondarily by the changes in LWP and CF (the cloud lifetime effect). The semi-direct effect estimated in this study is smaller in magnitude compared to previous modeling studies (e.g. Sakaeda et al., 2011), partially because of the heating in the boundary layer after BB aerosols entrained in MBL. The findings in our study are important because they may partially explain the underestimation of cloud radiative forcing as predicted by GCMs.

Dimethylsulfide oxidation over the tropical South Atlantic: OH and other oxidants

NASA Technical Reports Server (NTRS)

Hemming, Brooke L.; Vastano, John A.; Chatfield, Robert B.; Andreae, Meinrat O.; Hildemann, Lynn M.

1994-01-01

The general course of events in the formation of a marine cloud begins with the emission of species which can eventually serve as nuclei around which water can condense to form a cloud droplet. In remote marine regions, cloud condensation nuclei (CCN) are primarily composed of sulfate, in either its acid or ammonium salt form. Most sulfate in these regions is the product of atmospheric oxidation of dimethyl sulfide (DMS), a reduced sulfur gas that is released by phytoplankton at the ocean surface. Therefore, in order to effectively quantify the links in the cloud-formation cycle, one must begin with a well-defined description of the atmospheric chemistry of DMS. The intent of this project has been to initiate development of a comprehensive model of the chemistry and dynamics responsible for the formation of clouds in the remote marine boundary layer. The primary tool in this work has been the Global/Regional Atmospheric Chemistry Event Simulator (GRACES), a global atmospheric chemistry model, which is under development within the Atmospheric Chemistry and Dynamics Branch of NASA-Ames Research Center. In this effort, GRACES was used to explore the first chemical link between DMS and sulfate by modeling the diurnal variation of DMS.

Aerosol and Cloud Microphysical Properties in the Asir region of Saudi Arabia

NASA Astrophysics Data System (ADS)

Axisa, Duncan; Kucera, Paul; Burger, Roelof; Li, Runjun; Collins, Don; Freney, Evelyn; Posada, Rafael; Buseck, Peter

2010-05-01

In recent advertent and inadvertent weather modification studies, a considerable effort has been made to understand the impact of varying aerosol properties and concentration on cloud properties. Significant uncertainties exist with aerosol-cloud interactions for which complex microphysical processes link the aerosol and cloud properties. Under almost all environmental conditions, increased aerosol concentrations within polluted air masses will enhance cloud droplet concentration relative to that in unperturbed regions. The interaction between dust particles and clouds are significant, yet the conditions in which dust particles become cloud condensation nuclei (CCN) are uncertain. In order to quantify this aerosol effect on clouds and precipitation, a field campaign was launched in the Asir region of Saudi Arabia as part of a Precipitation Enhancement Feasibility Study. Ground measurements of aerosol size distributions, hygroscopic growth factor, CCN concentrations as well as aircraft measurements of cloud hydrometeor size distributions were done in the Asir region of Saudi Arabia in August 2009. Research aircraft operations focused primarily on conducting measurements in clouds that are targeted for cloud top-seeding, on their microphysical characterization, especially the preconditions necessary for precipitation; understanding the evolution of droplet coalescence, supercooled liquid water, cloud ice and precipitation hydrometeors is necessary if advances are to be made in the study of cloud modification by cloud seeding. Non-precipitating mixed-phase clouds less than 3km in diameter that developed on top of the stable inversion were characterized by flying at the convective cloud top just above the inversion. Aerosol measurements were also done during the climb to cloud base height. The presentation will include a summary of the analysis and results with a focus on the unique features of the Asir region in producing convective clouds, characterization of the aerosol prior to convective development and the microphysical properties of convective clouds in the Asir region of Saudi Arabia.

Water uptake of clay and desert dust aerosol particles at sub- and supersaturated water vapor conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Herich, Hanna; Tritscher, Torsten; Wiacek, Aldona

2009-11-01

Airborne mineral dust particles serve as cloud condensation nuclei (CCN), thereby influencing the formation and properties of warm clouds. It is therefore of particular interest how dust aerosols with different mineralogy behave when exposed to high relative humidity (RH) or supersaturation with respect to liquid water similar to atmospheric conditions. In this study the sub-saturated hygroscopic growth and the supersaturated cloud condensation nucleus activity of pure clays and real desert dust aerosols was determined using a hygroscopicity tandem differential mobility analyzer (HTDMA) and a cloud condensation nuclei counter (CCNC), respectively. Five different illite, montmorillonite and kaolinite clay samples as wellmore » as three desert dust samples (Saharan dust (SD), Chinese dust (CD) and Arizona test dust (ATD)) were used. Aerosols were generated both with a wet and a dry disperser and the water uptake was parameterized via the hygroscopicity parameter, κ. The hygroscopicity of dry generated dust aerosols was found to be negligible when compared to processed atmospheric aerosols, with CCNC derived κ values between 0.00 and 0.02. The latter value can be idealized as a particle consisting of 96.7% (by volume) insoluble material and ~3.3% ammonium sulfate. Pure clay aerosols were found to be generally less hygroscopic than real desert dust particles. All illite and montmorillonite samples had κ~0.003, kaolinites were least hygroscopic and had κ=0.001. SD (κ=0.023) was found to be the most hygroscopic dry-generated desert dust followed by CD (κ=0.007) and ATD (κ=0.003). Wet-generated dust showed an increased water uptake when compared to dry-generated samples. This is considered to be an artifact introduced by redistribution of soluble material between the particles while immersed in an aqueous medium during atomization, thus indicating that specification of the generation method is critically important when presenting such data. Any atmospheric processing of fresh mineral dust which leads to the addition of more than ~3% soluble material is expected to significantly enhance hygroscopicity and CCN activity.« less

Comparison of Aerosol Classification Results from Airborne High Spectral Resolution Lidar (HSRL) Measurements and the Calipso Vertical Feature Mask

NASA Technical Reports Server (NTRS)

Burton, S. P.; Ferrare, R. A.; Hostetler, C. A.; Hair, J. W.; Rogers, R. R.; Obland, M. D.; Butler, C. F.; Cook, A. L.; Harper, D. B.; Froyd, K. D.;

Stability of the Early Mars Atmosphere to Collapse into Permanent Polarcaps

NASA Technical Reports Server (NTRS)

Haberle, R. M.; Kahre, M. A.; Wordsworth, R.; Forget, F.

2016-01-01

The presence of a permanent CO2 polar ice cap on Mars has important consequences for the planet's climate system. The heat balance of such a cap, which is determined mainly by atmospheric heat transport, and the downward solar in infrared radiative fluxes, determines its surface temperature, which through the vapor pressure relation sets the mean annual surface pressure. On Mars today, for example, the south residual CO2 cap is present year-round with a mean annual temperature of approximately 145 K which corresponds to a mean annual CO2 vapor pressure of approximately 600 Pa. On early Mars, permanent polar caps are also possible especially since the sun was less luminous 3.5-4.0 Gya. Thus, the existence of permanent polar caps on early Mars is central to understanding the nature of the planets climate system in those ancient times and whether or not the atmosphere might have been capable of sustaining conditions suitable for liquid water flowing over the surface as is indicated in the geological record. Forget et al [1] showed that for present orbital properties atmospheric collapse into permanent polar caps could only be prevented for surface pressures roughly between 500 - 3000 hPa. Though follow-on studies confirm and extend the Forget et al. results [2], the full sensitivity of this "window" of stability has not been explored. There are many factors to consider such the albedo of the caps, dust content of the atmosphere, and the presence of water ice clouds. However, we begin our exploration of the stability of the early Martian atmosphere by focusing on the role of CO2 ice clouds. In some preliminary simulations with the Ames Mars General Circulation Model (GCM) we found that atmospheric collapse depends on assumptions regarding the fate of CO2 ice clouds. If, for example, we assume the clouds immediately fall to the surface, then in some cases collapse is favored. On the other hand if the clouds are allowed to fall and evaporate, collapse can be averted. This implies that CO2 ice cloud microphysics is important to the overall stability of the atmosphere. Though the Ames GCM has a sophisticated CO2 cloud microphysics package that includes nucleation, growth, and sedimentation (see accompanying poster by Kahre et al. [3]), we have implemented a simpler scheme based on the Forget et al. [1] approach to CO2 ice clouds. Our goal is to reproduce and expand their study. The key parameter in this approach is the concentration and vertical distribution of cloud condensation nuclei (CCN), i.e., dust particles. Fewer CCN lead to larger particles which fall faster, while higher CCN concentrations lead to smaller particles and thicker clouds that remain suspended for longer periods of time. We plan to explore the stability of the atmosphere to CCN concentrations and distributions and then assess the capability of thick early atmospheres to loft and distribute dust particles (CCN) around the planet. Thus, our work will shed light on the nature of the coupling between the dust and CO2 cycles and the implications it has for the early Mars climate system.

Temperature Dependence in Homogeneous and Heterogeneous Nucleation

DOE Office of Scientific and Technical Information (OSTI.GOV)

McGraw R. L.; Winkler, P. M.; Wagner, P. E.

2017-08-01

Heterogeneous nucleation on stable (sub-2 nm) nuclei aids the formation of atmospheric cloud condensation nuclei (CCN) by circumventing or reducing vapor pressure barriers that would otherwise limit condensation and new particle growth. Aerosol and cloud formation depend largely on the interaction between a condensing liquid and the nucleating site. A new paper published this year reports the first direct experimental determination of contact angles as well as contact line curvature and other geometric properties of a spherical cap nucleus at nanometer scale using measurements from the Vienna Size Analyzing Nucleus Counter (SANC) (Winkler et al., 2016). For water nucleating heterogeneouslymore » on silver oxide nanoparticles we find contact angles around 15 degrees compared to around 90 degrees for the macroscopically measured equilibrium angle for water on bulk silver. The small microscopic contact angles can be attributed via the generalized Young equation to a negative line tension that becomes increasingly dominant with increasing curvature of the contact line. These results enable a consistent theoretical description of heterogeneous nucleation and provide firm insight to the wetting of nanosized objects.« less

CCN activity of secondary aerosols from terpene ozonolysis under atmospheric relevant conditions

NASA Astrophysics Data System (ADS)

Yuan, Cheng; Ma, Yan; Diao, Yiwei; Yao, Lei; Zhou, Yaoyao; Wang, Xing; Zheng, Jun

2017-04-01

Gas-phase ozonolysis of terpenes is an important source of atmospheric secondary organic aerosol. The contribution of terpene-derived aerosols to the atmospheric cloud condensation nucleus (CCN) burden under atmospheric conditions, however, remains highly uncertain. The results obtained in previous studies under simple laboratory conditions may not be applicable to atmospheric relevant conditions. Here we present that CCN activities of aerosols from terpene ozonolysis can be significantly affected by atmospheric relevant species that can act as stabilized Criegee intermediate (SCI) or OH scavengers. Ozonolysis reactions of α-pinene, limonene, α-cedrene, and α-humulene were conducted in a 4.5 m3 collapsible fluoropolymer chamber at near-atmospheric concentrations in the presence of different OH scavengers (cyclohexane, 2-butanol, or CO) and SCI scavengers (CH3COOH, H2O, or SO2). The number size distribution and CCN activity of aerosol particles formed during ozonolysis were simultaneously determined. Additionally, particulate products were chemically analyzed by using a Filter Inlet for Gases and AEROsols High-Resolution Time-of-Flight Chemical-Ionization Mass Spectrometer. Results showed that aerosol CCN activity following monoterpene ozonolysis was more sensitive to the choice of OH scavengers, while that from sesquiterpene ozonolysis was significantly affected by SCI scavengers. Combined with chemical analysis results, it was concluded that the unimolecular decomposition of CIs giving hygroscopic organic products can be largely suppressed by bimolecular reactions during sesquiterpene ozonolysis but was not significantly impacted in monoterpene ozonolysis. Our study underscores the key role of CIs in the CCN activity of terpene ozonolysis-derived aerosols. The effects of atmospheric relevant species (e.g., SO2, H2O, and CO) need to be considered when assessing the contribution of biogenic terpenes to the atmospheric CCN burden under ambient conditions.

Biomass burning CCN enhance the dynamics of a mesoscale convective system over the La Plata Basin: a numerical approach

NASA Astrophysics Data System (ADS)

Camponogara, Gláuber; Assunção Faus da Silva Dias, Maria; Carrió, Gustavo G.

2018-02-01

High aerosol loadings are discharged into the atmosphere every year by biomass burning in the Amazon and central Brazil during the dry season (July-December). These particles, suspended in the atmosphere, can be carried via a low-level jet toward the La Plata Basin, one of the largest hydrographic basins in the world. Once they reach this region, the aerosols can affect mesoscale convective systems (MCSs), whose frequency is higher during the spring and summer over the basin. The present study is one of the first that seeks to understand the microphysical effects of biomass burning aerosols from the Amazon Basin on mesoscale convective systems over the La Plata Basin. We performed numerical simulations initialized with idealized cloud condensation nuclei (CCN) profiles for an MCS case observed over the La Plata Basin on 21 September 2010. The experiments reveal an important link between CCN number concentration and MCS dynamics, where stronger downdrafts were observed under higher amounts of aerosols, generating more updraft cells in response. Moreover, the simulations show higher amounts of precipitation as the CCN concentration increases. Despite the model's uncertainties and limitations, these results represent an important step toward the understanding of possible impacts on the Amazon biomass burning aerosols over neighboring regions such as the La Plata Basin.

Physical properties, chemical composition, and cloud forming potential of particulate emissions from a marine diesel engine at various load conditions.

PubMed

Petzold, A; Weingartner, E; Hasselbach, J; Lauer, P; Kurok, C; Fleischer, F

2010-05-15

Particulate matter (PM) emissions from one serial 4-stroke medium-speed marine diesel engine were measured for load conditions from 10% to 110% in test rig studies using heavy fuel oil (HFO). Testing the engine across its entire load range permitted the scaling of exhaust PM properties with load. Emission factors for particle number, particle mass, and chemical compounds were determined. The potential of particles to form cloud droplets (cloud condensation nuclei, CCN) was calculated from chemical composition and particle size. Number emission factors are (3.43 +/- 1.26) x 10(16) (kg fuel)(-1) at 85-110% load and (1.06 +/- 0.10) x 10(16) (kg fuel)(-1) at 10% load. CCN emission factors of 1-6 x 10(14) (kg fuel)(-1) are at the lower bound of data reported in the literature. From combined thermal and optical methods, black carbon (BC) emission factors of 40-60 mg/(kg fuel) were determined for 85-100% load and 370 mg/(kg fuel) for 10% load. The engine load dependence of the conversion efficiency for fuel sulfur into sulfate of (1.08 +/- 0.15)% at engine idle to (3.85 +/- 0.41)% at cruise may serve as input to global emission calculations for various load conditions.

Measurement Comparisons Towards Improving the Understanding of Aerosol-Cloud Processing

NASA Astrophysics Data System (ADS)

Noble, Stephen R.

Cloud processing of aerosol is an aerosol-cloud interaction that is not heavily researched but could have implications on climate. The three types of cloud processing are chemical processing, collision and coalescence processing, and Brownian capture of interstitial particles. All types improve cloud condensation nuclei (CCN) in size or hygroscopicity (kappa). These improved CCN affect subsequent clouds. This dissertation focuses on measurement comparisons to improve our observations and understanding of aerosol-cloud processing. Particle size distributions measured at the continental Southern Great Plains (SGP) site were compared with ground based measurements of cloud fraction (CF) and cloud base altitude (CBA). Particle size distributions were described by a new objective shape parameter to define bimodality rather than an old subjective one. Cloudy conditions at SGP were found to be correlated with lagged shape parameter. Horizontal wind speed and regional CF explained 42%+ of this lag time. Many of these surface particle size distributions were influenced by aerosol-cloud processing. Thus, cloud processing may be more widespread with more implications than previously thought. Particle size distributions measured during two aircraft field campaigns (MArine Stratus/stratocumulus Experiment; MASE; and Ice in Cloud Experiment-Tropical; ICE-T) were compared to CCN distributions. Tuning particle size to critical supersaturation revealed hygroscopicity expressed as ? when the distributions were overlain. Distributions near cumulus clouds (ICE-T) had a higher frequency of the same ?s (48% in ICE-T to 42% in MASE) between the accumulation (processed) and Aitken (unprocessed) modes. This suggested physical processing domination in ICE-T. More MASE (stratus cloud) kappa differences between modes pointed to chemical cloud processing. Chemistry measurements made in MASE showed increases in sulfates and nitrates with distributions that were more processed. This supported chemical cloud processing in MASE. This new method to determine kappa provides the needed information without interrupting ambient measurements. MODIS derived cloud optical thickness (COT), cloud liquid water path (LWP), and cloud effective radius (re) were compared to the same in situ derived variables from cloud probe measurements of two stratus/stratocumulus cloud campaigns (MASE and Physics Of Stratocumulus Tops; POST). In situ data were from complete vertical cloud penetrations, while MODIS data were from pixels along the aircraft penetration path. Comparisons were well correlated except that MODIS LWP (14-36%) and re (20-30%) were biased high. The LWP bias was from re bias and was not improved by using the vertically stratified assumption. MODIS re bias was almost removed when compared to cloud top maximum in situ re, but, that does not describe re for the full depth of the cloud. COT is validated by in situ COT. High correlations suggest that MODIS variables are useful in self-comparisons such as gradient changes in stratus cloud re during aerosol-cloud processing.

Approach for measuring the chemistry of individual particles in the size range critical for cloud formation.

PubMed

Zauscher, Melanie D; Moore, Meagan J K; Lewis, Gregory S; Hering, Susanne V; Prather, Kimberly A

2011-03-15

Aerosol particles, especially those ranging from 50 to 200 nm, strongly impact climate by serving as nuclei upon which water condenses and cloud droplets form. However, the small number of analytical methods capable of measuring the composition of particles in this size range, particularly at the individual particle level, has limited our knowledge of cloud condensation nuclei (CCN) composition and hence our understanding of aerosols effect on climate. To obtain more insight into particles in this size range, we developed a method which couples a growth tube (GT) to an ultrafine aerosol time-of-flight mass spectrometer (UF-ATOFMS), a combination that allows in situ measurements of the composition of individual particles as small as 38 nm. The growth tube uses water to grow particles to larger sizes so they can be optically detected by the UF-ATOFMS, extending the size range to below 100 nm with no discernible changes in particle composition. To gain further insight into the temporal variability of aerosol chemistry and sources, the GT-UF-ATOFMS was used for online continuous measurements over a period of 3 days.

Aerosol indirect effects from ground-based retrievals over the rain shadow region in Indian subcontinent

NASA Astrophysics Data System (ADS)

Harikishan, G.; Padmakumari, B.; Maheskumar, R. S.; Pandithurai, G.; Min, Q. L.

2016-03-01

Aerosol-induced changes in cloud microphysical and radiative properties have been studied for the first time using ground-based and airborne observations over a semiarid rain shadow region. The study was conducted for nonprecipitating, ice-free clouds during monsoon (July to September) and postmonsoon (October) months, when cloud condensation nuclei (CCN) concentrations over the region of interest increased monotonically and exhibited characteristics of continental origin. A multifilter rotating shadowband radiometer and microwave radiometric profiler were used to retrieve the cloud optical depth and liquid water path (LWP), respectively, from which cloud effective radius (CER) was obtained. CER showed wide variability from 10-18 µm and a decreasing trend toward the postmonsoon period. During monsoon, the estimated first aerosol indirect effect (AIE) increased from 0.01 to 0.23 with increase in LWP. AIE at different super saturations (SS) showed maximum value (significant at 95%) at 0.4% SS and higher LWP bin (250-300 g/m2). Also, statistically significant AIE values were found at 0.6% and 0.8% SSs but at lower LWP bin (200-250 g/m2). The relationship between CCN and CER showed high correlation at 0.4% SS at higher LWP bin, while at higher SSs good correlations were observed at lower LWPs. Data combined from ground-based and aircraft observations showed dominance of microphysical effect at aerosol concentrations up to 1500 cm-3 and radiative effect at higher concentrations. This combined cloud microphysical and aerosol radiative effect is more prominent during postmonsoon period due to an increase in aerosol concentration.

Properties of jet engine combustion particles during the PartEmis experiment: Microphysics and Chemistry

NASA Astrophysics Data System (ADS)

Petzold, A.; Stein, C.; Nyeki, S.; Gysel, M.; Weingartner, E.; Baltensperger, U.; Giebl, H.; Hitzenberger, R.; Döpelheuer, A.; Vrchoticky, S.; Puxbaum, H.; Johnson, M.; Hurley, C. D.; Marsh, R.; Wilson, C. W.

2003-07-01

The particles emitted from an aircraft engine combustor were investigated in the European project PartEmis. Measured aerosol properties were mass and number concentration, size distribution, mixing state, thermal stability of internally mixed particles, hygroscopicity, and cloud condensation nuclei (CCN) activation potential. The combustor operation conditions corresponded to modern and older engine gas path temperatures at cruise altitude, with fuel sulphur contents (FSC) of 50, 410, and 1270 μg g-1. Operation conditions and FSC showed only a weak influence on the microphysical aerosol properties, except for hygroscopic and CCN properties. Particles of size D >= 30 nm were almost entirely internally mixed. Particles of sizes D < 20 nm showed a considerable volume fraction of compounds that volatilise at 390 K (10-15%) and 573 K (4-10%), while respective fractions decreased to <5% for particles of size D >= 50 nm.

The enhancement and suppression of immersion mode heterogeneous ice-nucleation by solutes.

PubMed

Whale, Thomas F; Holden, Mark A; Wilson, Theodore W; O'Sullivan, Daniel; Murray, Benjamin J

2018-05-07

Heterogeneous nucleation of ice from aqueous solutions is an important yet poorly understood process in multiple fields, not least the atmospheric sciences where it impacts the formation and properties of clouds. In the atmosphere ice-nucleating particles are usually, if not always, mixed with soluble material. However, the impact of this soluble material on ice nucleation is poorly understood. In the atmospheric community the current paradigm for freezing under mixed phase cloud conditions is that dilute solutions will not influence heterogeneous freezing. By testing combinations of nucleators and solute molecules we have demonstrated that 0.015 M solutions (predicted melting point depression <0.1 °C) of several ammonium salts can cause suspended particles of feldspars and quartz to nucleate ice up to around 3 °C warmer than they do in pure water. In contrast, dilute solutions of certain alkali metal halides can dramatically depress freezing points for the same nucleators. At 0.015 M, solutes can enhance or deactivate the ice-nucleating ability of a microcline feldspar across a range of more than 10 °C, which corresponds to a change in active site density of more than a factor of 10 5 . This concentration was chosen for a survey across multiple solutes-nucleant combinations since it had a minimal colligative impact on freezing and is relevant for activating cloud droplets. Other nucleators, for instance a silica gel, are unaffected by these 'solute effects', to within experimental uncertainty. This split in response to the presence of solutes indicates that different mechanisms of ice nucleation occur on the different nucleators or that surface modification of relevance to ice nucleation proceeds in different ways for different nucleators. These solute effects on immersion mode ice nucleation may be of importance in the atmosphere as sea salt and ammonium sulphate are common cloud condensation nuclei (CCN) for cloud droplets and are internally mixed with ice-nucleating particles in mixed-phase clouds. In addition, we propose a pathway dependence where activation of CCN at low temperatures might lead to enhanced ice formation relative to pathways where CCN activation occurs at higher temperatures prior to cooling to nucleation temperature.

The enhancement and suppression of immersion mode heterogeneous ice-nucleation by solutes

PubMed Central

Holden, Mark A.; Wilson, Theodore W.; O'Sullivan, Daniel; Murray, Benjamin J.

2018-01-01

Heterogeneous nucleation of ice from aqueous solutions is an important yet poorly understood process in multiple fields, not least the atmospheric sciences where it impacts the formation and properties of clouds. In the atmosphere ice-nucleating particles are usually, if not always, mixed with soluble material. However, the impact of this soluble material on ice nucleation is poorly understood. In the atmospheric community the current paradigm for freezing under mixed phase cloud conditions is that dilute solutions will not influence heterogeneous freezing. By testing combinations of nucleators and solute molecules we have demonstrated that 0.015 M solutions (predicted melting point depression <0.1 °C) of several ammonium salts can cause suspended particles of feldspars and quartz to nucleate ice up to around 3 °C warmer than they do in pure water. In contrast, dilute solutions of certain alkali metal halides can dramatically depress freezing points for the same nucleators. At 0.015 M, solutes can enhance or deactivate the ice-nucleating ability of a microcline feldspar across a range of more than 10 °C, which corresponds to a change in active site density of more than a factor of 105. This concentration was chosen for a survey across multiple solutes–nucleant combinations since it had a minimal colligative impact on freezing and is relevant for activating cloud droplets. Other nucleators, for instance a silica gel, are unaffected by these ‘solute effects’, to within experimental uncertainty. This split in response to the presence of solutes indicates that different mechanisms of ice nucleation occur on the different nucleators or that surface modification of relevance to ice nucleation proceeds in different ways for different nucleators. These solute effects on immersion mode ice nucleation may be of importance in the atmosphere as sea salt and ammonium sulphate are common cloud condensation nuclei (CCN) for cloud droplets and are internally mixed with ice-nucleating particles in mixed-phase clouds. In addition, we propose a pathway dependence where activation of CCN at low temperatures might lead to enhanced ice formation relative to pathways where CCN activation occurs at higher temperatures prior to cooling to nucleation temperature. PMID:29780544

Polarimetric radar convective cell tracking reveals large sensitivity of cloud precipitation and electrification properties to CCN

NASA Astrophysics Data System (ADS)

Hu, J.; Rosenfeld, D.; Zhang, P.; Snyder, J.; Orville, R. E.; Ryzhkov, A.; Zrnic, D.; Williams, E. R.; Zhang, R.

2017-12-01

Here we apply the cell tracking methodology, shown in our companion poster, to quantifying factors affecting the vigor and the time-height evolution of hydrometeors and electrification properties of convective cells. Benefitting from the Dual-polarimetric NEXRAD radar network, we composite more than 5000 well-tracked cells among three radars (at Houston, Lubbock and Oklahoma City), stratified by CCN, CAPE and land/sea locations. The analyzed cell properties include Z, ZDR, Kdp, and ρhv, Dm (raindrop diameter) and Nw (raindrop concentration) by the algorithm of Bringi et al. (2003). Lightning Mapping Array (LMA) data is also included in the analysis, which provides a 3D structure of lightning occurrence and RF power. The contrasting CCN conditions over marine, land, pristine and polluted areas are identified based on the satellite retrieval technique described in Rosenfeld et al. (2016). The results show that more CCN are associated with: Increased echo top height, manifesting the invigoration effect. Enhanced reflectivities, especially above the freezing level at around 4.5 km. Raindrop sizes at the initial stage increase at the expense of their concentrations, due to the smaller cloud droplets and suppressed coalescence. Larger propensity for hail. Lightning sources increase with greater CCN concentration and is likely due to the delayed warm rain process and enhanced mixed phase process under more CCN condition, when activated CCN into cloud droplets is too high (> 1000 cm-3) the glaciation is delayed too much and leave little ice at lower levels and thus decrease lightning activity. Land pristine clouds have fewer lightning sources than polluted clouds. Marine pristine clouds seldom have lightning Increased CAPE had a similar effect to the effect of added CCN. The cloud tracking and properties are obtained by a new methodology of Multi-Cell Identification and Tracking (MCIT) algorithm (Hu et al, 2017), with details about the algorithm to be found in the author's accompanying poster session. References [1] Bringi, V. et al., J. Atmos. Sci., 60, 354-365. (2003) [2] Rosenfeld, D. et al., Proc. Natl. Acad. Sci., 113, 5828-5834. (2016) [3] Hu, J. et al., in preparation.

Climatic changes resulting from mass extinctions at the K-T boundary (and other bio-events)

NASA Technical Reports Server (NTRS)

Rampino, Michael R.; Volk, Tyler

1988-01-01

The mass extinctions at the Cretaceous-Tertiary (K-T) boundary include about 90 percent of marine calcareous nannoplankton (coccoliths), and carbon-isotope data show that marine primary productivity was drastically reduced for about 500,000 years after the boundary event, the so-called Strangelove Ocean effect. One result of the elimination of most marine phytoplankton would have been a severe reduction in production of dimethyl sulfide (DMS), a biogenic gas that is believed to be the major precursor of cloud condensation nuclei (CCN) over the oceans. A drastic reduction in marine CCN should lead to a cloud canopy with significantly lower reflectivity, and hence cause a significant warming at the earth's surface. Calculations suggest that, all other things being held constant, a reduction in CCN of more than 80 percent (a reasonable value for the K-T extinctions) could have produced a rapid global warming of 6 C or more. Oxygen-isotope analyses of marine sediments, and other kinds of paleoclimatic data, have provided for a marked warming, and a general instability of climate coincident with the killoff of marine plankton at the K-T boundary. Similar reductions in phytoplankton abundance at other boundaries, as indicated by marked shifts in carbon-isotope curves, suggest that severe temperature changes may have accompanied other mass extinctions, and raises the intriguing possibility that the extinction events themselves could have contributed to the climatic instabilities at critical bio-events in the geologic record.

Impacts of a Fire Smoke Plume on Deep Convective Clouds Observed during DC3

NASA Astrophysics Data System (ADS)

Takeishi, A.; Storelvmo, T.; Zagar, M.

2014-12-01

While the ability of aerosols to act as cloud condensation nuclei (CCN) and ice nuclei (IN) is well recognized, the effects of changing aerosol number concentrations on convective clouds have only been studied extensively in recent years. As deep convective clouds can produce heavy precipitation and may sometimes bring severe damages, especially in the tropics, we need to understand the changes in the convective systems that could stem from aerosol perturbations. By perturbing convective clouds, it has also been proposed that aerosols can affect large-scale climate. According to the convective invigoration mechanism, an increase in the aerosol concentration could lead to a larger amount of rainfall and higher vertical velocities in convective clouds, due to an increase in the latent heat release aloft. With some of the satellite observations supporting this mechanism, it is necessary to understand how sensitive the model simulations actually are to aerosol perturbations. This study uses the Weather Research and Forecasting (WRF) model as a cloud-resolving model to reproduce deep convective clouds observed during the Deep Convective Clouds and Chemistry (DC3) field campaign. The convective cloud of our interest was observed in northeastern Colorado on June 22nd in 2012, with a plume of forest fire smoke flowing into its core. Compared to other convective cells observed in the same area on different days, our aircraft data analysis shows that the convective cloud in question included more organic aerosols and more CCN. These indicate the influence of the biomass burning. We compare the results from simulations with different microphysics schemes and different cloud or ice number concentrations. These sensitivity tests tell us how different the amount and the pattern of precipitation would have been if the aerosol concentration had been higher or lower on that day. Both the sensitivity to aerosol perturbation and the reproducibility of the storm are shown to highly depend on the choice of the microphysics scheme.

Mapping the Impact of Aerosol-Cloud Interactions on Cloud Formation and Warm-season Rainfall in Mountainous Regions Using Observations and Models

NASA Astrophysics Data System (ADS)

Duan, Yajuan

Light rainfall (< 3 mm/hr) amounts to 30-70% of the annual water budget in the Southern Appalachian Mountains (SAM), a mid-latitude mid-mountain system in the SE CONUS. Topographic complexity favors the diurnal development of regional-scale convergence patterns that provide the moisture source for low-level clouds and fog (LLCF). Low-level moisture and cloud condensation nuclei (CCN) are distributed by ridge-valley circulations favoring LLCF formation that modulate the diurnal cycle of rainfall especially the mid-day peak. The overarching objective of this dissertation is to advance the quantitative understanding of the indirect effect of aerosols on the diurnal cycle of LLCF and warm-season precipitation in mountainous regions generally, and in the SAM in particular, for the purpose of improving the representation of orographic precipitation processes in remote sensing retrievals and physically-based models. The research approach consists of integrating analysis of in situ observations from long-term observation networks and an intensive field campaign, multi-sensor satellite data, and modeling studies. In the first part of this dissertation, long-term satellite observations are analyzed to characterize the spatial and temporal variability of LLCF and to elucidate the physical basis of the space-time error structure in precipitation retrievals. Significantly underestimated precipitation errors are attributed to variations in low-level rainfall microstructure undetected by satellites. Column model simulations including observed LLCF microphysics demonstrate that seeder-feeder interactions (SFI) among upper-level precipitation and LLCF contribute to an three-fold increase in observed rainfall accumulation and can enhance surface rainfall by up to ten-fold. The second part of this dissertation examines the indirect effect of aerosols on cloud formation and warm-season daytime precipitation in the SAM. A new entraining spectral cloud parcel model was developed and applied to provide the first assessment of aerosol-cloud interactions in the early development of mid-day cumulus congestus over the inner SAM. Leveraging comprehensive measurements from the Integrated Precipitation and Hydrology Experiment (IPHEx) in 2014, model results indicate that simulated spectra with a low value of condensation coefficient (0.01) are in good agreement with IPHEx aircraft observations. Further, to explore sensitivity of warm-season precipitation processes to CCN characteristics, detailed intercomparisons of Weather Research and Forecasting (WRF) model simulations using IPHEx and standard continental CCN spectra were conducted. The simulated CDNC using the local spectrum show better agreement with IPHEx airborne observations and better replicate the widespread low-level cloudiness around mid-day over the inner region. The local spectrum simulation also indicate suppressed early precipitation, enhanced ice processes tied to more vigorous vertical development of individual storm cells. The studied processes here are representative of dominant moist atmospheric processes in complex terrain and cloud forests in the humid tropics and extra-tropics, thus findings from this research in the SAM are transferable to mountainous areas elsewhere.

Review of isothermal haze chamber performance

NASA Technical Reports Server (NTRS)

Fitzgerald, J. W.; Rogers, C. F.; Hudson, J. G.

1981-01-01

The theory of this method of characterizing cloud condensation nuclei (CCN) over the critical supersaturation range of about 0.01% to 0.2% was reviewed, and guidelines for the design and operation of IHC's are given. IHC data are presented and critically analyzed. Two of the four IHC's agree to about 40% over the entire range of critical. a third chamber shows similar agreement with the first two over the lower part of the critical supersaturation range but only a factor of two agreement at higher supersaturation. Some reasons for the discrepancies are given.

Potential indirect effects of aerosol on tropical cyclone development

NASA Astrophysics Data System (ADS)

Krall, Geoffrey

Observational and model evidence suggest that a 2008 Western Pacific typhoon (NURI) came into contact with and ingested elevated concentrations of aerosol as it neared the Chinese coast. This study uses a regional model with two-moment bin emulating microphysics to simulate the typhoon as it enters the field of elevated aerosol concentration. A continental field of cloud condensation nuclei (CCN) was prescribed based on satellite and global aerosol model output, then increased for further sensitivity tests. The typhoon was simulated for 96 hours beginning 17 August 2008, the final 60 of which were under varying CCN concentrations as it neared the Philippines and coastal China. The model was initialized with both global reanalysis model data and irregularly spaced dropsonde data from a 2008 observational campaign using an objective analysis routine. At 36 hours, the internal nudging of the model was switched off and allowed to evolve on its own. As the typhoon entered the field of elevated CCN in the sensitivity tests, the presence of additional CCN resulted in a significant perturbation of windspeed, convective fluxes, and hydrometeor species behavior. Initially ingested in the outer rainbands of the storm, the additional CCN resulted in an initial damping and subsequent invigoration of convection. The increase in convective fluxes strongly lag-correlates with increased amounts of supercooled liquid water within the storm domain. As the convection intensified in the outer rainbands the storm drifted over the developing cold-pools, affecting the inflow of air into the convective towers of the typhoon. Changes in the timing and amount of rain produced in each simulation resulted in differing cold-pool strengths and size. The presence of additional CCN increased resulted in an amplification of convection within the storm, except for the extremely high CCN concentration simulation, which showed a damped convection due to the advection of pristine ice away from the storm. This study examines the physical mechanisms that could potentially alter a tropical cyclone (TC) in intensity and dynamics upon ingesting elevated levels of CCN.

Air pollution control and decreasing new particle formation lead to strong climate warming

NASA Astrophysics Data System (ADS)

Makkonen, R.; Asmi, A.; Kerminen, V.-M.; Boy, M.; Arneth, A.; Hari, P.; Kulmala, M.

2011-09-01

The number of cloud droplets determines several climatically relevant cloud properties. A major cause for the high uncertainty in the indirect aerosol forcing is the availability of cloud condensation nuclei (CCN), which in turn is highly sensitive to atmospheric new particle formation. Here we present the effect of new particle formation on anthropogenic aerosol forcing in present-day (year 2000) and future (year 2100) conditions. The total aerosol forcing (-1.61 W m-2 in year 2000) is simulated to be greatly reduced in the future, to -0.23 W m-2, mainly due to decrease in SO2 emissions and resulting decrease in new particle formation. With the total aerosol forcing decreasing in response to air pollution control measures taking effect, warming from increased greenhouse gas concentrations can potentially increase at a very rapid rate.

Influences of aerosol physiochemical properties and new particle formation on CCN activity from observation at a suburban site of China

NASA Astrophysics Data System (ADS)

Li, Yanan; Zhang, Fang; Li, Zhanqing; Sun, Li; Wang, Zhenzhu; Li, Ping; Sun, Yele; Ren, Jingye; Wang, Yuying; Cribb, Maureen; Yuan, Cheng

2017-05-01

With the aim of understanding the impact of aerosol particle size and chemical composition on CCN activity, the size-resolved cloud condensation nuclei (CCN) number concentration (NCCN), particle number size distribution (PSD) (10-600 nm), and bulk chemical composition of particles with a diameter < 1.0 μm (PM1) were measured simultaneously at Xinzhou, a suburban site in northern China, from 22 July to 26 August 2014. The NCCN was measured at five different supersaturations (SS) ranging from 0.075%-0.76%. Diurnal variations in the aerosol number concentration (NCN), NCCN, the bulk aerosol activation ratio (AR), the hygroscopicity parameter (κchem), and the ratio of 44 mass to charge ration (m/z 44) to total organic signal in the component spectrum (f44), and the PSD were examined integrally to study the influence of particle size and chemical composition on CCN activation. We found that particle size was more related to the CCN activation ratios in the morning, whereas in the afternoon ( 1400 LST), κchem and f44 were more closely associated with the bulk AR. Assuming the internal mixing of aerosol particles, NCCN was estimated using the bulk chemical composition and real-time PSD. We found that the predicted CCN number concentrations were underestimated by 20-30% at SS < 0.2% probably due to the measurement uncertainties. Estimates were more accurate at higher SS levels, suggesting that the hygroscopicity parameter based on bulk chemical composition information can provide a good estimate of CCN number concentrations. We studied the impacts of new particle formation (NPF) events on size-resolved CCN activity at the ;growth; stage and ;leveling-off; stage during a typical NPF event by comparing with the case during non-NPF event. It has been found that CCN activation was restrained at the ;growth; stage during which larger particle diameters were needed to reach an activation diameter(Da), and the bulk AR decreased as well. However, during the ;leveling-off; stage, a lower Da was observed and CCN activation was greatly enhanced.

Project Final Report: Linking Plant Stress, Biogenic SOA, and CCN Production - A New Feedback in the Climate System?

DOE Office of Scientific and Technical Information (OSTI.GOV)

VanReken, Timothy; Balasingam, Muhunthan

2017-05-01

This project worked toward understanding the role of variable biogenic emissions in the formation of secondary organic aerosol (SOA), and in turn the potential for this aerosol to affect cloud droplet formation. It was premised on the idea that a changing climate could impose biogenic and abiogenic stresses on plants that would affect the emissions of volatile organic compounds (VOCs). The transformation of these VOCs to SOA and cloud condensation nuclei (CCN) implied the possibility of a feedback mechanism within the biosphere/atmosphere/climate system. The project’s activities centered on laboratory experiments to study the effects of stresses on plants and plant-derivedmore » material under controlled conditions, observing both the VOC emissions and the aerosol that formed from the oxidation of those VOCs. The results highlighted the potentially important contributions of stress and decomposition mechanisms to biogenic SOA formation. Related field measurements elucidated the conditions when these factors could be important in the ambient environment. The project also revealed repeated the complexity of the stress/VOC emission relationship, and the difficulty in expressing these relationships in a comprehensive manner.« less

New Particle Formation and Growth in an Isoprene-Dominated Ozark Forest: From Sub-5 nm to CCN-Active Sizes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Huan; Ortega, John; Smith, James N.

Particle Investigations at a Northern Ozarks Tower: NOx, Oxidant, Isoprene Research (PINOT-NOIR) were conducted in a Missouri forest dominated by isoprene emissions, from May to October 2012. This study presents results of new particle formation (NPF) and the growth of new particles to cloud condensation nuclei (CCN)-active sizes (~100 nm) observed from this field campaign. The measured sub-5 nm particles were up to ~20000 cm-3 during a typical NPF event. Nucleation rates J1 were relatively high (11.0±10.6 cm-3s-1), and one order of magnitude higher than formation rates of 5 nm particles (J5). Sub-5 nm particle events were observed on 64%more » of the measurement days, with a high preference in biogenic volatile organic compounds (BVOCs)- and SO2-poor northwesterly (90%) air masses than in BVOCs-rich southerly air masses (13%). About 80% of sub-5 nm particle events led to the further growth. While high temperatures and high aerosol loadings in the southerly air masses were not favorable for nucleation, high BVOCs in the southerly air masses facilitated the growth of new particles to CCN-active sizes. In overall, 0.4-9.4% of the sub-5 nm particles grew to CCN-active sizes within a NPF event. During a regional NPF event period that took place consecutively over several days, concentrations of CCN size particles increased by a factor of 5 in average. This enhanced production of CCN particles from new particles was commonly observed during all 13 regional NPF events observed during the campaign.« less

Vertical velocity-CCN correlations

NASA Astrophysics Data System (ADS)

Hudson, J. G.; Noble, S. R.

2013-12-01

The realization that smaller cloud droplets evaporate more readily (Xue and Feingold 2006; Jiang et al. 2002) gives rise to an anti-indirect aerosol effect (IAE); less cloudiness with pollution. The greater latent heat exchange of the greater evaporation in more polluted clouds adds TKE and buoyancy gradients that can enhance vertical velocity (W), mixing and entrainment (Zhao and Austin 2005). Stronger W can increase horizontal motions, which can further enhance droplet evaporation, which further enhances latent heat exchange and vertical motions, thus, positive feedback. This could also include latent heat released during condensation (Lee and Feingold 2010), which is more rapid for the greater surface areas of the smaller more numerous droplets. These theories imply a positive relationship between within-cloud W variations; i.e., standard deviation of W (σw) and CCN concentration (NCCN) rather than W and NCCN. This implies greater turbulence in polluted clouds, which could possibly counteract the reduction of cloudiness of anti-IAE. During two stratus cloud projects, 50 cloud penetrations in 9 MASE flights and 34 cloud penetrations in 13 POST flights, within-cloud σw-NCCN showed correlation coefficients (R) of 0.50 and 0.39. Panel a shows similar within-cloud σw-NCCN R in all altitude bands for 17 RICO flights in small cumulus clouds. R for W-NCCN showed similar values but only at low altitudes. Out-of-cloud σw-NCCN showed similar high values except at the highest altitudes. Within-cloud σw showed higher R than within-cloud W with droplet concentrations (Nc), especially at higher altitudes. Panel b for 13 ICE-T cumulus cloud flights in the same location as RICO but during the opposite season, however, showed σw and W uncorrelated with NCCN at all altitudes; and W and σw correlated with Nc only at the highest altitudes. On the other hand, out-of-cloud σw was correlated with NCCN at all altitudes with R similar to the corresponding R of the other projects. Overall these results are consistent with the theories noted above. Supported by NSF AGS-1035230 and DOE SC0009162. Jiang, H., G. Feingold, and W.R. Cotton, 2002: J. Geophys. Res, 107, D24, 4813. Lee, S.-S., and G. Feingold, 2010: Geophys. Res. Lett., 37, L23806. Xue, H., and G. Feingold, 2006: J. Atmos. Sci., 63, 1605-1622. Zhao, M., and P.H. Austin, 2005: J. Atmos. Sci., 62, 1291-1310. Fig. Correlation coefficients (R) between mean and standard deviations of vertical velocity (W; σw within and outside of clouds) with CCN concentrations at 1% supersaturation (N1%) measured below the clouds and with droplet concentrations (Nc) within various altitude bands.

Simulation of Asia Dust and Cloud Interaction Over Pacific Ocean During Pacdex

NASA Astrophysics Data System (ADS)

Long, X.; Huang, J.; Cheng, C.; Wang, W.

2007-12-01

The effect of dust plume on the Pacific cloud systems and the associated radiative forcing is an outstanding problem for understanding climate change. Many studies showing that dust aerosol might be a good absorber for solar radiation, at the same time dust aerosols could affect the cloud's formation and precipitation by its capability as cloud condensation nuclei (CCN) and ice forming nuclei (IFN). But the role of aerosols in clouds and precipitation is very complex. Simulation of interaction between cloud and dust aerosols requires recognition that the aerosol cloud system comprises coupled components of dynamics, aerosol and cloud microphysics, radiation processes. In this study, we investigated the interaction between dust aerosols and cloud with WRF which coupled with detailed cloud microphysics processes and dust process. The observed data of SACOL (Semi-Arid Climate and Environment Observatory of Lanzhou University) and PACDEX (Pacific Dust Experiment) is used as the initialization which include the vertical distributions and concentration of dust particles. Our results show that dust aerosol not only impacts cloud microphysical processes but also cloud microstructure; Dust aerosols can act as effective ice nuclei and intensify the ice-forming processes.

The Impact of Aerosol Sources and Aging on CCN Formation in the Houston-Galveston-Gulf of Mexico Region

NASA Astrophysics Data System (ADS)

Quinn, P.; Bates, T.; Coffman, D.; Covert, D.

2007-12-01

The impact of anthropogenic aerosol on cloud properties, cloud lifetime, and precipitation processes is one of the largest uncertainties in our current understanding of climate change. Aerosols affect cloud properties by serving as cloud condensation nuclei (CCN) thereby leading to the formation of cloud droplets. The process of cloud drop activation is a function of both the size and chemistry of the aerosol particles which, in turn, depend on the source of the aerosol and transformations that occur downwind. In situ field measurements that can lead to an improved understanding of the process of cloud drop formation and simplifying parameterizations for improving the accuracy of climate models are highly desirable. During the Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS), the NOAA RV Ronald H. Brown encountered a wide variety of aerosol types ranging from marine near the Florida panhandle to urban and industrial in the Houston-Galveston area. These varied sources provided an opportunity to investigate the role of aerosol sources, aging, chemistry, and size in the activation of particles to form cloud droplets. Here, we use the correlation between variability in critical diameter for activation (determined empirically from measured CCN concentrations and the number size distribution) and aerosol composition to quantify the impact of composition on particle activation. Variability in aerosol composition is parameterized by the mass fraction of Hydrocarbon-like Organic Aerosol (HOA) for particle diameters less than 200 nm (vacuum aerodynamic). The HOA mass fraction in this size range is lowest for marine aerosol and higher for aerosol impacted by anthropogenic emissions. Combining all data collected at 0.44 percent supersaturation (SS) reveals that composition (defined in this way) explains 40 percent of the variance in the critical diameter. As expected, the dependence of activation on composition is strongest at lower SS. At the same time, correlations between HOA mass fraction and aerosol mean diameter show that these two parameters are essentially independent of one another for this data set. We conclude that, based on the variability of the HOA mass fraction observed during GoMACCS, composition plays a dominant role in determining the fraction of particles that are activated to form cloud droplets. Using Kohler theory, we estimate the error that results in calculated CCN concentrations if the organic fraction of the aerosol is neglected (i.e., a fully soluble composition of ammonium sulfate is assumed) for the range of organic mass fractions and mean diameters observed during GoMACCS. We then relate this error to the source and age of the aerosol. At 0.22 and 0.44 percent SS, the error is considerable for anthropogenic aerosol sampled near the source region as this aerosol has, on average, a high POM mass fraction and smaller particle mean diameter. The error is lower for more aged aerosol as it has a lower POM mass fraction and larger mean particle diameter. Hence, the percent error in calculated CCN concentration is expected to be larger for younger, organic- rich aerosol and smaller for aged, sulfate rich aerosol and for marine aerosol. We extend this analysis to continental and marine data sets recently reported by Dusek et al. [Science, 312, 1375, 2006] and Hudson [Geophys. Res., Lett., 34, L08801, 2007].

Aerosol and CCN in southwest Saudi Arabia

NASA Astrophysics Data System (ADS)

Collins, Don; Li, Runjun; Axisa, Duncan; Kucera, Paul; Burger, Roelof

2010-05-01

As part of an ongoing study of the microphysical and dynamical controls on precipitation in southwest Saudi Arabia, a number of surface and aircraft-based instruments were used in summer / fall 2009 to measure the size distribution, hygroscopic properties, and cloud droplet nucleation efficiency of the local aerosol. Submicron size distributions were measured using differential mobility analyzers both on the ground and on board the aircraft, while an aerodynamic particle sizer and a forward scattering spectrometer probe were used to measure the supermicron size distributions on the ground and from on board the aircraft, respectively. Identical continuous flow cloud condensation nuclei counters were used to measure CCN spectra at the surface and aloft and a humidified tandem differential mobility analyzer was operated on the ground to measure size-resolved hygroscopicity. The aerosol in this arid environment is characterized by a persistent accumulation mode having hygroscopic and CCN efficiency properties consistent with a sulfate-rich aged aerosol. The particles in that background aerosol are generally sufficiently large and hygroscopic to activate at those supersaturations expected in the convective clouds responsible for most of the regional precipitation, which consequently acts as a lower bound on the resulting cloud droplet concentrations. Though the concentration, size distribution, and properties of the submicron aerosol generally changed very slowly over periods of several hours, abrupt ~doubling in concentration almost always accompanied the arrival of the sea breeze front that began along the Red Sea. Interestingly, the hygroscopicity and the shape of the size distribution differed little in the pre- and post-sea breeze air masses. The dust-dominated coarse mode typically contributed significantly more to the aerosol mass concentration than did the submicron mode and likely controlled the ice nuclei concentration, though no direct measurements were made to confirm this. Results of routine flight patterns designed to examine the spatial, vertical, and day-to-day variability of the aerosol will be presented and the link between the aerosol at the surface and aloft will be quantified. This presentation will emphasize the regional character of the aerosol and will assess its influence on cloud microphysics.

Simulating the effect of photochemical aging on the oxidation state and hygroscopicity of organic aerosol

NASA Astrophysics Data System (ADS)

Tsimpidi, A.; Karydis, V.; Pandis, S. N.; Lelieveld, J.

2016-12-01

Hygroscopicity is an important property of aerosols which describes their propensity to absorb water vapor. The hygroscopicity of organic aerosol (OA) can change during its atmospheric aging affecting the total aerosol hygroscopicity. A more hygroscopic particle will grow more rapidly under humid conditions, scatter incident sunlight more efficiently; and it will more likely form cloud droplets. Both phenomena strongly influence the radiative forcing of climate through the direct and indirect effects of aerosols. Therefore, taking into account the hygrscopicity changes of OA during its atmospheric aging is of prime importance to accurately estimate the aerosol climatic impact. Here, we use a computationally efficient module for the description of OA composition and evolution in the atmosphere (ORACLE) (Tsimpidi et al., 2014) in the frame of the global chemistry climate model EMAC to simulate the global distribution of the OA oxidation state and hygroscopicity. To track the evolution of the OA oxidation state during its atmospheric aging, ORACLE is modified to include the description of the OA oxygen content change when mass from any OA surrogate species reacts with the OH radical. Subsequently, it is assumed that the cloud condensation nuclei (CCN) activity of OA, expressed in the form of the hygroscopicity parameter κ, will increase with increasing oxygen content (expressed by the oxygen per carbon ratio, O:C) and will range from κ = 0 (for O:C ≤ 0.2) to κ = 0.35 (for O:C = 1). The exact relationship between O:C and κ is determined based on aerosol mass spectrometer (AMS) and continuous flow CCN (CCNC) measurements of SOA (Lambe et al., 2011). Following a straightforward mixing rule, the hygroscopicity and oxygen content of total OA is calculated based on the hygroscopicities of the individual OA compounds and their degree of oxidation. A global dataset of O:C measurements is used to validate the model results. ReferencesLambe, A. T., et al. : Laboratory studies of the chemical composition and cloud condensation nuclei (CCN) activity of secondary organic aerosol (SOA) and oxidized primary organic aerosol (OPOA), Atmos. Chem. Phys., 11, 8913-8928, 2011. Tsimpidi, A. P., et al. : ORACLE (v1.0): module to simulate the organic aerosol composition and evolution in the atmosphere, Geo. Mod. Devel., 7, 3153-3172, 2014.

Cloud Condensation Nuclei Prediction Error from Application of Kohler Theory: Importance for the Aerosol Indirect Effect

NASA Technical Reports Server (NTRS)

Sotiropoulou, Rafaella-Eleni P.; Nenes, Athanasios; Adams, Peter J.; Seinfeld, John H.

2007-01-01

In situ observations of aerosol and cloud condensation nuclei (CCN) and the GISS GCM Model II' with an online aerosol simulation and explicit aerosol-cloud interactions are used to quantify the uncertainty in radiative forcing and autoconversion rate from application of Kohler theory. Simulations suggest that application of Koehler theory introduces a 10-20% uncertainty in global average indirect forcing and 2-11% uncertainty in autoconversion. Regionally, the uncertainty in indirect forcing ranges between 10-20%, and 5-50% for autoconversion. These results are insensitive to the range of updraft velocity and water vapor uptake coefficient considered. This study suggests that Koehler theory (as implemented in climate models) is not a significant source of uncertainty for aerosol indirect forcing but can be substantial for assessments of aerosol effects on the hydrological cycle in climatically sensitive regions of the globe. This implies that improvements in the representation of GCM subgrid processes and aerosol size distribution will mostly benefit indirect forcing assessments. Predictions of autoconversion, by nature, will be subject to considerable uncertainty; its reduction may require explicit representation of size-resolved aerosol composition and mixing state.

Properties of Arctic Aerosol Particles and Residuals of Warm Clouds: Cloud Activation Efficiency and the Aerosol Indirect Effect

NASA Astrophysics Data System (ADS)

Zelenyuk, A.; Imre, D. G.; Leaitch, R.; Ovchinnikov, M.; Liu, P.; Macdonald, A.; Strapp, W.; Ghan, S. J.; Earle, M. E.

2012-12-01

Single particle mass spectrometer, SPLAT II, was used to characterize the size, composition, number concentration, density, and shape of individual Arctic spring aerosol. Background particles, particles above and below the cloud, cloud droplet residuals, and interstitial particles were characterized with goal to identify the properties that separate cloud condensation nuclei (CCN) from background aerosol particles. The analysis offers a comparison between warm clouds formed on clean and polluted days, with clean days having maximum particle concentrations (Na) lower than ~250 cm-3, as compared with polluted days, in which maximum concentration was tenfold higher. On clean days, particles were composed of organics, organics mixed with sulfates, biomass burning (BB), sea salt (SS), and few soot and dust particles. On polluted days, BB, organics associated with BB, and their mixtures with sulfate dominated particle compositions. Based on the measured compositions and size distributions of cloud droplet residuals, background aerosols, and interstitial particles, we conclude that these three particle types had virtually the same compositions, which means that cloud activation probabilities were surprisingly nearly composition independent. Moreover, these conclusions hold in cases in which less than 20% or more than 90% of background particles got activated. We concluded that for the warm clouds interrogated in this study particle size played a more important factor on aerosol CCN activity. Comparative analysis of all studied clouds reveals that aerosol activation efficiency strongly depends on the aerosol concentrations, such that at Na <200 cm-3, nearly all particles activate, and at higher concentrations the activation efficiency is lower. For example, when Na was greater than 1500 cm-3, less than ~30% of particles activated. The data suggest that as the number of nucleated droplets increases, condensation on existing droplets effectively competes with particle activation, limiting maximum droplet concentrations Nd = 525 ± 50 cm-3, which is lower than the 750 cm-3 limit found by Leaitch et al. (1986) for mid-latitude continental cloud that had generally larger updraft speeds than the clouds interrogated in Arctic. These findings are important for the aerosol indirect effect, in which increase in aerosol particle number concentrations is expected to result in increase in Nd and decrease in droplet size, leading to increased cloud albedo and potentially lifetimes. Our conclusions point to limited susceptibility to changes in ambient aerosol concentrations, providing simple explanation for the finding of weaker than expected indirect effect. In summary, the data presented here show that Nd increases as the cloud base particle number concentration increases; however, they also show a limit on Nd that is in the range of 500-600 cm-3.

Global Survey of the Relationship Between Cloud Droplet Size and Albedo Using ISCCP

NASA Technical Reports Server (NTRS)

Han, Qingyuan; Rossow, William B.; Chou, Joyce; Welch, Ronald M.

1997-01-01

Aerosols affect climate through direct and indirect effects. The direct effect of aerosols (e.g., sulfates) includes reflection of sunlight back toward space and for some aerosols (e.g., smoke particles), absorption in the atmosphere; both effects cool the Earth's surface. The indirect effect of aerosols refers to the modification of cloud microphysical properties, thereby affecting the radiation balance. Higher concentrations of Cloud Condensation Nuclei (CCN) generally produce higher concentrations of cloud droplets, which are also usually assumed to lead to decreased cloud droplet sizes. The result is an increase in cloud albedo, producing a net radiative cooling, opposite to the warming caused by greenhouse gases (Charlson et al. 1992). The change in clouds that is directly induced by an increase of aerosol concentration is an increase of cloud droplet number density, N; but is is usually assumed that cloud droplet size decreases as if the water mass density Liquid Water Content (LWC) were constant. There is actually no reason why this should be the case. Shifting the cloud droplet size distribution to more numerous smaller droplets can change the relative rates of condensational and coalescence growth, leading to different LWC (e.g., Rossow 1978). Moreover, the resulting change in cloud albedo is usually ascribed to more efficient scattering by smaller droplets, when in fact it is the increase in droplet number density (assuming constant LWC) that produces the most important change in cloud albedo: e.g., holding N constant and decreasing the droplet size would actually decrease the scattering cross-section and, thus, the albedo much more than it is increased by the increased scattering efficiency.

Trade-Wind Cloudiness and Climate

NASA Technical Reports Server (NTRS)

Randall, David A.

1997-01-01

Closed Mesoscale Cellular Convection (MCC) consists of mesoscale cloud patches separated by narrow clear regions. Strong radiative cooling occurs at the cloud top. A dry two-dimensional Bousinesq model is used to study the effects of cloud-top cooling on convection. Wide updrafts and narrow downdrafts are used to indicate the asymmetric circulations associated with the mesoscale cloud patches. Based on the numerical results, a conceptual model was constructed to suggest a mechanism for the formation of closed MCC over cool ocean surfaces. A new method to estimate the radioative and evaporative cooling in the entrainment layer of a stratocumulus-topped boundary layer has been developed. The method was applied to a set of Large-Eddy Simulation (LES) results and to a set of tethered-balloon data obtained during FIRE. We developed a statocumulus-capped marine mixed layer model which includes a parameterization of drizzle based on the use of a predicted Cloud Condensation Nuclei (CCN) number concentration. We have developed, implemented, and tested a very elaborate new stratiform cloudiness parameterization for use in GCMs. Finally, we have developed a new, mechanistic parameterization of the effects of cloud-top cooling on the entrainment rate.

Aerosol-Cloud Interactions During Puijo Cloud Experiments - The effects of weather and local sources

NASA Astrophysics Data System (ADS)

Komppula, Mika; Portin, Harri; Leskinen, Ari; Romakkaniemi, Sami; Brus, David; Neitola, Kimmo; Hyvärinen, Antti-Pekka; Kortelainen, Aki; Hao, Liqing; Miettinen, Pasi; Jaatinen, Antti; Ahmad, Irshad; Lihavainen, Heikki; Laaksonen, Ari; Lehtinen, Kari E. J.

2013-04-01

The Puijo measurement station has provided continuous data on aerosol-cloud interactions since 2006. The station is located on top of the Puijo observation tower (306 m a.s.l, 224 m above the surrounding lake level) in Kuopio, Finland. The top of the tower is covered by cloud about 15 % of the time, offering perfect conditions for studying aerosol-cloud interactions. With a twin-inlet setup (total and interstitial inlets) we are able to separate the activated particles from the interstitial (non-activated) particles. The continuous twin-inlet measurements include aerosol size distribution, scattering and absorption. In addition cloud droplet number and size distribution are measured continuously with weather parameters. During the campaigns the twin-inlet system was additionally equipped with aerosol mass spectrometer (AMS) and Single Particle Soot Photometer (SP-2). This way we were able to define the differences in chemical composition of the activated and non-activated particles. Potential cloud condensation nuclei (CCN) in different supersaturations were measured with two CCN counters (CCNC). The other CCNC was operated with a Differential Mobility Analyzer (DMA) to obtain size selected CCN spectra. Other additional measurements included Hygroscopic Tandem Differential Mobility Analyzer (HTDMA) for particle hygroscopicity. Additionally the valuable vertical wind profiles (updraft velocities) are available from Halo Doppler lidar during the 2011 campaign. Cloud properties (droplet number and effective radius) from MODIS instrument onboard Terra and Aqua satellites were retrieved and compared with the measured values. This work summarizes the two latest intensive campaigns, Puijo Cloud Experiments (PuCE) 2010 & 2011. We study especially the effect of the local sources on the cloud activation behaviour of the aerosol particles. The main local sources include a paper mill, a heating plant, traffic and residential areas. The sources can be categorized and identified by wind direction. Clear changes can be seen in the aerosol and cloud properties when being under the influence of a local pollutant source. Also differences in the chemical composition of aerosol activated to cloud droplet and those staying interstitial has been observed. For example, the light absorption by cloud interstitial particles is higher when the wind blows from the local pollutant sources compared to a cleaner sector. This may be due to the fact that the absorptive material, e.g. fresh soot, is generally hydrophobic and therefore inhibits activation. Another point of interest is the occasional freezing conditions during the campaign (temperature below zero), which also affects the activation behaviour. The full usage of this special data set will provide new information on the properties and differences of activating and non-activating aerosol particles, as well as on the variables affecting the activation.

Gas exchange in wetlands: Controls and remote sensing

NASA Technical Reports Server (NTRS)

Hines, Mark E.

1992-01-01

This project was directed toward the quantification of fluxes of gaseous biogenic sulfur compounds from freshwater wetlands. These compounds (primarily hydrogen sulfide (H2S), dimethyl sulfide (DMS), and carbonyl sulfide (OCS)) have been implicated in the regulation of planetary albedo by the formation of microscopic atmospheric aerosols when they oxidize, and the further role of these aerosols as cloud condensation nuclei (CCN). The role of continental sources and sinks for these compounds is poorly understood. The present study was undertaken to quantify the source and sink strength of high latitude wetlands, and to delineate factors that regulate this flux.

A numerical study of the effect of different aerosol types on East Asian summer clouds and precipitation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Yiquan; Liu, Xiaohong; Yang, Xiuqun

2013-05-01

The impact of anthropogenic aerosol on the East Asian summer monsoon (EASM) is investigated with NCAR CAM5, a state-of-the-art climate model with aerosol’s direct and indirect effects. Results indicate that anthropogenic aerosol tends to cause a weakened EASM with a southward shift of precipitation in East Asia mostly by its radiative effect. Anthropogenic aerosol induced surface cooling stabilizes the boundary layer, suppresses the convection and latent heat release in northern China, and reduces the tropospheric temperature over land and land-sea thermal contrast, thus leading to a weakened EASM. Meanwhile, acting as cloud condensation nuclei (CCN), anthropogenic aerosol can significantly increasemore » the cloud droplet number concentration but decrease the cloud droplet effective radius over Indochina and Indian Peninsulas as well as over southwestern and northern China, inhibiting the precipitation in these regions. Thus, anthropogenic aerosol tends to reduce Southeast and South Asian summer monsoon precipitation by its indirect effect.« less

Impact of Aerosols on Convective Clouds and Precipitation

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Chen, Jen-Ping; Li, Zhanqing; Wang, Chien; Zhang, Chidong; Li, Xiaowen

2012-01-01

Aerosols are a critical.factor in the atmospheric hydrological cycle and radiation budget. As a major agent for clouds to form and a significant attenuator of solar radiation, aerosols affect climate in several ways. Current research suggests that aerosols have a major impact on the dynamics, microphysics, and electrification properties of continental mixed-phase convective clouds. In addition, high aerosol concentrations in urban environments could affect precipitation variability by providing a significant source of cloud condensation nuclei (CCN). Such pollution . effects on precipitation potentially have enormous climatic consequences both in terms of feedbacks involving the land surface via rainfall as well as the surface energy budget and changes in latent heat input to the atmosphere. Basically, aerosol concentrations can influence cloud droplet size distributions, the warm-rain process, the cold-rain process, cloud-top heights, the depth of the mixed-phase region, and the occurrence of lightning. Recently, many cloud resolution models (CRMs) have been used to examine the role of aerosols on mixed-phase convective clouds. These modeling studies have many differences in terms of model configuration (two- or three-dimensional), domain size, grid spacing (150-3000 m), microphysics (two-moment bulk, simple or sophisticated spectral-bin), turbulence (1st or 1.5 order turbulent kinetic energy (TKE)), radiation, lateral boundary conditions (i.e., closed, radiative open or cyclic), cases (isolated convection, tropical or midlatitude squall lines) and model integration time (e.g., 2.5 to 48 hours). Among these modeling studies, the most striking difference is that cumulative precipitation can either increase or decrease in response to higher concentrations of CCN. In this presentation, we review past efforts and summarize our current understanding of the effect of aerosols on convective precipitation processes. Specifically, this paper addresses the following topics: observational evidence of the effect of aerosols on precipitation processes, and results from (CRM) simulations. Note that this presentation is mainly based on a recent paper published in Geophy. Rev. (Tao et al. 2012).

Laboratory and Numerical Modeling of Smoke Characteristics for Superfog Formation

NASA Astrophysics Data System (ADS)

Bartolome, C.; Lu, V.; Tsui, K.; Princevac, M.; Venkatram, A.; Mahalingam, S.; Achtemeier, G.; Weise, D.

2011-12-01

Land management techniques in wildland areas include prescribed fires to promote biodiversity and reduce risk of severe wildfires across the United States. Several fatal car pileups have been associated with smoke-related visibility reduction from prescribed burns. Such events have occurred in year 2000 on the interstate highways I-10 and I-95, 2001 on the I-4, 2006 on the I-95, and 2008 on the I-4 causing numerous fatalities, injuries, and damage to property. In some of the cases visibility reduction caused by smoke and fog combinations traveling over roadways have been reported to be less than 3 meters, defined as superfog. Our research focuses on delineating the conditions that lead to formation of the rare phenomena of superfog and creating a tool to enable land managers to effectively plan prescribed burns and prevent tragic events. It is hypothesized that the water vapor from combustion, live fuels, soil moisture, and ambient air condense onto the cloud condensation nuclei (CCN) particles emitted from low intensity smoldering fires. Physical and numerical modeling has been used to investigate these interactions. A physical model in the laboratory has been developed to characterize the properties of smoke resulting from smoldering pine needle litters at the PSW Forest Service in Riverside, CA. Temporal measurements of temperature, relative humidity, sensible heat flux, radiation heat flux, convective heat flux, particulate matter concentrations and visibilities have been measured for specific cases. The size distribution and number concentrations of the fog droplets formed inside the chamber by mixing cool dry and moist warm air masses to produce near superfog visibilities were measured by a Phase Doppler Particle Analyzer. Thermodynamic modeling of smoke and ambient air was conducted to estimate liquid water contents (LWC) available to condense into droplets and form significant reductions in visibility. The results show that LWC of less than 2 g m-3 can be sufficient for superfog formation. Sensitivity modeling of the size distribution and number concentrations of the fog droplets suggested that distributions centered on droplets with less than 1μm, limited distribution size spread and number concentrations of 105 CCN per cubic centimeter could readily form superfog. A modified Kohler theory predicts significant impact of CCN concentration on the ability to readily condense numerous droplets and reduce visibility. In this presentation modeled and measured effects of the pollutant CCN concentration, LWC and droplet size distribution on visibility will be discussed.

Role of organic aerosols in CCN activation and closure over a rural background site in Western Ghats, India

NASA Astrophysics Data System (ADS)

Singla, V.; Mukherjee, S.; Safai, P. D.; Meena, G. S.; Dani, K. K.; Pandithurai, G.

2017-06-01

The cloud condensation nuclei (CCN) closure study was performed to exemplify the effect of aerosol chemical composition on the CCN activity of aerosols at Mahabaleshwar, a high altitude background site in the Western Ghats, India. For this, collocated aerosol, CCN, Elemental Carbon (EC), Organic Carbon (OC), sub-micron aerosol chemical speciation for the period from 3rd June to 19th June 2015 was used. The chemical composition of non-refractory particulate matter (<1 μm) as measured by Time of Flight - Aerosol Chemical Speciation Monitor (ToF-ACSM) was dominated by organics with average concentration of 3.81 ± 1.6, 0.32 ± 0.06, 0.15 ± 0.02, 0.13 ± 0.03 and 0.95 ± 0.12 μg m-3 for organics, ammonium, chloride, nitrate and sulphate, respectively. The PM1 number concentration as obtained by Wide Range Aerosol Spectrometer (WRAS) varied from 750 to 6480 cm-3. The average mass concentration of elemental carbon (EC) as measured by OC-EC analyzer was 1.16 ± 0.4 μg m-3. The average CCN concentrations obtained from CCN counter (CCNC) at five super-saturations (SS's) was 118 ± 58 cm-3 (0.1% SS), 873 ± 448 cm-3 (0.31% SS), 1308 ± 603 cm-3 (0.52% SS), 1610 ± 838 cm-3 (0.73% SS) and 1826 ± 985 cm-3 (0.94% SS). The CCN concentrations were predicted using Köhler theory on the basis of measured aerosol particle number size distribution, size independent NR-PM1 chemical composition and calculated hygroscopicity. The CCN closure study was evaluated for 3 scenarios, B-I (all soluble inorganics), B-IO (all soluble organics and inorganics) and B-IOOA (all soluble inorganic and soluble oxygenated organic aerosol, OOA). OOA component was derived from the positive matrix factorization (PMF) analysis of organic aerosol mass spectra. Considering the bulk composition as internal mixture, CCN closure study was underestimated by 16-39% for B-I and overestimated by 47-62% for B-IO. The CCN closure result was appreciably improved for B-IOOA where the knowledge of OOA fraction was introduced and uncertainty reduced to within 8-10%.

Uptake of Alkylamines on Dicarboxylic Acids Relevant to Secondary Organic Aerosol Formation

NASA Astrophysics Data System (ADS)

Marrero-Ortiz, W.; Secrest, J.; Zhang, R.

2017-12-01

Aerosols play a critical role in climate directly by scattering and absorbing solar radiation, and indirectly by functioning as cloud condensation nuclei (CCN); both represent the largest uncertainties in climate predictions. New particle formation contributes significantly to CCN production; however, the mechanisms related to particle nucleation and growth processes are not well understood. Organic acids are atmospherically abundant, and their neutralization by low molecular weight amines may result in the formation of stable low volatility aminium salt products contributing to the growth of secondary organic aerosols and even the alteration of the aerosol properties. The acid-base neutralization of particle phase succinic acid and tartaric acid by low molecular weight aliphatic amines, i.e. methylamine, dimethylamine, and trimethylamine, has been investigated by employing a low-pressure fast flow reactor at 298K with an ion drift - chemical ionization mass spectrometer (ID-CIMS). The heterogeneous uptake is time dependent and influenced by organic acids functionality, alkylamines basicity, and steric effect. The implications of our results to atmospheric nanoparticle growth will be discussed.

Numerical investigation of the coagulation mixing between dust and hygroscopic aerosol particles and its impacts

NASA Astrophysics Data System (ADS)

Tsai, I.-Chun; Chen, Jen-Ping; Lin, Yi-Chiu; Chung-Kuang Chou, Charles; Chen, Wei-Nai

2015-05-01

A statistical-numerical aerosol parameterization was incorporated into the Community Multiscale Air Quality modeling system to study the coagulation mixing process focusing on a dust storm event that occurred over East Asia. Simulation results show that the coagulation mixing process tends to decrease aerosol mass, surface area, and number concentrations over the dust source areas. Over the downwind oceanic areas, aerosol concentrations generally increased due to enhanced sedimentation as particles became larger upon coagulation. The mixture process can reduce the overall single-scattering albedo by up to 10% as a result of enhanced core with shell absorption by dust and reduction in the number of scattering particles. The enhanced dry deposition speed also altered the vertical distribution. In addition, the ability of aerosol particles to serve as cloud condensation nuclei (CCN) increased from around 107 m-3 to above 109 m-3 over downwind areas because a large amount of mineral dust particles became effective CCN with solute coating, except over the highly polluted areas where multiple collections of hygroscopic particles by dust in effect reduced CCN number. This CCN effect is much stronger for coagulation mixing than by the uptake of sulfuric acid gas on dust, although the nitric acid gas uptake was not investigated. The ability of dust particles to serve as ice nuclei may decrease or increase at low or high subzero temperatures, respectively, due to the switching from deposition nucleation to immersion freezing or haze freezing.

CCN concentrations and BC warming influenced by maritime ship emitted aerosol plumes over southern Bay of Bengal.

PubMed

Ramana, M V; Devi, Archana

2016-08-02

Significant quantities of carbon soot aerosols are emitted into pristine parts of the atmosphere by marine shipping. Soot impacts the radiative balance of the Earth-atmosphere system by absorbing solar-terrestrial radiation and modifies the microphysical properties of clouds. Here we examined the impact of black carbon (BC) on net warming during monsoon season over southern Bay-of-Bengal, using surface and satellite measurements of aerosol plumes from shipping. Shipping plumes had enhanced the BC concentrations by a factor of four around the shipping lane and exerted a strong positive influence on net warming. Compiling all the data, we show that BC atmospheric heating rates for relatively-clean and polluted-shipping corridor locations to be 0.06 and 0.16 K/day respectively within the surface layer. Emissions from maritime ships had directly heated the lower troposphere by two-and-half times and created a gradient of around 0.1 K/day on either side of the shipping corridor. Furthermore, we show that ship emitted aerosol plumes were responsible for increase in the concentration of cloud condensation nuclei (CCN) by an order of magnitude that of clean air. The effects seen here may have significant impact on the monsoonal activity over Bay-of-Bengal and implications for climate change mitigation strategies.

A new chemistry option in WRF/Chem v. 3.4 for the simulation of direct and indirect aerosol effects using VBS: evaluation against IMPACT-EUCAARI data

NASA Astrophysics Data System (ADS)

Tuccella, P.; Curci, G.; Grell, G. A.; Visconti, G.; Crumeroylle, S.; Schwarzenboeck, A.; Mensah, A. A.

2015-02-01

A parameterization for secondary organic aerosol (SOA) production based on the volatility basis set (VBS) approach has been coupled with microphysics and radiative scheme in WRF/Chem model. The new chemistry option called "RACM/MADE/VBS" was evaluated on a cloud resolving scale against ground-based and aircraft measurements collected during the IMPACT-EUCAARI campaign, and complemented with satellite data from MODIS. The day-to-day variability and the diurnal cycle of ozone (O3) and nitrogen oxides (NOx) at the surface is captured by the model. Surface aerosol mass of sulphate (SO4), nitrate (NO3), ammonium (NH4), and organic matter (OM) is simulated with a correlation larger than 0.55. WRF/Chem captures the vertical profile of the aerosol mass in both the planetary boundary layer (PBL) and free troposphere (FT) as a function of the synoptic condition, but the model does not capture the full range of the measured concentrations. Predicted OM concentration is at the lower end of the observed mass. The bias may be attributable to the missing aqueous chemistry processes of organic compounds, the uncertainties in meteorological fields, the assumption on the deposition velocity of condensable organic vapours, and the uncertainties in the anthropogenic emissions of primary organic carbon. Aerosol particle number concentration (condensation nuclei, CN) is overestimated by a factor 1.4 and 1.7 within PBL and FT, respectively. Model bias is most likely attributable to the uncertainties of primary particle emissions (mostly in the PBL) and to the nucleation rate. The overestimation of simulated cloud condensation nuclei (CCN) is more contained with respect to that of CN. The CCN efficiency, which is a measure of the ability of aerosol particles to nucleate cloud droplets, is underestimated by a factor of 1.5 and 3.8 in the PBL and FT, respectively. The comparison with MODIS data shows that the model overestimates the aerosol optical thickness (AOT). The domain averages (for one day) are 0.38 ± 0.12 and 0.42 ± 0.10 for MODIS and WRF/Chem data, respectively. Cloud water path (CWP) is overestimated on average by a factor of 1.7, whereas modelled cloud optical thickness (COT) agrees with observations within 10%. In a sensitivity test where the SOA was not included, simulated CWP is reduced by 40%, and its distribution function shifts toward lower values with respect to the reference run with SOA. The sensitivity test exhibits also 10% more optically thin clouds (COT < 40) and an average COT roughly halved. Moreover, the run with SOA shows convective clouds with an enhanced content of liquid and frozen hydrometers, and stronger updrafts and downdrafts. Considering that the previous version of WRF/Chem coupled with a modal aerosol module predicted very low SOA content (SORGAM mechanism) the new proposed option may lead to a better characterization of aerosol-cloud feedbacks.

MCS precipitation and downburst intensity response to increased aerosol concentrations

NASA Astrophysics Data System (ADS)

Clavner, M.; Cotton, W. R.; van den Heever, S. C.

2015-12-01

Mesoscale convective systems (MCSs) are important contributors to rainfall in the High Plains of the United States as well as producers of severe weather such as hail, tornados and straight-line wind events known as derechos. Past studies have shown that changes in aerosol concentrations serving as cloud condensation nuclei (CCN) alter the MCS hydrometeor characteristics which in turn modify precipitation yield, downdraft velocity, cold-pool strength, storm propagation and the potential for severe weather to occur. In this study, the sensitivity of MCS precipitation characteristics and convective downburst velocities associated with a derecho to changes in CCN concentrations were examined by simulating a case study using the Regional Atmospheric Modeling System (RAMS). The case study of the 8 May 2009 "Super-Derecho" MCS was chosen since it produced a swath of widespread wind damage in association with an embedded large-scale bow echo, over a broad region from the High Plains of western Kansas to the foothills of the Appalachians. The sensitivity of the storm to changes in CCN concentrations was examined by conducting a set of three simulations which differed in the initial aerosol concentration based on output from the 3D chemical transport model, GEOS-Chem. Results from this study indicate that while increasing CCN concentrations led to an increase in precipitation rates, the changes to the derecho strength were not linear. A moderate increase in aerosol concentration reduced the derecho strength, while the simulation with the highest aerosol concentrations increased the derecho intensity. These changes are attributed to the impact of enhanced CCN concentration on the production of convective downbursts. An analysis of aerosol loading impacts on these MCS features will be presented.

Inclusion of biomass burning in WRF-Chem: Impact of wildfires on weather forecasts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grell, G. A.; Freitas, Saulo; Stuefer, Martin

2011-06-06

A plume rise algorithm for wildfires was included in WRF-Chem, and applied to look at the impact of intense wildfires during the 2004 Alaska wildfire season on weather forecasts using model resolutions of 10km and 2km. Biomass burning emissions were estimated using a biomass burning emissions model. In addition, a 1-D, time-dependent cloud model was used online in WRF-Chem to estimate injection heights as well as the final emission rates. It was shown that with the inclusion of the intense wildfires of the 2004 fire season in the model simulations, the interaction of the aerosols with the atmospheric radiation ledmore » to significant modifications of vertical profiles of temperature and moisture in cloud-free areas. On the other hand, when clouds were present, the high concentrations of fine aerosol (PM2.5) and the resulting large numbers of Cloud Condensation Nuclei (CCN) had a strong impact on clouds and microphysics, with decreased precipitation coverage and precipitation amounts during the first 12 hours of the integration, but significantly stronger storms during the afternoon hours.« less

Interannual Variations in Aerosol Sources and Their Impact on Orographic Precipitation over California's Central Sierra Nevada

NASA Astrophysics Data System (ADS)

Creamean, J.; Ault, A. P.; White, A. B.; Neiman, P. J.; Minnis, P.; Prather, K. A.

2014-12-01

Aerosols that serve as cloud condensation nuclei (CCN) and ice nuclei (IN) have the potential to profoundly influence precipitation processes. Furthermore, changes in orographic precipitation have broad implications for reservoir storage and flood risks. As part of the CalWater I field campaign (2009-2011), the impacts of aerosol sources on precipitation were investigated in the California Sierra Nevada Mountains. In 2009, the precipitation collected on the ground was influenced by both local biomass burning and long-range transported dust and biological particles, while in 2010, by mostly local sources of biomass burning and pollution, and in 2011 by mostly long-range transport of dust and biological particles from distant sources. Although vast differences in the sources of residues were observed from year-to-year, dust and biological residues were omnipresent (on average, 55% of the total residues combined) and were associated with storms consisting of deep convective cloud systems and larger quantities of precipitation initiated in the ice phase. Further, biological residues were dominant during storms with relatively warm cloud temperatures (up to -15°C), suggesting biological components were more efficient IN than mineral dust. On the other hand, when precipitation quantities were lower, local biomass burning and pollution residues were observed (on average 31% and 9%, respectively), suggesting these residues potentially served as CCN at the base of shallow cloud systems and that lower level polluted clouds of storm systems produced less precipitation than non-polluted (i.e., marine) clouds. The direct connection of the sources of aerosols within clouds and precipitation type and quantity can be used in models to better assess how local emissions versus long-range transported dust and biological aerosols play a role in impacting regional weather and climate, ultimately with the goal of more accurate predictive weather forecast models and water resource management.

Potential climatic impact of organic haze on early Earth.

PubMed

Hasenkopf, Christa A; Freedman, Miriam A; Beaver, Melinda R; Toon, Owen B; Tolbert, Margaret A

2011-03-01

We have explored the direct and indirect radiative effects on climate of organic particles likely to have been present on early Earth by measuring their hygroscopicity and cloud nucleating ability. The early Earth analog aerosol particles were generated via ultraviolet photolysis of an early Earth analog gas mixture, which was designed to mimic possible atmospheric conditions before the rise of oxygen. An analog aerosol for the present-day atmosphere of Saturn's moon Titan was tested for comparison. We exposed the early Earth aerosol to a range of relative humidities (RHs). Water uptake onto the aerosol was observed to occur over the entire RH range tested (RH=80-87%). To translate our measurements of hygroscopicity over a specific range of RHs into their water uptake ability at any RH < 100% and into their ability to act as cloud condensation nuclei (CCN) at RH > 100%, we relied on the hygroscopicity parameter κ, developed by Petters and Kreidenweis. We retrieved κ=0.22 ±0.12 for the early Earth aerosol, which indicates that the humidified aerosol (RH < 100 %) could have contributed to a larger antigreenhouse effect on the early Earth atmosphere than previously modeled with dry aerosol. Such effects would have been of significance in regions where the humidity was larger than 50%, because such high humidities are needed for significant amounts of water to be on the aerosol. Additionally, Earth organic aerosol particles could have activated into CCN at reasonable-and even low-water-vapor supersaturations (RH > 100%). In regions where the haze was dominant, it is expected that low particle concentrations, once activated into cloud droplets, would have created short-lived, optically thin clouds. Such clouds, if predominant on early Earth, would have had a lower albedo than clouds today, thereby warming the planet relative to current-day clouds. © Mary Ann Liebert, Inc.

Observational Study and Parameterization of Aerosol-fog Interactions

NASA Astrophysics Data System (ADS)

Duan, J.; Guo, X.; Liu, Y.; Fang, C.; Su, Z.; Chen, Y.

2014-12-01

Studies have shown that human activities such as increased aerosols affect fog occurrence and properties significantly, and accurate numerical fog forecasting depends on, to a large extent, parameterization of fog microphysics and aerosol-fog interactions. Furthermore, fogs can be considered as clouds near the ground, and enjoy an advantage of permitting comprehensive long-term in-situ measurements that clouds do not. Knowledge learned from studying aerosol-fog interactions will provide useful insights into aerosol-cloud interactions. To serve the twofold objectives of understanding and improving parameterizations of aerosol-fog interactions and aerosol-cloud interactions, this study examines the data collected from fogs, with a focus but not limited to the data collected in Beijing, China. Data examined include aerosol particle size distributions measured by a Passive Cavity Aerosol Spectrometer Probe (PCASP-100X), fog droplet size distributions measured by a Fog Monitor (FM-120), Cloud Condensation Nuclei (CCN), liquid water path measured by radiometers and visibility sensors, along with meteorological variables measured by a Tethered Balloon Sounding System (XLS-Ⅱ) and Automatic Weather Station (AWS). The results will be compared with low-level clouds for similarities and differences between fogs and clouds.

Growth rates of fine aerosol particles at a site near Beijing in June 2013

NASA Astrophysics Data System (ADS)

Zhao, Chuanfeng; Li, Yanan; Zhang, Fang; Sun, Yele; Wang, Pucai

2018-02-01

Growth of fine aerosol particles is investigated during the Aerosol-CCN-Cloud Closure Experiment campaign in June 2013 at an urban site near Beijing. Analyses show a high frequency (˜ 50%) of fine aerosol particle growth events, and show that the growth rates range from 2.1 to 6.5 nm h-1 with a mean value of ˜ 5.1 nm h-1. A review of previous studies indicates that at least four mechanisms can affect the growth of fine aerosol particles: vapor condensation, intramodal coagulation, extramodal coagulation, and multi-phase chemical reaction. At the initial stage of fine aerosol particle growth, condensational growth usually plays a major role and coagulation efficiency generally increases with particle sizes. An overview of previous studies shows higher growth rates over megacity, urban and boreal forest regions than over rural and oceanic regions. This is most likely due to the higher condensational vapor, which can cause strong condensational growth of fine aerosol particles. Associated with these multiple factors of influence, there are large uncertainties for the aerosol particle growth rates, even at the same location.

Using different assumptions of aerosol mixing state and chemical composition to predict CCN concentrations based on field measurements in urban Beijing

NASA Astrophysics Data System (ADS)

Ren, Jingye; Zhang, Fang; Wang, Yuying; Collins, Don; Fan, Xinxin; Jin, Xiaoai; Xu, Weiqi; Sun, Yele; Cribb, Maureen; Li, Zhanqing

2018-05-01

Understanding the impacts of aerosol chemical composition and mixing state on cloud condensation nuclei (CCN) activity in polluted areas is crucial for accurately predicting CCN number concentrations (NCCN). In this study, we predict NCCN under five assumed schemes of aerosol chemical composition and mixing state based on field measurements in Beijing during the winter of 2016. Our results show that the best closure is achieved with the assumption of size dependent chemical composition for which sulfate, nitrate, secondary organic aerosols, and aged black carbon are internally mixed with each other but externally mixed with primary organic aerosol and fresh black carbon (external-internal size-resolved, abbreviated as EI-SR scheme). The resulting ratios of predicted-to-measured NCCN (RCCN_p/m) were 0.90 - 0.98 under both clean and polluted conditions. Assumption of an internal mixture and bulk chemical composition (INT-BK scheme) shows good closure with RCCN_p/m of 1.0 -1.16 under clean conditions, implying that it is adequate for CCN prediction in continental clean regions. On polluted days, assuming the aerosol is internally mixed and has a chemical composition that is size dependent (INT-SR scheme) achieves better closure than the INT-BK scheme due to the heterogeneity and variation in particle composition at different sizes. The improved closure achieved using the EI-SR and INT-SR assumptions highlight the importance of measuring size-resolved chemical composition for CCN predictions in polluted regions. NCCN is significantly underestimated (with RCCN_p/m of 0.66 - 0.75) when using the schemes of external mixtures with bulk (EXT-BK scheme) or size-resolved composition (EXT-SR scheme), implying that primary particles experience rapid aging and physical mixing processes in urban Beijing. However, our results show that the aerosol mixing state plays a minor role in CCN prediction when the κorg exceeds 0.1.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jian; Krejci, Radovan; Giangrande, Scott

A necessary prerequisite of cloud formation, aerosol particles represent one of the largest uncertainties in computer simulations of climate change1,2, in part because of a poor understanding of processes under natural conditions3,4. The Amazon rainforest is one of the few continental regions where aerosol particles and their precursors can be studied under near-natural conditions5-7. Cloud condensation nuclei (CCN) in clean Amazonia are mostly produced by the growth of smaller particles in the boundary layer8-10, whereas these smaller particles themselves 31 appear to be produced elsewhere5,11. Key questions are in what part of the atmosphere they might 32 be produced andmore » what could be the transport processes that deliver them to the boundary layer, where they grow into CCN. Here, using recent aircraft measurements above central Amazonia, we show high concentrations of small particles in the lower free troposphere. The particle size spectrum shifts towards larger sizes with decreasing altitude, implying particle growth as air descends from the free troposphere towards Earth's surface. Complementary measurements at ground sites show that free tropospheric air having high concentrations of small particles (diameters of less than 50 nm) is transported into the boundary layer during precipitation events, both by strong convective downdrafts and by weaker downward motions in the trailing stratiform region. This vertical transport helps maintain the population of small particles and ultimately CCN in the boundary layer, thereby playing an important role in controlling the climate state under natural conditions. In contrast, this mechanism becomes masked under polluted conditions, which sometimes prevail at times in Amazonia as well as over other tropical continental regions5,12.« less

Cloud Formation Potential of Biomass Burning Aerosol Surrogate-Particles Chemically Aged by OH

NASA Astrophysics Data System (ADS)

Slade, J. H.; Thalman, R. M.; Wang, J.; Li, Z. Q.; Knopf, D. A.

2014-12-01

Heterogeneous or multiphase reactions between trace gases such as OH and atmospheric aerosol can influence physicochemical properties of the particles including composition, morphology and lifetime. In this work, the cloud condensation nuclei (CCN) activity of laboratory-generated biomass burning aerosol (BBA) exposed to OH radicals is evaluated by determining the hygroscopicity parameter, κ, as a function of particle type and OH exposure ([OH]×time) using a CCN counter coupled to a custom-built aerosol flow reactor (AFR). The composition of particles collected by a micro-orifice uniform deposit impactor (MOUDI) first subjected to different OH exposures is analyzed by Raman and scanning transmission X-ray microscopy coupled with near edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS). Levoglucosan (LEV), 4-methyl-5-nitrocatechol (MNC), and potassium sulfate (KS) serve as representative compounds found in BBA that have different hygroscopicity, chemical functionalities, and reactivity with OH radicals. BBA surrogate-particles are generated following atomization of aqueous solutions with mass ratios LEV:MNC:KS of 1:0:0, 0:1:0, 0:0:1, 1:1:0, 0:1:1, 1:0:1, 1:1:1, and 1:0.03:0.3. OH radicals are generated in the AFR following photolysis of O3 in the presence of H2O using a variable intensity ultra-violet (UV) lamp, which allows equivalent atmospheric OH exposures from days to weeks. In addition, we investigate how κ changes i) in response to varying [O3] with and without OH, and ii) at a fixed OH exposure while varying RH. The impact of OH exposure on the CCN activity of BBA will be presented and its atmospheric implications will be discussed.

Hygroscopicity of Early Earth and Titan Laboratory Aerosol Analogs

NASA Astrophysics Data System (ADS)

Hasenkopf, C. A.; Beaver, M. R.; Freedman, M. A.; Toon, O. B.; Tolbert, M. A.

2009-12-01

We have explored the ability of organic hazes, known to exist in the atmosphere of Titan and postulated to have existed in the Archean Earth atmosphere, to act as cloud condensation nuclei (CCN). These laboratory aerosol analogs are generated via UV-photolysis of early Earth and Titan analog gas mixtures and are designed to mimic the present day atmospheric conditions on Titan and the early Earth atmosphere before the rise of oxygen. Water uptake is observed to occur on the early Earth and Titan aerosol analogs at relative humidities of 80% - 90% via optical growth measurements using cavity ring-down aerosol extinction spectroscopy. We find the optical growth of these aerosols is similar to known slightly-soluble organic acids, such as phthalic and pyromellitic acids. On average, the optical growth of the early Earth analog is slightly larger than the Titan analog. In order to translate our measurements obtained in a subsaturated regime into the CCN ability of these particles, we rely on the hygroscopicity parameter κ, developed by Petters & Kreidenweis (2007). We retrieve κ = 0.17±0.03 and 0.06±0.01 for the early Earth and Titan analogs, respectively. This early Earth analog hygroscopicity value indicates that the aerosol could activate at reasonable water vapor supersaturations. We use previous aerosol mass spectrometry results to correlate the chemical structure of the two types of analog with their hygroscopicity. The hygroscopicity of the early Earth aerosol analog, coupled with the apparent lack of other good CCN during the Archean, helps explain the role of the organic haze in the indirect effect of clouds on the early Earth and indicates that it may have had a significant impact on the hydrological cycle.

Effects of Wildfire Pollution on the Microphysical and Electrical Properties of Pyrocumulus

NASA Astrophysics Data System (ADS)

Duff, R.; Grant, L. D.; van den Heever, S. C.

2014-12-01

Pyrocumulus clouds form over wildfires when hot, smoke-filled air rises, cools and condenses. These clouds have higher cloud condensation nuclei (CCN) concentrations, which affect their microphysical and electrical properties. It is important to better understand pyrocumulus cloud microphysical characteristics and lightning formation, which have implications for the prediction of wildfire growth as well as the radiative and chemical characteristics of the upper troposphere. A recent observational study documented an electrified pyrocumulus over the May 2012 Hewlett Gulch fire located to the west of Fort Collins, Colorado. This cloud produced approximately 20 intracloud lightning flashes, and its electrical activity differed from surrounding convection that was not directly impacted by the fire and associated smoke. The goal of this research is to investigate aerosol-induced cloud-scale microphysical differences between clean clouds and polluted pyrocumulus to better characterize the mechanisms that cause pyrocumulus electrification. In order to address this goal, idealized cloud-resolving model simulations were performed using the Regional Atmospheric Modeling System (RAMS). The model environment was initialized with an average of the 12Z 16 May and 00Z 17 May 2012 observed Denver soundings to represent the conditions when the Hewlett Gulch pyrocumulus occurred. Five simulations were performed using surface aerosol concentrations from 100 to 5000 #/mg. The results demonstrate that in moderately polluted pyrocumulus, rain processes are suppressed while graupel production increases. Extremely polluted pyrocumulus, however, experience a complete shut-down of graupel production, which favors the production of large amounts of liquid water and smaller ice species such as ice crystals and snowflakes. The processes responsible for these microphysical changes, as well as inferred pyrocumulus electrification mechanisms, will be compared with those discussed in previous observational studies of this case.

Modeling and observational constraints on the sulfur cycle in the marine troposphere: a focus on reactive halogens and multiphase chemistry

NASA Astrophysics Data System (ADS)

Chen, Q.; Breider, T.; Schmidt, J.; Sherwen, T.; Evans, M. J.; Xie, Z.; Quinn, P.; Bates, T. S.; Alexander, B.

2017-12-01

The radiative forcing from marine boundary layer clouds is still highly uncertain, which partly stems from our poor understanding of cloud condensation nuclei (CCN) formation. The oxidation of dimethyl sulfide (DMS) and subsequent chemical evolution of its products (e.g. DMSO) are key processes in CCN formation, but are generally very simplified in large-scale models. Recent research has pointed out the importance of reactive halogens (e.g. BrO and Cl) and multiphase chemistry in the tropospheric sulfur cycle. In this study, we implement a series of sulfur oxidation mechanisms into the GEOS-Chem global chemical transport model, involving both gas-phase and multiphase oxidation of DMS, DMSO, MSIA and MSA, to improve our understanding of the sulfur cycle in the marine troposphere. DMS observations from six locations around the globe and MSA/nssSO42- ratio observations from two ship cruises covering a wide range of latitudes and longitudes are used to assess the model. Preliminary results reveal the important role of BrO for DMS oxidation at high latitudes (up to 50% over Southern Ocean). Oxidation of DMS by Cl radicals is small in the model (within 10% in the marine troposphere), probably due to an underrepresentation of Cl sources. Multiphase chemistry (e.g. oxidation by OH and O3 in cloud droplets) is not important for DMS oxidation but is critical for DMSO oxidation and MSA production and removal. In our model, about half of the DMSO is oxidized in clouds, leading to the formation of MSIA, which is further oxidized to form MSA. Overall, with the addition of reactive halogens and multiphase chemistry, the model is able to better reproduce observations of seasonal variations of DMS and MSA/nssSO42- ratios.

A new chemistry option in WRF-Chem v. 3.4 for the simulation of direct and indirect aerosol effects using VBS: evaluation against IMPACT-EUCAARI data

NASA Astrophysics Data System (ADS)

Tuccella, P.; Curci, G.; Grell, G. A.; Visconti, G.; Crumeyrolle, S.; Schwarzenboeck, A.; Mensah, A. A.

2015-09-01

A parameterization for secondary organic aerosol (SOA) production based on the volatility basis set (VBS) approach has been coupled with microphysics and radiative schemes in the Weather Research and Forecasting model with Chemistry (WRF-Chem) model. The new chemistry option called "RACM-MADE-VBS-AQCHEM" was evaluated on a cloud resolving scale against ground-based and aircraft measurements collected during the IMPACT-EUCAARI (Intensive Cloud Aerosol Measurement Campaign - European Integrated project on Aerosol Cloud Climate and Air quality interaction) campaign, and complemented with satellite data from MODIS. The day-to-day variability and the diurnal cycle of ozone (O3) and nitrogen oxides (NOx) at the surface are captured by the model. Surface aerosol mass concentrations of sulfate (SO4), nitrate (NO3), ammonium (NH4), and organic matter (OM) are simulated with correlations larger than 0.55. WRF-Chem captures the vertical profile of the aerosol mass concentration in both the planetary boundary layer (PBL) and free troposphere (FT) as a function of the synoptic condition, but the model does not capture the full range of the measured concentrations. Predicted OM concentration is at the lower end of the observed mass concentrations. The bias may be attributable to the missing aqueous chemistry processes of organic compounds and to uncertainties in meteorological fields. A key role could be played by assumptions on the VBS approach such as the SOA formation pathways, oxidation rate, and dry deposition velocity of organic condensable vapours. Another source of error in simulating SOA is the uncertainties in the anthropogenic emissions of primary organic carbon. Aerosol particle number concentration (condensation nuclei, CN) is overestimated by a factor of 1.4 and 1.7 within the PBL and FT, respectively. Model bias is most likely attributable to the uncertainties of primary particle emissions (mostly in the PBL) and to the nucleation rate. Simulated cloud condensation nuclei (CCN) are also overestimated, but the bias is more contained with respect to that of CN. The CCN efficiency, which is a characterization of the ability of aerosol particles to nucleate cloud droplets, is underestimated by a factor of 1.5 and 3.8 in the PBL and FT, respectively. The comparison with MODIS data shows that the model overestimates the aerosol optical thickness (AOT). The domain averages (for 1 day) are 0.38 ± 0.12 and 0.42 ± 0.10 for MODIS and WRF-Chem data, respectively. The droplet effective radius (Re) in liquid-phase clouds is underestimated by a factor of 1.5; the cloud liquid water path (LWP) is overestimated by a factor of 1.1-1.6. The consequence is the overestimation of average liquid cloud optical thickness (COT) from a few percent up to 42 %. The predicted cloud water path (CWP) in all phases displays a bias in the range +41-80 %, whereas the bias of COT is about 15 %. In sensitivity tests where we excluded SOA, the skills of the model in reproducing the observed patterns and average values of the microphysical and optical properties of liquid and all phase clouds decreases. Moreover, the run without SOA (NOSOA) shows convective clouds with an enhanced content of liquid and frozen hydrometers, and stronger updrafts and downdrafts. Considering that the previous version of WRF-Chem coupled with a modal aerosol module predicted very low SOA content (secondary organic aerosol model (SORGAM) mechanism) the new proposed option may lead to a better characterization of aerosol-cloud feedbacks.

Campaign datasets for Two-Column Aerosol Project (TCAP)

DOE Data Explorer

Berg,Larry; Mei,Fan; Cairns,Brian; Chand,Duli; Comstock,Jennifer; Cziczo,Daniel; Hostetler,Chris; Hubbe,John; Long,Chuck; Michalsky,Joseph; Pekour,Mikhail; Russell,Phil; Scott,Herman; Sedlacek,Arthur; Shilling,John; Springston,Stephen; Tomlinson,Jason; Watson,Thomas; Zelenyuk-Imre,Alla

2013-12-30

This campaign was designed to provide a detailed set of observations with which to 1) perform radiative and cloud condensation nuclei (CCN) closure studies, 2) evaluate a new retrieval algorithm for aerosol optical depth (AOD) in the presence of clouds using passive remote sensing 3) extend a previously developed technique to investigate aerosol indirect effects, and 4) evaluate the performance of a detailed regional-scale model and a more parameterized global-scale model in simulating particle activation and AOD associated with the aging of anthropogenic aerosols. To meet these science objectives, the ARM Mobile Facility (AMF) and the Mobile Aerosol Observing System (MAOS) was deployed on Cape Cod, Massachusetts for a 12-month period starting in the summer of 2012 in order to quantify aerosol properties, radiation and cloud characteristics at a location subject to both clear- and cloudy- conditions, and clean- and polluted-conditions. These observations were supplemented by two aircraft intensive observation periods (IOPS), one in the summer and a second in the winter. Each IOP required two aircraft.

Evidence for Natural Variability in Marine Stratocumulus Cloud Properties Due to Cloud-Aerosol

NASA Technical Reports Server (NTRS)

Albrecht, Bruce; Sharon, Tarah; Jonsson, Haf; Minnis, Patrick; Minnis, Patrick; Ayers, J. Kirk; Khaiyer, Mandana M.

2004-01-01

In this study, aircraft observations from the Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter are used to characterize the variability in drizzle, cloud, and aerosol properties associated with cloud rifts and the surrounding solid clouds observed off the coast of California. A flight made on 16 July 1999 provided measurements directly across an interface between solid and rift cloud conditions. Aircraft instrumentation allowed for measurements of aerosol, cloud droplet, and drizzle spectra. CCN concentrations were measured in addition to standard thermodynamic variables and the winds. A Forward Scatter Spectrometer Probe (FSSP) measured size distribution of cloud-sized droplets. A Cloud Imaging Probe (CIP) was used to measure distributions of drizzle-sized droplets. Aerosol distributions were obtained from a Cloud Aerosol Scatterprobe (CAS). The CAS probe measured aerosols, cloud droplets and drizzle-sized drops; for this study. The CAS probe was used to measure aerosols in the size range of 0.5 micron - 1 micron. Smaller aerosols were characterized using an Ultrafine Condensation Particle Counter (CPC) sensor. The CPC was used to measure particles with diameters greater than 0.003 micron. By subtracting different count concentrations measured with the CPC, this probe was capable of identifying ultrafine particles those falling in the size range of 3 nanometers - 7 nanometers that are believed to be associated with new particle production.

The impact of Saharan Dust on the genesis and evolution of Hurricane Earl (2010)

NASA Astrophysics Data System (ADS)

Pan, B.; Wang, Y.; Hsieh, J. S.; Lin, Y.; Hu, J.; Zhang, R.

2017-12-01

Dust, one of the most abundant natural aerosols, can exert substantial radiative and microphysical effects on the regional climate and has potential impacts on the genesis and intensification of tropical cyclones (TCs). A Weather Research and Forecasting Model and the Regional Oceanic Modeling System coupled model (WRF-ROMS) is used to simulate the evolution of Hurricane Earl (2010), of which Earl was interfered by Saharan dust at the TC genesis stage. A new dust module has been implemented to the TAMU two-moment microphysics scheme in the WRF model. It accounts for both dust as Cloud Condensation Nuclei (CCN) and Ice Nuclei (IN). The hurricane track, intensity and precipitation have been compared to the best track data and TRMM precipitation, respectively. The influences of Saharan dust on Hurricane Earl are investigated with dust-CCN, dust-IN, and dust-free scenarios. The analysis shows that Saharan dust changes the latent heat and moisture distribution, invigorates the convections in the hurricane's eyewall, and suppresses the development of Earl. This finding addresses the importance of accounting dust microphysics effect on hurricane predictions.

Antarctic new particle formation from continental biogenic precursors

NASA Astrophysics Data System (ADS)

Kyrö, E.-M.; Kerminen, V.-M.; Virkkula, A.; Dal Maso, M.; Parshintsev, J.; Ruíz-Jimenez, J.; Forsström, L.; Manninen, H. E.; Riekkola, M.-L.; Heinonen, P.; Kulmala, M.

2012-12-01

Over Antarctica, aerosol particles originate almost entirely from marine areas, with minor contribution from long-range transported dust or anthropogenic material. The Antarctic continent itself, unlike all other continental areas, has been thought to be practically free of aerosol sources. Here we present evidence of local aerosol production associated with melt-water ponds in the continental Antarctica. We show that in air masses passing such ponds, new aerosol particles are efficiently formed and these particles grow up to sizes where they may act as cloud condensation nuclei (CCN). The precursor vapours responsible for aerosol formation and growth originate very likely from highly abundant cyanobacteria Nostoc commune (Vaucher) communities of local ponds. This is the first time when freshwater vegetation has been identified as an aerosol precursor source. The influence of the new source on clouds and climate may increase in future Antarctica, and possibly elsewhere undergoing accelerating summer melting of semi-permanent snow cover.

Antarctic new particle formation from continental biogenic precursors

NASA Astrophysics Data System (ADS)

Kyrö, E.-M.; Kerminen, V.-M.; Virkkula, A.; Dal Maso, M.; Parshintsev, J.; Ruíz-Jimenez, J.; Forsström, L.; Manninen, H. E.; Riekkola, M.-L.; Heinonen, P.; Kulmala, M.

2013-04-01

Over Antarctica, aerosol particles originate almost entirely from marine areas, with minor contribution from long-range transported dust or anthropogenic material. The Antarctic continent itself, unlike all other continental areas, has been thought to be practically free of aerosol sources. Here we present evidence of local aerosol production associated with melt-water ponds in continental Antarctica. We show that in air masses passing such ponds, new aerosol particles are efficiently formed and these particles grow up to sizes where they may act as cloud condensation nuclei (CCN). The precursor vapours responsible for aerosol formation and growth originate very likely from highly abundant cyanobacteria Nostoc commune (Vaucher) communities of local ponds. This is the first time freshwater vegetation has been identified as an aerosol precursor source. The influence of the new source on clouds and climate may increase in future Antarctica, and possibly elsewhere undergoing accelerating summer melting of semi-permanent snow cover.

The Modification of Orographic Snow Growth Processes by Cloud Nucleating Aerosols

NASA Astrophysics Data System (ADS)

Cotton, W. R.; Saleeby, S.

2011-12-01

Cloud nucleating aerosols have been found to modify the amount and spatial distribution of snowfall in mountainous areas where riming growth of snow crystals is known to contribute substantially to the total snow water equivalent precipitation. In the Park Range of Colorado, a 2km deep supercooled liquid water orographic cloud frequently enshrouds the mountaintop during snowfall events. This leads to a seeder-feeder growth regime in which snow falls through the orographic cloud and collects cloud water prior to surface deposition. The addition of higher concentrations of cloud condensation nuclei (CCN) modifies the cloud droplet spectrum toward smaller size droplets and suppresses riming growth. Without rime growth, the density of snow crystals remains low and horizontal trajectories carry them further downwind due to slower vertical fall speeds. This leads to a downwind shift in snowfall accumulation at high CCN concentrations. Cloud resolving model simulations were performed (at 600m horizontal grid spacing) for six snowfall events over the Park Range. The chosen events were well simulated and occurred during intensive observations periods as part of two winter field campaigns in 2007 and 2010 based at Storm Peak Laboratory in Steamboat Springs, CO. For each event, sensitivity simulations were run with various initial CCN concentration vertical profiles that represent clean to polluted aerosol environments. Microphysical budget analyses were performed for these simulations in order to determine the relative importance of the various cloud properties and growth processes that contribute to precipitation production. Observations and modeling results indicate that initial vapor depositional growth of snow tends to be maximized within about 1km of mountaintop above the windward slope while the majority of riming growth occurs within 500m of mountaintop. This suggests that precipitation production is predominantly driven by locally enhanced orography. The large scale synoptic flow simply provides the background dynamics and moisture that impinge upon the steep terrain. The addition of cloud nucleating aerosols to this scenario tends to reduce the amount of riming and leads to greater snow vapor growth. Increased vapor growth leads to larger snow crystals but does not necessarily increase their density or fall speed. There is frequently a zone on the periphery of the orographic cloud where water saturation is low and ice saturation remains high. Here the Bergeron process allows for snow to continue growing at the expense of the cloud water. Furthermore, since less cloud water is removed by riming, and droplets are smaller in polluted conditions, there is an increase in cloud water evaporation along the lee slope. This enhanced droplet evaporation in polluted conditions allows for more saturated air to persist to the lee of the ridge. Higher saturation reduces the amount of snow crystal sublimation prior to surface deposition. In very moist winter events, the lee slope evaporation relative to the primary mountain barrier can saturate the air relative to a downstream ridge and aid in further orographic cloud development. The combination of reduced riming, the Bergeron process, and reduced lee-side sublimation leads to the snowfall spillover effect under polluted conditions.

Aerosol scattering properties measured by an integrating nephelometer in Seoul, Korea

NASA Astrophysics Data System (ADS)

Shim, S.; Kim, J. H.; Cha, J.; Yum, S.; Yoon, Y.; Kim, J.

2008-12-01

The aerosol optical properties are known to have a significant impact on regional and global radiation budget and therefore climate change, and are a crucial factor to determine atmospheric visibility. As an effort to understand the influence of anthropogenic pollution aerosols, we analyzed the scattering coefficient (σsp) measured by an integrating nephelometer (TSI, model 3563) for the one year period of Feb. 2007 to Feb. 2008 in the highly populated city of Seoul, Korea and compared with total aerosol (CN) concentration and cloud condensations nuclei (CCN) concentration measured at the same location. Daily, weekly and seasonal statistics are calculated. Additionally, three Asian dust events that occurred during the measurement period were investigated in more detail. To reduce the humidity effect, only the cases when the instrument RH was less than 40% were selected for analysis. The daily mean σsp measured at 550 nm varied from 3.4±0.5 to 986.8±318.0 Mm-1. Seasonally σsp was the highest and the Ångström exponent calculated with the σsp for the three wavelengths (450, 550 and 700 nm) was the lowest in spring. Specifically, the Ångström exponent was significantly low during the Asian dust events. The mean diurnal variation of σsp showed different trends in weekdays and weekends; a primary and a secondary peak of σsp occurred at about 9 a.m. and 7 p.m., respectively, in weekdays, while only a single peak of σsp occurred at about 11 a.m. in weekends, 2 hours later than the time of the primary peak in weekdays. Despite different measurement principles, σsp tends to show similar time variation trend to the CN concentration but even more so to CCN concentrations. This may demonstrate that the aerosols that can act as CCN can also contribute to scattering. These aerosols can doubly contribute to the cooling effects directly by scattering the sunlight and indirectly by acting as CCN and making the cloud bright. Ammonium sulfate will be an excellent candidate for this kind of aerosols. More detailed analysis will be shown at the conference.

The Role of Atmospheric Aerosol Concentration on Deep Convective Precipitation: Cloud-Resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Li, Xiaowen; Khain, Alexander; Matsui, Toshihisa; Lang, Stephen; Simpson, Joanne

2010-01-01

Aerosols and especially their effect on clouds are one of the key components of the climate system and the hydrological cycle [Ramanathan et al., 2001]. Yet, the aerosol effect on clouds remains largely unknown and the processes involved not well understood. A recent report published by the National Academy of Science states "The greatest uncertainty about the aerosol climate forcing - indeed, the largest of all the uncertainties about global climate forcing - is probably the indirect effect of aerosols on clouds NRC [2001]." The aerosol effect on Clouds is often categorized into the traditional "first indirect (i.e., Twomey)" effect on the cloud droplet sizes for a constant liquid water path and the "semi-direct" effect on cloud coverage. The aerosol effect on precipitation processes, also known as the second type of aerosol indirect effect, is even more complex, especially for mixed-phase convective clouds. In this paper, a cloud-resolving model (CRM) with detailed spectral-bin microphysics was used to examine the effect of aerosols on three different deep convective cloud systems that developed in different geographic locations: South Florida, Oklahoma and the Central Pacific, In all three cases, rain reaches the ground earlier for the low CCN (clean) case. Rain suppression is also evident in all three cases with high CCN (dirty) case. However, this suppression only occurs during the first hour of the simulations. During the mature stages of the simulations, the effects of increasing aerosol concentration range from rain suppression in the Oklahoma case, to almost no effect in the Florida case, to rain enhancement in the Pacific case. These results show the complexity of aerosol interactions with convection. The model results suggest that evaporative cooling is a key process in determining whether high CCN reduces or enhances precipitation. Stronger evaporative cooling can produce a stronger cold pool and thus stronger low-level convergence through interactions with the low-level wind shear. Consequently, precipitation processes can be more vigorous. For example,, the evaporative cooling is more than two times stronger in the lower troposphere with high CCN for the Pacific case. Sensitivity tests also suggest that ice processes are crucial for suppressing precipitation in the Oklahoma case with high CCN.

Microphysical properties of the Shuttle exhaust cloud

NASA Technical Reports Server (NTRS)

Keller, V. W.; Anderson, B. J.

1983-01-01

A data base describing the properties of the exhaust cloud produced by the launch of the STS has been developed based on data from a series of ground and aircraft based measurements made during the launches of STS 2, 3, and 4. Aircraft observations were performed during the STS-3 launch with a NOAA WP-3D Orion hurricane research aircraft which contained instrumentation for cloud condensation nucleus and ice nucleus counting, Aitken particle counting, and pH determination. Ground observations were conducted at 50 different sites, as well as in the direct exhaust from the solid rocket booster flame trench at all three launches. The data is analyzed in order to determine any possible adverse impacts of the exhaust products on human health and/or the environment. Analyses of the exhaust cloud measurements indicate that in the case of the ground cloud where plenty of large water drops are present and considerable scavenging and fallout of aerosol takes place, possible adverse impacts of the remaining aerosols (CCN and IN) on natural precipitation processes which may occur in the launch area hours after the launch are remote. However, it is determined that under certain atmospheric conditions there could be short term adverse effects on visibility.

Biomass burning emissions of trace gases and particles in marine air at Cape Grim, Tasmania, 41° S

NASA Astrophysics Data System (ADS)

Lawson, S. J.; Keywood, M. D.; Galbally, I. E.; Gras, J. L.; Cainey, J. M.; Cope, M. E.; Krummel, P. B.; Fraser, P. J.; Steele, L. P.; Bentley, S. T.; Meyer, C. P.; Ristovski, Z.; Goldstein, A. H.

2015-07-01

Biomass burning (BB) plumes were measured at the Cape Grim Baseline Air Pollution Station during the 2006 Precursors to Particles campaign, when emissions from a fire on nearby Robbins Island impacted the station. Measurements made included non methane organic compounds (NMOCs) (PTR-MS), particle number size distribution, condensation nuclei (CN) > 3 nm, black carbon (BC) concentration, cloud condensation nuclei (CCN) number, ozone (O3), methane (CH4), carbon monixide (CO), hydrogen (H2), carbon dioxide (CO2), nitrous oxide (N2O), halocarbons and meteorology. During the first plume strike event (BB1), a four hour enhancement of CO (max ~ 2100 ppb), BC (~ 1400 ng m-3) and particles > 3 nm (~ 13 000 cm-3) with dominant particle mode of 120 nm were observed overnight. Dilution of the plume resulted in a drop in the dominant particle mode to 50 nm, and then growth to 80 nm over 5 h. This was accompanied by an increase in O3, suggesting that photochemical processing of air and condensation of low volatility oxidation products may be driving particle growth. The ability of particles > 80 nm (CN80) to act as CCN at 0.5 % supersaturation was investigated. The ΔCCN / ΔCN80 ratio was lowest during the fresh BB plume (56 %), higher during the particle growth event (77 %) and higher still (104 %) in background marine air. Particle size distributions indicate that changes to particle chemical composition, rather than particle size, are driving these changes. Hourly average CCN during both BB events were between 2000-5000 CCN cm-3, which were enhanced above typical background levels by a factor of 6-34, highlighting the dramatic impact BB plumes can have on CCN number in clean marine regions. During the 29 h of the second plume strike event (BB2) CO, BC and a range of NMOCs including acetonitrile and hydrogen cyanide (HCN) were clearly enhanced and some enhancements in O3 were observed (ΔO3 / ΔCO 0.001-0.074). A shortlived increase in NMOCs by a factor of 10 corresponded with a large CO enhancement, an increase of the NMOC / CO emission ratio (ER) by a factor of 2-4 and a halving of the BC / CO ratio. Rainfall on Robbins Island was observed by radar during this period which likely resulted in a lower fire combustion efficiency, and higher emission of compounds associated with smouldering. This highlights the importance of relatively minor meterological events on BB emissions. Emission factors (EF) were derived for a range of trace gases, some never before reported for Australian conditions, (including hydrogen, phenol and toluene) using a calculated ER to CO and a published CO EF. The EF derived for most species are comparable to other temperate Australian studies but lower than Northern Hemisphere temperate studies. This work demonstrates the substantial impact that BB plumes have on the composition of marine air, and the significant changes that can occur as the plume is diluted and interacts with other emission sources. We also provide new trace gas and particle EF for temperate southern Australia.

Interannual Variations in Aerosol Sources and Their Impact on Orographic Precipitation Over California's Central Sierra Nevada

NASA Technical Reports Server (NTRS)

Creamean, J. M.; Ault, A. P.; White, A. B.; Neiman, P. J.; Ralph, F. M.; Minnis, Patrick; Prather, K. A.

2014-01-01

Aerosols that serve as cloud condensation nuclei (CCN) and ice nuclei (IN) have the potential to profoundly influence precipitation processes. Furthermore, changes in orographic precipitation have broad implications for reservoir storage and flood risks. As part of the CalWater I field campaign (2009-2011), the impacts of aerosol sources on precipitation were investigated in the California Sierra Nevada. In 2009, the precipitation collected on the ground was influenced by both local biomass burning (up to 79% of the insoluble residues found in precipitation) and long-range transported dust and biological particles (up to 80% combined), while in 2010, by mostly local sources of biomass burning and pollution (30-79% combined), and in 2011 by mostly long-range transport from distant sources (up to 100% dust and biological). Although vast differences in the source of residues was observed from year-to-year, dust and biological residues were omnipresent (on average, 55% of the total residues combined) and were associated with storms consisting of deep convective cloud systems and larger quantities of precipitation initiated in the ice phase. Further, biological residues were dominant during storms with relatively warm cloud temperatures (up to -15 C), suggesting these particles were more efficient IN compared to mineral dust. On the other hand, lower percentages of residues from local biomass burning and pollution were observed (on average 31% and 9%, respectively), yet these residues potentially served as CCN at the base of shallow cloud systems when precipitation quantities were low. The direct connection of the source of aerosols within clouds and precipitation type and quantity can be used in models to better assess how local emissions versus long-range transported dust and biological aerosols play a role in impacting regional weather and climate, ultimately with the goal of more accurate predictive weather forecast models and water resource management.

Landscape-precipitation feedback mediated by ice nuclei: an example from the Arctic

NASA Astrophysics Data System (ADS)

Stopelli, Emiliano; Conen, Franz; Zimmermann, Lukas; Morris, Cindy; Alewell, Christine

2016-04-01

The Arctic is one of the regions on Earth which are particularly sensitive to the effects of climate change. One of the largest uncertainties in describing climate and climate change is constituted by the characterisation of the behaviour of clouds. Specifically in the Arctic region there is a low abundance of cloud condensation nuclei (CCN) resulting in low droplet concentrations in clouds. Ice nucleating particles (INPs) in the atmosphere promote the aggregation of water molecules into ice, increasing the chance for precipitation. Therefore, a change in the absolute abundance of INPs and their relative presence compared to CCN is expected to have strong impacts on climate in the Arctic in terms of the radiative budget and of precipitation. In July 2015 we sampled particles from air at Haldde Observatory, Norway (69° 55'45" N, 22° 48'30" E, 905 m a.s.l.) on PM10 filters. We determined the number of INPs active at moderate supercooling temperatures (≥ -15 ° C, INPs-15) by immersion freezing. To identify potential sources of airborne INPs we also collected samples of soil from a highland and decaying leaf litter. Air masses passing over the land were enriched in INPs-15, with concentrations twice to three times larger than those found in air masses directly coming from the Barents Sea. Ice nucleation spectra suggest that it is mainly litter which accounts for this enrichment in INPs-15. This example helps elucidating the feedback linking landscapes and atmosphere mediated by INPs in the frame of climate change. While the snow coverage is progressively reducing in the Arctic, areas with decaying leaf litter and vegetation that are exposed to wind and grazing are expected to increase, resulting into a larger abundance of INPs in the local atmosphere. This increase in airborne INPs can promote a change in the freezing of clouds, with impact on the lifetime and on the radiative properties of clouds, and ultimately on the occurrence of precipitation in the Arctic region.

In-Situ Characterization of Cloud Condensation Nuclei, Interstitial, and background Particles using Single Particle Mass Spectrometer, SPLAT II

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zelenyuk, Alla; Imre, D.; Earle, Michael

2010-10-01

Aerosol indirect effect remains the most uncertain aspect of climate change modeling because proper test requires knowledge of individual particles sizes and compositions with high spatial and temporal resolution. We present the first deployment of a single particle mass spectrometer (SPLAT II) that is operated in a dual data acquisition mode to measure all the required individual particle properties with sufficient temporal resolution to definitively resolve the aerosol-cloud interaction in this exemplary case. We measured particle number concentrations, asphericity, and individual particle size, composition, and density with better than 60 seconds resolution. SPLAT II measured particle number concentrations between 70more » particles cm-3and 300 particles cm-3, an average particle density of 1.4 g cm-3. Found that most particles are composed of oxygenated organics, many of which are mixed with sulfates. Biomass burn particles some with sulfates were prevalent, particularly at higher altitudes, and processed sea-salt was observed over the ocean. Analysis of cloud residuals shows that with time cloud droplets acquire sulfate by the reaction of peroxide with SO2. Based on the particle mass spectra and densities we find that the compositions of cloud condensation nuclei are similar to those of background aerosol but, contain on average ~7% more sulfate, and do not include dust and metallic particles. A comparison between the size distributions of background, activated, and interstitial particles shows that while nearly none of the activated particles is smaller than 115 nm, more than 80% of interstitial particles are smaller than 115 nm. We conclude that for this cloud the most important difference between CCN and background aerosol is particle size although having more sulfate also helps.« less

Aircraft-Measured Indirect Cloud Effects from Biomass Burning Smoke in the Arctic and Subarctic

NASA Technical Reports Server (NTRS)

Zamora, L. M.; Kahn, R. A.; Cubison, M. J.; Diskin, G. S.; Jimenez, J. L.; Kondo, Y.; McFarquhar, G. M.; Nenes, A.; Thornhill, K. L.; Wisthaler, A.;

Aircraft-measured indirect cloud effects from biomass burning smoke in the Arctic and subarctic

DOE PAGES

Zamora, Lauren M.; Kahn, R. A.; Cubison, M. J.; ...

2016-01-21

The incidence of wildfires in the Arctic and subarctic is increasing; in boreal North America, for example, the burned area is expected to increase by 200–300% over the next 50–100 years, which previous studies suggest could have a large effect on cloud microphysics, lifetime, albedo, and precipitation. However, the interactions between smoke particles and clouds remain poorly quantified due to confounding meteorological influences and remote sensing limitations. Here, we use data from several aircraft campaigns in the Arctic and subarctic to explore cloud microphysics in liquid-phase clouds influenced by biomass burning. Median cloud droplet radii in smoky clouds were ~40–60% smallermore » than in background clouds. Based on the relationship between cloud droplet number ( N liq) and various biomass burning tracers (BB t) across the multi-campaign data set, we calculated the magnitude of subarctic and Arctic smoke aerosol–cloud interactions (ACIs, where ACI = (1/3) × d ln( N liq)/d ln(BB t)) to be ~0.16 out of a maximum possible value of 0.33 that would be obtained if all aerosols were to nucleate cloud droplets. Interestingly, in a separate subarctic case study with low liquid water content (~0.02gm –3) and very high aerosol concentrations (2000–3000 cm –3) in the most polluted clouds, the estimated ACI value was only 0.05. In this case, competition for water vapor by the high concentration of cloud condensation nuclei (CCN) strongly limited the formation of droplets and reduced the cloud albedo effect, which highlights the importance of cloud feedbacks across scales. Using our calculated ACI values, we estimate that the smoke-driven cloud albedo effect may decrease local summertime short-wave radiative flux by between 2 and 4 Wm –2 or more under some low and homogeneous cloud cover conditions in the subarctic, although the changes should be smaller in high surface albedo regions of the Arctic. Furthermore, we lastly explore evidence suggesting that numerous northern-latitude background Aitken particles can interact with combustion particles, perhaps impacting their properties as cloud condensation and ice nuclei.« less

Aerosol impacts on deep convective storms in the tropics: A combination of modeling and observations

NASA Astrophysics Data System (ADS)

Storer, Rachel Lynn

It is widely accepted that increasing the number of aerosols available to act as cloud condensation nuclei (CCN) will have significant effects on cloud properties, both microphysical and dynamical. This work focuses on the impacts of aerosols on deep convective clouds (DCCs), which experience more complicated responses than warm clouds due to their strong dynamical forcing and the presence of ice processes. Several previous studies have seen that DCCs may be invigorated by increasing aerosols, though this is not the case in all scenarios. The precipitation response to increased aerosol concentrations is also mixed. Often precipitation is thought to decrease due to a less efficient warm rain process in polluted clouds, yet convective invigoration would lead to an overall increase in surface precipitation. In this work, modeling and observations are both used in order to enhance our understanding regarding the effects of aerosols on DCCs. Specifically, the area investigated is the tropical East Atlantic, where dust from the coast of Africa frequently is available to interact with convective storms over the ocean. The first study investigates the effects of aerosols on tropical DCCs through the use of numerical modeling. A series of large-scale, two-dimensional cloud-resolving model simulations was completed, differing only in the concentration of aerosols available to act as CCN. Polluted simulations contained more deep convective clouds, wider storms, higher cloud tops and more convective precipitation across the entire domain. Differences in the warm cloud microphysical processes were largely consistent with aerosol indirect theory, and the average precipitation produced in each DCC column decreased with increasing aerosol concentration. A detailed microphysical budget analysis showed that the reduction in collision and coalescence largely dominated the trend in surface precipitation; however the production of rain through the melting of ice, though it also decreased, became more important as the aerosol concentration increased. The DCCs in polluted simulations contained more frequent, stronger updrafts and downdrafts, but the average updraft speed decreased with increasing aerosols in DCCs above 6 km. An examination of the buoyancy term of the vertical velocity equation demonstrates that the drag associated with condensate loading is an important factor in determining the average updraft strength. The largest contributions to latent heating in DCCs were cloud nucleation and vapor deposition onto water and ice, but changes in latent heating were, on average, an order of magnitude smaller than those in the condensate loading term. It is suggested that the average updraft is largely influenced by condensate loading in the more extensive stratiform regions of the polluted storms, while invigoration in the convective core leads to stronger updrafts and higher cloud tops. The goal of the second study was to examine observational data for evidence that would support the findings of the modeling work. In order to do this, four years of CloudSat data were analyzed over a region of the East Atlantic, chosen for the similarity (in meteorology and the presence of aerosols) to the modeling study. The satellite data were combined with information about aerosols taken from the output of a global transport model, and only those profiles fitting the definition of deep convective clouds were analyzed. Overall, the cloud center of gravity, cloud top, rain top, and ice water path were all found to increase with increased aerosol loading. These findings are in agreement with what was found in the modeling work, and are suggestive of convective invigoration with increased aerosols. In order to separate environmental effects from that due to aerosols, the data were sorted by environmental convective available potential energy (CAPE) and lower tropospheric static stability (LTSS). The aerosol effects were found to be largely independent of the environment. A simple statistical test suggests that the difference between the cleanest and most polluted clouds sampled are significant, lending credence to the hypothesis of convective invigoration. This is the first time evidence of deep convective invigoration has been demonstrated within a large region and over a long time period, and it is quite promising that there are many similarities between the modeling and observational results.

Improving aerosol interaction with clouds and precipitation in a regional chemical weather modeling system

NASA Astrophysics Data System (ADS)

Zhou, C.; Zhang, X.; Gong, S.

2015-12-01

A comprehensive aerosol-cloud-precipitation interaction (ACI) scheme has been developed under CMA chemical weather modeling system GRAPES/CUACE. Calculated by a sectional aerosol activation scheme based on the information of size and mass from CUACE and the thermal-dynamic and humid states from the weather model GRAPES at each time step, the cloud condensation nuclei (CCN) is fed online interactively into a two-moment cloud scheme (WDM6) and a convective parameterization to drive the cloud physics and precipitation formation processes. The modeling system has been applied to study the ACI for January 2013 when several persistent haze-fog events and eight precipitation events occurred. The results show that interactive aerosols with the WDM6 in GRAPES/CUACE obviously increase the total cloud water, liquid water content and cloud droplet number concentrations while decrease the mean diameter of cloud droplets with varying magnitudes of the changes in each case and region. These interactive micro-physical properties of clouds improve the calculation of their collection growth rates in some regions and hence the precipitation rate and distributions in the model, showing 24% to 48% enhancements of TS scoring for 6-h precipitation in almost all regions. The interactive aerosols with the WDM6 also reduce the regional mean bias of temperature by 3 °C during certain precipitation events, but the monthly means bias is only reduced by about 0.3°C.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zamora, Lauren M.; Kahn, R. A.; Cubison, M. J.

The incidence of wildfires in the Arctic and subarctic is increasing; in boreal North America, for example, the burned area is expected to increase by 200–300% over the next 50–100 years, which previous studies suggest could have a large effect on cloud microphysics, lifetime, albedo, and precipitation. However, the interactions between smoke particles and clouds remain poorly quantified due to confounding meteorological influences and remote sensing limitations. Here, we use data from several aircraft campaigns in the Arctic and subarctic to explore cloud microphysics in liquid-phase clouds influenced by biomass burning. Median cloud droplet radii in smoky clouds were ~40–60% smallermore » than in background clouds. Based on the relationship between cloud droplet number ( N liq) and various biomass burning tracers (BB t) across the multi-campaign data set, we calculated the magnitude of subarctic and Arctic smoke aerosol–cloud interactions (ACIs, where ACI = (1/3) × d ln( N liq)/d ln(BB t)) to be ~0.16 out of a maximum possible value of 0.33 that would be obtained if all aerosols were to nucleate cloud droplets. Interestingly, in a separate subarctic case study with low liquid water content (~0.02gm –3) and very high aerosol concentrations (2000–3000 cm –3) in the most polluted clouds, the estimated ACI value was only 0.05. In this case, competition for water vapor by the high concentration of cloud condensation nuclei (CCN) strongly limited the formation of droplets and reduced the cloud albedo effect, which highlights the importance of cloud feedbacks across scales. Using our calculated ACI values, we estimate that the smoke-driven cloud albedo effect may decrease local summertime short-wave radiative flux by between 2 and 4 Wm –2 or more under some low and homogeneous cloud cover conditions in the subarctic, although the changes should be smaller in high surface albedo regions of the Arctic. Furthermore, we lastly explore evidence suggesting that numerous northern-latitude background Aitken particles can interact with combustion particles, perhaps impacting their properties as cloud condensation and ice nuclei.« less

Heterogeneous chemistry of atmospheric mineral dust particles and their resulting cloud-nucleation properties

NASA Astrophysics Data System (ADS)

Sullivan, Ryan Christopher

Mineral dust particles are a major component of tropospheric aerosol mass and affect regional and global atmospheric chemistry and climate. Dust particles experience heterogeneous reactions with atmospheric gases that alter the gas and particle-phase chemistry. These in turn influence the warm and cold cloud nucleation ability and optical properties of the dust particles. This dissertation investigates the atmospheric chemistry of mineral dust particles and their role in warm cloud nucleation through a combination of synergistic field measurements, laboratory experiments, and theoretical modeling. In-situ measurements made with a single-particle mass spectrometer during the ACE-Asia field campaign in 2001 provide the motivation for this work. The observed mixing state of the individual ambient particles with secondary organic and inorganic components is described in Chapter 2. A large Asian dust storm occurred during the campaign and produced dramatic changes in the aerosol's composition and mixing state. The effect of particle size and mineralogy on the atmospheric processing of individual dust particles is explored in Chapters 3 & 4. Sulfate was found to accumulate preferentially in submicron iron and aluminosilicate-rich dust particles, while nitrate and chloride were enriched in supermicron calcite-rich dust. The mineral dust (and sea salt particles) were also enriched in oxalic acid, the dominant component of water soluble organic carbon. Chapter 5 explores the roles of gas-phase photochemistry and partitioning of the diacids to the alkaline particles in producing this unique behavior. The effect of the dust's mixing state with secondary organic and inorganic components on the dust particles' solubility, hygroscopicity, and thus warm cloud nucleation properties is explored experimentally and theoretically in Chapter 6. Cloud condensation nucleation (CCN) activation curves revealed that while calcium nitrate and calcium chloride particles were very hygroscopic and CCN-active, due to the high solubility of these compounds, calcium sulfate and calcium oxalate were not. Particles composed of these two sparingly soluble compounds had apparent hygroscopicities similar to pure calcium carbonate. This implies that the commonly made assumption that all dust particles become more hygroscopic after atmospheric processing must be revisited. Calcium sulfate and oxalate represent two forms of aged mineral dust particles that remain non-hygroscopic and thus have poor CCN nucleation ability. The particle generation method (dry versus wet) was found to significantly affect the chemistry and hygroscopicity of the aerosolized particles. Finally, in Chapter 7 the timescale for the atmospheric conversion of insoluble calcite particles to soluble, CCN-active calcium nitrate particles was derived from aerosol flow tube experiments. The reaction rate is rapid was used to estimate the conversion of calcite particles to very hygroscopic particles can occur in just a few hours of exposure to tropospheric levels of nitric acid. This process will therefore be controlled by the availability of nitric acid and its precursors, as opposed to the available atmospheric reaction time.

Droplet Growth Kinetics in Various Environments

NASA Astrophysics Data System (ADS)

Raatikainen, T. E.; Lathem, T. L.; Moore, R.; Lin, J. J.; Cerully, K. M.; Padro, L.; Lance, S.; Cozic, J.; Anderson, B. E.; Nenes, A.

2012-12-01

The largest uncertainties in the effects of atmospherics aerosols on the global radiation budget are related to their indirect effects on cloud properties (IPCC, the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007). Cloud formation is a kinetic process where the resulting cloud properties depend on aerosol properties and meteorological parameters such as updraft velocity (e.g. McFiggans et al., Atmos. Chem. Phys., 6, 2593-2649, 2006). Droplet growth rates are limited by the water vapor diffusion, but additional kinetic limitations, e.g., due to organic surface films, slow solute dissociation or highly viscous or glassy aerosol states have been hypothesized. Significant additional kinetic limitations can lead to increased cloud droplet number concentration, thus the effect is similar to those of increased aerosol number concentration or changes in vertical velocity (e.g. Nenes et al., Geophys. Res. Lett., 29, 1848, 2002). There are a few studies where slow droplet growth has been observed (e.g. Ruehl et al., Geophys. Res. Lett., 36, L15814, 2009), however, little is currently known about their global occurrence and magnitude. Cloud micro-physics models often describe kinetic limitations by an effective water vapor uptake coefficient or similar parameter. Typically, determining aerosol water vapor uptake coefficients requires experimental observations of droplet growth which are interpreted by a numerical droplet growth model where the uptake coefficient is an adjustable parameter (e.g. Kolb et al., Atmos. Chem. Phys., 10, 10561-10605, 2010). Such methods have not been practical for high time-resolution or long term field measurements, until a model was recently developed for analyzing Droplet Measurement Technologies (DMT) cloud condensation nuclei (CCN) counter data (Raatikainen et al., Atmos. Chem. Phys., 12, 4227-4243, 2012). Model verification experiments showed that the calibration aerosol droplet size can be predicted accurately for various instrument settings and also in the case of high CCN concentrations when water vapor depletion decreases supersaturation and droplet size (Lathem and Nenes, Aerosol Sci. Tech., 45, 604-615, 2011). The model also accounts for aerosol hygroscopicity and size distribution variations, which can have significant effects on the droplet size. We have examined cloud droplet activation and growth kinetics by analyzing several DMT CCN counter data sets collected from various environments including boreal forests, arctic areas, fresh and aged biomass burning plumes, and polluted and biogenically influenced urban areas (Raatikainen et al., In preparation, 2012). Model simulations show that the variations in observed droplet size are caused by water vapor depletion effects, changes in dry particle size distributions and hygroscopicity, and changes in instrument supersaturation profiles. This means that fast droplet growth kinetics with water uptake coefficient close to 0.2 is prevalent at least for the studied environments.

The Impact of Aerosols on Cloud and Precipitation Processes: Cloud-Resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Li, Xiaowen; Khain, Alexander; Matsui, Toshihisa; Lang, Stephen; Simpson, Joanne

2008-01-01

Aerosols and especially their effect on clouds are one of the key components of the climate system and the hydrological cycle [Ramanathan et al., 2001]. Yet, the aerosol effect on clouds remains largely unknown and the processes involved not well understood. A recent report published by the National Academy of Science states "The greatest uncertainty about the aerosol climate forcing - indeed, the largest of all the uncertainties about global climate forcing - is probably the indirect effect of aerosols on clouds [NRC, 2001]." The aerosol effect on clouds is often categorized into the traditional "first indirect (i.e., Twomey)" effect on the cloud droplet sizes for a constant liquid water path [Twomey, 1977] and the "semi-direct" effect on cloud coverage [e.g., Ackerman et al ., 2001]." Enhanced aerosol concentrations can also suppress warm rain processes by producing a narrow droplet spectrum that inhibits collision and coalescence processes [e.g., Squires and Twomey, 1961; Warner and Twomey, 1967; Warner, 1968; Rosenfeld, 19991. The aerosol effect on precipitation processes, also known as the second type of aerosol indirect effect [Albrecht, 1989], is even more complex, especially for mixed-phase convective clouds. Table 1 summarizes the key observational studies identifying the microphysical properties, cloud characteristics, thermodynamics and dynamics associated with cloud systems from high-aerosol continental environments. For example, atmospheric aerosol concentrations can influence cloud droplet size distributions, warm-rain process, cold-rain process, cloud-top height, the depth of the mixed phase region, and occurrence of lightning. In addition, high aerosol concentrations in urban environments could affect precipitation variability by providing an enhanced source of cloud condensation nuclei (CCN). Hypotheses have been developed to explain the effect of urban regions on convection and precipitation [van den Heever and Cotton, 2007 and Shepherd, 2005]. Please see Tao et al. (2007) for more detailed description on aerosol impact on precipitation. Recently, a detailed spectral-bin microphysical scheme was implemented into the Goddard Cumulus Ensemble (GCE) model. Atmospheric aerosols are also described using number density size-distribution functions. A spectral-bin microphysical model is very expensive from a computational point of view and has only been implemented into the 2D version of the GCE at the present time. The model is tested by studying the evolution of deep tropical clouds in the west Pacific warm pool region and summertime convection over a mid-latitude continent with different concentrations of CCN: a low "clean" concentration and a high "dirty" concentration. The impact of atmospheric aerosol concentration on cloud and precipitation will be investigated.

Chemical and physical properties of biomass burning aerosols and their CCN activity: A case study in Beijing, China.

PubMed

Wu, Zhijun; Zheng, Jing; Wang, Yu; Shang, Dongjie; Du, Zhoufei; Zhang, Yuanhang; Hu, Min

2017-02-01

Biomass burning emits large amounts of both trace gases and particles into the atmosphere. It plays a profound role in regional air quality and climate change. In the present study, an intensive campaign was carried out at an urban site in Beijing, China, in June 2014, which covered the winter wheat harvest season over the North China Plain (NCP). Meanwhile, two evident biomass-burning events were observed. A clear burst in ultrafine particles (below 100nm in diameter, PM 1 ) and subsequent particle growth took place during the events. With the growth of the ultrafine particles, the organic fraction of PM 1 increased significantly. The ratio of oxygen to carbon (O:C), which had an average value of 0.23±0.04, did not show an obvious enhancement, indicating that a significant chemical aging process of the biomass-burning aerosols was not observed during the course of events. This finding might have been due to the fact that the biomass-burning events occurred in the late afternoon and grew during the nighttime, which is associated with a low atmospheric oxidation capacity. On average, organics and black carbon (BC) were dominant in the biomass-burning aerosols, accounting for 60±10% and 18±3% of PM 1 . The high organic and BC fractions led to a significant suppression of particle hygroscopicity. Comparisons among hygroscopicity tandem differential mobility analyzer (HTDMA)-derived, cloud condensation nuclei counter (CCNc)-derived, and aerosol mass spectrometer-based hygroscopicity parameter (κ) values were consistent. The mean κ values of biomass-burning aerosols derived from both HTDMA and CCNc measurements were approximately 0.1, regardless of the particle size, indicating that the biomass-burning aerosols were less active. The burst in particle count during the biomass-burning events resulted in an increased number of cloud condensation nuclei (CCN) at supersaturation (SS)=0.2-0.8%. Copyright © 2016 Elsevier B.V. All rights reserved.

Air pollution control and decreasing new particle formation lead to strong climate warming

NASA Astrophysics Data System (ADS)

Makkonen, R.; Asmi, A.; Kerminen, V.-M.; Boy, M.; Arneth, A.; Hari, P.; Kulmala, M.

2012-02-01

The number concentration of cloud droplets determines several climatically relevant cloud properties. A major cause for the high uncertainty in the indirect aerosol forcing is the availability of cloud condensation nuclei (CCN), which in turn is highly sensitive to atmospheric new particle formation. Here we present the effect of new particle formation on anthropogenic aerosol forcing in present-day (year 2000) and future (year 2100) conditions. The present-day total aerosol forcing is increased from -1.0 W m-2 to -1.6 W m-2 when nucleation is introduced into the model. Nucleation doubles the change in aerosol forcing between years 2000 and 2100, from +0.6 W m-2 to +1.4 W m-2. Two climate feedbacks are studied, resulting in additional negative forcings of -0.1 W m-2 (+10% DMS emissions in year 2100) and -0.5 W m-2 (+50% BVOC emissions in year 2100). With the total aerosol forcing diminishing in response to air pollution control measures taking effect, warming from increased greenhouse gas concentrations can potentially increase at a very rapid rate.

Application of an online-coupled regional climate model, WRF-CAM5, over East Asia for examination of ice nucleation schemes. Part II. Sensitivity to heterogeneous ice nucleation parameterizations and dust emissions

DOE PAGES

Zhang, Yang; Chen, Ying; Fan, Jiwen; ...

2015-09-14

Aerosol particles can affect cloud microphysical properties by serving as ice nuclei (IN). Large uncertainties exist in the ice nucleation parameterizations (INPs) used in current climate models. In this Part II paper, to examine the sensitivity of the model predictions to different heterogeneous INPs, WRF-CAM5 simulation using the INP of Niemand et al. (N12) [1] is conducted over East Asia for two full years, 2006 and 2011, and compared with simulation using the INP of Meyers et al. (M92) [2], which is the original INP used in CAM5. M92 calculates the nucleated ice particle concentration as a function of icemore » supersaturation, while N12 represents the nucleated ice particle concentration as a function of temperature and the number concentrations and surface areas of dust particles. Compared to M92, the WRF-CAM5 simulation with N12 produces significantly higher nucleated ice crystal number concentrations (ICNCs) in the northern domain where dust sources are located, leading to significantly higher cloud ice number and mass concentrations and ice water path, but the opposite is true in the southern domain where temperatures and moistures play a more important role in ice formation. Overall, the simulation with N12 gives lower downward shortwave radiation but higher downward longwave radiation, cloud liquid water path, cloud droplet number concentrations, and cloud optical depth. The increase in cloud optical depth and the decrease in downward solar flux result in a stronger shortwave and longwave cloud forcing, and decreases temperature at 2-m and precipitation. Changes in temperature and radiation lower surface concentrations of OH, O₃, SO₄²⁻, and PM 2.5, but increase surface concentrations of CO, NO₂, and SO₂ over most of the domain. By acting as cloud condensation nuclei (CCN) and IN, dust particles have different impacts on cloud water and ice number concentrations, radiation, and temperature at 2-m and precipitation depending on whether the dominant role of dust is CCN or IN. These results indicate the importance of the heterogeneous ice nucleation treatments and dust emissions in accurately simulating regional climate and air quality.« less

Application of an online-coupled regional climate model, WRF-CAM5, over East Asia for examination of ice nucleation schemes. Part II. Sensitivity to heterogeneous ice nucleation parameterizations and dust emissions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yang; Chen, Ying; Fan, Jiwen

Aerosol particles can affect cloud microphysical properties by serving as ice nuclei (IN). Large uncertainties exist in the ice nucleation parameterizations (INPs) used in current climate models. In this Part II paper, to examine the sensitivity of the model predictions to different heterogeneous INPs, WRF-CAM5 simulation using the INP of Niemand et al. (N12) [1] is conducted over East Asia for two full years, 2006 and 2011, and compared with simulation using the INP of Meyers et al. (M92) [2], which is the original INP used in CAM5. M92 calculates the nucleated ice particle concentration as a function of icemore » supersaturation, while N12 represents the nucleated ice particle concentration as a function of temperature and the number concentrations and surface areas of dust particles. Compared to M92, the WRF-CAM5 simulation with N12 produces significantly higher nucleated ice crystal number concentrations (ICNCs) in the northern domain where dust sources are located, leading to significantly higher cloud ice number and mass concentrations and ice water path, but the opposite is true in the southern domain where temperatures and moistures play a more important role in ice formation. Overall, the simulation with N12 gives lower downward shortwave radiation but higher downward longwave radiation, cloud liquid water path, cloud droplet number concentrations, and cloud optical depth. The increase in cloud optical depth and the decrease in downward solar flux result in a stronger shortwave and longwave cloud forcing, and decreases temperature at 2-m and precipitation. Changes in temperature and radiation lower surface concentrations of OH, O₃, SO₄²⁻, and PM 2.5, but increase surface concentrations of CO, NO₂, and SO₂ over most of the domain. By acting as cloud condensation nuclei (CCN) and IN, dust particles have different impacts on cloud water and ice number concentrations, radiation, and temperature at 2-m and precipitation depending on whether the dominant role of dust is CCN or IN. These results indicate the importance of the heterogeneous ice nucleation treatments and dust emissions in accurately simulating regional climate and air quality.« less

Application of an Online-Coupled Regional Climate Model, WRF-CAM5, over East Asia for Examination of Ice Nucleation Schemes: Part II. Sensitivity to Heterogeneous Ice Nucleation Parameterizations and Dust Emissions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Yang; Chen, Ying; Fan, Jiwen

Aerosol particles can affect cloud microphysical properties by serving as ice nuclei (IN). Large uncertainties exist in the ice nucleation parameterizations (INPs) used in current climate models. In this Part II paper, to examine the sensitivity of the model predictions to different heterogeneous INPs, WRF-CAM5 simulation using the INP of Niemand et al. (N12) [1] is conducted over East Asia for two full years, 2006 and 2011, and compared with simulation using the INP of Meyers et al. (M92) [2], which is the original INP used in CAM5. M92 calculates the nucleated ice particle concentration as a function of icemore » supersaturation, while N12 represents the nucleated ice particle concentration as a function of temperature and the number concentrations and surface areas of dust particles. Compared to M92, the WRF-CAM5 simulation with N12 produces significantly higher nucleated ice crystal number concentrations (ICNCs) in the northern domain where dust sources are located, leading to significantly higher cloud ice number and mass concentrations and ice water path, but the opposite is true in the southern domain where temperatures and moistures play a more important role in ice formation. Overall, the simulation with N12 gives lower downward shortwave radiation but higher downward longwave radiation, cloud liquid water path, cloud droplet number concentrations, and cloud optical depth. The increase in cloud optical depth and the decrease in downward solar flux result in a stronger shortwave and longwave cloud forcing, and decreases temperature at 2-m and precipitation. Changes in temperature and radiation lower surface concentrations of OH, O 3, SO 4 2-, and PM2.5, but increase surface concentrations of CO, NO 2, and SO 2 over most of the domain. By acting as cloud condensation nuclei (CCN) and IN, dust particles have different impacts on cloud water and ice number concentrations, radiation, and temperature at 2-m and precipitation depending on whether the dominant role of dust is CCN or IN. These results indicate the importance of the heterogeneous ice nucleation treatments and dust emissions in accurately simulating regional climate and air quality.« less

Implementation of warm-cloud processes in a source-oriented WRF/Chem model to study the effect of aerosol mixing state on fog formation in the Central Valley of California

NASA Astrophysics Data System (ADS)

Lee, Hsiang-He; Chen, Shu-Hua; Kleeman, Michael J.; Zhang, Hongliang; DeNero, Steven P.; Joe, David K.

2016-07-01

The source-oriented Weather Research and Forecasting chemistry model (SOWC) was modified to include warm cloud processes and was applied to investigate how aerosol mixing states influence fog formation and optical properties in the atmosphere. SOWC tracks a 6-D chemical variable (X, Z, Y, size bins, source types, species) through an explicit simulation of atmospheric chemistry and physics. A source-oriented cloud condensation nuclei module was implemented into the SOWC model to simulate warm clouds using the modified two-moment Purdue Lin microphysics scheme. The Goddard shortwave and long-wave radiation schemes were modified to interact with source-oriented aerosols and cloud droplets so that aerosol direct and indirect effects could be studied. The enhanced SOWC model was applied to study a fog event that occurred on 17 January 2011, in the Central Valley of California. Tule fog occurred because an atmospheric river effectively advected high moisture into the Central Valley and nighttime drainage flow brought cold air from mountains into the valley. The SOWC model produced reasonable liquid water path, spatial distribution and duration of fog events. The inclusion of aerosol-radiation interaction only slightly modified simulation results since cloud optical thickness dominated the radiation budget in fog events. The source-oriented mixture representation of particles reduced cloud droplet number relative to the internal mixture approach that artificially coats hydrophobic particles with hygroscopic components. The fraction of aerosols activating into cloud condensation nuclei (CCN) at a supersaturation of 0.5 % in the Central Valley decreased from 94 % in the internal mixture model to 80 % in the source-oriented model. This increased surface energy flux by 3-5 W m-2 and surface temperature by as much as 0.25 K in the daytime.

Impact of aerosol intrusions on sea-ice melting rates and the structure Arctic boundary layer clouds

NASA Astrophysics Data System (ADS)

Cotton, W.; Carrio, G.; Jiang, H.

2003-04-01

The Los Alamos National Laboratory sea-ice model (LANL CICE) was implemented into the real-time and research versions of the Colorado State University-Regional Atmospheric Modeling System (RAMS@CSU). The original version of CICE was modified in its structure to allow module communication in an interactive multigrid framework. In addition, some improvements have been made in the routines involved in the coupling, among them, the inclusion of iterative methods that consider variable roughness lengths for snow-covered ice thickness categories. This version of the model also includes more complex microphysics that considers the nucleation of cloud droplets, allowing the prediction of mixing ratios and number concentrations for all condensed water species. The real-time version of RAMS@CSU automatically processes the NASA Team SSMI F13 25km sea-ice coverage data; the data are objectively analyzed and mapped to the model grid configuration. We performed two types of cloud resolving simulations to assess the impact of the entrainment of aerosols from above the inversion on Arctic boundary layer clouds. The first series of numerical experiments corresponds to a case observed on May 4 1998 during the FIRE-ACE/SHEBA field experiment. Results indicate a significant impact on the microstructure of the simulated clouds. When assuming polluted initial profiles above the inversion, the liquid water fraction of the cloud monotonically decreases, the total condensate paths increases and downward IR tends to increase due to a significant increase in the ice water path. The second set of cloud resolving simulations focused on the evaluation of the potential effect of aerosol concentration above the inversion on melting rates during spring-summer period. For these multi-month simulations, the IFN and CCN profiles were also initialized assuming the 4 May profiles as benchmarks. Results suggest that increasing the aerosol concentrations above the boundary layer increases sea-ice melting rates when mixed phase clouds are present.

Development and impact of hooks of large droplet concentration on remote southeast Pacific stratocumulus

NASA Astrophysics Data System (ADS)

George, R. C.; Wood, R.; Bretherton, C. S.; Painter, G.

2013-01-01

Over the southeastern Pacific (SEP), droplet concentration (Nd) in the typically unpolluted marine stratocumulus west of 80° W (> 1000 km offshore) is periodically strongly enhanced in zonally-elongated "hook"-shaped arcs that increase albedo. Here, we examine three hook events using the chemistry version of the Weather Research and Forecasting model (WRF-Chem) with 14 km horizontal resolution, satellite data and aircraft data from the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx). A particularly strong hook yields insights to the development, decay, and radiative impact of these features. Hook development occurs with Nd increasing to polluted levels over the remote ocean primarily due to entrainment of cloud condensation nuclei (CCN) from the free troposphere (FT). The feature advects northwestward until the FT CCN source is depleted, after which Nd decreases over a few days due to precipitation and dilution. The model suggests that the FT CCN source supplying the hook consists of high concentrations of small accumulation mode aerosols that contribute a relatively small amount of aerosol mass to the MBL. The aerosol particles originate mainly from a pulse of offshore flow that transports Santiago region (33-35° S) emissions to the marine FT. To provide a sustained hook CCN source, the FT transport of pollution plumes to the remote ocean requires strong, deep offshore flow. Such flow is favored by a trough approaching the South American coast and a southeastward shift of the climatological subtropical high pressure system. The model simulations show precipitation suppression in the hook and a corresponding increase in liquid water path (LWP) compared with a simulation without anthropogenic sources. LWP also increases in time as the hook evolves due to increasing stability and decreasing subsidence. WRF-Chem suggests that DMS significantly influences the aerosol number and size distributions in a hook, but that hooks do not form without FT CCN. The Twomey effect contributes ~ 50-70% of the albedo increase due the presence of the hook, while secondary aerosol indirect effects and meteorological influences also contribute significantly. The source of hook aerosols is difficult to determine with the available observations alone. The model explains the observations and puts them in context of the factors influencing hook formation. Two other weaker hooks during VOCALS-REx are not as well simulated but are also associated with FT offshore flow near Santiago. Hooks demonstrate the importance of free-tropospheric transport of aerosols in modulating the droplet concentration in the southeastern Pacific stratocumulus deck, and present a formidable challenge to simulate accurately in large scale models.

Parameterizations of Cloud Microphysics and Indirect Aerosol Effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tao, Wei-Kuo

1. OVERVIEW Aerosols and especially their effect on clouds are one of the key components of the climate system and the hydrological cycle [Ramanathan et al., 2001]. Yet, the aerosol effect on clouds remains largely unknown and the processes involved not well understood. A recent report published by the National Academy of Science states "The greatest uncertainty about the aerosol climate forcing - indeed, the largest of all the uncertainties about global climate forcing - is probably the indirect effect of aerosols on clouds [NRC, 2001]." The aerosol effect on clouds is often categorized into the traditional "first indirect (i.e.,more » Twomey)" effect on the cloud droplet sizes for a constant liquid water path [Twomey, 1977] and the "semi-direct" effect on cloud coverage [e.g., Ackerman et al., 2000]. Enhanced aerosol concentrations can also suppress warm rain processes by producing a narrow droplet spectrum that inhibits collision and coalescence processes [e.g., Squires and Twomey, 1961; Warner and Twomey, 1967; Warner, 1968; Rosenfeld, 1999]. The aerosol effect on precipitation processes, also known as the second type of aerosol indirect effect [Albrecht, 1989], is even more complex, especially for mixed-phase convective clouds. Table 1 summarizes the key observational studies identifying the microphysical properties, cloud characteristics, thermodynamics and dynamics associated with cloud systems from high-aerosol continental environments. For example, atmospheric aerosol concentrations can influence cloud droplet size distributions, warm-rain process, cold-rain process, cloud-top height, the depth of the mixed phase region, and occurrence of lightning. In addition, high aerosol concentrations in urban environments could affect precipitation variability by providing an enhanced source of cloud condensation nuclei (CCN). Hypotheses have been developed to explain the effect of urban regions on convection and precipitation [van den Heever and Cotton, 2007 and Shepherd, 2005]. Recently, a detailed spectral-bin microphysical scheme was implemented into the Goddard Cumulus Ensemble (GCE) model. Atmospheric aerosols are also described using number density size-distribution functions. A spectral-bin microphysical model is very expensive from a computational point of view and has only been implemented into the 2D version of the GCE at the present time. The model is tested by studying the evolution of deep tropical clouds in the west Pacific warm pool region and summertime convection over a mid-latitude continent with different concentrations of CCN: a low "clean" concentration and a high "dirty" concentration. The impact of atmospheric aerosol concentration on cloud and precipitation will be investigated. 2. MODEL DESCRIPTION AND CASE STUDIES 2.1 GCE MODEL The model used in this study is the 2D version of the GCE model. Modeled flow is anelastic. Second- or higher-order advection schemes can produce negative values in the solution. Thus, a Multi-dimensional Positive Definite Advection Transport Algorithm (MPDATA) has been implemented into the model. All scalar variables (potential temperature, water vapor, turbulent coefficient and all five hydrometeor classes) use forward time differencing and the MPDATA for advection. Dynamic variables, u, v and w, use a second-order accurate advection scheme and a leapfrog time integration (kinetic energy semi-conserving method). Short-wave (solar) and long-wave radiation as well as a subgrid-scale TKE turbulence scheme are also included in the model. Details of the model can be found in Tao and Simpson (1993) and Tao et al. (2003). 2.2 Microphysics (Bin Model) The formulation of the explicit spectral-bin microphysical processes is based on solving stochastic kinetic equations for the size distribution functions of water droplets (cloud droplets and raindrops), and six types of ice particles: pristine ice crystals (columnar and plate-like), snow (dendrites and aggregates), graupel and frozen drops/hail. Each type is described by a special size distribution function containing 33 categories (bins). Atmospheric aerosols are also described using number density size-distribution functions (containing 33 bins). Droplet nucleation (activation) is derived from the analytical calculation of super-saturation, which is used to determine the sizes of aerosol particles to be activated and the corresponding sizes of nucleated droplets. Primary nucleation of each type of ice crystal takes place within certain temperature ranges. A detailed description of these explicitly parameterized processes can be found in Khain and Sednev (1996) and Khain et al. (1999, 2001). 2.3 Case Studies Three cases, a tropical oceanic squall system observed during TOGA COARE (Tropical Ocean and Global Atmosphere Coupled Ocean-Atmosphere Response Experiment, which occurred over the Pacific Ocean warm pool from November 1992 to February 1993), a midlatitude continental squall system observed during PRESTORM (Preliminary Regional Experiment for STORM-Central, which occurred in Kansas and Oklahoma during May-June 1985), and mid-afternoon convection observed during CRYSTAL-FACE (Cirrus Regional Study of Tropical Anvils and Cirrus Layers – Florida Area Cumulus Experiment, which occurred in Florida during July 2002), will be used to examine the impact of aerosols on deep, precipitating systems. 3. SUMMARY of RESULTS • For all three cases, higher CCN produces smaller cloud droplets and a narrower spectrum. Dirty conditions delay rain formation, increase latent heat release above the freezing level, and enhance vertical velocities at higher altitude for all cases. Stronger updrafts, deeper mixed-phase regions, and more ice particles are simulated with higher CCN in good agreement with observations. • In all cases, rain reaches the ground early with lower CCN. Rain suppression is also evident in all three cases with high CCN in good agreement with observations (Rosenfeld, 1999, 2000 and others). Rain suppression, however, only occurs during the first hour of simulation. This result suggests that microphysical processes dominate the impact of aerosols on precipitation in the early stage of precipitation development. • During the mature stage of the simulations, the effect of increasing aerosol concentration ranges from rain suppression in the PRESTORM case to little effect on surface rainfall in the CRYSTAL-FACE case to rain enhancement in the TOGA COARE case. • The model results suggest that evaporative cooling is a key process in determining whether higher CCN reduces or enhances precipitation. Cold pool strength can be enhanced by stronger evaporation. When cold pool interacts with the near surface wind shear, the low-level convergence can be stronger, facilitating secondary cloud formation and more vigorous precipitation processes. Evaporative cooling is more than two times stronger at low levels with higher CCN for the TOGA COARE case during the early stages of precipitation development. However, evaporative cooling is slightly stronger at lower levels with lower CCN for the PRESTORM case. The early formation of rain in the clean environment could allow for the formation of an earlier and stronger cold pool compared to a dirty environment. PRESTORM has a very dry environment and both large and small rain droplets can evaporate. Consequently, the cold pool is relatively weaker, and the system is relatively less intense with higher CCN. • Sensitivity tests are conducted to determine the impact of ice processes on aerosol-precipitation interaction. The results suggested that ice processes are crucial for suppressing precipitation due to high CCN for the PRESTORM case. More and smaller ice particles are generated in the dirty case and transported to the trailing stratiform region. This reduces the heavy convective rain and contributes to the weakening of the cold pool. Warm rain processes dominate the TOGA COARE case. Therefore, ice processes only play a secondary role in terms of aerosol-precipitation interaction. • Two of the three cloud systems presented in this paper formed a line structure (squall system). A 2D simulation, therefore, gives a good approximation to such a line of convective clouds. Since the real atmosphere is 3D, further 3D cloud-resolving simulations are needed to address aerosol-precipitation interactions. 4. REFERENCES Tao, W.-K., X. Li, A. Khain, T. Matsui, S. Lang, and J. Simpson, 2007: The role of atmospheric aerosol concentration on deep convective precipitation: Cloud-resolving model simulations. J. Geophy. Res., 112, D24S18, doi:10.1029/2007JD008728. All other references can be found in above paper. 5. Acknowledgements The GCE model is mainly supported by the NASA Headquarters Atmospheric Dynamics and Thermodynamics Program and the NASA Tropical Rainfall Measuring Mission (TRMM). The research was also supported by the Office of Science (BER), U. S. Department of Energy/Atmospheric Radiation Measurement (DOE/ARM) Interagency. The authors acknowledge NASA Goddard Space Flight Center for computer time used in this research.« less

Summertime observations of elevated levels of ultrafine particles in the high Arctic marine boundary layer

NASA Astrophysics Data System (ADS)

Burkart, Julia; Willis, Megan D.; Bozem, Heiko; Thomas, Jennie L.; Law, Kathy; Hoor, Peter; Aliabadi, Amir A.; Köllner, Franziska; Schneider, Johannes; Herber, Andreas; Abbatt, Jonathan P. D.; Leaitch, W. Richard

2017-05-01

Motivated by increasing levels of open ocean in the Arctic summer and the lack of prior altitude-resolved studies, extensive aerosol measurements were made during 11 flights of the NETCARE July 2014 airborne campaign from Resolute Bay, Nunavut. Flights included vertical profiles (60 to 3000 m above ground level) over open ocean, fast ice, and boundary layer clouds and fogs. A general conclusion, from observations of particle numbers between 5 and 20 nm in diameter (N5 - 20), is that ultrafine particle formation occurs readily in the Canadian high Arctic marine boundary layer, especially just above ocean and clouds, reaching values of a few thousand particles cm-3. By contrast, ultrafine particle concentrations are much lower in the free troposphere. Elevated levels of larger particles (for example, from 20 to 40 nm in size, N20 - 40) are sometimes associated with high N5 - 20, especially over low clouds, suggestive of aerosol growth. The number densities of particles greater than 40 nm in diameter (N > 40) are relatively depleted at the lowest altitudes, indicative of depositional processes that will lower the condensation sink and promote new particle formation. The number of cloud condensation nuclei (CCN; measured at 0.6 % supersaturation) are positively correlated with the numbers of small particles (down to roughly 30 nm), indicating that some fraction of these newly formed particles are capable of being involved in cloud activation. Given that the summertime marine Arctic is a biologically active region, it is important to better establish the links between emissions from the ocean and the formation and growth of ultrafine particles within this rapidly changing environment.

Field and Laboratory Studies of Atmospheric Organic Aerosol

NASA Astrophysics Data System (ADS)

Coggon, Matthew Mitchell

This thesis is the culmination of field and laboratory studies aimed at assessing processes that affect the composition and distribution of atmospheric organic aerosol. An emphasis is placed on measurements conducted using compact and high-resolution Aerodyne Aerosol Mass Spectrometers (AMS). The first three chapters summarize results from aircraft campaigns designed to evaluate anthropogenic and biogenic impacts on marine aerosol and clouds off the coast of California. Subsequent chapters describe laboratory studies intended to evaluate gas and particle-phase mechanisms of organic aerosol oxidation. The 2013 Nucleation in California Experiment (NiCE) was a campaign designed to study environments impacted by nucleated and/or freshly formed aerosol particles. Terrestrial biogenic aerosol with > 85% organic mass was observed to reside in the free troposphere above marine stratocumulus. This biogenic organic aerosol (BOA) originated from the Northwestern United States and was transported to the marine atmosphere during periodic cloud-clearing events. Spectra recorded by a cloud condensation nuclei counter demonstrated that BOA is CCN active. BOA enhancements at latitudes north of San Francisco, CA coincided with enhanced cloud water concentrations of organic species such as acetate and formate. Airborne measurements conducted during the 2011 Eastern Pacific Emitted Aerosol Cloud Experiment (E-PEACE) were aimed at evaluating the contribution of ship emissions to the properties of marine aerosol and clouds off the coast of central California. In one study, analysis of organic aerosol mass spectra during periods of enhanced shipping activity yielded unique tracers indicative of cloud-processed ship emissions (m/z 42 and 99). The variation of their organic fraction (f42 and f 99) was found to coincide with periods of heavy (f 42 > 0.15; f99 > 0.04), moderate (0.05 < f42 < 0.15; 0.01 < f99 < 0.04), and negligible (f42 < 0.05; f99 < 0.01) ship influence. Application of these conditions to all measurements conducted during E-PEACE demonstrated that a large fraction of cloud droplet (72%) and dry aerosol mass (12%) sampled in the California coastal study region was heavily or moderately influenced by ship emissions. Another study investigated the chemical and physical evolution of a controlled organic plume emitted from the R/V Point Sur. Under sunny conditions, nucleated particles composed of oxidized organic compounds contributed nearly an order of magnitude more cloud condensation nuclei (CCN) than less oxidized particles formed under cloudy conditions. The processing time necessary for particles to become CCN active was short ( 4 hr). Laboratory chamber experiments were also conducted to evaluate particle-phase processes influencing aerosol phase and composition. In one study, ammonium sulfate seed was coated with a layer of secondary organic aerosol (SOA) from toluene oxidation followed by a layer of SOA from α-pinene oxidation. The system exhibited different evaporative properties than ammonium sulfate seed initially coated with α-pinene SOA followed by a layer of toluene SOA. This behavior is consistent with a shell-and-core model and suggests limited mixing among different SOA types. Another study investigated the reactive uptake of isoprene epoxy diols (IEPOX) onto non-acidified aerosol. It was demonstrated that particle acidity has limited influence on organic aerosol formation onto ammonium sulfate seed, and that the chemical system is limited by the availability of nucleophiles such as sulfate. Flow tube experiments were conducted to examine the role of iron in the reactive uptake and chemical oxidation of glycolaldehyde. Aerosol particles doped with iron and hydrogen peroxide were mixed with gas-phase glycolaldehyde and photochemically aged in a custom-built flow reactor. Compared to particles free of iron, iron-doped aerosols significantly enhanced the oxygen to carbon (O/C) ratio of accumulated organic mass. The primary oxidation mechanism is suggested to be a combination of Fenton and photo-Fenton reactions which enhance particle-phase OH radical concentrations.

Time dependent charging of layer clouds in the global electric circuit

NASA Astrophysics Data System (ADS)

Zhou, Limin; Tinsley, Brian A.

2012-09-01

There is much observational data consistent with the hypothesis that the ionosphere-earth current density (Jz) in the global electric circuit, which is modulated by both solar activity and thunderstorm activity, affects atmospheric dynamics and cloud cover. One candidate mechanism involves Jz causing the accumulation of space charge on droplets and aerosol particles, that affects the rate of scavenging of the latter, notably those of Cloud Condensation Nuclei (CCN) and Ice Forming Nuclei (IFN) (Tinsley, 2008, 2010). Space charge is the difference, per unit volume, between total positive and total negative electrical charge that is on droplets, aerosol particles (including the CCN and IFN) and air ions. The cumulative effects of the scavenging in stratiform clouds and aerosol layers in an air mass over the lifetime of the aerosol particles of 1-10 days affects the concentration and size distribution of the CCN, so that in subsequent episodes of cloud formation (including deep convective clouds) there can be effects on droplet size distribution, coagulation, precipitation processes, and even storm dynamics.Because the time scales for charging for some clouds can be long compared to cloud lifetimes, the amount of charge at a given time, and its effect on scavenging, depend more on the charging rate than on the equilibrium charge that would eventually be attained. To evaluate this, a new time-dependent charging model has been developed. The results show that for typical altostratus clouds with typical droplet radii 10 μm and aerosol particles of radius of 0.04 μm, the time constant for charging in response to a change in Jz is about 800 s, which is comparable to cloud formation and dissipation timescales for some cloud situations. The charging timescale is found to be strong functions of altitude and aerosol concentration, with the time constant for droplet charging at 2 km in air with a high concentration of aerosols being about an hour, and for clouds at 10 km in clean air being about a minute. The charging timescale is also a strong function of droplet size, with the rate for 15 μm radii droplets being about 70% longer than that for 10 μm droplets, and the rate for 5 μm radii droplets being about 50% smaller. The equilibrium charges accumulated on droplets ranged from tens to hundreds of elementary charges, which is comparable to observed values, and to vary approximately directly with Jz and inversely with the ion production rate q, which is due to the Galactic Cosmic Ray (GCR) flux and depends strongly on altitude.For the case of Jz varying directly with q, which to some extent is the case during Forbush decreases of the GCR flux, the effects on the equilibrium charge tend to cancel. In one run with the model, both q and Jz were decreased by 30%. There was little change in equilibrium charge, but the timescale for charging increased by about 40%, or equivalently, the rate of charging decreased by about 40%. Thus, for exploring the hypothesis that space charge provides a link between GCR (and other inputs that modulate Jz) and changes in clouds and atmospheric dynamics, it is necessary to consider variations in the rate of charging. The present work is intended to provide illustrative examples of time dependent charging for several different types of layer clouds.

An aerosol activation metamodel of v1.2.0 of the pyrcel cloud parcel model: development and offline assessment for use in an aerosol–climate model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rothenberg, Daniel; Wang, Chien

We describe an emulator of a detailed cloud parcel model which has been trained to assess droplet nucleation from a complex, multimodal aerosol size distribution simulated by a global aerosol–climate model. The emulator is constructed using a sensitivity analysis approach (polynomial chaos expansion) which reproduces the behavior of the targeted parcel model across the full range of aerosol properties and meteorology simulated by the parent climate model. An iterative technique using aerosol fields sampled from a global model is used to identify the critical aerosol size distribution parameters necessary for accurately predicting activation. Across the large parameter space used tomore » train them, the emulators estimate cloud droplet number concentration (CDNC) with a mean relative error of 9.2% for aerosol populations without giant cloud condensation nuclei (CCN) and 6.9% when including them. Versus a parcel model driven by those same aerosol fields, the best-performing emulator has a mean relative error of 4.6%, which is comparable with two commonly used activation schemes also evaluated here (which have mean relative errors of 2.9 and 6.7%, respectively). We identify the potential for regional biases in modeled CDNC, particularly in oceanic regimes, where our best-performing emulator tends to overpredict by 7%, whereas the reference activation schemes range in mean relative error from -3 to 7%. The emulators which include the effects of giant CCN are more accurate in continental regimes (mean relative error of 0.3%) but strongly overestimate CDNC in oceanic regimes by up to 22%, particularly in the Southern Ocean. Finally, the biases in CDNC resulting from the subjective choice of activation scheme could potentially influence the magnitude of the indirect effect diagnosed from the model incorporating it.« less

An aerosol activation metamodel of v1.2.0 of the pyrcel cloud parcel model: development and offline assessment for use in an aerosol–climate model

DOE PAGES

Rothenberg, Daniel; Wang, Chien

2017-04-27

We describe an emulator of a detailed cloud parcel model which has been trained to assess droplet nucleation from a complex, multimodal aerosol size distribution simulated by a global aerosol–climate model. The emulator is constructed using a sensitivity analysis approach (polynomial chaos expansion) which reproduces the behavior of the targeted parcel model across the full range of aerosol properties and meteorology simulated by the parent climate model. An iterative technique using aerosol fields sampled from a global model is used to identify the critical aerosol size distribution parameters necessary for accurately predicting activation. Across the large parameter space used tomore » train them, the emulators estimate cloud droplet number concentration (CDNC) with a mean relative error of 9.2% for aerosol populations without giant cloud condensation nuclei (CCN) and 6.9% when including them. Versus a parcel model driven by those same aerosol fields, the best-performing emulator has a mean relative error of 4.6%, which is comparable with two commonly used activation schemes also evaluated here (which have mean relative errors of 2.9 and 6.7%, respectively). We identify the potential for regional biases in modeled CDNC, particularly in oceanic regimes, where our best-performing emulator tends to overpredict by 7%, whereas the reference activation schemes range in mean relative error from -3 to 7%. The emulators which include the effects of giant CCN are more accurate in continental regimes (mean relative error of 0.3%) but strongly overestimate CDNC in oceanic regimes by up to 22%, particularly in the Southern Ocean. Finally, the biases in CDNC resulting from the subjective choice of activation scheme could potentially influence the magnitude of the indirect effect diagnosed from the model incorporating it.« less

Probing aerosol indirect effect on deep convection using idealized cloud-resolving simulations with parameterized large-scale dynamics.

NASA Astrophysics Data System (ADS)

Anber, U.; Wang, S.; Gentine, P.; Jensen, M. P.

2017-12-01

A framework is introduced to investigate the indirect impact of aerosol loading on tropical deep convection using 3-dimentional idealized cloud-system resolving simulations with coupled large-scale circulation. The large scale dynamics is parameterized using a spectral weak temperature gradient approximation that utilizes the dominant balance in the tropics between adiabatic cooling and diabatic heating. Aerosol loading effect is examined by varying the number concentration of nuclei (CCN) to form cloud droplets in the bulk microphysics scheme over a wide range from 30 to 5000 without including any radiative effect as the radiative cooling is prescribed at a constant rate, to isolate the microphysical effect. Increasing aerosol number concentration causes mean precipitation to decrease monotonically, despite the increase in cloud condensates. Such reduction in precipitation efficiency is attributed to reduction in the surface enthalpy fluxes, and not to the divergent circulation, as the gross moist stability remains unchanged. We drive a simple scaling argument based on the moist static energy budget, that enables a direct estimation of changes in precipitation given known changes in surfaces enthalpy fluxes and the constant gross moist stability. The impact on cloud hydrometers and microphysical properties is also examined and is consistent with the macro-physical picture.

Sea Spray Aerosol Production over the North Atlantic

NASA Astrophysics Data System (ADS)

Bates, T. S.; Quinn, P.

2017-12-01

Breaking waves on the ocean surface generate air bubbles that scavenge organic matter from the surrounding seawater. When injected into the atmosphere, these bubbles burst, yielding sea spray aerosol (SSA), a mixture of organic and inorganic compounds with the organic matter enriched relative to seawater. SSA mass is well documented as the dominant component of aerosol light scattering over the remote oceans. The importance of SSA number to marine boundary layer cloud condensation nuclei (CCN) is much less certain. During the Western Atlantic Climate Study cruises (WACS-1 - August 2012 and WACS-2 - May-June 2014) and the North Atlantic Aerosols and Marine Ecosystem Study cruises (NAAMES-1 - November 2015, NAAMES-2 - May 2016, and NAAMES-3 - September 2017), we generated and measured freshly emitted SSA using the Sea Sweep SSA generator. During the 2017 cruise we also generated SSA with a Marine Aerosol Reference Tank (MART). Using the data generated on these 5 cruises and a large database of remote marine boundary layer aerosol measurements we will address three questions during this presentation: 1 - Do phytoplankton ecosystems affect the organic enrichment of freshly emitted SSA?, 2 - Do plankton ecosystems affect the number production flux of SSA?, and 3 - Is SSA a significant source of atmospheric CCN?

Examining Model Atmospheric Particles Inside and Out

NASA Astrophysics Data System (ADS)

Wingen, L. M.; Zhao, Y.; Fairhurst, M. C.; Perraud, V. M.; Ezell, M. J.; Finlayson-Pitts, B. J.

2017-12-01

Atmospheric particles scatter incoming solar radiation and act as cloud condensation nuclei (CCN), thereby directly and indirectly affecting the earth's radiative balance and reducing visibility. These atmospheric particles may not be uniform in composition. Differences in the composition of a particle's outer surface from its core can arise during particle growth, (photo)chemical aging, and exchange of species with the gas phase. The nature of the surface on a molecular level is expected to impact growth mechanisms as well as their ability to act as CCN. Model laboratory particle systems are explored using direct analysis in real time-mass spectrometry (DART-MS), which is sensitive to surface composition, and contrasted with average composition measurements using high resolution, time-of-flight aerosol mass spectrometry (HR-ToF-AMS). Results include studies of the heterogeneous reactions of amines with solid dicarboxylic acid particles, which are shown to generate aminium dicarboxylate salts at the particle surface, leaving an unreacted core. Combination of both mass spectrometric techniques reveals a trend in reactivity of C3-C7 dicarboxylic acids with amines and allows calculation of the DART probe depth into the particles. The results of studies on additional model systems that are currently being explored will also be reported.

Semi-continuous measurement and characteristics of water-soluble organic carbon and ions of PM2.5 aerosol with PILS-TOC-IC in Baengnyeong Island

NASA Astrophysics Data System (ADS)

Kang, S.; Kim, K.; Park, G.; Ban, J.; Park, D.; Bae, M. S.; Shin, H. J.; Lee, M.; Seo, Y.; Choi, J.; Jung, D.; Seo, S.; Lee, T.; Kim, D. S.

2016-12-01

Aerosols have an important effect from scattering and absorbing the solar energy and indirectly by acting as cloud condensation nuclei and also some of the effects of aerosols are reduction in visibility, deterioration of human health, and deposition of pollutants to ecosystems. In various experimental results were showed that organic compounds have an important fraction from 10 to 70% of the total aerosol mass. Organic carbon contains water-soluble organic carbon (WSOC) and water insoluble organic carbon. WSOC are involved in the most unknown liquid-phase chemistry of wet aerosol and clouds. It is also worked as cloud condensation nuclei (CCN). Formation of secondary organic aerosol by chemical reaction of hydrocarbon compounds is a source of main pollution of WSOC compounds. Study of pollution source of WSOC is important method for creation process of secondary organic aerosol that completely has not studied.Analysis of WSOC is important and need to real-time measurement system for definition of chemical cause and sources. In this study, Particle-into-liquid sampler (PILS) coupled with total organic carbon (TOC) analyser and ion chromatography (PILS-TOC-IC), was used for semi-continuous measurement of WSOC and ionic compounds of PM2.5 during April-June 2016 at Baengnyeong Island Atmospheric Research Center, operated by the Korea National Institute of Environmental Research (NIER). PILS-TOC-IC can provide chemical information about real-time changes from ions composition and concentrations of WSOC and ionic compounds.

Lagrangian Particle Tracking Simulation for Warm-Rain Processes in Quasi-One-Dimensional Domain

NASA Astrophysics Data System (ADS)

Kunishima, Y.; Onishi, R.

2017-12-01

Conventional cloud simulations are based on the Euler method and compute each microphysics process in a stochastic way assuming infinite numbers of particles within each numerical grid. They therefore cannot provide the Lagrangian statistics of individual particles in cloud microphysics (i.e., aerosol particles, cloud particles, and rain drops) nor discuss the statistical fluctuations due to finite number of particles. We here simulate the entire precipitation process of warm-rain, with tracking individual particles. We use the Lagrangian Cloud Simulator (LCS), which is based on the Euler-Lagrangian framework. In that framework, flow motion and scalar transportation are computed with the Euler method, and particle motion with the Lagrangian one. The LCS tracks particle motions and collision events individually with considering the hydrodynamic interaction between approaching particles with a superposition method, that is, it can directly represent the collisional growth of cloud particles. It is essential for trustworthy collision detection to take account of the hydrodynamic interaction. In this study, we newly developed a stochastic model based on the Twomey cloud condensation nuclei (CCN) activation for the Lagrangian tracking simulation and integrated it into the LCS. Coupling with the Euler computation for water vapour and temperature fields, the initiation and condensational growth of water droplets were computed in the Lagrangian way. We applied the integrated LCS for a kinematic simulation of warm-rain processes in a vertically-elongated domain of, at largest, 0.03×0.03×3000 (m3) with horizontal periodicity. Aerosol particles with a realistic number density, 5×107 (m3), were evenly distributed over the domain at the initial state. Prescribed updraft at the early stage initiated development of a precipitating cloud. We have confirmed that the obtained bulk statistics fairly agree with those from a conventional spectral-bin scheme for a vertical column domain. The centre of the discussion will be the Lagrangian statistics which is collected from the individual behaviour of the tracked particles.

Long-term observation of aerosol cloud relationships in the Mid-Atlantic region

NASA Astrophysics Data System (ADS)

Li, S.; Joseph, E.; Min, Q.; Yin, B.

2013-12-01

Long-term ground-based observations of aerosol and cloud properties derived from measurements of Multifilter Rotating Shadow Band Radiometer and microwave radiometer at an atmospheric measurement field station in the Baltimore-Washington corridor operated by Howard University are used to examine the temporal variation of aerosol and cloud properties and moreover aerosol indirect effect on clouds. Through statistical analysis of five years (from 2006 to 2010) of these observations, the proportion of polluted cases is found larger in 2006 and 2007 and the proportion of optically thick clouds cases is also larger in 2006 and 2007 than that in 2008, 2009 and 2010. Both the mean aerosol optical depth (AOD) and cloud optical depth (COD) are observed decreasing from 2006 to 2010 but there is no obvious trend observed on cloud liquid water path (LWP). Because of the limit of AOD retrievals under cloudy conditions surface measurements of fine particle particulate matter 2.5 (PM2.5) were used for assessing aerosol indirect effect. A positive relationship between LWP and cloud droplets effective radius (Re) and a negative relationship between PM2.5 and Re are observed based on a stringent case selection method which is used to reduce the uncertainties from retrieval and meteorological impacts. The total 5 years summer time observations are segregated according to the value of PM2.5. Examination of distributions of COD, cloud condensation nuclei (CCN), cloud droplets effective radius and LWP under polluted and pristine conditions further confirm that the high aerosol loading decreases cloud droplets effective radius and increases cloud optical depth.

Simulating southwestern U.S. desert dust influences on supercell thunderstorms

NASA Astrophysics Data System (ADS)

Lerach, David G.; Cotton, William R.

2018-05-01

Three-dimensional numerical simulations were performed to evaluate potential southwestern U.S. dust indirect microphysical and direct radiative impacts on a real severe storms outbreak. Increased solar absorption within the dust plume led to modest increases in pre-storm atmospheric stability at low levels, resulting in weaker convective updrafts and less widespread precipitation. Dust microphysical impacts on convection were minor in comparison, due in part to the lofted dust concentrations being relatively few in number when compared to the background (non-dust) aerosol population. While dust preferentially serving as cloud condensation nuclei (CCN) versus giant CCN had opposing effects on warm rain production, both scenarios resulted in ample supercooled water and subsequent glaciation aloft, yielding larger graupel and hail. Associated latent heating from condensation and freezing contributed little to overall updraft invigoration. With reduced rain production overall, the simulations that included dust effects experienced slightly reduced grid-cumulative precipitation and notably warmer and spatially smaller cold pools. Dust serving as ice nucleating particles did not appear to play a significant role. The presence of dust ultimately reduced the number of supercells produced but allowed for supercell evolution characterized by consistently higher values of relative vertical vorticity within simulated mesocyclones. Dust radiative and microphysical effects were relatively small in magnitude when compared to those from altering the background convective available potential energy and vertical wind shear. It is difficult to generalize such findings from a single event, however, due to a number of case-specific environmental factors. These include the nature of the low-level moisture advection and characteristics of the background aerosol distribution.

Toward the Characterization of Mixed-Phase Clouds Using Remote Sensing

NASA Astrophysics Data System (ADS)

Andronache, C.

2015-12-01

Mixed-phase clouds consist of a mixture of ice particles and liquid droplets at temperatures below 0 deg C. They are present in all seasons in many regions of the world, account for about 30% of the global cloud coverage, and are linked to cloud electrification and aircraft icing. The mix of ice particles, liquid droplets, and water vapor is unstable, and such clouds are thought to have a short lifetime. A characteristic parameter is the phase composition of mixed-phase clouds. It affects the cloud life cycle and the rate of precipitation. This parameter is important for cloud parameters retrievals by radar, lidar, and satellite and is relevant for climate modeling. The phase transformation includes the remarkable Wegener-Bergeron-Findeisen (WBF) process. The direction and the rate of the phase transformations depend on the local thermodynamic and microphysical properties. Cloud condensation nuclei (CCN) and ice nuclei (IN) particles determine to a large extent cloud microstructure and the dynamic response of clouds to aerosols. The complexity of dynamics and microphysics involved in mixed-phase clouds requires a set of observational and modeling tools that continue to be refined. Among these techniques, the remote sensing methods provide an increasing number of parameters, covering large regions of the world. Thus, a series of studies were dedicated to stratiform mixed-phase clouds revealing longer lifetime than previously thought. Satellite data and aircraft in situ measurements in deep convective clouds suggest that highly supercooled water often occurs in vigorous continental convective storms. In this study, we use cases of convective clouds to discuss the feasibility of mixed-phase clouds characterization and potential advantages of remote sensing.

What have we learned from HaChi (HAZE IN CHINA) project?

NASA Astrophysics Data System (ADS)

Zhao, Chunsheng; Wiedensohler, Alfred

2016-04-01

HaChi (Haze in China) project, a joint research between Chinese NSFC and German DFG, focuses on investigating the aerosol hygroscopic properties in the North China Plain and their relationships to aerosol optics, radiation, cloud physics and ozone photochemistry. As we know, Eastern China has suffered from severe pollution caused by large concentrations of aerosol particles resulting from emissions from fossil fuel and biomass burning, transportation and some other combustion sources. Low visibility events are frequently encountered and mainly accompanied with haze as a result of either high aerosol loading or the strong hygroscopic growth of the aerosol particles. Especially at relative humidities between 90 and 99%, the aerosol particles grow exponentially. The hygroscopic behaviors at relative humidities close to 100% are also strongly linked to the particles ability to grow into cloud droplets at supersaturation. In my talk, I will present an overview of the up to date results from a serial of intensive and comprehensive field campaigns conducted at the sites of Wuqing and Xianghe, China, between 2009 and 2014. The measurements of the ambient aerosol hygroscopic properties at high RH between 90 and 98.5% are reported first. These in situ field measurements of atmospheric aerosol are unique with respect to their high RH range and especially of importance to better understand the widespread anthropogenic haze over the North China Plain. Then I will introduce the methods for calculating of aerosol hygroscopicity and their parameterization schemes derived from size-segregated chemical composition and the light scattering enhancement factor measurements in the North China Plain. A new method was proposed to retrieve the ratio of the externally mixed light absorbing carbon mass to the total mass of light absorbing carbon. A new parameterization scheme of light extinction for low visibilities on hazy days is proposed based on visibility, relative humidity, aerosol hygroscopic growth factors and particle number size distributions measured. Cloud Condensation Nuclei (CCN) closure study is conducted with bulk CCN number concentration and calculated CCN number concentration based on the aerosol number size distribution and size-resolved activation properties. An evaluation of various methods for CCN parameterization is presented based on in situ measurements of aerosol activation properties within HaChi project. Hygroscopic growth of aerosol particles can significantly affect their single-scattering albedo, and consequently alters the aerosol effect on tropospheric photochemistry. At last, I will introduce the results on the relationship between aerosol hygroscopic properties and aerosol radiation including impacts of aerosol hygroscopic growth on the NO2 photolysis rate coefficient and the estimation of direct aerosol radiative effect in the North China Plan.

The Relationship Between Latent Heating, Vertical Velocity, and Precipitation Processes: the Impact of Aerosols on Precipitation in Organized Deep Convective Systems

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Li, Xiaowen

2016-01-01

A high-resolution, two-dimensional cloud-resolving model with spectral-bin microphysics is used to study the impact of aerosols on precipitation processes in both a tropical oceanic and a midlatitude continental squall line with regard to three processes: latent heating (LH), cold pool dynamics, and ice microphysics. Evaporative cooling in the lower troposphere is found to enhance rainfall in low cloud condensation nuclei (CCN) concentration scenarios in the developing stages of a midlatitude convective precipitation system. In contrast, the tropical case produced more rainfall under high CCN concentrations. Both cold pools and low-level convergence are stronger for those configurations having enhanced rainfall. Nevertheless, latent heat release is stronger (especially after initial precipitation) in the scenarios having more rainfall in both the tropical and midlatitude environment. Sensitivity tests are performed to examine the impact of ice and evaporative cooling on the relationship between aerosols, LH, and precipitation processes. The results show that evaporative cooling is important for cold pool strength and rain enhancement in both cases. However, ice microphysics play a larger role in the midlatitude case compared to the tropics. Detailed analysis of the vertical velocity-governing equation shows that temperature buoyancy can enhance updraftsdowndrafts in the middlelower troposphere in the convective core region; however, the vertical pressure gradient force (PGF) is of the same order and acts in the opposite direction. Water loading is small but of the same order as the net PGF-temperature buoyancy forcing. The balance among these terms determines the intensity of convection.

Aerosols and Aerosol-related haze forecasting in China Meteorological Adminstration

NASA Astrophysics Data System (ADS)

Zhou, Chunhong; Zhang, Xiaoye; Gong, Sunling; Liu, Hongli; Xue, Min

2017-04-01

CMA Unified Atmospheric Chemistry Environmental Forecasting System (CUACE) is a unified numerical chemical weather forecasting system with BC, OC, Sulfate, Nitrate, Ammonia, Dust and Sea-Salt aerosols and their sources, gas to particle processes, SOA, microphysics and transformation. With an open interface, CUACE has been online coupled to mesoscale model MM5 and the new NWP system GRAPES (Global/Regional Assimilation and Prediction Enhanced System)min CMA. With Chinese Emissions from Cao and Zhang(2012 and 2013), a forecasting system called CUACE/Haze-fog has been running in real time in CMA and issue 5-days PM10, O3 and Visibility forecasts. A comprehensive ACI scheme has also been developed in CUACE Calculated by a sectional aerosol activation scheme based on the information of size and mass from CUACE and the thermal-dynamic and humid states from the weather model at each time step, the cloud condensation nuclei (CCN) is fed online interactively into a two-moment cloud scheme (WDM6) and a convective parameterization to drive the cloud physics and precipitation formation processes. The results show that interactive aerosols with the WDM6 in CUACE obviously improve the clouds properties and the precipitation, showing 24% to 48% enhancements of TS scoring for 6-h precipitation .

Variability of and Factors Controlling Precipitation Production in Shallow Cumulus - Results from the ARM Eastern North Atlantic Site

NASA Astrophysics Data System (ADS)

Luke, E. P.; Kollias, P.

2016-12-01

Shallow cumulus clouds are by far the most frequently observed cloud type over the Earth's oceans and frequently produce warm rain. However, quantitative rainfall estimates from these clouds are challenging to acquire from satellites due to their small horizontal scale. Here, two years of observations from the US Department of Energy Atmospheric Radiation Measurement Program (ARM) Eastern North Atlantic (ENA) site located on Graciosa Island in the Azores are used to characterize the frequency, intensity, and fractional coverage of shallow cumulus precipitation. The analyzed dataset is the most comprehensive of its type, considering both its temporal extent and the sophistication of the ground-based observations. The precipitation rate at the base of shallow cumulus is estimated using combined radar-lidar observations and the rain retrievals are compared to the rainfall measurements available at the ground by optical disdrometers. Using synergy between surfaced-based observations of aerosols and thermodynamic soundings, the vertical structure of the Marine Boundary Layer and the temporal variability of the cloud condensation nuclei (CCN) number concentration are determined. The observed variability in shallow cumulus precipitation is examined in relation to the variability of the large-scale environment as captured by the humidity profile, the magnitude of the low-level horizontal winds and aerosol loading.

Aerosols in polluted versus nonpolluted air masses Long-range transport and effects on clouds

NASA Technical Reports Server (NTRS)

Pueschel, R. F.; Van Valin, C. C.; Castillo, R. C.; Kadlecek, J. A.; Ganor, E.

1986-01-01

To assess the influence of anthropogenic aerosols on the physics and chemistry of clouds in the northeastern United States, aerosol and cloud-drop size distributions, elemental composition of aerosols as a function of size, and ionic content of cloud water were measured on Whiteface Mountain, NY, during the summers of 1981 and 1982. In several case studies, the data were cross-correlated with different air mass types - background continental, polluted continental, and maritime - that were advected to the sampling site. The results are the following: (1) Anthropogenic sources hundreds of kilometers upwind cause the small-particle (accumulation) mode number to increase from hundreds of thousands per cubic centimeter and the mass loading to increase from a few to several tens of micrograms per cubic meter, mostly in the form of sulfur aerosols. (2) A significant fraction of anthropogenic sulfur appears to act as cloud condensation nuclei (CCN) to affect the cloud drop concentration. (3) Clouds in Atlantic maritime air masses have cloud drop spectra that are markedly different from those measured in continental clouds. The drop concentration is significantly lower, and the drop size spectra are heavily skewed toward large drops. (4) Effects of anthropogenic pollutants on cloud water ionic composition are an increase of nitrate by a factor of 50, an increase of sulfate by more than one order of magnitude, and an increase of ammonium ion by a factor of 7. The net effect of the changes in ionic concentrations is an increase in cloud water acidity. An anion deficit even in maritime clouds suggests an unknown, possibly biogenic, source that could be responsible for a pH below neutral, which is frequently observed in nonpolluted clouds.

Potential of polarization lidar to provide profiles of CCN- and INP-relevant aerosol parameters

NASA Astrophysics Data System (ADS)

Mamouri, R. E.; Ansmann, A.

2015-12-01

We investigate the potential of polarization lidar to provide vertical profiles of aerosol parameters from which cloud condensation nucleus (CCN) and ice nucleating particle (INP) number concentrations can be estimated. We show that height profiles of number concentrations of aerosol particles with radius > 50 nm (APC50, reservoir of favorable CCN) and with radius > 250 nm (APC250, reservoir of favorable INP), as well as profiles of the aerosol particle surface area concentration (ASC, used in INP parameterization) can be retrieved from lidar-derived aerosol extinction coefficients (AEC) with relative uncertainties of a factor of around 2 (APC50), and of about 25-50 % (APC250, ASC). Of key importance is the potential of polarization lidar to identify mineral dust particles and to distinguish and separate the aerosol properties of basic aerosol types such as mineral dust and continental pollution (haze, smoke). We investigate the relationship between AEC and APC50, APC250, and ASC for the main lidar wavelengths of 355, 532 and 1064 nm and main aerosol types (dust, pollution, marine). Our study is based on multiyear Aerosol Robotic Network (AERONET) photometer observations of aerosol optical thickness and column-integrated particle size distribution at Leipzig, Germany, and Limassol, Cyprus, which cover all realistic aerosol mixtures of continental pollution, mineral dust, and marine aerosol. We further include AERONET data from field campaigns in Morocco, Cabo Verde, and Barbados, which provide pure dust and pure marine aerosol scenarios. By means of a simple relationship between APC50 and the CCN-reservoir particles (APCCCN) and published INP parameterization schemes (with APC250 and ASC as input) we finally compute APCCCN and INP concentration profiles. We apply the full methodology to a lidar observation of a heavy dust outbreak crossing Cyprus with dust up to 8 km height and to a case during which anthropogenic pollution dominated.

Development and impact of hooks of high droplet concentration on remote southeast Pacific stratocumulus

NASA Astrophysics Data System (ADS)

George, R. C.; Wood, R.; Bretherton, C. S.; Painter, G.

2013-07-01

Over the southeastern Pacific (SEP), droplet concentration (Nd) in the typically unpolluted marine stratocumulus west of 80° W (> 1000 km offshore) is periodically strongly enhanced in zonally elongated "hook"-shaped features that increase albedo. Here, we examine three hook events using the chemistry version of the Weather Research and Forecasting model (WRF-Chem) with 14 km horizontal resolution, satellite data, and aircraft data from the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx). A particularly strong hook yields insights into the development, decay, and radiative impact of these features. Hook development occurs with Nd increasing to polluted levels over the remote ocean primarily due to entrainment of cloud condensation nuclei (CCN) from the lower free troposphere (FT). The feature advects northwestward until the FT CCN source is depleted, after which Nd decreases over a few days due to precipitation and dilution. The model suggests that the FT CCN source supplying the hook consists of high concentrations of small accumulation-mode aerosols that contribute a relatively small amount of aerosol mass to the MBL, in agreement with near-coast VOCALS measurements of polluted layers in the FT. The aerosol particles in this hook originate mainly from a pulse of offshore flow that transports Santiago-region (33-35° S) emissions to the remote marine FT. To provide pollution CCN that can sustain hooks, the FT transport of pollution plumes to the remote ocean requires strong, deep offshore flow. Such flow is favored by a trough approaching the South American coast and a southeastward shift of the climatological subtropical high-pressure system. The model simulations show precipitation suppression in the hook and a corresponding increase in liquid water path (LWP) compared with a simulation without anthropogenic sources. LWP also increases as the hook evolves over time due to increasing stability and decreasing subsidence. WRF-Chem suggests that dimethyl sulfide (DMS) significantly influences the aerosol number and size distributions in a hook, but that hooks do not form without FT CCN. The Twomey effect contributes ~ 50-70% of the albedo increase due to the presence of the hook, while secondary aerosol indirect effects and meteorological influences also contribute significantly. The source of hook aerosols is difficult to determine with the available observations alone. The model provides further explanation of the factors influencing hook formation. Two other weaker hooks during VOCALS-REx are not as well simulated but are also associated with FT offshore flow near Santiago. Hooks demonstrate the importance of free-tropospheric transport of aerosols in modulating the droplet concentration in the southeastern Pacific stratocumulus deck, and present a formidable challenge to simulate accurately in large-scale models.

Development and Initial Testing of a Multi-Sensor Platform for Cloud-Aerosol Interactions in the Lower Troposphere

NASA Astrophysics Data System (ADS)

Nehrir, A. R.; Hoffman, D. S.; Repasky, K. S.; Todt, B.; Sharpe, T.; Half Red, C.; Carlsten, J. L.

2009-12-01

Coupled atmospheric components of the lower troposphere including aerosols and water vapor have a large affect on the chemical processes that drive the earth’s complex climate system. Aerosols can affect the earth’s global radiation budget directly by absorbing or reflecting incoming solar radiation, and indirectly by changing the microphysical properties of clouds by serving as cloud condensation nuclei (CCN). An increase in CCN results in higher cloud droplet concentration which has been shown to suppress drizzle formation and lead to more reflective clouds. The changes in the cloud microphysical structure due to the interaction of aerosols and water vapor result in more incoming solar radiation being reflected back into space, leading to a net negative radiative forcing in the global radiation budget. The uncertainty in this radiative forcing reflects the uncertainty in the understanding of the aerosol indirect effect and its role in the climate system. To better understand the aerosol direct and indirect effects, lidar measurements of aerosol properties and water vapor distributions can provide important information to enhance our understanding of the role of aerosols in the climate system. The LIDAR group at Montana State University has initiated a program to simultaneously study aerosols, water vapor, and cloud formation with high spatial and temporal resolution using both active and passive sensors. Aerosol distributions and radiative properties are currently being studied with a two-color LIDAR system at 1064 and 532 nm. In addition, a three color, high spectral resolution LIDAR system at 1064,532, and 355 nm has also been developed and is starting to take initial data. Daytime and nighttime boundary layer water vapor number density profiles are also currently being studied with an external cavity diode oscillator/diode amplifier based micro-pulsed differential absorption lidar (DIAL) instrument at the 830 nm water vapor absorption band. Cloud formation studies are being conducted by a simultaneous, spatially correlated digital sky imaging camera system where aerosol loading and water vapor distributions are monitored as a function of lateral distance to clouds. Furthermore, a commercially purchased sun/sky scanning solar radiometer (CIMEL 318) as part of the NASA run AERONET program is also being used to study aerosol loading and radiative transfer through the atmosphere. A brief description of these instruments will be presented as well as initial simultaneous results showing correlated data between lower tropospheric aerosols and boundary layer water vapor distributions over extended periods if time.

Improving aerosol interaction with clouds and precipitation in a regional chemical weather modeling system

NASA Astrophysics Data System (ADS)

Zhou, C.; Zhang, X.; Gong, S.; Wang, Y.; Xue, M.

2016-01-01

A comprehensive aerosol-cloud-precipitation interaction (ACI) scheme has been developed under a China Meteorological Administration (CMA) chemical weather modeling system, GRAPES/CUACE (Global/Regional Assimilation and PrEdiction System, CMA Unified Atmospheric Chemistry Environment). Calculated by a sectional aerosol activation scheme based on the information of size and mass from CUACE and the thermal-dynamic and humid states from the weather model GRAPES at each time step, the cloud condensation nuclei (CCN) are interactively fed online into a two-moment cloud scheme (WRF Double-Moment 6-class scheme - WDM6) and a convective parameterization to drive cloud physics and precipitation formation processes. The modeling system has been applied to study the ACI for January 2013 when several persistent haze-fog events and eight precipitation events occurred.

The results show that aerosols that interact with the WDM6 in GRAPES/CUACE obviously increase the total cloud water, liquid water content, and cloud droplet number concentrations, while decreasing the mean diameters of cloud droplets with varying magnitudes of the changes in each case and region. These interactive microphysical properties of clouds improve the calculation of their collection growth rates in some regions and hence the precipitation rate and distributions in the model, showing 24 to 48 % enhancements of threat score for 6 h precipitation in almost all regions. The aerosols that interact with the WDM6 also reduce the regional mean bias of temperature by 3 °C during certain precipitation events, but the monthly means bias is only reduced by about 0.3 °C.

Vertical profiling of aerosol particles and trace gases over the central Arctic Ocean during summer

NASA Astrophysics Data System (ADS)

Kupiszewski, P.; Leck, C.; Tjernström, M.; Sjogren, S.; Sedlar, J.; Graus, M.; Müller, M.; Brooks, B.; Swietlicki, E.; Norris, S.; Hansel, A.

2013-12-01

Unique measurements of vertical size-resolved aerosol particle concentrations, trace gas concentrations and meteorological data were obtained during the Arctic Summer Cloud Ocean Study (ASCOS, www.ascos.se), an International Polar Year project aimed at establishing the processes responsible for formation and evolution of low-level clouds over the high Arctic summer pack ice. The experiment was conducted from on board the Swedish icebreaker Oden, and provided both ship- and helicopter-based measurements. This study focuses on the vertical helicopter profiles and onboard measurements obtained during a three-week period when Oden was anchored to a drifting ice floe, and sheds light on the characteristics of Arctic aerosol particles and their distribution throughout the lower atmosphere. Distinct differences in aerosol particle characteristics within defined atmospheric layers are identified. Within the lowermost couple hundred metres, transport from the marginal ice zone (MIZ), condensational growth and cloud processing develop the aerosol population. During two of the four representative periods defined in this study, such influence is shown. At altitudes above about 1 km, long-range transport occurs frequently. However, only infrequently does large-scale subsidence descend such air masses to become entrained into the mixed layer in the high Arctic, and therefore long-range transport plumes are unlikely to directly influence low-level stratiform cloud formation. Nonetheless, such plumes can influence the radiative balance of the planetary boundary layer (PBL) by influencing formation and evolution of higher clouds, as well as through precipitation transport of particles downwards. New particle formation was occasionally observed, particularly in the near-surface layer. We hypothesize that the origin of these ultrafine particles could be in biological processes, both primary and secondary, within the open leads between the pack ice and/or along the MIZ. In general, local sources, in combination with upstream boundary-layer transport of precursor gases from the MIZ, are considered to constitute the origin of cloud condensation nuclei (CCN) particles and thus be of importance for the formation of interior Arctic low-level clouds during summer, and subsequently, through cloud influences, for the melting and freezing of sea ice.

Sea Spray Aerosol Production in the North Atlantic: A Comparison from 4 Cruises in 3 Seasons

NASA Astrophysics Data System (ADS)

Bates, T. S.; Quinn, P.

2016-12-01

Breaking waves on the ocean surface generate air bubbles that scavenge organic matter from the surrounding seawater. When injected into the atmosphere, these bubbles burst, yielding sea spray aerosol (SSA), a mixture of organic and inorganic compounds with the organic matter enriched relative to seawater. SSA mass is well documented as the dominant component of aerosol light scattering over the remote oceans. The importance of SSA number to marine boundary layer cloud condensation nuclei (CCN) is much less certain. During the Western Atlantic Climate Study cruises (WACS-1 - August 2012 and WACS-2 - May-June 2014) and the North Atlantic Aerosols and Marine Ecosystem Study cruises (NAAMES-1 - November 2015, NAAMES-2 - May 2016, and NAAMES-3 - September 2017), we generated and measured freshly emitted SSA using the Sea Sweep SSA generator. During the 2017 cruise we also generated SSA with a Marine Aerosol Reference Tank (MART). Using the data generated on these 5 cruises and a large database of remote marine boundary layer aerosol measurements we will address three questions during this presentation: 1 - Do phytoplankton ecosystems affect the organic enrichment of freshly emitted SSA?, 2 - Do plankton ecosystems affect the number production flux of SSA?, and 3 - Is SSA a significant source of atmospheric CCN?

Direct evidence for coastal iodine particles from Laminaria macroalgae - linkage to emissions of molecular iodine

NASA Astrophysics Data System (ADS)

McFiggans, G.; Coe, H.; Burgess, R.; Allan, J.; Cubison, M.; Rami Alfarra, M.; Saunders, R.; Saiz-Lopez, A.; Plane, J. M. C.; Wevill, D.; Carpenter, L.; Rickard, A. R.; Monks, P. S.

2004-02-01

Renewal of ultrafine aerosols in the marine boundary layer may lead to repopulation of the marine distribution and ultimately determine the concentration of cloud condensation nuclei (CCN). Thus the formation of nanometre-scale particles can lead to enhanced scattering of incoming radiation and a net cooling of the atmosphere. The recent demonstration of the chamber formation of new particles from the photolytic production of condensable iodine-containing compounds from diiodomethane (CH2I2), (O'Dowd et al., 2002; Kolb, 2002; Jimenez et al., 2003a; Burkholder and Ravishankara, 2003), provides an additional mechanism to the gas-to-particle conversion of sulphuric acid formed in the photo-oxidation of dimethylsulphide for marine aerosol repopulation. CH2I2 is emitted from seaweeds (Carpenter et al., 1999, 2000) and has been suggested as an initiator of particle formation. We demonstrate here for the first time that ultrafine iodine-containing particles are produced by intertidal macroalgae exposed to ambient levels of ozone. The particle composition is very similar both to those formed in the chamber photo-oxidation of diiodomethane and in the oxidation of molecular iodine by ozone. The particles formed in all three systems are similarly aspherical and behave alike when exposed to increased humidity environments. Direct coastal boundary layer observations of molecular iodine, ultrafine particle production and iodocarbons are reported. Using a newly measured molecular iodine photolysis rate, it is shown that, if atomic iodine is involved in the observed particle bursts, it is of the order of at least 1000 times more likely to result from molecular iodine photolysis than diiodomethane photolysis. A hypothesis for molecular iodine release from intertidal macroalgae is presented and the potential importance of macroalgal iodine particles in their contribution to CCN and global radiative forcing are discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsui, H.; Koike, Makoto; Takegawa, Nobuyuki

The new particle formation (NPF)-explicit version of the WRF-chem model, which we developed recently, can calculate the growth and sink of nucleated clusters explicitly with 20 aerosol size bins from 1 nm to 10 μm. In this study, the model is used to understand spatial and temporal variations of the frequency of NPF events and the concentrations of aerosols (condensation nuclei, CN) and cloud condensation nuclei (CCN) within the boundary layer in East Asia in spring 2009. Model simulations show distinct north-south contrast in the frequency and mechanism of NPF in East Asia. NPF mostly occurred over limited periods andmore » regions between 30° and 45°N, such as northeast China, Korea, and Japan, including regions around active volcanoes (Miyakejima and Sakurajima). At these latitudes, NPF was considerably suppressed by high concentrations of preexisting particles under stagnant air conditions associated with high-pressure systems, while nucleation occurred more extensively on most days during the simulation period. Conversely, neither nucleation nor NPF occurred frequently south of 30°N because of lower SO2 emissions and H2SO4 concentrations. The period-averaged NPF frequency was 3 times higher at latitudes of 30° - 45°N than at latitudes of 20° - 30°N. The north-south contrast of NPF frequency is validated by surface measurements in outflow regions in East Asia. The period- and domain-averaged contribution of secondary particles is estimated to be 44% for CN (> 10 nm) and 26% for CCN at a supersaturation of 1.0% in our simulation, though the contribution is highly sensitive to the magnitudes and size distributions of primary aerosol emissions and the coefficients in the nucleation parameterizations.« less

CCN activation and efficiency of nucleation and impaction removal process of biomass burning aerosols in Brazil: preliminary results.

NASA Astrophysics Data System (ADS)

Sánchez Gácita, Madeleine; Longo, Karla M.; Freitas, Saulo R.; Martin, Scot T.

2015-04-01

The biomass burning activity constitutes an important source of aerosols and trace gases to the atmosphere globally. In South America, during the dry season, aerosols prevenient from biomass burning are typically transported to long distances from its sources before being removed though contributing significantly to the aerosol budget on a continental scale. The uncertainties in the magnitude of the impacts on the hydrological cycle, the radiation budget and the biogeochemical cycles on a continental scale are still noteworthy. The still unknowns on the efficiency of biomass burning aerosol to act as cloud condensation nuclei (CCN) and the effectiveness of the nucleation and impaction scavenging mechanisms in removing them from the atmosphere contribute to such uncertainties. In the present work, the explicit modelling of the early stages of cloud development using a parcel model for the typical conditions of the dry season and dry-to-wet transition periods in Amazonia allowed an estimation of the efficiency of nucleation scavenging process and the ability of South American biomass burning aerosol to act as CCN. Additionally, the impaction scavenging was simulated for the same aerosol population following a method based on the widely used concept of the efficiency of collision between a raindrop and an aerosol particle. DMPS and H-TDMA data available in the literature for biomass burning aerosol population in the region indicated the presence of a nearly hydrophobic fraction (on average, with specific hygroscopic parameter κ=0.04, and relative abundance of 73 %) and nearly hygroscopic fraction (κ=0.13, 27 %), externally mixed. The hygroscopic parameters and relative abundances of each hygroscopic group, as well as the weighted average specific hygroscopic parameter for the entire population κ=0.06, were used in calculations of aerosol activation and population mass and number concentration scavenged by nucleation. Results from both groups of simulations are presented and discussed. This work provides an insight on the importance of the inclusion of these processes in regional/global models. The authors thank the Sao Paulo Research Foundation FAPESP for supporting this work through the projects DR 2012/09934-3 and BEPE-DR 2013/02101-9.

Oxalate metal complexes in aerosol particles: implications for the hygroscopicity of oxalate-containing particles

NASA Astrophysics Data System (ADS)

Furukawa, T.; Takahashi, Y.

2011-05-01

Atmospheric aerosols have both a direct and an indirect cooling effect that influences the radiative balance at the Earth's surface. It has been estimated that the degree of cooling is large enough to weaken the warming effect of carbon dioxide. Among the cooling factors, secondary organic aerosols (SOA) play an important role in the solar radiation balance in the troposphere as SOA can act as cloud condensation nuclei (CCN) and extend the lifespan of clouds because of their high hygroscopic and water soluble nature. Oxalic acid is an important component of SOA, and is produced via several formation pathways in the atmosphere. However, it is not certain whether oxalic acid exists as free oxalic acid or as metal oxalate complexes in aerosols, although there is a marked difference in their solubility in water and their hygroscopicity. We employed X-ray absorption fine structure spectroscopy to characterize the calcium (Ca) and zinc (Zn) in aerosols collected at Tsukuba in Japan. Size-fractionated aerosol samples were collected for this purpose using an impactor aerosol sampler. It was shown that 10-60% and 20-100% of the total Ca and Zn in the finer particles (<2.1 μm) were present as Ca and Zn oxalate complexes, respectively. Oxalic acid is hygroscopic and can thus increase the CCN activity of aerosol particles, while complexes with various polyvalent metal ions such as Ca and Zn are not hygroscopic, which cannot contribute to the increase of the CCN activity of aerosols. Based on the concentrations of noncomplexed and metal-complexed oxalate species, we found that most of the oxalic acid is present as metal oxalate complexes in the aerosols, suggesting that oxalic acid does not always increase the hygroscopicity of aerosols in the atmosphere. Similar results are expected for other dicarboxylic acids, such as malonic and succinic acids. Thus, it is advisable that the cooling effect of organic aerosols should be estimated by including the information on metal oxalate complexes and metal complexes with other dicarboxylic acids in aerosols.

Space Weather Connections to Clouds and Climate

NASA Astrophysics Data System (ADS)

Tinsley, B. A.

2004-12-01

There is now a considerable amount of observational data and theoretical work pointing to a link between space weather and atmospheric electricity, and then between atmospheric electricity and cloud cover and precipitation, which ultimately affect climate and the biosphere. Studies so far have been largely confined to the Earth, but may be applicable to all planets with clouds in their atmospheres. The current density Jz, that is the return current flowing downward through clouds in the global circuit, is modulated by the galactic cosmic ray flux; by solar energetic particles; by the dawn-dusk polar cap potential difference; and by the precipitation of relativistic electrons from the radiation belts. The flow of Jz through clouds generates unipolar space charge, which is positive at cloud tops and negative at cloud base. This charge attaches to aerosol particles, and affects their interaction with other particles and droplets. Ultrafine aerosol particles are formed around ions and are preserved from scavenging on background aerosols, and preserved for growth by vapor deposition, by space charge at the bases and tops of layer clouds. There is electro-preservation of both ultrafines and of existing CCN that leads to increases in CCN concentration, and increases in cloud cover and reduction in both droplet size and precipitation by the `indirect aerosol effect'. For cold clouds and larger aerosol particles that act as ice forming nuclei, the rate of scavenging of the IFN by large supercooled droplets varies with space charge. Changes in space weather affect both ion production and Jz in planetary atmospheres. In addition, changes in cosmic ray flux affect conductivity within thunderclouds and may affect the output of the thundercloud generators in the global circuit. Thus all four processes, (a) ion-induced nucleation, (b) electro-preservation of leading to increases in CCN concentration and the indirect aerosol effect, (c) contact ice nucleation affecting the production of ices, (d) cosmic ray effects on the generators of the global circuit, are potential links between space weather and life on planets.

Observations of the boundary layer, cloud, and aerosol variability in the southeast Pacific coastal marine stratocumulus during VOCALS-REx

NASA Astrophysics Data System (ADS)

Zheng, X.; Albrecht, B.; Jonsson, H. H.; Khelif, D.; Feingold, G.; Minnis, P.; Ayers, K.; Chuang, P.; Donaher, S.; Rossiter, D.; Ghate, V.; Ruiz-Plancarte, J.; Sun-Mack, S.

2011-05-01

Aircraft observations made off the coast of northern Chile in the Southeastern Pacific (20° S, 72° W; named Point Alpha) from 16 October to 13 November 2008 during the VAMOS Ocean-Cloud-Atmosphere-Land Study-Regional Experiment (VOCALS-REx), combined with meteorological reanalysis, satellite measurements, and radiosonde data, are used to investigate the boundary layer (BL) and aerosol-cloud-drizzle variations in this region. The BL at Point Alpha was typical of a non-drizzling stratocumulus-topped BL on days without predominately synoptic and meso-scale influences. The BL had a depth of 1140 ± 120 m, was well-mixed and capped by a sharp inversion. The wind direction generally switched from southerly within the BL to northerly above the inversion. The cloud liquid water path (LWP) varied between 15 g m-2 and 160 g m-2. From 29 October to 4 November, when a synoptic system affected conditions at Point Alpha, the cloud LWP was higher than on the other days by around 40 g m-2. On 1 and 2 November, a moist layer above the inversion moved over Point Alpha. The total-water specific humidity above the inversion was larger than that within the BL during these days. Entrainment rates (average of 1.5 ± 0.6 mm s-1) calculated from the near cloud-top fluxes and turbulence (vertical velocity variance) in the BL at Point Alpha appeared to be weaker than those in the BL over the open ocean west of Point Alpha and the BL near the coast of the northeast Pacific. The accumulation mode aerosol varied from 250 to 700 cm-3 within the BL, and CCN at 0.2 % supersaturation within the BL ranged between 150 and 550 cm-3. The main aerosol source at Point Alpha was horizontal advection within the BL from south. The average cloud droplet number concentration ranged between 80 and 400 cm-3, which was consistent with the satellite-derived values. The relationship of cloud droplet number concentration and CCN at 0.2 % supersaturation from 18 flights is Nd =4.6 × CCN0.71. While the mean LWP retrieved from GOES was in good agreement with the in situ measurements, the GOES-derived cloud droplet effective radius tended to be larger than that from the aircraft {in situ} observations near cloud top. The aerosol and cloud LWP relationship reveals that during the typical well-mixed BL days the cloud LWP increased with the CCN concentrations. On the other hand, meteorological factors and the decoupling processes have large influences on the cloud LWP variation as well.

Laboratory Experiments and Instrument Intercomparison Studies of Carbonaceous Aerosol Particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Davidovits, Paul

Aerosols containing black carbon (and some specific types of organic particulate matter) directly absorb incoming light, heating the atmosphere. In addition, all aerosol particles backscatter solar light, leading to a net-cooling effect. Indirect effects involve hydrophilic aerosols, which serve as cloud condensation nuclei (CCN) that affect cloud cover and cloud stability, impacting both atmospheric radiation balance and precipitation patterns. At night, all clouds produce local warming, but overall clouds exert a net-cooling effect on the Earth. The effect of aerosol radiative forcing on climate may be as large as that of the greenhouse gases, but predominantly opposite in sign andmore » much more uncertain. The uncertainties in the representation of aerosol interactions in climate models makes it problematic to use model projections to guide energy policy. The objective of our program is to reduce the uncertainties in the aerosol radiative forcing in the two areas highlighted in the ASR Science and Program Plan. That is, (1) addressing the direct effect by correlating particle chemistry and morphology with particle optical properties (i.e. absorption, scattering, extinction), and (2) addressing the indirect effect by correlating particle hygroscopicity and CCN activity with particle size, chemistry, and morphology. In this connection we are systematically studying particle formation, oxidation, and the effects of particle coating. The work is specifically focused on carbonaceous particles where the uncertainties in the climate relevant properties are the highest. The ongoing work consists of laboratory experiments and related instrument inter-comparison studies both coordinated with field and modeling studies, with the aim of providing reliable data to represent aerosol processes in climate models. The work is performed in the aerosol laboratory at Boston College. At the center of our laboratory setup are two main sources for the production of aerosol particles: (a) two well-characterized source of soot particles and (b) a flow reactor for controlled OH and/or O3 oxidation of relevant gas phase species to produce well-characterized SOA particles. After formation, the aerosol particles are subjected to physical and chemical processes that simulate aerosol growth and aging. A suite of instruments in our laboratory is used to characterize the physical and chemical properties of aerosol particles before and after processing. The Time of Flight Aerosol Mass Spectrometer (ToF-AMS) together with a Scanning Mobility Particle Sizer (SMPS) measures particle mass, volume, density, composition (including black carbon content), dynamic shape factor, and fractal dimension. The–ToF-AMS was developed at ARI with Boston College participation. About 120 AMS instruments are now in service (including 5 built for DOE laboratories) performing field and laboratory studies world-wide. Other major instruments include a thermal denuder, two Differential Mobility Analyzers (DMA), a Cloud Condensation Nuclei Counter (CCN), a Thermal desorption Aerosol GC/MS (TAG) and the new Soot Particle Aerosol Mass Spectrometer (SP-AMS). Optical instrumentation required for the studies have been brought to our laboratory as part of ongoing and planned collaborative projects with colleagues from DOE, NOAA and university laboratories. Optical instruments that will be utilized include a Photoacoustic Spectrometer (PAS), a Cavity Ring Down Aerosol Extinction Spectrometer (CRD-AES), a Photo Thermal Interferometer (PTI), a new 7-wavelength Aethalometer and a Cavity Attenuated Phase Shift Extinction Monitor (CAPS). These instruments are providing aerosol absorption, extinction and scattering coefficients at a range of atmospherically relevant wavelengths. During the past two years our work has continued along the lines of our original proposal. We report on 12 completed and/or continuing projects conducted during the period 08/14 to 0814/2015. These projects are described in 17 manuscripts published in refereed journals.« less

Towards closing the gap between hygroscopic growth and activation for secondary organic aerosol: Part 1 - Evidence from measurements

NASA Astrophysics Data System (ADS)

Wex, H.; Petters, M. D.; Carrico, C. M.; Hallbauer, E.; Massling, A.; McMeeking, G. R.; Poulain, L.; Wu, Z.; Kreidenweis, S. M.; Stratmann, F.

2009-01-01

Secondary Organic Aerosols (SOA) studied in laboratory experiments generally was found to show only slight hygroscopic growth, but a much better activity as a CCN (Cloud Condensation Nucleus) than indicated by the hygroscopic growth. This discrepancy was examined at LACIS (Leipzig Aerosol Cloud Interaction Simulator), using a portable generator that produced SOA particles from the ozonolysis of α-pinene, and adding butanol or butanol and water vapor during some of the experiments. The light scattering signal of dry SOA-particles was measured by the LACIS optical particle spectrometer and was used to derive a refractive index for SOA of 1.45. LACIS also measured the hygroscopic growth of SOA particles up to 99.6% relative humidity (RH), and a CCN counter was used to measure the particle activation. SOA-particles were CCN active with critical diameters of e.g. 100 and 55 nm at supersaturations of 0.4 and 1.1%, respectively. But only slight hygroscopic growth with hygroscopic growth factors ≤1.05 was observed at RH<98% RH. The hygroscopic growth increased slightly with the OH concentration present during the SOA-generation. At RH>98%, the hygroscopic growth increased stronger than would be expected if a constant hygroscopicity parameter for the particle/droplet solution was assumed. An increase of the hygroscopicity parameter by a factor of 4-6 was observed in the RH-range from below 90 to 99.6%, and this increase continued for increasingly diluted particle solutions for activating particles. This explains an observation already made in the past: that the relation between critical supersaturation and dry diameter for activation is steeper than what would be expected for a constant value of the hygroscopicity. The increase in the hygroscopicity parameter could be explained by either an increase in the number of ions/molecules in solution (e.g. due to the presence of slightly soluble particles with deliquescence RHs above 98%), or a change in the non-ideal behaviour (see companion paper Petters et al., 2008). Combining measurements of hygroscopic growth and activation, it was found that the surface tension that has to be assumed to interpret the measurements consistently is greater than 55 mN/m, possibly close to that of pure water, depending on the different SOA-types produced, and therefore only in part accounts for the discrepancy between hygroscopic growth and CCN activity observed for SOA particles in the past.

Biogenic influence on the composition and growth of summertime Arctic aerosol

NASA Astrophysics Data System (ADS)

Willis, M. D.; Burkart, J.; Thomas, J. L.; Koellner, F.; Schneider, J.; Bozem, H.; Hoor, P. M.; Aliabadi, A. A.; Schulz, H.; Herber, A. B.; Leaitch, R.; Abbatt, J.

2016-12-01

The summertime Arctic lower troposphere is a relatively pristine background aerosol environment dominated by nucleation and Aitken mode particles. Understanding the mechanisms that control the formation and growth of aerosol is crucial for our ability to predict cloud properties and therefore radiative balance and climate. We present aircraft-based observations of submicron aerosol composition from an aerosol mass spectrometer made during the NETCARE 2014 summertime arctic campaign, based in the Canadian High Arctic, at Resolute Bay, NU (74°N). Under stable and regionally influenced atmospheric conditions with low carbon monoxide and black carbon concentrations (< 100 ppbv and < 50 ng/m3, respectively), we observed organic aerosol (OA)-to-sulfate ratios ranging from 0.5 to > 6 with evidence for enhancement within the lower boundary layer. Methanesulfonic acid (MSA), a marker for the contribution of ocean-derived biogenic sulphur, was also observed in submicron aerosol. MSA-to-sulfate ratios ranged from near zero to 0.3 and tended to increase within the lower boundary layer, suggesting a contribution to aerosol loading from the ocean. In one notable case while flying in the lower boundary layer above open water in Lancaster Sound, we observed growth of small particles, <20 nm in diameter, into sizes above 50 nm. Aerosol growth was correlated with the presence of organic species, trimethylamine, and MSA in particles 80 nm and larger, where the organics were similar to those previously observed in marine settings. The organic-rich aerosol contributed significantly to particles active as cloud condensation nuclei (CCN, supersaturation = 0.6%). Our results highlight the potential importance of secondary organic aerosol formation and its role in growing nucleation mode aerosol into CCN-active sizes in this remote marine environment.

Aerosol and Cloud Properties during the Cloud Cheju ABC Plume -Asian Monsoon Experiment (CAPMEX) 2008: Linking between Ground-based and UAV Measurements

NASA Astrophysics Data System (ADS)

Kim, S.; Yoon, S.; Venkata Ramana, M.; Ramanathan, V.; Nguyen, H.; Park, S.; Kim, M.

2009-12-01

Cheju Atmospheric Brown Cloud (ABC) Plume-Monsoon Experiment (CAPMEX), comprehsensive ground-based measurements and a series of data-gathering flights by specially equipped autonomous unmanned aerial vehicles (AUAVs) for aerosol and cloud, had conducted at Jeju (formerly, Cheju), South Korea during August-September 2008, to improve our understanding of how the reduction of anthropogenic emissions in China (so-called “great shutdown” ) during and after the Summer Beijing Olympic Games 2008 effcts on the air quliaty and radiation budgets and how atmospheric brown clouds (ABCs) influences solar radiation budget off Asian continent. Large numbers of in-situ and remote sensing instruments at the Gosan ABC observatory and miniaturized instruments on the aircraft measure a range of properties such as the quantity of soot, size-segregated aerosol particle numbers, total particle numbers, size-segregated cloud droplet numbers (only AUAV), aerosol scattering properties (only ground), aerosol vertical distribution, column-integrated aerosol properties, and meteorological variables. By integrating ground-level and high-elevation AUAV measurements with NASA-satellite observations (e.g., MODIS, CALIPSO), we investigate the long range transport of aerosols, the impact of ABCs on clouds, and the role of biogenic and anthropogenic aerosols on cloud condensation nuclei (CCN). In this talk, we will present the results from CAPMEX focusing on: (1) the characteristics of aerosol optical, physical and chemical properties at Gosan observatory, (2) aerosol solar heating calculated from the ground-based micro-pulse lidar and AERONET sun/sky radiometer synergy, and comparison with direct measurements from UAV, and (3) aerosol-cloud interactions in conjunction with measurements by satellites and Gosan observatory.

Lidar characterizations of atmospheric aerosols and clouds

NASA Astrophysics Data System (ADS)

Ferrare, R. A.; Hostetler, C. A.; Hair, J. W.; Burton, S. P.

2017-12-01

Knowledge of the vertical profile, composition, concentration, and size distribution of aerosols is required to quantify the impacts of aerosols on human health, global and regional climate, clouds and precipitation. In particular, radiative forcing due to anthropogenic aerosols is the most uncertain part of anthropogenic radiative forcing, with aerosol-cloud interactions (ACI) as the largest source of uncertainty in current estimates of global radiative forcing. Improving aerosol transport model predictions of the vertical profile of aerosol optical and microphysical characteristics is crucial for improving assessments of aerosol radiative forcing. Understanding how aerosols and clouds interact is essential for investigating the aerosol indirect effect and ACI. Through its ability to provide vertical profiles of aerosol and cloud distributions as well as important information regarding the optical and physical properties of aerosols and clouds, lidar is a crucial tool for addressing these science questions. This presentation describes how surface, airborne, and satellite lidar measurements have been used to address these questions, and in particular how High Spectral Resolution Lidar (HSRL) measurements provide profiles of aerosol properties (backscatter, extinction, depolarization, concentration, size) important for characterizing radiative forcing. By providing a direct measurement of aerosol extinction, HSRL provides more accurate aerosol measurement profiles and more accurate constraints for models than standard retrievals from elastic backscatter lidar, which loses accuracy and precision at lower altitudes due to attenuation from overlying layers. Information regarding particle size and abundance from advanced lidar retrievals provides better proxies for cloud-condensation-nuclei (CCN), which are required for assessing aerosol-cloud interactions. When combined with data from other sensors, advanced lidar measurements can provide information on aerosol and cloud properties for addressing both direct and indirect radiative forcing.

CCN activity and organic hygroscopicity of aerosols downwind of an urban region in central Amazonia: seasonal and diel variations and impact of anthropogenic emissions

NASA Astrophysics Data System (ADS)

Thalman, Ryan; de Sá, Suzane S.; Palm, Brett B.; Barbosa, Henrique M. J.; Pöhlker, Mira L.; Lizabeth Alexander, M.; Brito, Joel; Carbone, Samara; Castillo, Paulo; Day, Douglas A.; Kuang, Chongai; Manzi, Antonio; Ng, Nga Lee; Sedlacek, Arthur J., III; Souza, Rodrigo; Springston, Stephen; Watson, Thomas; Pöhlker, Christopher; Pöschl, Ulrich; Andreae, Meinrat O.; Artaxo, Paulo; Jimenez, Jose L.; Martin, Scot T.; Wang, Jian

2017-10-01

During the Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) campaign, size-resolved cloud condensation nuclei (CCN) spectra were characterized at a research site (T3) 60 km downwind of the city of Manaus, Brazil, in central Amazonia for 1 year (12 March 2014 to 3 March 2015). Particle hygroscopicity (κCCN) and mixing state were derived from the size-resolved CCN spectra, and the hygroscopicity of the organic component of the aerosol (κorg) was then calculated from κCCN and concurrent chemical composition measurements. The annual average κCCN increased from 0.13 at 75 nm to 0.17 at 171 nm, and the increase was largely due to an increase in sulfate volume fraction. During both wet and dry seasons, κCCN, κorg, and particle composition under background conditions exhibited essentially no diel variations. The constant κorg of ˜ 0. 15 is consistent with the largely uniform and high O : C value (˜ 0. 8), indicating that the aerosols under background conditions are dominated by the aged regional aerosol particles consisting of highly oxygenated organic compounds. For air masses strongly influenced by urban pollution and/or local biomass burning, lower values of κorg and organic O : C atomic ratio were observed during night, due to accumulation of freshly emitted particles, dominated by primary organic aerosol (POA) with low hygroscopicity, within a shallow nocturnal boundary layer. The O : C, κorg, and κCCN increased from the early morning hours and peaked around noon, driven by the formation and aging of secondary organic aerosol (SOA) and dilution of POA emissions into a deeper boundary layer, while the development of the boundary layer, which leads to mixing with aged particles from the residual layer aloft, likely also contributed to the increases. The hygroscopicities associated with individual organic factors, derived from PMF (positive matrix factorization) analysis of AMS (aerosol mass spectrometry) spectra, were estimated through multivariable linear regression. For the SOA factors, the variation of the κ value with O : C agrees well with the linear relationship reported from earlier laboratory studies of SOA hygroscopicity. On the other hand, the variation in O : C of ambient aerosol organics is largely driven by the variation in the volume fractions of POA and SOA factors, which have very different O : C values. As POA factors have hygroscopicity values well below the linear relationship between SOA hygroscopicity and O : C, mixtures with different POA and SOA fractions exhibit a steeper slope for the increase in κorg with O : C, as observed during this and earlier field studies. This finding helps better understand and reconcile the differences in the relationships between κorg and O : C observed in laboratory and field studies, therefore providing a basis for improved parameterization in global models, especially in a tropical context.

CCN activity and organic hygroscopicity of aerosols downwind of an urban region in central Amazonia: Seasonal and diel variations and impact of anthropogenic emissions

DOE PAGES

Thalman, Ryan; de Sá, Suzane S.; Palm, Brett B.; ...

2017-10-05

During the Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) campaign, size-resolved cloud condensation nuclei (CCN) spectra were characterized at a research site (T3) 60km downwind of the city of Manaus, Brazil, in central Amazonia for one year (12 March 2014 to 3 March 2015). Particle hygroscopicity (κCCN) and mixing state were derived from the size-resolved CCN spectra, and the hygroscopicity of the organic component of the aerosol (κorg) was then calculated from κCCN and concurrent chemical composition measurements. The annual average κCCN increased from 0.13 at 75 nm to 0.17 at 171 nm, and the increase was largely duemore » to an increase in sulfate volume fraction. Also, during both wet and dry seasons, κCCN, κorg, and particle composition under background conditions exhibited essentially no diel variations. The constant κorg of ~0.15 is consistent with the largely uniform and high O:C value (~0.8), indicating that the aerosols under background conditions are dominated by the aged regional aerosol particles consisting of highly oxygenated organic compounds. For air masses strongly influenced by urban pollution and/or local biomass burning, lower values of κorg and organic O:C atomic ratio were observed during night, due to accumulation of freshly emitted particles, dominated by primary organic aerosol (POA) with low hygroscopicity, within a shallow nocturnal boundary layer. The O:C, κorg, and κCCN increased from the early morning hours and peaked around noon, driven by the formation and aging of secondary organic aerosol (SOA) and dilution of POA emissions into a deeper boundary layer, while the development of the boundary layer, which leads to mixing with aged particles from the residual layer aloft, likely also contributed to the increases. The hygroscopicities associated with individual organic factors, derived from PMF analysis of AMS spectra, were estimated through multi-variable linear regression. For the SOA factors, the variation of the κ value with O:C agrees well with the linear relationship reported from earlier laboratory studies of SOA hygroscopicity. On the other hand, the variation in O:C of ambient aerosol organics is largely driven by the variation in the volume fractions of POA and SOA factors, which have very different O:C values. As POA factors have hygroscopicity values well below the linear relationship between SOA hygroscopicity and O:C, mixtures with different POA and SOA fractions exhibit a steeper slope for the increase of κorg with O:C, as observed during this and earlier field studies. Our finding helps better understand and reconcile the differences in the relationships between κorg and O:C observed in laboratory and field studies, therefore providing a basis for improved parameterization in global models, especially in a tropical context.« less

CCN activity and organic hygroscopicity of aerosols downwind of an urban region in central Amazonia: Seasonal and diel variations and impact of anthropogenic emissions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thalman, Ryan; de Sá, Suzane S.; Palm, Brett B.

During the Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) campaign, size-resolved cloud condensation nuclei (CCN) spectra were characterized at a research site (T3) 60km downwind of the city of Manaus, Brazil, in central Amazonia for one year (12 March 2014 to 3 March 2015). Particle hygroscopicity (κCCN) and mixing state were derived from the size-resolved CCN spectra, and the hygroscopicity of the organic component of the aerosol (κorg) was then calculated from κCCN and concurrent chemical composition measurements. The annual average κCCN increased from 0.13 at 75 nm to 0.17 at 171 nm, and the increase was largely duemore » to an increase in sulfate volume fraction. Also, during both wet and dry seasons, κCCN, κorg, and particle composition under background conditions exhibited essentially no diel variations. The constant κorg of ~0.15 is consistent with the largely uniform and high O:C value (~0.8), indicating that the aerosols under background conditions are dominated by the aged regional aerosol particles consisting of highly oxygenated organic compounds. For air masses strongly influenced by urban pollution and/or local biomass burning, lower values of κorg and organic O:C atomic ratio were observed during night, due to accumulation of freshly emitted particles, dominated by primary organic aerosol (POA) with low hygroscopicity, within a shallow nocturnal boundary layer. The O:C, κorg, and κCCN increased from the early morning hours and peaked around noon, driven by the formation and aging of secondary organic aerosol (SOA) and dilution of POA emissions into a deeper boundary layer, while the development of the boundary layer, which leads to mixing with aged particles from the residual layer aloft, likely also contributed to the increases. The hygroscopicities associated with individual organic factors, derived from PMF analysis of AMS spectra, were estimated through multi-variable linear regression. For the SOA factors, the variation of the κ value with O:C agrees well with the linear relationship reported from earlier laboratory studies of SOA hygroscopicity. On the other hand, the variation in O:C of ambient aerosol organics is largely driven by the variation in the volume fractions of POA and SOA factors, which have very different O:C values. As POA factors have hygroscopicity values well below the linear relationship between SOA hygroscopicity and O:C, mixtures with different POA and SOA fractions exhibit a steeper slope for the increase of κorg with O:C, as observed during this and earlier field studies. Our finding helps better understand and reconcile the differences in the relationships between κorg and O:C observed in laboratory and field studies, therefore providing a basis for improved parameterization in global models, especially in a tropical context.« less

A Campaign Study of Sea Spray Aerosol Properties in the Bay of Aarhus

NASA Astrophysics Data System (ADS)

Nguyen, Quynh; Rasmussen, Berit; Kristensen, Kasper; Sloth Nielsen, Lærke; Bilde, Merete

2016-04-01

The oceans of the world are a dominant source of atmospheric aerosol. Together with mineral dust, sea spray aerosols (SSA) constitute the largest mass flux of particulate matter in the atmosphere (Andreae and Rosenfeld, 2008). Due to their effects on the global radiative budget - both directly as scatterers and absorbers of solar and terrestrial radiation, and indirectly as cloud condensation nuclei (CCN), SSA are considered an important component of the climate system. The sea-surface microlayer (SML) is an ultra-thin boundary layer between the ocean and the atmosphere. The high concentration of surface-active organic compounds in the SML, compared to that of the underlying water column, creates rigid film-like layer over the surface of the ocean. The SML is believed to play an important role in the formation and composition of SSA. However, current knowledge on the SML and its impacts on SSA remain limited. To characterize the SML of natural seawater and examine its impacts on aerosol properties, a field campaign was conducted in the bay of Aarhus, Denmark, during spring 2015. Bulk seawater was collected 1-2 times every week along with selective sampling of the SML. Characterization of the sea water and SML included a wide range of measurements, including surface tension, water activity, dissolved organic matter, and chemical composition analysis by liquid chromatography/electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (UPLC/ESI-HR-Q-TOFMS). SSA was generated from sampled sea water by diffusion of air bubbles through a 10L seawater sample situated in a sea spray tank. Particle number concentration and CCN measurements were conducted along with measurements of the organic share in the aerosol phase as indicated by volatility measurements. To investigate the effect of the SML, spiking of the seawater samples with additional SML was performed and measurements repeated for comparison. Preliminary results show that the SML samples only displayed slightly lower surface tension compared to subsurface seawater. A number of overlapping masses were observed in dissolved organic matter extracted from SML and slick samples, which requires further identification. Spiking bulk seawater with SML seems to lead to a small increase in organic share in the aerosol phase as indicated by volatility measurements, while the trend is unclear in CCN measurements. Andreae, M. O., and Rosenfeld, D.: Aerosol-cloud-precipitation interactions. Part 1. The nature and sources of cloud-active aerosols, Earth-Sci Rev, 89, 13-41, 2008.

Comprehensive mapping and characteristic regimes of aerosol effects on the formation and evolution of pyro-convective clouds

DOE PAGES

Chang, D.; Cheng, Y.; Reutter, P.; ...

2015-09-21

Here, a recent parcel model study (Reutter et al., 2009) showed three deterministic regimes of initial cloud droplet formation, characterized by different ratios of aerosol concentrations ( N CN) to updraft velocities. This analysis, however, did not reveal how these regimes evolve during the subsequent cloud development. To address this issue, we employed the Active Tracer High Resolution Atmospheric Model (ATHAM) with full microphysics and extended the model simulation from the cloud base to the entire column of a single pyro-convective mixed-phase cloud. A series of 2-D simulations (over 1000) were performed over a wide range of N CN andmore » dynamic conditions. The integrated concentration of hydrometeors over the full spatial and temporal scales was used to evaluate the aerosol and dynamic effects. The results show the following. (1) The three regimes for cloud condensation nuclei (CCN) activation in the parcel model (namely aerosol-limited, updraft-limited, and transitional regimes) still exist within our simulations, but net production of raindrops and frozen particles occurs mostly within the updraft-limited regime. (2) Generally, elevated aerosols enhance the formation of cloud droplets and frozen particles. The response of raindrops and precipitation to aerosols is more complex and can be either positive or negative as a function of aerosol concentrations. The most negative effect was found for values of N CN of ~ 1000 to 3000 cm –3. (3) The nonlinear properties of aerosol–cloud interactions challenge the conclusions drawn from limited case studies in terms of their representativeness, and ensemble studies over a wide range of aerosol concentrations and other influencing factors are strongly recommended for a more robust assessment of the aerosol effects.« less

Biomass burning emissions of trace gases and particles in marine air at Cape Grim, Tasmania

NASA Astrophysics Data System (ADS)

Lawson, S. J.; Keywood, M. D.; Galbally, I. E.; Gras, J. L.; Cainey, J. M.; Cope, M. E.; Krummel, P. B.; Fraser, P. J.; Steele, L. P.; Bentley, S. T.; Meyer, C. P.; Ristovski, Z.; Goldstein, A. H.

2015-12-01

Biomass burning (BB) plumes were measured at the Cape Grim Baseline Air Pollution Station during the 2006 Precursors to Particles campaign, when emissions from a fire on nearby Robbins Island impacted the station. Measurements made included non-methane organic compounds (NMOCs) (PTR-MS), particle number size distribution, condensation nuclei (CN) > 3 nm, black carbon (BC) concentration, cloud condensation nuclei (CCN) number, ozone (O3), methane (CH4), carbon monoxide (CO), hydrogen (H2), carbon dioxide (CO2), nitrous oxide (N2O), halocarbons and meteorology. During the first plume strike event (BB1), a 4 h enhancement of CO (max ~ 2100 ppb), BC (~ 1400 ng m-3) and particles > 3 nm (~ 13 000 cm-3) with dominant particle mode of 120 nm were observed overnight. A wind direction change lead to a dramatic reduction in BB tracers and a drop in the dominant particle mode to 50 nm. The dominant mode increased in size to 80 nm over 5 h in calm sunny conditions, accompanied by an increase in ozone. Due to an enhancement in BC but not CO during particle growth, the presence of BB emissions during this period could not be confirmed. The ability of particles > 80 nm (CN80) to act as CCN at 0.5 % supersaturation was investigated. The ΔCCN / ΔCN80 ratio was lowest during the fresh BB plume (56 ± 8 %), higher during the particle growth period (77 ± 4 %) and higher still (104 ± 3 %) in background marine air. Particle size distributions indicate that changes to particle chemical composition, rather than particle size, are driving these changes. Hourly average CCN during both BB events were between 2000 and 5000 CCN cm-3, which were enhanced above typical background levels by a factor of 6-34, highlighting the dramatic impact BB plumes can have on CCN number in clean marine regions. During the 29 h of the second plume strike event (BB2) CO, BC and a range of NMOCs including acetonitrile and hydrogen cyanide (HCN) were clearly enhanced and some enhancements in O3 were observed (ΔO3 / ΔCO 0.001-0.074). A short-lived increase in NMOCs by a factor of 10 corresponded with a large CO enhancement, an increase of the NMOC / CO emission ratio (ER) by a factor of 2-4 and a halving of the BC / CO ratio. Rainfall on Robbins Island was observed by radar during this period which likely resulted in a lower fire combustion efficiency, and higher emission of compounds associated with smouldering. This highlights the importance of relatively minor meteorological events on BB emission ratios. Emission factors (EFs) were derived for a range of trace gases, some never before reported for Australian fires, (including hydrogen, phenol and toluene) using the carbon mass balance method. This provides a unique set of EFs for Australian coastal heathland fires. Methyl halide EFs were higher than EFs reported from other studies in Australia and the Northern Hemisphere which is likely due to high halogen content in vegetation on Robbins Island. This work demonstrates the substantial impact that BB plumes can have on the composition of marine air, and the significant changes that can occur as the plume interacts with terrestrial, aged urban and marine emission sources.

A technique for the measurement of organic aerosol hygroscopicity, oxidation level, and volatility distributions

NASA Astrophysics Data System (ADS)

Cain, Kerrigan P.; Pandis, Spyros N.

2017-12-01

Hygroscopicity, oxidation level, and volatility are three crucial properties of organic pollutants. This study assesses the feasibility of a novel measurement and analysis technique to determine these properties and establish their relationship. The proposed experimental setup utilizes a cloud condensation nuclei (CCN) counter to quantify hygroscopic activity, an aerosol mass spectrometer to measure the oxidation level, and a thermodenuder to evaluate the volatility. The setup was first tested with secondary organic aerosol (SOA) formed from the ozonolysis of α-pinene. The results of the first experiments indicated that, for this system, the less volatile SOA contained species that had on average lower O : C ratios and hygroscopicities. In this SOA system, both low- and high-volatility components can have comparable oxidation levels and hygroscopicities. The method developed here can be used to provide valuable insights about the relationships among organic aerosol hygroscopicity, oxidation level, and volatility.

Aerosol and Cloud Experiments in Eastern North Atlantic (ACE-ENA) Science Plan

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jian; Dong, Xiquan; Wood, Robert

With their extensive coverage, low clouds greatly impact global climate. Presently, low clouds are poorly represented in global climate models (GCMs), and the response of low clouds to changes in atmospheric greenhouse gases and aerosols remains the major source of uncertainty in climate simulations. The poor representations of low clouds in GCMs are in part due to inadequate observations of their microphysical and macrophysical structures, radiative effects, and the associated aerosol distribution and budget in regions where the aerosol impact is the greatest. The Eastern North Atlantic (ENA) is a region of persistent but diverse subtropical marine boundary-layer (MBL) clouds,more » whose albedo and precipitation are highly susceptible to perturbations in aerosol properties. Boundary-layer aerosol in the ENA region is influenced by a variety of sources, leading to strong variations in cloud condensation nuclei (CCN) concentration and aerosol optical properties. Recently a permanent ENA site was established by the U.S. Department of Energy (DOE)’s Atmospheric Radiation Measurement (ARM) Climate Research Facility on Graciosa Island in the Azores, providing invaluable information on MBL aerosol and low clouds. At the same time, the vertical structures and horizontal variabilities of aerosol, trace gases, cloud, drizzle, and atmospheric thermodynamics are critically needed for understanding and quantifying the budget of MBL aerosol, the radiative properties, precipitation efficiency, and lifecycle of MBL clouds, and the cloud response to aerosol perturbations. Much of this data can be obtained only through aircraft-based measurements. In addition, the interconnected aerosol and cloud processes are best investigated by a study involving simultaneous in situ aerosol, cloud, and thermodynamics measurements. Furthermore, in situ measurements are also necessary for validating and improving ground-based retrieval algorithms at the ENA site. This project is motivated by the need for comprehensive in situ characterizations of boundary-layer structure, and associated vertical distributions and horizontal variabilities of low clouds and aerosol over the Azores. ARM Aerial Facility (AAF) Gulfstream-1 (G-1) aircraft will be deployed at the ENA site during two intensive operational periods (IOPs) of early summer (June to July) of 2017 and winter (January to February) of 2018, respectively. Deployments during both seasons allow for examination of key aerosol and cloud processes under a variety of representative meteorological and cloud conditions. The science themes for the deployments include: 1) Budget of MBL CCN and its seasonal variation; 2) Effects of aerosol on cloud and precipitation; 3) Cloud microphysical and macrophysical structures, and entrainment mixing; 4) Advancing retrievals of turbulence, cloud, and drizzle; and 5) Model evaluation and processes studies. A key advantage of the deployments is the strong synergy between the measurements onboard the G-1 and the routine measurements at the ENA site, including state-of-the-art profiling and scanning radars. The 3D cloud structures provided by the scanning radars will put the detailed in situ measurements into mesoscale and cloud lifecycle contexts. On the other hand, high quality in situ measurements will enable validation and improvements of ground-based retrieval algorithms at the ENA site, leading to high-quality and statistically robust data sets from the routine measurements. The deployments, combined with the routine measurements at the ENA site, will have a long lasting impact on the research and modeling of low clouds and aerosols in the remote marine environment.« less

Implementation of warm-cloud processes in a source-oriented WRF/Chem model to study the effect of aerosol mixing state on fog formation in the Central Valley of California

NASA Astrophysics Data System (ADS)

Lee, H.-H.; Chen, S.-H.; Kleeman, M. J.; Zhang, H.; DeNero, S. P.; Joe, D. K.

2015-11-01

The source-oriented Weather Research and Forecasting chemistry model (SOWC) was modified to include warm cloud processes and applied to investigate how aerosol mixing states influence fog formation and optical properties in the atmosphere. SOWC tracks a 6-dimensional chemical variable (X, Z, Y, Size Bins, Source Types, Species) through an explicit simulation of atmospheric chemistry and physics. A source-oriented cloud condensation nuclei module was implemented into the SOWC model to simulate warm clouds using the modified two-moment Purdue Lin microphysics scheme. The Goddard shortwave and longwave radiation schemes were modified to interact with source-oriented aerosols and cloud droplets so that aerosol direct and indirect effects could be studied. The enhanced SOWC model was applied to study a fog event that occurred on 17 January 2011, in the Central Valley of California. Tule fog occurred because an atmospheric river effectively advected high moisture into the Central Valley and nighttime drainage flow brought cold air from mountains into the valley. The SOWC model produced reasonable liquid water path, spatial distribution and duration of fog events. The inclusion of aerosol-radiation interaction only slightly modified simulation results since cloud optical thickness dominated the radiation budget in fog events. The source-oriented mixture representation of particles reduced cloud droplet number relative to the internal mixture approach that artificially coats hydrophobic particles with hygroscopic components. The fraction of aerosols activating into CCN at a supersaturation of 0.5 % in the Central Valley decreased from 94 % in the internal mixture model to 80 % in the source-oriented model. This increased surface energy flux by 3-5 W m-2 and surface temperature by as much as 0.25 K in the daytime.

Structural isomers of C2N(+) - A selected-ion flow tube study

NASA Technical Reports Server (NTRS)

Knight, J. S.; Petrie, S. A. H.; Freeman, C. G.; Mcewan, M. J.; Mclean, A. D.

1988-01-01

Reactivities of the structural isomers CCN(+) and CNC(+) were examined in a selected-ion flow tube at 300 + or - 5 K. The less reactive CNC(+) isomer was identified as the product of the reactions of C(+) + HCN and C(+) + C2N2; in these reactions only CNC(+) can be produced because of energy constraints. Rate coefficients and branching ratios are reported for the reactions of each isomer with H2, CH4, NH3, H2O, C2H2, HCN, N2, O2, N2O, and CO2. Ab initio calculations are presented for CCN(+) and CNC(+); a saddle point for the reaction CCN(+) yielding CNC(+) is calculated to be 195 kJ/mol above CNC(+). The results provide evidence that the more reactive CCN(+) isomer is unlikely to be present in measurable densities in interstellar clouds.

Characterization of CCN and IN activity of bacterial isolates collected in Atlanta, GA

NASA Astrophysics Data System (ADS)

Purdue, Sara; Waters, Samantha; Karthikeyan, Smruthi; Konstantinidis, Kostas; Nenes, Athanasios

2016-04-01

Characterization of CCN activity of bacteria, other than a few select types such as Pseudomonas syringae, is limited, especially when looked at in conjunction with corresponding IN activity. The link between these two points is especially important for bacteria as those that have high CCN activity are likely to form an aqueous phase required for immersion freezing. Given the high ice nucleation temperature of bacterial cells, especially in immersion mode, it is important to characterize the CCN and IN activity of many different bacterial strains. To this effect, we developed a droplet freezing assay (DFA) which consists of an aluminum cold plate, cooled by a continuous flow of an ethylene glycol-water mixture, in order to observe immersion freezing of the collected bacteria. Here, we present the initial results on the CCN and IN activities of bacterial samples we have collected in Atlanta, GA. Bacterial strains were collected and isolated from rainwater samples taken from different storms throughout the year. We then characterized the CCN activity of each strain using a DMT Continuous Flow Streamwise Thermal Gradient CCN Counter by exposing the aerosolized bacteria to supersaturations ranging from 0.05% to 0.6%. Additionally, using our new DFA, we characterized the IN activity of each bacterial strain at temperatures ranging from -20oC to 0oC. The combined CCN and IN activity gives us valuable information on how some uncharacterized bacteria contribute to warm and mixed-phase cloud formation in the atmosphere.

Aerosol properties associated with air masses arriving into the North East Atlantic during the 2008 Mace Head EUCAARI intensive observing period: an overview

NASA Astrophysics Data System (ADS)

Dall'Osto, M.; Ceburnis, D.; Martucci, G.; Bialek, J.; Dupuy, R.; Jennings, S. G.; Berresheim, H.; Wenger, J.; Healy, R.; Facchini, M. C.; Rinaldi, M.; Giulianelli, L.; Finessi, E.; Worsnop, D.; Ehn, M.; Mikkilä, J.; Kulmala, M.; O'Dowd, C. D.

2010-09-01

As part of the EUCAARI Intensive Observing Period, a 4-week campaign to measure aerosol physical, chemical and optical properties, atmospheric structure, and cloud microphysics was conducted from mid-May to mid-June, 2008 at the Mace Head Atmospheric Research Station, located at the interface of Western Europe and the N. E. Atlantic and centered on the west Irish coastline. During the campaign, continental air masses comprising both young and aged continental plumes were encountered, along with polar, Arctic and tropical air masses. Polluted-continental aerosol concentrations were of the order of 3000 cm-3, while background marine air aerosol concentrations were between 400-600 cm-3. The highest marine air concentrations occurred in polar air masses in which a 15 nm nucleation mode, with concentration of 1100 cm-3, was observed and attributed to open ocean particle formation. Continental air submicron chemical composition (excluding refractory sea salt) was dominated by organic matter, closely followed by sulphate mass. Although the concentrations and size distribution spectral shape were almost identical for the young and aged continental cases, hygroscopic growth factors (GF) and cloud condensation nuclei (CCN) to total condensation nuclei (CN) concentration ratios were significantly less in the younger pollution plume, indicating a more oxidized organic component to the aged continental plume. The difference in chemical composition and hygroscopic growth factor appear to result in a 40-50% impact on aerosol scattering coefficients and Aerosol Optical Depth, despite almost identical aerosol microphysical properties in both cases, with the higher values been recorded for the more aged case. For the CCN/CN ratio, the highest ratios were seen in the more age plume. In marine air, sulphate mass dominated the sub-micron component, followed by water soluble organic carbon, which, in turn, was dominated by methanesulphonic acid (MSA). Sulphate concentrations were highest in marine tropical air - even higher than in continental air. MSA was present at twice the concentrations of previously-reported concentrations at the same location and the same season. Both continental and marine air exhibited aerosol GFs significantly less than ammonium sulphate aerosol pointing to a significant organic contribution to all air mass aerosol properties.

Top-down and Bottom-up aerosol-cloud-closure: towards understanding sources of unvertainty in deriving cloud radiative flux

NASA Astrophysics Data System (ADS)

Sanchez, K.; Roberts, G.; Calmer, R.; Nicoll, K.; Hashimshoni, E.; Rosenfeld, D.; Ovadnevaite, J.; Preissler, J.; Ceburnis, D.; O'Dowd, C. D. D.; Russell, L. M.

2017-12-01

Top-down and bottom-up aerosol-cloud shortwave radiative flux closures were conducted at the Mace Head atmospheric research station in Galway, Ireland in August 2015. Instrument platforms include ground-based, unmanned aerial vehicles (UAV), and satellite measurements of aerosols, clouds and meteorological variables. The ground-based and airborne measurements of aerosol size distributions and cloud condensation nuclei (CCN) concentration were used to initiate a 1D microphysical aerosol-cloud parcel model (ACPM). UAVs were equipped for a specific science mission, with an optical particle counter for aerosol distribution profiles, a cloud sensor to measure cloud extinction, or a 5-hole probe for 3D wind vectors. These are the first UAV measurements at Mace Head. ACPM simulations are compared to in-situ cloud extinction measurements from UAVs to quantify closure in terms of cloud shortwave radiative flux. Two out of seven cases exhibit sub-adiabatic vertical temperature profiles within the cloud, which suggests that entrainment processes affect cloud microphysical properties and lead to an overestimate of simulated cloud shortwave radiative flux. Including an entrainment parameterization and explicitly calculating the entrainment fraction in the ACPM simulations both improved cloud-top radiative closure. Entrainment reduced the difference between simulated and observation-derived cloud-top shortwave radiative flux (δRF) by between 25 W m-2 and 60 W m-2. After accounting for entrainment, satellite-derived cloud droplet number concentrations (CDNC) were within 30% of simulated CDNC. In cases with a well-mixed boundary layer, δRF is no greater than 20 W m-2 after accounting for cloud-top entrainment, and up to 50 W m-2 when entrainment is not taken into account. In cases with a decoupled boundary layer, cloud microphysical properties are inconsistent with ground-based aerosol measurements, as expected, and δRF is as high as 88 W m-2, even high (> 30 W m-2) after accounting for cloud-top entrainment. This work demonstrates the need to take in-situ measurements of aerosol properties for cases where the boundary layer is decoupled as well as consider cloud-top entrainment to accurately model stratocumulus cloud radiative flux.

Top-down and Bottom-up aerosol-cloud-closure: towards understanding sources of unvertainty in deriving cloud radiative flux

NASA Astrophysics Data System (ADS)

Sanchez, K.; Roberts, G.; Calmer, R.; Nicoll, K.; Hashimshoni, E.; Rosenfeld, D.; Ovadnevaite, J.; Preissler, J.; Ceburnis, D.; O'Dowd, C. D. D.; Russell, L. M.

2016-12-01

Top-down and bottom-up aerosol-cloud shortwave radiative flux closures were conducted at the Mace Head atmospheric research station in Galway, Ireland in August 2015. Instrument platforms include ground-based, unmanned aerial vehicles (UAV), and satellite measurements of aerosols, clouds and meteorological variables. The ground-based and airborne measurements of aerosol size distributions and cloud condensation nuclei (CCN) concentration were used to initiate a 1D microphysical aerosol-cloud parcel model (ACPM). UAVs were equipped for a specific science mission, with an optical particle counter for aerosol distribution profiles, a cloud sensor to measure cloud extinction, or a 5-hole probe for 3D wind vectors. These are the first UAV measurements at Mace Head. ACPM simulations are compared to in-situ cloud extinction measurements from UAVs to quantify closure in terms of cloud shortwave radiative flux. Two out of seven cases exhibit sub-adiabatic vertical temperature profiles within the cloud, which suggests that entrainment processes affect cloud microphysical properties and lead to an overestimate of simulated cloud shortwave radiative flux. Including an entrainment parameterization and explicitly calculating the entrainment fraction in the ACPM simulations both improved cloud-top radiative closure. Entrainment reduced the difference between simulated and observation-derived cloud-top shortwave radiative flux (δRF) by between 25 W m-2 and 60 W m-2. After accounting for entrainment, satellite-derived cloud droplet number concentrations (CDNC) were within 30% of simulated CDNC. In cases with a well-mixed boundary layer, δRF is no greater than 20 W m-2 after accounting for cloud-top entrainment, and up to 50 W m-2 when entrainment is not taken into account. In cases with a decoupled boundary layer, cloud microphysical properties are inconsistent with ground-based aerosol measurements, as expected, and δRF is as high as 88 W m-2, even high (> 30 W m-2) after accounting for cloud-top entrainment. This work demonstrates the need to take in-situ measurements of aerosol properties for cases where the boundary layer is decoupled as well as consider cloud-top entrainment to accurately model stratocumulus cloud radiative flux.

Measurements of aerosol and CCN properties in the Mackenzie River delta (Canadian Arctic) during spring-summer transition in May 2014

NASA Astrophysics Data System (ADS)

Herenz, Paul; Wex, Heike; Henning, Silvia; Bjerring Kristensen, Thomas; Rubach, Florian; Roth, Anja; Borrmann, Stephan; Bozem, Heiko; Schulz, Hannes; Stratmann, Frank

2018-04-01

Within the framework of the RACEPAC (Radiation-Aerosol-Cloud Experiment in the Arctic Circle) project, the Arctic aerosol, arriving at a ground-based station in Tuktoyaktuk (Mackenzie River delta area, Canada), was characterized during a period of 3 weeks in May 2014. Basic meteorological parameters and particle number size distributions (PNSDs) were observed and two distinct types of air masses were found. One type were typical Arctic haze air masses, termed accumulation-type air masses, characterized by a monomodal PNSD with a pronounced accumulation mode at sizes above 100 nm. These air masses were observed during a period when back trajectories indicate an air mass origin in the north-east of Canada. The other air mass type is characterized by a bimodal PNSD with a clear minimum around 90 nm and with an Aitken mode consisting of freshly formed aerosol particles. Back trajectories indicate that these air masses, termed Aitken-type air masses, originated from the North Pacific. In addition, the application of the PSCF receptor model shows that air masses with their origin in active fire areas in central Canada and Siberia, in areas of industrial anthropogenic pollution (Norilsk and Prudhoe Bay Oil Field) and the north-west Pacific have enhanced total particle number concentrations (NCN). Generally, NCN ranged from 20 to 500 cm-3, while cloud condensation nuclei (CCN) number concentrations were found to cover a range from less than 10 up to 250 cm-3 for a supersaturation (SS) between 0.1 and 0.7 %. The hygroscopicity parameter κ of the CCN was determined to be 0.23 on average and variations in κ were largely attributed to measurement uncertainties. Furthermore, simultaneous PNSD measurements at the ground station and on the Polar 6 research aircraft were performed. We found a good agreement of ground-based PNSDs with those measured between 200 and 1200 m. During two of the four overflights, particle number concentrations at 3000 m were found to be up to 20 times higher than those measured below 2000 m; for one of these two flights, PNSDs measured above 2000 m showed a different shape than those measured at lower altitudes. This is indicative of long-range transport from lower latitudes into the Arctic that can advect aerosol from different regions in different heights.

Cellulose and Their Characteristic Ice Nucleation Activity- Freezing on a Chip

NASA Astrophysics Data System (ADS)

Häusler, Thomas; Felgitsch, Laura; Grothe, Hinrich

2016-04-01

The influence of clouds on the Earth's climate system is well known (IPCC, 2013). Cloud microphysics determines for example cloud lifetime and precipitation properties. Clouds are cooling the climate system by reflecting incoming solar radiation and warm its surface by trapping outgoing infrared radiation (Baker and Peter, 2008). In all these processes, aerosol particles play a crucial role by acting as cloud condensation nuclei (CCN) for liquid droplets and as an ice nucleation particle (INP) for the formation of ice particles. Freezing processes at higher temperatures than -38°C occur heterogeneously (Pruppacher and Klett 1997). Therefore aerosol particles act like a catalyst, which reduces the energy barrier for nucleation. The nucleation mechanisms, especially the theory of functional sites are not entirely understood. It remains unclear which class of compound nucleates ice. Here we present a unique technique to perform drop- freezing experiments in a more efficient way. A self-made freezing- chip will be presented. Measurements done to proof the efficiency of our setup as well as advantages compared with other setups will be discussed. Furthermore we present a proxy for biological INPs, microcrystalline cellulose. Cellulose is the main component of herbal cell walls (about 50 wt%). It is a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose can contribute to the diverse spectrum of ice nucleation particles. We present results of the nucleation activity measurements of MCCs as well as the influence of concentration, preparation or chemical modification.

Azores 2017 Field Campaign Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wehner, Birgit; Chevallier, Karine; Weinhold, Kay

Aerosol particles play an important role for the regional and global climate. Therefore, a network of measurement sites has been established worldwide, but only a small fraction of them is capturing the marine boundary layer (MBL) while approximately 70% of the Earth’s surface is covered with water. The main focus of this project is to improve the knowledge of sources and exchange processes of aerosol particles in general (German Research Foundation [DFG] project WE 2757/2-1) and of cloud condensation nuclei in particular (DFG project HE 6770/2-1) in the MBL in the northeastern Atlantic Ocean where the influence of local anthropogenicmore » sources is negligible. The main hypothesis of the project is that long-range transport of aerosols from North America as well as new particle formation in the free troposphere (FT) and at cloud edges followed by vertical transport contribute significantly to the aerosol budget in the MBL. The knowledge of sources and sinks of aerosol particles in combination with vertical exchange between FT and MBL is a prerequisite to predict aerosol particle number concentrations in the lowest regions of the MBL and its influence on the formation of clouds. These processes are not sufficiently quantified over the ocean up to now. To verify the hypothesis stated above, vertical exchange processes and particle sources over the Azores will be quantified using data of 17 measurement flights with high spatial resolution using a helicopter-borne platform developed at the Leibniz Institute for Tropospheric Research (TROPOS). Here, aerosol particle number concentration and vertical wind speed have been measured with a temporal resolution allowing the direct estimate of the vertical turbulent flux of aerosol particles in different heights for the first time. In addition, aerosol particle number size distributions, number concentrations of cloud condensation nuclei (CCN), cloud droplet number concentration (CDNC), and particle absorption at three different wavelengths have been determined. The data analysis is ongoing and final results are not available yet. The detailed analysis of these data will be used to conclude sources and origin of the investigated aerosol particles.« less

Nucleation and growth of sub-3 nm particles in the polluted urban atmosphere of a megacity in China

NASA Astrophysics Data System (ADS)

Yu, Huan; Zhou, Luyu; Dai, Liang; Shen, Wenchao; Dai, Wei; Zheng, Jun; Ma, Yan; Chen, Mindong

2016-03-01

Particle size distribution down to 1.4 nm was measured in the urban atmosphere of Nanjing, China, in spring, summer, and winter during 2014-2015. Sub-3 nm particle event, which is equivalent to nucleation event, occurred on 42 out of total 90 observation days, but new particles could grow to cloud condensation nuclei (CCN)-active sizes on only 9 days. In summer, infrequent nucleation was limited by both unfavorable meteorological conditions (high temperature and relative humidity - RH) and reduced anthropogenic precursor availability due to strict emission control measures during the 2014 Youth Olympic Games in Nanjing. The limiting factors for nucleation in winter and spring were meteorological conditions (radiation, temperature, and RH) and condensation sink, but for the further growth of sub-3 nm particles to CCN-active sizes, anthropogenic precursors again became limiting factors. Nucleation events were strong in the polluted urban atmosphere. Initial J1.4 at the onset and peak J1.4 at the noontime could be up to 2.1 × 102 and 2.5 × 103 cm-3 s-1, respectively, during the eight nucleation events selected from different seasons. Time-dependent J1.4 usually showed good linear correlations with a sulfuric acid proxy for every single event (R2 = 0.56-0.86, excluding a day with significant nocturnal nucleation), but the correlation among all eight events deteriorated (R2 = 0.17) due to temperature or season change. We observed that new particle growth rate (GR) did not increase monotonically with particle size, but had a local maximum up to 25 nm h-1 between 1 and 3 nm. The existence of local maxima GR in sub-3 nm size range, though sensitive to measurement uncertainties, gives new insight into cluster dynamics in polluted environments. In this study such growth rate behavior was interpreted as the solvation effect of organic activating vapor in newly formed inorganic nuclei.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, S.; Wang, Minghuai; Ghan, Steven J.

Aerosol-cloud interactions continue to constitute a major source of uncertainty for the estimate of climate radiative forcing. The variation of aerosol indirect effects (AIE) in climate models is investigated across different dynamical regimes, determined by monthly mean 500 hPa vertical pressure velocity (ω500), lower-tropospheric stability (LTS) and large-scale surface precipitation rate derived from several global climate models (GCMs), with a focus on liquid water path (LWP) response to cloud condensation nuclei (CCN) concentrations. The LWP sensitivity to aerosol perturbation within dynamic regimes is found to exhibit a large spread among these GCMs. It is in regimes of strong large-scale ascendmore » (ω500 < -25 hPa/d) and low clouds (stratocumulus and trade wind cumulus) where the models differ most. Shortwave aerosol indirect forcing is also found to differ significantly among different regimes. Shortwave aerosol indirect forcing in ascending regimes is as large as that in stratocumulus regimes, which indicates that regimes with strong large-scale ascend are as important as stratocumulus regimes in studying AIE. 42" It is further shown that shortwave aerosol indirect forcing over regions with high monthly large-scale surface precipitation rate (> 0.1 mm/d) contributes the most to the total aerosol indirect forcing (from 64% to nearly 100%). Results show that the uncertainty in AIE is even larger within specific dynamical regimes than that globally, pointing to the need to reduce the uncertainty in AIE in different dynamical regimes.« less

Aircraft-Measured Indirect Cloud Effects from Biomass Burning Smoke in the Arctic and Subarctic

NASA Technical Reports Server (NTRS)

Zamora, Lauren; Kahn, R. A.; Cubison, M. C.; Diskin, G. S.; Jimenez, J. L.; Kondo, Y.; McFarquhar, G. M.; Nenes, A.; Wisthaler, A.; Zelenyuk, A.;

Study of Aerosol - Cloud Interaction over Indo - Gangetic Basin During Normal Monsoon and Drought Years

NASA Astrophysics Data System (ADS)

Tiwari, S.; Ramachandran, S.

2017-12-01

Clouds are one of the major factors that influence the Earth's radiation budget and also change the precipitation pattern. Atmospheric aerosols play a crucial role in modifying the cloud properties acting as cloud condensation nuclei (CCN). It can change cloud droplet number concentration, cloud droplet size and hence cloud albedo. Therefore, the effects of aerosol on cloud parameters are one of the most important topics in climate change study. In the present study, we investigate the spatial variability of aerosol - cloud interactions during normal monsoon years and drought years over entire Indo - Gangetic Basin (IGB) which is one of the most polluted regions of the world. Based on aerosol loading and their major emission sources, we divided the entire IGB in to six major sub regions (R1: 66 - 71 E, 24 - 29 N; R2: 71 - 76 E, 29 - 34 N; R3: 76 - 81 E, 26 - 31 N; R4: 81 - 86 E, 23 - 28 N; R5: 86 - 91 E, 22 - 27 N and R6: 91 - 96 E, 23 - 28 N). With this objective, fifteen years (2001 - 2015), daily mean aerosol optical depth, cloud parameters and rainfall data obtained from MODerate resolution Imaging Spectroradiometer (MODIS) on board of Terra satellite and Tropical Rainfall Measuring Mission (TRMM) is analyzed over each sub regions of IGB for monsoon season (JJAS : June, July, August and September months). Preliminary results suggest that a slightly change in aerosol optical depth can affect the significant contribution of cloud fraction and other cloud properties which also show a large spatial heterogeneity. During drought years, higher cloud effective radius (i.e. CER > 20µm) decreases from western to eastern IGB suggesting the enhancement in cloud albedo. Relatively week correlation between cloud optical thickness and rainfall is found during drought years than the normal monsoon years over western IGB. The results from the present study will be helpful to reduce uncertainty in understanding of aerosol - cloud interaction over IGB. Further details will be presented during the conference.

The Arctic Summer Cloud Ocean Study (ASCOS): overview and experimental design

NASA Astrophysics Data System (ADS)

Tjernström, M.; Leck, C.; Birch, C. E.; Bottenheim, J. W.; Brooks, B. J.; Brooks, I. M.; Bäcklin, L.; Chang, R. Y.-W.; de Leeuw, G.; Di Liberto, L.; de la Rosa, S.; Granath, E.; Graus, M.; Hansel, A.; Heintzenberg, J.; Held, A.; Hind, A.; Johnston, P.; Knulst, J.; Martin, M.; Matrai, P. A.; Mauritsen, T.; Müller, M.; Norris, S. J.; Orellana, M. V.; Orsini, D. A.; Paatero, J.; Persson, P. O. G.; Gao, Q.; Rauschenberg, C.; Ristovski, Z.; Sedlar, J.; Shupe, M. D.; Sierau, B.; Sirevaag, A.; Sjogren, S.; Stetzer, O.; Swietlicki, E.; Szczodrak, M.; Vaattovaara, P.; Wahlberg, N.; Westberg, M.; Wheeler, C. R.

2014-03-01

The climate in the Arctic is changing faster than anywhere else on earth. Poorly understood feedback processes relating to Arctic clouds and aerosol-cloud interactions contribute to a poor understanding of the present changes in the Arctic climate system, and also to a large spread in projections of future climate in the Arctic. The problem is exacerbated by the paucity of research-quality observations in the central Arctic. Improved formulations in climate models require such observations, which can only come from measurements in situ in this difficult-to-reach region with logistically demanding environmental conditions. The Arctic Summer Cloud Ocean Study (ASCOS) was the most extensive central Arctic Ocean expedition with an atmospheric focus during the International Polar Year (IPY) 2007-2008. ASCOS focused on the study of the formation and life cycle of low-level Arctic clouds. ASCOS departed from Longyearbyen on Svalbard on 2 August and returned on 9 September 2008. In transit into and out of the pack ice, four short research stations were undertaken in the Fram Strait: two in open water and two in the marginal ice zone. After traversing the pack ice northward, an ice camp was set up on 12 August at 87°21' N, 01°29' W and remained in operation through 1 September, drifting with the ice. During this time, extensive measurements were taken of atmospheric gas and particle chemistry and physics, mesoscale and boundary-layer meteorology, marine biology and chemistry, and upper ocean physics. ASCOS provides a unique interdisciplinary data set for development and testing of new hypotheses on cloud processes, their interactions with the sea ice and ocean and associated physical, chemical, and biological processes and interactions. For example, the first-ever quantitative observation of bubbles in Arctic leads, combined with the unique discovery of marine organic material, polymer gels with an origin in the ocean, inside cloud droplets suggests the possibility of primary marine organically derived cloud condensation nuclei in Arctic stratocumulus clouds. Direct observations of surface fluxes of aerosols could, however, not explain observed variability in aerosol concentrations, and the balance between local and remote aerosols sources remains open. Lack of cloud condensation nuclei (CCN) was at times a controlling factor in low-level cloud formation, and hence for the impact of clouds on the surface energy budget. ASCOS provided detailed measurements of the surface energy balance from late summer melt into the initial autumn freeze-up, and documented the effects of clouds and storms on the surface energy balance during this transition. In addition to such process-level studies, the unique, independent ASCOS data set can and is being used for validation of satellite retrievals, operational models, and reanalysis data sets.

Development of an aerosol microphysical module: Aerosol Two-dimensional bin module for foRmation and Aging Simulation (ATRAS)

NASA Astrophysics Data System (ADS)

Matsui, H.; Koike, M.; Kondo, Y.; Fast, J. D.; Takigawa, M.

2014-09-01

Number concentrations, size distributions, and mixing states of aerosols are essential parameters for accurate estimations of aerosol direct and indirect effects. In this study, we develop an aerosol module, designated the Aerosol Two-dimensional bin module for foRmation and Aging Simulation (ATRAS), that can explicitly represent these parameters by considering new particle formation (NPF), black carbon (BC) aging, and secondary organic aerosol (SOA) processes. A two-dimensional bin representation is used for particles with dry diameters from 40 nm to 10 μm to resolve both aerosol sizes (12 bins) and BC mixing states (10 bins) for a total of 120 bins. The particles with diameters between 1 and 40 nm are resolved using additional eight size bins to calculate NPF. The ATRAS module is implemented in the WRF-Chem model and applied to examine the sensitivity of simulated mass, number, size distributions, and optical and radiative parameters of aerosols to NPF, BC aging, and SOA processes over East Asia during the spring of 2009. The BC absorption enhancement by coating materials is about 50% over East Asia during the spring, and the contribution of SOA processes to the absorption enhancement is estimated to be 10-20% over northern East Asia and 20-35% over southern East Asia. A clear north-south contrast is also found between the impacts of NPF and SOA processes on cloud condensation nuclei (CCN) concentrations: NPF increases CCN concentrations at higher supersaturations (smaller particles) over northern East Asia, whereas SOA increases CCN concentrations at lower supersaturations (larger particles) over southern East Asia. The application of ATRAS in East Asia also shows that the impact of each process on each optical and radiative parameter depends strongly on the process and the parameter in question. The module can be used in the future as a benchmark model to evaluate the accuracy of simpler aerosol models and examine interactions between NPF, BC aging, and SOA processes under different meteorological conditions and emissions.

On the link between hygroscopicity, volatility, and oxidation state of ambient and water-soluble aerosol in the Southeastern United States

NASA Astrophysics Data System (ADS)

Cerully, K. M.; Bougiatioti, A.; Hite, J. R., Jr.; Guo, H.; Xu, L.; Ng, N. L.; Weber, R.; Nenes, A.

2014-12-01

The formation of secondary organic aerosol (SOA) combined with the partitioning of semi-volatile organic components can impact numerous aerosol properties including cloud condensation nuclei (CCN) activity, hygroscopicity and volatility. During the summer 2013 Southern Oxidant and Aerosol Study (SOAS) field campaign in a rural site in the Southeastern United States, a suite of instruments including a CCN counter, a thermodenuder (TD) and a high resolution time-of-flight aerosol mass spectrometer (AMS) were used to measure CCN activity, aerosol volatility, composition and oxidation state. Particles were either sampled directly from ambient or through a Particle Into Liquid Sampler (PILS), allowing the investigation of the water-soluble aerosol component. Ambient aerosol exhibited size-dependent composition with larger particles being more hygroscopic. The hygroscopicity of thermally-denuded aerosol was similar between ambient and PILS-generated aerosol and showed limited dependence on volatilization. Results of AMS 3-factor Positive Matrix Factorization (PMF) analysis for the PILS-generated aerosol showed that the most hygroscopic components are most likely the most and the least volatile features of the aerosol. No clear relationship was found between organic hygroscopicity and oxygen-to-carbon ratio; in fact, Isoprene organic aerosol (Isoprene-OA) was found to be the most hygroscopic factor, while at the same time being the least oxidized and likely most volatile of all PMF factors. Considering the diurnal variation of each PMF factor and its associated hygroscopicity, Isoprene-OA and More Oxidized - Oxidized Oxygenated Organic Aerosol (MO-OOA) are the prime contributors to hygroscopicity and covary with Less Oxidized - Oxidized Oxygenated Organic Aerosol (LO-OOA) in a way that induces the observed diurnal invariance in total organic hygroscopicity. Biomass Burning Organic Aerosol (BBOA) contributed little to aerosol hygroscopicity, which is expected since there was little biomass burning activity during the sampling period examined.

Seasonal variations in physical characteristics of aerosol particles at the King Sejong Station, Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Kim, Jaeseok; Yoon, Young Jun; Gim, Yeontae; Kang, Hyo Jin; Choi, Jin Hee; Park, Ki-Tae; Lee, Bang Yong

2017-11-01

Seasonal variability in the physical characteristics of aerosol particles sampled from the King Sejong Station in the Antarctic Peninsula was investigated over the period between March 2009 and February 2015. Clear seasonal cycles for the total particle concentration (CN) were observed. The mean monthly concentration of particles larger than 2.5 nm (CN2.5) was highest during the austral summer, with an average value of 1080.39 ± 595.05 cm-3, and lowest during the austral winter, with a mean value of 197.26 ± 71.71 cm-3. The seasonal patterns in the concentrations of cloud condensation nuclei (CCN) and CN coincide, with both concentrations being at a minimum in winter and maximum in summer. The measured CCN spectra were approximated by fitting a power-law function relating the number of CCN for a given supersaturation (SS) to each SS value, with fitting coefficients C and kT. The values for C varied from 6.35 to 837.24 cm-3, with a mean of 171.48 ± 62.00 cm-3. The values for kT ranged from 0.07 to 2.19, with a mean of 0.41 ± 0.10. In particular, the kT values during the austral summer were higher than those during the winter, indicating that aerosol particles are more sensitive to SS changes during summer. Furthermore, the annual mean hygroscopicity parameter, κ, was estimated as 0.15 ± 0.05, for a SS of 0.4 %. The effects of the origin and pathway travelled by the air mass on the physical characteristics of the aerosol particles were also determined. The modal diameter of aerosol particles originating in the South Pacific Ocean showed a seasonal variation varying from 0.023 µm in winter to 0.034 µm in summer for the Aitken mode, and from 0.086 µm in winter to 0.109 µm in summer for the accumulation mode.

Characterization of Aircraft Produced Soot and Contrails Near the Tropopause

NASA Technical Reports Server (NTRS)

Hallett, John; Gudson, James G.

1997-01-01

Participation in the SUCCESS project primarily involved development and deployment of specific instruments for characterizing jet aircraft exhaust emissions as particulates and their subsequent evolution as contrail particles, either liquid or solid, as cirrus. Observations can be conveniently considered in two categories - close or distant from the aircraft. Thus close to the aircraft the exhaust is mixing through the engine turbulence with a much drier and colder environment and developing water/ ice supersaturation along the trail depending on circumstances (near field), whereas distant from the aircraft (far field) the exhaust has cooled essentially to ambient temperature, the turbulence has decayed and any particle growth or evaporation is controlled by the prevailing ambient conditions. Intermediate between these two regions the main aircraft vortices form (one on each side of the aircraft) which tend to inhibit mixing under some conditions, a region extending from a few aircraft lengths to sometimes a hundred times this distance. Our approach to the problem lay in experience gained in characterizing the smoke from hydrocarbon combustion in terms of its cloud forming properties and its potential influence on the radiation properties of the smoke and subsequent cloud from the viewpoint of reduction (absorbtion and scattering ) of solar radiation flux leading to significant global cooling (Hudson et al 1991; Hallett and Hudson 1991). Engine exhaust contains a much smaller proportion of the fuel carbon than is sometimes present in ordinary combustion (less than 0.01% compared with 10%) and influences condensation in quite different ways, to be characterized by the Cloud Condensation Nucleus, CCN - supersaturation spectrum. The transition to ice is to be related to the dilution of solution droplets to freeze by homogeneous nucleation at temperatures somewhat below -40C (Pueschel et al 1998). The subsequent growth of ice particles depends critically on temperature, supersaturation and to some extent pressure, as is demonstrated in an NSF funded project being carried out in parallel with the work reported here. As will be discussed below, nucleation processes themselves and also exhaust impurities also influence the growth of ice particles and may control some aspects of growth of ice in contrails. Instrumentation was designed to give insight into these questions and to be flown on the NASA DC- 8 as a platform. In addition a modest program was undertaken to investigate the properties of laboratory produced smoke produced under controlled conditions from the viewpoint of forming both CCN and CN. The composition of the smoke could inferred from a thermal characterization technique; larger particles were captured by formvar replicator for detailed analysis; ice particles were captured and evaporated in flight on a new instrument, the cloudscope, to give their mass, density and impurity content.

Effective density measurements of fresh particulate matter emitted by an aircraft engine

NASA Astrophysics Data System (ADS)

Abegglen, Manuel; Durdina, Lukas; Mensah, Amewu; Brem, Benjamin; Corbin, Joel; Rindlisbacher, Theo; Wang, Jing; Lohmann, Ulrike; Sierau, Berko

2014-05-01

Introduction Carbonaceous particulate matter (commonly referred to as soot), once emitted into the atmosphere affects the global radiation budget by absorbing and scattering solar radiation. Furthermore, it can alter the formation, lifetime and distribution of clouds by acting as cloud condensation nuclei (CCN) or ice nuclei (IN). The ability of soot particles to act as CCN and IN depends on their size, morphology and chemical composition. Soot particles are known to consist of spherical, primary particles that tend to arrange in chain-like structures. The structure of soot particles typically changes in the atmosphere when the particles are coated with secondary material, thus changing their radiative and cloud microphysical properties. Bond et al. (Journal of Geophysical Research, 2013: Bounding the Role of Black Carbon in the Climate System.) estimated the total industrial-era (1750 to 2005) climate forcing of black carbon to be 1.1 W/m2 ranging from the uncertainty bonds of 0.17 W/m2 to 2.1 W/m2. Facing the large uncertainty range, there is a need for a better characterization of soot particles abundant in the atmosphere. We provide experimental data on physical properties such as size, mass, density and morphology of freshly produced soot particles from a regularly used aircraft engine and from four laboratory generated soot types. This was done using a Differential Mobility Analyzer (DMA) and a Centrifugal Particle Mass Analyzer (CPMA), a relatively new instrument that records mass distributions of aerosol particles. Experimental Aircraft engine exhaust particles were collected and analysed during the Aviation Particle Regulatory Instrumentation Demonstration Experiments (A-PRIDE) campaigns in a test facility at the Zurich airport in November 2012 and August 2013. The engines were operated at different relative thrust levels spanning 7 % to 100 %. The sample was led into a heated line in order to prevent condensation of water and evolution of secondary organic aerosols. The soot masses/densities were determined using a DMA-CPMA system as described in the following. The freshly generated soot particles were first charge equilibrated to account for multiple charging and selected according to their mobility size (dm) by a DMA. The monodisperse flow then entered the CPMA which measured the corresponding mass. A condensation particle counter counted the particle number concentration. The effective density (ρeff) can be derived using the fractal relationship between mass and dm and the definition of the effective density. Additionally, we investigated four different laboratory-generated soot types at ETHZ. In detail, a Combustion Aerosol Standard burner ((1) fuel-rich and (2) fuel-lean), a (3) PALAS GFG aerosol generator and (4) carbon black (Cabot Regal Black) from an atomizer, were used. The corresponding results are compared to the aircraft engine exhaust measurements. Results The size, mass, effective density distributions, and the corresponding mobility based fractal dimensions (Dfm) from fresh soot particles emitted by a common aircraft engine and from four laboratory generated soot types were analysed. Dfm is used to describe aggregate particles. It relates the number of primary particles to dm. In general, the effective density decreases with increasing mobility diameter and depends on engine thrust.

Quantifying the impact of anthropogenic pollution on cloud properties derived from ground based remote sensors at the North Slope of Alaska

NASA Astrophysics Data System (ADS)

Maahn, M.; Acquistapace, C.; de Boer, G.; Cox, C.; Feingold, G.; Marke, T.; Williams, C. R.

2017-12-01

When acting as cloud condensation nuclei (CCN) or ice nucleating particles (INPs), aerosols have a strong potential to influence cloud properties. In particular, they can impact the number, size, and phase of cloud particles and potentially cloud lifetime through aerosol indirect and semi-direct effects. In polar regions, these effects are of great importance for the radiation budget due to the shortwave albedo and longwave emissivity of mixed-phase clouds. The Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program operates two super sites equipped with state of the art ground-based remote sensing instruments in northern Alaska. The sites are both coastal and are highly correlated with respect to large scale synoptic patterns. While the site at Utqiaġvik (formerly known as Barrow) generally represents a relatively pristine Arctic environment lacking significant anthropogenic sources, the site at Oliktok Point, approximately 250 km to the east, is surrounded by the Prudhoe Bay Oil Field, which is the largest oil field in North America. Based on aircraft measurement, the authors recently showed that differences in the properties of liquid clouds properties between the sites can be attributed to local emissions associated with the industrial activities in the Prudhoe Bay region (Maahn et al. 2017, ACPD). However, aircraft measurements do not provide a representative sample of cloud properties due to temporal limitations in the amount of data. In order to investigate how frequently and to what extent liquid cloud properties and processes are modified, we use ground based remote sensing observations such as e.g., cloud radar, Doppler lidar, and microwave radiometer obtained continuously at the two sites. In this way, we are able to quantify inter-site differences with respect to cloud drizzle production, liquid water path, frequency of cloud occurrence, and cloud radiative properties. Turbulence and the coupling of clouds to the boundary layer is investigated in order to infer the potential role of locally emitted aerosols in modulating the observed differences.

Cloud-edge mixing: Direct numerical simulation and observations in Indian Monsoon clouds

NASA Astrophysics Data System (ADS)

Kumar, Bipin; Bera, Sudarsan; Prabha, Thara V.; Grabowski, Wojceich W.

2017-03-01

A direct numerical simulation (DNS) with the decaying turbulence setup has been carried out to study cloud-edge mixing and its impact on the droplet size distribution (DSD) applying thermodynamic conditions observed in monsoon convective clouds over Indian subcontinent during the Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX). Evaporation at the cloud-edges initiates mixing at small scale and gradually introduces larger-scale fluctuations of the temperature, moisture, and vertical velocity due to droplet evaporation. Our focus is on early evolution of simulated fields that show intriguing similarities to the CAIPEEX cloud observations. A strong dilution at the cloud edge, accompanied by significant spatial variations of the droplet concentration, mean radius, and spectral width, are found in both the DNS and in observations. In DNS, fluctuations of the mean radius and spectral width come from the impact of small-scale turbulence on the motion and evaporation of inertial droplets. These fluctuations decrease with the increase of the volume over which DNS data are averaged, as one might expect. In cloud observations, these fluctuations also come from other processes, such as entrainment/mixing below the observation level, secondary CCN activation, or variations of CCN activation at the cloud base. Despite large differences in the spatial and temporal scales, the mixing diagram often used in entrainment/mixing studies with aircraft data is remarkably similar for both DNS and cloud observations. We argue that the similarity questions applicability of heuristic ideas based on mixing between two air parcels (that the mixing diagram is designed to properly represent) to the evolution of microphysical properties during turbulent mixing between a cloud and its environment.

A Numerical Study of Convection in a Condensing CO2 Atmosphere under Early Mars-Like Conditions

NASA Astrophysics Data System (ADS)

Nakajima, Kensuke; Yamashita, Tatsuya; Odaka, Masatsugu; Sugiyama, Ko-ichiro; Ishiwatari, Masaki; Nishizawa, Seiya; Takahashi, Yoshiyuki O.; Hayashi, Yoshi-Yuki

2017-10-01

Cloud convection of a CO2 atmosphere where the major constituent condenses is numerically investigated under a setup idealizing a possible warm atmosphere of early Mars, utilizing a two-dimensional cloud-resolving model forced by a fixed cooling profile as a substitute for a radiative process. The authors compare two cases with different critical saturation ratios as condensation criteria and also examine sensitivity to number mixing ratio of condensed particles given externally.When supersaturation is not necessary for condensation, the entire horizontal domain above the condensation level is continuously covered by clouds irrespective of number mixing ratio of condensed particles. Horizontal-mean cloud mass density decreases exponentially with height. The circulations below and above the condensation level are dominated by dry cellular convection and buoyancy waves, respectively.When 1.35 is adopted as the critical saturation ratio, clouds appear exclusively as intense, short-lived, quasi-periodic events. Clouds start just above the condensation level and develop upward, but intense updrafts exist only around the cloud top; they do not extend to the bottom of the condensation layer. The cloud layer is rapidly warmed by latent heat during the cloud events, and then the layer is slowly cooled by the specified thermal forcing, and supersaturation gradually develops leading to the next cloud event. The periodic appearance of cloud events does not occur when number mixing ratio of condensed particles is large.

The Green Ocean Amazon Experiment (GoAmazon2014/5) Observes Pollution Affecting Gases, Aerosols, Clouds, and Rainfall over the Rain Forest

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martin, S. T.; Artaxo, P.; Machado, L.

The Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) experiment took place around the urban region of Manaus in central Amazonia across two years. The urban pollution plume was used to study the susceptibility of gases, aerosols, clouds, and rainfall to human activities in a tropical environment. Many aspects of air quality, weather, terrestrial ecosystems, and climate work differently in the tropics than in the more thoroughly studied USA, employed an unparalleled suite of measurements at nine ground sites and onboard two aircraft to investigate the flow of background air into Manaus, the emissions into the air over themore » city, and the advection of the pollution downwind of the city. Herein, to visualize this train of processes and its effects, observations aboard a low-flying aircraft are presented. Comparative measurements within and adjacent to the plume followed the emissions of biogenic volatile organic carbon compounds (BVOCs) from the tropical forest, their transformations by the atmospheric oxidant cycle, alterations of this cycle by the influence of the pollutants, transformations of the chemical products into aerosol particles, the relationship of these particles to cloud condensation nuclei (CCN) activity, and the differences in cloud properties and rainfall for background compared to polluted conditions. The observations of the GoAmazon2014/5 experiment illustrate how the hydrologic cycle, radiation balance, and carbon recycling may be affected by present-day as well as future economic development and pollution over the Amazonian tropical forest.« less

High abundances of oxalic, azelaic, and glyoxylic acids and methylglyoxal in the open ocean with high biological activity: Implication for secondary OA formation from isoprene

NASA Astrophysics Data System (ADS)

Bikkina, Srinivas; Kawamura, Kimitaka; Miyazaki, Yuzo; Fu, Pingqing

2014-05-01

Atmospheric dicarboxylic acids (DCA) are a ubiquitous water-soluble component of secondary organic aerosols (SOA), which can act as cloud condensation nuclei (CCN), affecting the Earth's climate. Despite the high abundances of oxalic acid and related compounds in the marine aerosols, there is no consensus on what controls their distributions over the open ocean. Marine biological productivity could play a role in the production of DCA, but there is no substantial evidence to support this hypothesis. Here we present latitudinal distributions of DCA, oxoacids and α-dicarbonyls in the marine aerosols from the remote Pacific. Their concentrations were found several times higher in more biologically influenced aerosols (MBA) than less biologically influenced aerosols. We propose isoprene and unsaturated fatty acids as sources of DCA as inferred from significantly higher abundances of isoprene-SOA tracers and azelaic acid in MBA. These results have implications toward the reassessment of climate forcing feedbacks of marine-derived SOA.

Modeling Optical and Radiative Properties of Clouds Constrained with CARDEX Observations

NASA Astrophysics Data System (ADS)

Mishra, S. K.; Praveen, P. S.; Ramanathan, V.

2013-12-01

Carbonaceous aerosols (CA) have important effects on climate by directly absorbing solar radiation and indirectly changing cloud properties. These particles tend to be a complex mixture of graphitic carbon and organic compounds. The graphitic component, called as elemental carbon (EC), is characterized by significant absorption of solar radiation. Recent studies showed that organic carbon (OC) aerosols absorb strongly near UV region, and this faction is known as Brown Carbon (BrC). The indirect effect of CA can occur in two ways, first by changing the thermal structure of the atmosphere which further affects dynamical processes governing cloud life cycle; secondly, by acting as cloud condensation nuclei (CCN) that can change cloud radiative properties. In this work, cloud optical properties have been numerically estimated by accounting for CAEDEX (Cloud Aerosol Radiative Forcing Dynamics Experiment) observed cloud parameters and the physico-chemical and optical properties of aerosols. The aerosol inclusions in the cloud drop have been considered as core shell structure with core as EC and shell comprising of ammonium sulfate, ammonium nitrate, sea salt and organic carbon (organic acids, OA and brown carbon, BrC). The EC/OC ratio of the inclusion particles have been constrained based on observations. Moderate and heavy pollution events have been decided based on the aerosol number and BC concentration. Cloud drop's co-albedo at 550nm was found nearly identical for pure EC sphere inclusions and core-shell inclusions with all non-absorbing organics in the shell. However, co-albedo was found to increase for the drop having all BrC in the shell. The co-albedo of a cloud drop was found to be the maximum for all aerosol present as interstitial compare to 50% and 0% inclusions existing as interstitial aerosols. The co-albedo was found to be ~ 9.87e-4 for the drop with 100% inclusions existing as interstitial aerosols externally mixed with micron size mineral dust with 2% hematite content. The cloud spectral optical properties and the radiative properties for the aforesaid cases during CARDEX observations will be discussed in detail.

Effect of Morphology and Composition on the Hygroscopicity of Soot Aerosols

NASA Astrophysics Data System (ADS)

Williams, L.; Slowik, J.; Davidovits, P.; Jayne, J.; Kolb, C.; Worsnop, D.; Rudich, Y.

2003-12-01

Freshly generated soot aerosols are initially hydrophobic and unlikely to act as cloud condensation nuclei (CCN). However, during combustion many low vapor pressure gas products are formed that may then condense on existing soot aerosols. Additionally, soot particles may acquire coatings as they age, such as acids, salts, and oxygenated organics. An understanding of this aging process and its effect on soot hygroscopicity is necessary to address the potential of soot to act as a CCN. The transformation of soot from hydrophobic to hydrophilic is the focus of this work. An aim here is to determine the minimum coating required for hygroscopic growth. Soot particles produced by combustion of mixtures of fuel and air are size selected by a Differential Mobility Analyzer (DMA) and entrained in a laminar flow passing through a flow tube. The size selected soot particles are mixed with a controlled amount of the gas phase precursors to produce the coatings to be studied. Initial studies are focused on coatings of H2SO4, NH4NO3, and selected organics. The number of particles per unit volume of air is counted by a Condensation Particle Counter (CPC) and the particles are isokinetically sampled into an Aerosol Mass Spectrometer (AMS). Two distinct types of soot aerosols have been observed depending on the type of fuel and air mixture. With soot produced by the combustion of propane and air, the AMS shows a polydisperse particle size distribution with aerodynamic diameters ranging from 100 nm to 400 nm. The aerodynamic diameter is linearly related to the DMA-determined mobility diameter with the product density x shape factor = 1.2. The organic molecules in this soot are mostly PAH compounds. However, when kerosene is added to the propane flame, the soot particle morphology and composition is strikingly altered. While the DMA shows an essentially unchanged mobility diameter distribution, in the range 100 nm to 400, aerodynamic particle diameter is constant at about 100 nm, independent of the mobility diameter. This type of constancy of the aerodynamic diameter has been observed for soot particles in diesel engine exhaust and has been interpreted in terms of a size-dependent effective density. The soot chemical composition is also altered. In this soot the organics are mainly linear hydrocarbons. The differences between these two types of soot with respect to hygroscopicity and effective area are being investigated.

Vertical distributions of fluorescent aerosol over the Eastern U.S.

NASA Astrophysics Data System (ADS)

Perring, A. E.; Robinson, E. S.; Schwarz, J. P.; Gao, R. S.

2016-12-01

The prevalence of bioaerosol in the atmosphere is relevant to atmospheric chemistry, microbial ecology and climate. These particles can act as effective cloud condensation nuclei (CCN) and ice nuclei (IN), representing a potential feedback between vegetation and precipitation. As bioaerosol frequently account for a substantial fraction of coarse mode aerosol in the boundary layer, they may have significant impacts on mixed-phase and/or cirrus cloud formation and climate. Very few measurements are available, however, to constrain loadings of bioaerosol in the free troposphere. Here we present vertical profiles of fluorescent aerosol concentration as a proxy for bioaerosol. The data were obtained over the eastern U.S. during the summer of 2016 using a Wide Band Integrated Bioaerosol Sensor (WIBS) installed aboard a NOAA Twin Otter research aircraft. The airspeed and inlet configuration were chosen to permit efficient sampling of aerosol with diameters of up to 10 μm. Vertical profiles extend from 1000 to 17,500 feet AGL, spanning a temperature range relevant to ice formation. 100 hours of data cover a latitude range from 30N to 46N and target a variety of potential bioaerosol source regions including forests, croplands, the Gulf of Mexico, and Lake Michigan. Observed vertical profiles are compared to expected loadings based on current model parameterizations and implications are discussed.

The Role of Atmospheric Aerosol Concentration on Deep Convective Precipitation: Cloud-resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, W.-K.; Li, X.; Khain, A.; Mastsui, T.; Lang, S.; Simpson, J.

2007-01-01

Aerosols and especially their effect on clouds are one of the key components of the climate system and the hydrological cycle [Ramanathan et al., 20011. Yet, the aerosol effect on clouds remains largely unknown and the processes involved not well understood. A recent report published by the National Academy of Science states "The greatest uncertainty about the aerosol climate forcing - indeed, the largest of all the uncertainties about global climate forcing - is probably the indirect effect of aerosols on clouds NRC [2001]." The aerosol effect on clouds is often categorized into the traditional "first indirect (i.e., Twomey)" effect on the cloud droplet sizes for a constant liquid water path and the "semi-direct" effect on cloud coverage. The aerosol effect on precipitation processes, also known as the second type of aerosol indirect effect, is even more complex, especially for mixed-phase convective clouds. ln this paper, a cloud-resolving model (CRM) with detailed spectral-bin microphysics was used to examine the effect of aerosols on three different deep convective cloud systems that developed in different geographic locations: South Florida, Oklahoma and the Central Pacific. In all three cases, rain reaches the ground earlier for the low CCN (clean) case. Rain suppression is also evident in all three cases with high CCN (dirty) case. However, this suppression only occurs during the first hour of the simulations. During the mature stages of the simulations, the effects of increasing aerosol concentration range from rain suppression in the Oklahoma case, to almost no effect in the Florida case, to rain enhancement in the Pacific case. These results show the complexity of aerosol interactions with convection.

The chemical composition of fine ambient aerosol particles in the Beijing area

NASA Astrophysics Data System (ADS)

Nekat, Bettina; van Pinxteren, Dominik; Iinuma, Yoshiteru; Gnauk, Thomas; Müller, Konrad; Herrmann, Hartmut

2010-05-01

The strong economical growth in China during the last few decades led to heavy air pollution caused by significantly increased particle emissions. The aerosol particles affect not only the regional air quality and visibility, but can also influence cloud formation processes and the radiative balance of the atmosphere by their optical and microphysical properties. The ability to act as Cloud Condensation Nuclei (CCN) is related to microphysical properties like the hygroscopic growth or the cloud droplet activation. The chemical composition of CCN plays an important role on these properties and varies strongly with the particle size and the time of day. Hygroscopic or surface active substances can increase the hygroscopicity and lower the surface tension of the particle liquid phase, respectively. The presence of such compounds may result in faster cloud droplet activation by faster water uptake. The DFG project HaChi (Haze in China) aimed at studying physical and chemical parameters of urban aerosol particles in the Beijing area in order to associate the chemical composition of aerosol particles with their ability to act as CCN. To this end, two measurement campaigns were performed at the Wuqing National Ordinary Meteorological Observing Station, which is a background site near Beijing. The winter campaign was realized in March 2009 and the summer campaign took place from mid July 2009 to mid August 2009. Fine particles with an aerodynamic diameter smaller than or equal 1 μm were continuously sampled for 24h over the two campaigns using a DIGITEL high volume sampler (DHA-80). The present contribution presents and discusses the results of the chemical characterization of the DIGITEL filters samples. The filters were analyzed for the mass concentration, inorganic ions and carbon sum parameters like elemental (EC), organic (OC) and water soluble organic carbon (WSOC). The WSOC fraction was further characterized for hygroscopic substances like low molecular dicarboxylic acids as well as sugars and sugar related compounds. Additionally fatty acids were analyzed to investigate surface active substances. Usually, the highest PM1 concentrations were observed during periods with prevailing wind directions from southern areas, while northern wind directions led to significantly lower concentrations. The main components of the fine particles are inorganic ions like the secondary formed ammonium nitrate und ammonium sulphate, as well as carbonaceous material. The organic carbon fraction is mostly dominated by water soluble organic carbon (80% in average). High concentrations of tracers like the anhydrosugar levoglucosan (Iinuma et al., 2007) suggest biomass burning emissions as a dominant source of organic particles in the area. A significant fraction of PM1 remains unidentified and most likely consists of crust material like dust as well as water. Iinuma, Y., E. Brüggemann, T. Gnauk, K. Müller, M. O. Andreae, G. Helas, R. Parmar, and H. Herrmann (2007), Source characterization of biomass burning particles: The combustion of selected European conifers, African hardwood, savanna grass, and German and Indonesian peat, J. Geophys. Res. [Atmos.], 112(D8), Doi 10.1029/2006jd007120.

The Goddard Cumulus Ensemble Model (GCE): Improvements and Applications for Studying Precipitation Processes

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Lang, Stephen E.; Zeng, Xiping; Li, Xiaowen; Matsui, Toshi; Mohr, Karen; Posselt, Derek; Chern, Jiundar; Peters-Lidard, Christa; Norris, Peter M.;

The climate penalty for clean fossil fuel combustion

NASA Astrophysics Data System (ADS)

Junkermann, W.; Vogel, B.; Sutton, M. A.

2011-12-01

To cope with the world's growing demand for energy, a large number of coal-fired power plants are currently in operation or under construction. To prevent environmental damage from acidic sulphur and particulate emissions, many such installations are equipped with flue gas cleaning technology that reduces the emitted amounts of sulphur dioxide (SO2) and nitrogen dioxide (NO2). However, the consequences of this technology for aerosol emissions, and in particular the regional scale impact on cloud microphysics, have not been studied until now. We performed airborne investigations to measure aerosol size distributions in the air masses downwind of coal-fired power installations. We show how the current generation of clean technology reduces the emission of sulphur and fine particulate matter, but leads to an unanticipated increase in the direct emission of ultrafine particles (1-10 nm median diameter) which are highly effective precursors of cloud condensation nuclei (CCN). Our analysis shows how these additional ultrafine particles probably modify cloud microphysics, as well as precipitation intensity and distribution on a regional scale downwind of emission sources. Effectively, the number of small water droplets might be increased, thus reducing the water available for large droplets and rain formation. The possible corresponding changes in the precipitation budget with a shift from more frequent steady rain to occasionally more vigorous rain events, or even a significant regional reduction of annual precipitation, introduce an unanticipated risk for regional climate and agricultural production, especially in semi-arid climate zones.

The climate penalty for clean fossil fuel combustion

NASA Astrophysics Data System (ADS)

Junkermann, W.; Vogel, B.; Sutton, M. A.

2011-09-01

To cope with the world's growing demand for energy, a large number of coal-fired power plants are currently in operation or under construction. To prevent environmental damage from acidic sulphur and particulate emissions, many such installations are equipped with flue gas cleaning technology that reduces the emitted amounts of sulphur dioxide (SO2) and nitrogen dioxide (NO2). However, the consequences of this technology for aerosol emissions, and in particular the regional scale impact on cloud microphysics, have not been studied until now. We performed airborne investigations to measure aerosol size distributions in the air masses downwind of coal-fired power installations. We show how the current generation of clean technology reduces the emission of sulphur and fine particulate matter, but leads to an unanticipated increase in the direct emission of ultrafine particles (1-10 nm median diameter) which are highly effective precursors of cloud condensation nuclei (CCN). Our analysis shows how these additional ultrafine particles modify cloud microphysics, as well as precipitation intensity and distribution on a regional scale downwind of emission sources. Effectively, the number of small water droplets is increased, thus reducing the water available for large droplets and rain formation. The corresponding changes in the precipitation budget with a shift from more frequent steady rain to occasionally more vigorous rain events, or even a significant regional reduction of annual precipitation, introduce an unanticipated risk for regional climate and agricultural production, especially in semi-arid climate zones.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Shipeng; Wang, Minghuai; Ghan, Steven J.

Aerosol–cloud interactions continue to constitute a major source of uncertainty for the estimate of climate radiative forcing. The variation of aerosol indirect effects (AIE) in climate models is investigated across different dynamical regimes, determined by monthly mean 500 hPa vertical pressure velocity ( ω 500), lower-tropospheric stability (LTS) and large-scale surface precipitation rate derived from several global climate models (GCMs), with a focus on liquid water path (LWP) response to cloud condensation nuclei (CCN) concentrations. The LWP sensitivity to aerosol perturbation within dynamic regimes is found to exhibit a large spread among these GCMs. It is in regimes of strongmore » large-scale ascent ( ω 500  <  −25 hPa day −1) and low clouds (stratocumulus and trade wind cumulus) where the models differ most. Shortwave aerosol indirect forcing is also found to differ significantly among different regimes. Shortwave aerosol indirect forcing in ascending regimes is close to that in subsidence regimes, which indicates that regimes with strong large-scale ascent are as important as stratocumulus regimes in studying AIE. It is further shown that shortwave aerosol indirect forcing over regions with high monthly large-scale surface precipitation rate (> 0.1 mm day −1) contributes the most to the total aerosol indirect forcing (from 64 to nearly 100 %). Results show that the uncertainty in AIE is even larger within specific dynamical regimes compared to the uncertainty in its global mean values, pointing to the need to reduce the uncertainty in AIE in different dynamical regimes.« less

Aerosol properties associated with air masses arriving into the North East Atlantic during the 2008 Mace Head EUCAARI intensive observing period: an overview

NASA Astrophysics Data System (ADS)

Dall'Osto, M.; Ceburnis, D.; Martucci, G.; Bialek, J.; Dupuy, R.; Jennings, S. G.; Berresheim, H.; Wenger, J. C.; Sodeau, J. R.; Healy, R. M.; Facchini, M. C.; Rinaldi, M.; Giulianelli, L.; Finessi, E.; Worsnop, D.; O'Dowd, C. D.

2009-12-01

As part of the EUCAARI Intensive Observing Period, a 4-week campaign to measure aerosol physical, chemical and optical properties, atmospheric structure, and cloud microphysics was conducted from mid-May to mid-June 2008 at the Mace Head Atmospheric Research Station, located at the interface of Western Europe and the NE Atlantic and centered on the west Irish coastline. During the campaign, continental air masses comprising both young and aged continental plumes were encountered, along with polar, Arctic and tropical air masses. Polluted-continental aerosol concentrations were of the order of 3000 cm-3, while background marine air aerosol concentrations were between 400-600 cm-3. The highest marine air concentrations occurred in polar air masses in which a 15 nm nucleation mode, with concentration of 1100 cm-3, was observed and attributed to open ocean particle formation. Black carbon concentrations in polluted air were between 300-400 ng m-3, and in clean marine air were less than 50 ng m-3. Continental air submicron chemical composition (excluding refractory sea salt) was dominated by organic matter, closely followed by sulphate mass. Although the concentrations and size distribution spectral shape were almost identical for the young and aged continental cases, hygroscopic growth factors (GF) and cloud condensation nuclei (CCN) to total condensation nuclei (CN) concentration ratios were significantly less in the younger pollution plume, indicating a more oxidized organic component to the aged continental plume. The difference in chemical composition and hygroscopic growth factor appear to result in a 40-50% impact on aerosol scattering coefficients and Aerosol Optical Depth, despite almost identical aerosol microphysical properties in both cases, with the higher values been recorded for the more aged case. For the CCN/CN ratio, the highest ratios were seen in the more age plume. In marine air, sulphate mass dominated the sub-micron component, followed by water soluble organic carbon, which, in turn, was dominated by methanesulphonic acid (MSA). Sulphate concentrations were highest in marine tropical air - even higher than in continental air. MSA was present at twice the concentrations of previously-reported concentrations at the same location and the same season. Both continental and marine air exhibited aerosol GFs significantly less than ammonium sulphate and even less in terms of sea salt aerosol pointing to a significant organic contribution to all air mass aerosol properties.

Modeling CCN effects on tropical convection: An statistical perspective

NASA Astrophysics Data System (ADS)

Carrio, G. G.; Cotton, W. R.; Massie, S. T.

2012-12-01

This modeling study examines the response of tropical convection to the enhancement of CCN concentrations from a statistical perspective. The sensitivity runs were performed using RAMS version 6.0, covering almost the entire Amazonian Aerosol Characterization Experiment period (AMAZE, wet season of 2008). The main focus of the analysis was the indirect aerosol effects on the probability density functions (PDFs) of various cloud properties. RAMS was configured to work with four two-way interactive nested grids with 42 vertical levels and horizontal grid spacing of 150, 37.5, 7.5, and 1.5 km. Grids 2 and 3 were used to simulate the synoptic and mesoscale environments, while grid 4 was used to resolve deep convection. Comparisons were made using the finest grid with a domain size of 300 X 300km, approximately centered on the city of Manaus (3.1S, 60.01W). The vertical grid was stretched using with 75m spacing at the finest levels to provide better resolution within the first 1.5 km, and the model top extended to approximately 22 km above ground level. RAMS was initialized on February 10 2008 (00:00 UTC), the length of simulations was 32 days, and GSF data were used for initialization and nudging of the coarser-grid boundaries. The control run considered a CCN concentration of 300cm-3 while other several other simulations considered an influx of higher CCN concentrations (up to 1300/cc) . The latter concentration was observed near the end of the AMAZE project period. Both direct and indirect effects of these CCN particles were considered. Model output data (finest grid) every 15 min were used to compute the PDFs for each model level. When increasing aerosol concentrations, significant impacts were simulated for the PDFs of the water contents of various hydrometeors, vertical motions, area with precipitation, latent heat releases, among other quantities. In most cases, they exhibited a peculiar non-monotonic response similar to that seen in two previous studies of ours (for isolated cloud systems). It is well known that a reduction in sizes of cloud droplets reduces coalescence, increases their probability of reaching super-cooled levels, and convective cells are intensified by additional release of latent heat of freezing. However, indirect aerosol effects tend to revert when aerosol concentrations are greatly enhanced due to the riming efficiency reduction of ice particles. However, some quantities show a different response; for instance, the water content associated with small ice crystals large contents are always more likely at high levels when considering air masses more polluted in terms of CCN. Conversely, the PDF's of water contents of larger ice crystals at high altitudes exhibit the aforementioned non-monotonic behavior.

Isoprene suppression of new particle formation: Potential mechanisms and implications

NASA Astrophysics Data System (ADS)

Lee, Shan-Hu; Uin, Janek; Guenther, Alex B.; de Gouw, Joost A.; Yu, Fangqun; Nadykto, Alex B.; Herb, Jason; Ng, Nga L.; Koss, Abigail; Brune, William H.; Baumann, Karsten; Kanawade, Vijay P.; Keutsch, Frank N.; Nenes, Athanasios; Olsen, Kevin; Goldstein, Allen; Ouyang, Qi

2016-12-01

Secondary aerosols formed from anthropogenic pollutants and natural emissions have substantial impacts on human health, air quality, and the Earth's climate. New particle formation (NPF) contributes up to 70% of the global production of cloud condensation nuclei (CCN), but the effects of biogenic volatile organic compounds (BVOCs) and their oxidation products on NPF processes in forests are poorly understood. Observations show that isoprene, the most abundant BVOC, suppresses NPF in forests. But the previously proposed chemical mechanism underlying this suppression process contradicts atmospheric observations. By reviewing observations made in other forests, it is clear that NPF rarely takes place during the summer when emissions of isoprene are high, even though there are sufficient concentrations of monoterpenes. But at present it is not clear how isoprene and its oxidation products may change the oxidation chemistry of terpenes and how NOx and other atmospheric key species affect NPF in forest environments. Future laboratory experiments with chemical speciation of gas phase nucleation precursors and clusters and chemical composition of particles smaller than 10 nm are required to understand the role of isoprene in NPF. Our results show that climate models can overpredict aerosol's first indirect effect when not considering the absence of NPF in the southeastern U.S. forests during the summer using the current nucleation algorithm that includes only sulfuric acid and total concentrations of low-volatility organic compounds. This highlights the importance of understanding NPF processes as function of temperature, relative humidity, and BVOC compositions to make valid predictions of NPF and CCN at a wide range of atmospheric conditions.

New particle formation around the globe: From laboratory experiments to the Everest Base Camp (Arne Richter Award for Outstanding ECSs Lecture)

NASA Astrophysics Data System (ADS)

Bianchi, Federico

2017-04-01

Atmospheric aerosols affect the climate directly by absorbing or scattering incoming radiation and also indirectly by acting as cloud condensation nuclei (CCN) changing therefore the cloud albedo. A major fraction of these CCN comes from gas to particle conversion (nucleation). During the last decade, several nucleation studies have been published based on field observations, however most of them in the planetary boundary layer (PBL). Therefore, only little information is available about the free troposphere. The aim of this lecture is to elucidate the last founding about what species contribute to new particle formation (NPF) in the free troposphere. In the last years, we used a number of state-of-the-art instruments, first at the Swiss high alpine research station Jungfraujoch (3580 m asl) and then at the Himalayan Nepal Climate Observatory Pyramid (NCO-P) site on the southern slope of the Himalayas, not far from Everest base camp (5079 m asl). Previous studies have already showed that at both of these locations NPF takes place frequently. However, no chemical information of the vapours was retrieved. At the Nepal Climate Observatory Pyramid, we deployed an atmospheric pressure interface time-of-flight mass spectrometer (APi-TOF), a particle size magnifier (PSM) and a neutral cluster and air ion spectrometer (NAIS). The APi-TOF measured the chemical composition of either the positive or negative ions during many the nucleation events and when equipped with a chemical ionization source (CI-APi-TOF) it provided information on the chemical composition of the neutral species. In this medal lecture, in addition to present the results of these two studies, I will also compare them with other locations as the boreal forest (Hyytiälä) and polluted area as Shanghai but also with laboratory experiments (i.e. CLOUD experiment at CERN). I will present a detailed analysis of the particles evolution during nucleation and also the chemical composition of the small clusters measured with these advanced mass spectrometers. I will also show that these processes are potentially very interesting in order to understand the aerosol conditions in the pre-industrial era where information are really scares. At the end of the lecture I will also give some insight regarding future project above the Amazon and as well above the Alps.

A perspective on SOA generated in aerosol water from glyoxal and methylglyoxal and its impacts on climate-relevant aerosol properties

NASA Astrophysics Data System (ADS)

Sareen, N.; McNeill, V. F.

2011-12-01

In recent years, glyoxal and methylglyoxal have emerged to be potentially important SOA precursors with significant implications for climate-related aerosol properties. Here we will discuss how the chemistry of these and similar organic compounds in aerosol water can affect the aerosol optical and cloud formation properties. Aqueous-phase SOA production from glyoxal and methylglyoxal is a potential source of strongly light-absorbing organics, or "brown carbon". We characterized the kinetics of brown carbon formation from these precursors in mixtures of ammonium sulfate and water using UV-Vis spectrophotometry. This mechanism has been incorporated into a photochemical box model with coupled gas phase-aqueous aerosol chemistry. Methylglyoxal and related compounds also may impact an aerosol's ability to act as a cloud condensation nucleus. We recently showed via pendant drop tensiometry and aerosol chamber studies that uptake of methylglyoxal from the gas phase driven by aqueous-phase oligomerization chemistry is a potentially significant, previously unidentified source of surface-active organic material in aerosols. Results from pendant drop tensiometry showed significantly depressed surface tension in methylglyoxal-ammonium sulfate solutions. We further found that ammonium sulfate particles exposed to gas-phase methylglyoxal in a 3.5 m3 aerosol reaction chamber activate into cloud droplets at sizes up to 15% lower at a given supersaturation than do pure ammonium sulfate particles. The observed enhancement exceeds that predicted based on Henry's Law and our measurements of surface tension depression in bulk solutions, suggesting that surface adsorption of methylglyoxal plays a role in determining CCN activity. Methylglyoxal and similar gas-phase surfactants may be an important and overlooked source of enhanced CCN activity in the atmosphere. To characterize the SOA products formed in these solutions, an Aerosol Chemical Ionization Mass Spectrometer (CIMS) was used. These compounds included (hemi)acetals, aldol condensation products, and oligomeric species up to 759 amu. Since these products are vulnerable to oxidants such as O3 and OH in the atmosphere, kinetic studies were conducted to study their affect upon exposure to O3 and OH. Custom-designed flow tube reactors were coupled with the Aerosol-CIMS to monitor aerosol composition, and consequently this data was used to determine reactive uptake coefficients (γO3~10-8 and γOH~ 10-6). Additionally, the lifetime of these SOA species in the atmosphere can be estimated and if these time scales are sufficiently long, they may affect aerosol optical properties. The effect of oxidation on the optical properties is also currently being tested by collecting aerosol particles before and after oxidation on a quartz window and testing changes in absorption using the UV-Vis spectrophotometer. The results of all these studies will be integrated to understand the role of methylglyoxal as a SOA precursor and the effect on various aerosol properties, and this will be used as a model system to predict the fate of similar organics in the atmosphere.

On the Chemical Characterization of Organic Matter in Rain at Mexico City.

NASA Astrophysics Data System (ADS)

Montero-Martinez, G.; Andraca-Ayala, G. L.; Hernández-Nagay, D. P.; Mendoza-Trejo, A.; Rivera-Arellano, J.; Rosado-Abon, A.; Roy, P. D.

2016-12-01

The chemical composition of the aerosol plays a central role in atmospheric processes and has influence on the hydrological cycle. Clouds form through the nucleation of water vapor on certain atmospheric aerosol particles, called cloud condensation nuclei (CCN). Also, precipitating particles scavenge some other aerosol particles on their way to the surface. Atmospheric particles are a mixture of organic and inorganic materials, both soluble and insoluble in water. Aerosol chemical characterization indicates a larger variety of compounds in urban areas respect to other regions. Thus, chemical composition of rainwater may represent an important aspect for estimating atmospheric air pollution. It has been recognized that organic species present in aerosol particles are important in the formation of cloud droplets. Therefore, the information about the organic compounds in precipitation samples may be helpful to understand their effects on the formation of clouds and rain, as well as their sources. Organic acids are ubiquitous components of aerosols and have been identified in precipitation water. In this work, preliminary results of the content of soluble organic (neutral and acidic) matter in rainwater samples collected in Mexico City during 2015 will be presented. The organic compounds content was performed by using an ionic chromatographic methodology with gradient elution; so the total amount was evaluated as the sum of four fractions: neutral/basic, mono-, bi-, and poly-acid compounds. The outcomes suggest that most of the amount of organic substances soluble in water is contained by the neutral/basic and mono-acid fractions. Regarding the total amount of water soluble organic compounds, the rain samples collected in Mexico City are in agreement with some others reported for large urban areas.

The Green Ocean Amazon Experiment (GoAmazon2014/5) Observes Pollution Affecting Gases, Aerosols, Clouds, and Rainfall over the Rain Forest

DOE PAGES

Martin, S. T.; Artaxo, P.; Machado, L.; ...

2017-05-15

The Observations and Modeling of the Green Ocean Amazon 2014–2015 (GoAmazon2014/5) experiment took place around the urban region of Manaus in central Amazonia across 2 years. The urban pollution plume was used to study the susceptibility of gases, aerosols, clouds, and rainfall to human activities in a tropical environment. Many aspects of air quality, weather, terrestrial ecosystems, and climate work differently in the tropics than in the more thoroughly studied temperate regions of Earth. GoAmazon2014/5, a cooperative project of Brazil, Germany, and the United States, employed an unparalleled suite of measurements at nine ground sites and on board two aircraftmore » to investigate the flow of background air into Manaus, the emissions into the air over the city, and the advection of the pollution downwind of the city. Here in this paper, to visualize this train of processes and its effects, observations aboard a low-flying aircraft are presented. Comparative measurements within and adjacent to the plume followed the emissions of biogenic volatile organic carbon compounds (BVOCs) from the tropical forest, their transformations by the atmospheric oxidant cycle, alterations of this cycle by the influence of the pollutants, transformations of the chemical products into aerosol particles, the relationship of these particles to cloud condensation nuclei (CCN) activity, and the differences in cloud properties and rainfall for background compared to polluted conditions. The observations of the GoAmazon2014/5 experiment illustrate how the hydrologic cycle, radiation balance, and carbon recycling may be affected by present-day as well as future economic development and pollution over the Amazonian tropical forest.« less

The Green Ocean Amazon Experiment (GoAmazon2014/5) Observes Pollution Affecting Gases, Aerosols, Clouds, and Rainfall over the Rain Forest

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martin, S. T.; Artaxo, P.; Machado, L.

The Observations and Modeling of the Green Ocean Amazon 2014–2015 (GoAmazon2014/5) experiment took place around the urban region of Manaus in central Amazonia across 2 years. The urban pollution plume was used to study the susceptibility of gases, aerosols, clouds, and rainfall to human activities in a tropical environment. Many aspects of air quality, weather, terrestrial ecosystems, and climate work differently in the tropics than in the more thoroughly studied temperate regions of Earth. GoAmazon2014/5, a cooperative project of Brazil, Germany, and the United States, employed an unparalleled suite of measurements at nine ground sites and on board two aircraftmore » to investigate the flow of background air into Manaus, the emissions into the air over the city, and the advection of the pollution downwind of the city. Here in this paper, to visualize this train of processes and its effects, observations aboard a low-flying aircraft are presented. Comparative measurements within and adjacent to the plume followed the emissions of biogenic volatile organic carbon compounds (BVOCs) from the tropical forest, their transformations by the atmospheric oxidant cycle, alterations of this cycle by the influence of the pollutants, transformations of the chemical products into aerosol particles, the relationship of these particles to cloud condensation nuclei (CCN) activity, and the differences in cloud properties and rainfall for background compared to polluted conditions. The observations of the GoAmazon2014/5 experiment illustrate how the hydrologic cycle, radiation balance, and carbon recycling may be affected by present-day as well as future economic development and pollution over the Amazonian tropical forest.« less

Direct evidence for coastal iodine particles from Laminaria macroalgae - linkage to emissions of molecular iodine

NASA Astrophysics Data System (ADS)

McFiggans, G.; Coe, H.; Burgess, R.; Allan, J.; Cubison, M.; Alfarra, M. R.; Saunders, R.; Saiz-Lopez, A.; Plane, J. M. C.; Wevill, D.; Carpenter, L.; Rickard, A. R.; Monks, P. S.

2004-05-01

Renewal of ultrafine aerosols in the marine boundary layer may lead to repopulation of the marine distribution and ultimately determine the concentration of cloud condensation nuclei (CCN). Thus the formation of nanometre-scale particles can lead to enhanced scattering of incoming radiation and a net cooling of the atmosphere. The recent demonstration of the chamber formation of new particles from the photolytic production of condensable iodine-containing compounds from diiodomethane (CH2I2), (O'Dowd et al., 2002; Kolb, 2002; Jimenez et al., 2003a; Burkholder and Ravishankara, 2003), provides an additional mechanism to the gas-to-particle conversion of sulphuric acid formed in the photo-oxidation of dimethylsulphide for marine aerosol repopulation. CH2I2 is emitted from seaweeds (Carpenter et al., 1999, 2000) and has been suggested as an initiator of particle formation. We demonstrate here for the first time that ultrafine iodine-containing particles are produced by intertidal macroalgae exposed to ambient levels of ozone. The particle composition is very similar both to those formed in the chamber photo-oxidation of diiodomethane and in the oxidation of molecular iodine by ozone. The particles formed in all three systems are similarly aspherical. When small, those formed in the molecular iodine system swell only moderately when exposed to increased humidity environments, and swell progressively less with increasing size; this behaviour occurs whether they are formed in dry or humid environments, in contrast to those in the CH2I2 system. Direct coastal boundary layer observations of molecular iodine, ultrafine particle production and iodocarbons are reported. Using a newly measured molecular iodine photolysis rate, it is shown that, if atomic iodine is involved in the observed particle bursts, it is of the order of at least 1000 times more likely to result from molecular iodine photolysis than diiodomethane photolysis. A hypothesis for molecular iodine release from intertidal macroalgae is presented and the potential importance of macroalgal iodine particles in their contribution to CCN and global radiative forcing are discussed.

Autoxidation as a source of gas-phase highly-oxidized multifunctional compounds (HOM) - measured by chemical ionization spectrometry (CIMS) utilizing various reagent ion chemistries

NASA Astrophysics Data System (ADS)

Rissanen, M.; Kurten, T.; Mauldin, L.; Ehn, M.

2017-12-01

Secondary organic aerosol (SOA) constitutes the largest fraction of atmospheric submicron particulate matter. Despite its importance to the Earth's radiative balance, mainly by acting as a source of cloud condensation nuclei (CCN), the molecular details of the first-steps of atmospheric new particle formation keep eluding researchers. Recently a gas-phase autocatalytic oxidation mechanism (=autoxidation) was invoked to explain the very fast formation of highly-oxidized multifunctional organic compounds (HOMs), and it was shown to provide the needed prompt condensable matter that forms the smallest of the atmospheric particles. Of detailed autoxidation progressions, only cyclohexene ozonolysis initiated oxidation has been described by quantum chemical computations, and it was quickly recognized that further reaction steps are needed (such as endoperoxidation) to explain the formation of the observed HOM products from biogenic terpenes. Also it was realized that the simplest group additivity principles commonly applied to derive saturation vapor pressures do not suffice to determine the vapor pressures of multiple hydroperoxide and other oxidized functionalities containing HOM products. Thereby the fraction of the lowest volatility products is less than previously assumed, which could indicate reactive uptake of HOM products. In the AGU fall meeting I will present our most recent findings on resolving the (i) detailed molecular mechanisms generating HOMs, (ii) their actual vapor pressures, and (iii) their interaction with the environment.

A dichotomy in primary marine organic aerosol-cloud-climate system

NASA Astrophysics Data System (ADS)

Ceburnis, D.; Ovadnevaite, J.; Martucci, G.; Bialek, J.; Monahan, C.; Rinaldi, M.; Facchini, C.; Berresheim, H.; Worsnop, D. R.; O'Dowd, C.

2011-12-01

D. Ceburnis1, J. Ovadnevaite1, G. Martucci1, J. Bialek1, C. Monahan1, M. Rinaldi2, M. C. Facchini2, H. Berresheim1, D. R. Worsnop3,4 and C. D. O'Dowd1 1School of Physics & Centre for Climate and Air Pollution Studies, National University of Ireland Galway, University Road, Galway, Ireland 2Institute of Atmospheric Sciences and Climate, National Research Council, Bologna, 20129, Italy. 3 Aerodyne Research, Inc., 45 Manning Road, Billerica, MA 01821-3976, USA 4 Physics Department, University of Helsinki, P.O. Box 64, 00014, Helsinki, Finland Organic matter has been observed to significantly contribute to particulate matter in every environment including pristine remote oceans. A significant if not dominant contribution of insoluble organic matter to marine aerosol has been proved to be of biogenic origin1,2. High time resolution measurements of marine organic matter have demonstrated a dynamic system with regular organic matter plume events occurring during summer3 as well as frequent open ocean particle formation events4. High-time resolution measurements of primary marine organic sea-spray physico-chemical properties reveal an apparent dichotomous behavior in terms of water uptake: specifically sea-spray aerosol enriched in organic matter possesses a low hygroscopic Growth Factor (GF~1.25) while simultaneously having a cloud condensation nucleus/condensation nuclei (CCN/CN) activation efficiency of between 83% at 0.25% supersaturation and 100% at 0.75%5. Simultaneous retrieval of Cloud Droplet Number Concentration (CDNC) during primary organic aerosol plumes reveal CDNC concentrations of 350 cm-3 in newly formed marine stratocumulus cloud for boundary layer organic mass concentrations of 3-4 ug m-36. It is suggested that marine hydrogels are responsible for this dichotomous behavior which has profound impacts to aerosol-cloud-climate system along with a better understood process analysis of aerosol formation by sea-spray7. A hydrophobic character of organic matter dominated aerosol in sub-saturated conditions should have significant implications for direct radiative effect while effectively forming cloud condensation nuclei should have significant contribution to indirect effect. 1 O'Dowd, C. D. et al. Nature 431, 676-680, doi:10.1038/Nature02959 (2004). 2 Ceburnis, D. et al. Atmos. Chem. Phys. Discuss. 11, 2749-2772, doi:doi:10.5194/acpd-11-2749-2011 (2011). 3 Ovadnevaite, J. et al. Geophys Res Lett 38, L02807, doi:10.1029/2010gl046083 (2011). 4 O'Dowd, C., et al. Geophys Res Lett 37, doi:L19805 10.1029/2010gl044679 (2010). 5 Ovadnevaite, J. et al. Geophys Res Lett (2011). 6 Martucci, G. and O'Dowd, C. D. Atmos. Meas. Tech. Discuss., 4, 4825-4865, doi:10.5194/amtd-4-4825-2011 (2011) 7 Gantt, B. et al. Atmos. Chem. Phys. Discuss. 11, 10525-10555, doi:10.5194/acpd-11-10525-2011 (2011).

The Exoplanet Cloud Atlas

NASA Astrophysics Data System (ADS)

Gao, Peter; Marley, Mark S.; Morley, Caroline; Fortney, Jonathan J.

2017-10-01

Clouds have been readily inferred from observations of exoplanet atmospheres, and there exists great variability in cloudiness between planets, such that no clear trend in exoplanet cloudiness has so far been discerned. Equilibrium condensation calculations suggest a myriad of species - salts, sulfides, silicates, and metals - could condense in exoplanet atmospheres, but how they behave as clouds is uncertain. The behavior of clouds - their formation, evolution, and equilibrium size distribution - is controlled by cloud microphysics, which includes processes such as nucleation, condensation, and evaporation. In this work, we explore the cloudy exoplanet phase space by using a cloud microphysics model to simulate a suite of cloud species ranging from cooler condensates such as KCl/ZnS, to hotter condensates like perovskite and corundum. We investigate how the cloudiness and cloud particle sizes of exoplanets change due to variations in temperature, metallicity, gravity, and cloud formation mechanisms, and how these changes may be reflected in current and future observations. In particular, we will evaluate where in phase space could cloud spectral features be observable using JWST MIRI at long wavelengths, which will be dependent on the cloud particle size distribution and cloud species.

Observations and implications of liquid–liquid phase separation at high relative humidities in secondary organic material produced by α-pinene ozonolysis without inorganic salts

DOE PAGES

Renbaum-Wolff, Lindsay; Song, Mijung; Marcolli, Claudia; ...

2016-07-01

Particles consisting of secondary organic material (SOM) are abundant in the atmosphere. In order to predict the role of these particles in climate, visibility and atmospheric chemistry, information on particle phase state (i.e., single liquid, two liquids and solid) is needed. Our paper focuses on the phase state of SOM particles free of inorganic salts produced by the ozonolysis of α-pinene. Phase transitions were investigated in the laboratory using optical microscopy and theoretically using a thermodynamic model at 290 K and for relative humidities ranging from < 0.5 to 100%. In the laboratory studies, a single phase was observed frommore » 0 to 95% relative humidity (RH) while two liquid phases were observed above 95% RH. For increasing RH, the mechanism of liquid–liquid phase separation (LLPS) was spinodal decomposition. The RH range over which two liquid phases were observed did not depend on the direction of RH change. In the modeling studies, the SOM took up very little water and was a single organic-rich phase at low RH values. At high RH, the SOM underwent LLPS to form an organic-rich phase and a water-rich phase, consistent with the laboratory studies. The presence of LLPS at high RH values can have consequences for the cloud condensation nuclei (CCN) activity of SOM particles. In the simulated Köhler curves for SOM particles, two local maxima were observed. Depending on the composition of the SOM, the first or second maximum can determine the critical supersaturation for activation. Recently researchers have observed inconsistencies between measured CCN properties of SOM particles and hygroscopic growth measured below water saturation (i.e., hygroscopic parameters measured below water saturation were inconsistent with hygroscopic parameters measured above water saturation). Furthermore, the work presented here illustrates that such inconsistencies are expected for systems with LLPS when the water uptake at subsaturated conditions represents the hygroscopicity of an organic-rich phase while the barrier for CCN activation can be determined by the second maximum in the Köhler curve when the particles are water rich.« less

Turbulent aerosol fluxes over the Arctic Ocean: 2. Wind-driven sources from the sea

NASA Astrophysics Data System (ADS)

Nilsson, E. D.; Rannik, Ü.; Swietlicki, E.; Leck, C.; Aalto, P. P.; Zhou, J.; Norman, M.

2001-12-01

An eddy-covariance flux system was successfully applied over open sea, leads and ice floes during the Arctic Ocean Expedition in July-August 1996. Wind-driven upward aerosol number fluxes were observed over open sea and leads in the pack ice. These particles must originate from droplets ejected into the air at the bursting of small air bubbles at the water surface. The source flux F (in 106 m-2 s-1) had a strong dependency on wind speed, log>(F>)=0.20U¯-1.71 and 0.11U¯-1.93, over the open sea and leads, respectively (where U¯ is the local wind speed at about 10 m height). Over the open sea the wind-driven aerosol source flux consisted of a film drop mode centered at ˜100 nm diameter and a jet drop mode centered at ˜1 μm diameter. Over the leads in the pack ice, a jet drop mode at ˜2 μm diameter dominated. The jet drop mode consisted of sea-salt, but oxalate indicated an organic contribution, and bacterias and other biogenic particles were identified by single particle analysis. Particles with diameters less than -100 nm appear to have contributed to the flux, but their chemical composition is unknown. Whitecaps were probably the bubble source at open sea and on the leads at high wind speed, but a different bubble source is needed in the leads owing to their small fetch. Melting of ice in the leads is probably the best candidate. The flux over the open sea was of such a magnitude that it could give a significant contribution to the condensation nuclei (CCN) population. Although the flux from the leads were roughly an order of magnitude smaller and the leads cover only a small fraction of the pack ice, the local source may till be important for the CCN population in Arctic fogs. The primary marine aerosol source will increase both with increased wind speed and with decreased ice fraction and extent. The local CCN production may therefore increase and influence cloud or fog albedo and lifetime in response to greenhouse warming in the Arctic Ocean region.

The hygroscopicity parameter (κ) of ambient organic aerosol at a field site subject to biogenic and anthropogenic influences: relationship to degree of aerosol oxidation

NASA Astrophysics Data System (ADS)

Chang, R. Y.-W.; Slowik, J. G.; Shantz, N. C.; Vlasenko, A.; Liggio, J.; Sjostedt, S. J.; Leaitch, W. R.; Abbatt, J. P. D.

2010-06-01

Cloud condensation nuclei (CCN) concentrations were measured at Egbert, a rural site in Ontario, Canada during the spring of 2007. The CCN concentrations were compared to values predicted from the aerosol chemical composition and size distribution using κ-Köhler theory, with the specific goal of this work being to determine the hygroscopic parameter (κ) of the oxygenated organic component of the aerosol, assuming that oxygenation drives the hygroscopicity for the entire organic fraction of the aerosol. The hygroscopicity of the oxygenated fraction of the organic component, as determined by an Aerodyne aerosol mass spectrometer (AMS), was characterised by two methods. First, positive matrix factorization (PMF) was used to separate oxygenated and unoxygenated organic aerosol factors. By assuming that the unoxygenated factor is completely non-hygroscopic and by varying κ of the oxygenated factor so that the predicted and measured CCN concentrations are internally consistent and in good agreement, κ of the oxygenated organic factor was found to be 0.22±0.04 for the suite of measurements made during this five-week campaign. In a second, equivalent approach, we continue to assume that the unoxygenated component of the aerosol, with a mole ratio of atomic oxygen to atomic carbon (O/C) ≈ 0, is completely non-hygroscopic, and we postulate a simple linear relationship between κorg and O/C. Under these assumptions, the κ of the entire organic component for bulk aerosols measured by the AMS can be parameterised as κorg=(0.29±0.05)·(O/C), for the range of O/C observed in this study (0.3 to 0.6). These results are averaged over our five-week study at one location using only the AMS for composition analysis. Empirically, our measurements are consistent with κorg generally increasing with increasing particle oxygenation, but high uncertainties preclude us from testing this hypothesis. Lastly, we examine select periods of different aerosol composition, corresponding to different air mass histories, to determine the generality of the campaign-wide findings described above.

Development of an aerosol microphysical module: Aerosol Two-dimensional bin module for foRmation and Aging Simulation (ATRAS)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsui, H.; Koike, Makoto; Kondo, Yutaka

2014-09-30

Number concentrations, size distributions, and mixing states of aerosols are essential parameters for accurate estimation of aerosol direct and indirect effects. In this study, we developed an aerosol module, designated Aerosol Two-dimensional bin module for foRmation and Aging Simulation (ATRAS), that can represent these parameters explicitly by considering new particle formation (NPF), black carbon (BC) aging, and secondary organic aerosol (SOA) processes. A two-dimensional bin representation is used for particles with dry diameters from 40 nm to 10 µm to resolve both aerosol size (12 bins) and BC mixing state (10 bins) for a total of 120 bins. The particlesmore » with diameters from 1 to 40 nm are resolved using an additional 8 size bins to calculate NPF. The ATRAS module was implemented in the WRF-chem model and applied to examine the sensitivity of simulated mass, number, size distributions, and optical and radiative parameters of aerosols to NPF, BC aging and SOA processes over East Asia during the spring of 2009. BC absorption enhancement by coating materials was about 50% over East Asia during the spring, and the contribution of SOA processes to the absorption enhancement was estimated to be 10 – 20% over northern East Asia and 20 – 35% over southern East Asia. A clear north-south contrast was also found between the impacts of NPF and SOA processes on cloud condensation nuclei (CCN) concentrations: NPF increased CCN concentrations at higher supersaturations (smaller particles) over northern East Asia, whereas SOA increased CCN concentrations at lower supersaturations (larger particles) over southern East Asia. Application of ATRAS to East Asia also showed that the impact of each process on each optical and radiative parameter depended strongly on the process and the parameter in question. The module can be used in the future as a benchmark model to evaluate the accuracy of simpler aerosol models and examine interactions between NPF, BC aging, and SOA processes under different meteorological conditions and emissions.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Renbaum-Wolff, Lindsay; Song, Mijung; Marcolli, Claudia

Particles consisting of secondary organic material (SOM) are abundant in the atmosphere. In order to predict the role of these particles in climate, visibility and atmospheric chemistry, information on particle phase state (i.e., single liquid, two liquids and solid) is needed. Our paper focuses on the phase state of SOM particles free of inorganic salts produced by the ozonolysis of α-pinene. Phase transitions were investigated in the laboratory using optical microscopy and theoretically using a thermodynamic model at 290 K and for relative humidities ranging from < 0.5 to 100%. In the laboratory studies, a single phase was observed frommore » 0 to 95% relative humidity (RH) while two liquid phases were observed above 95% RH. For increasing RH, the mechanism of liquid–liquid phase separation (LLPS) was spinodal decomposition. The RH range over which two liquid phases were observed did not depend on the direction of RH change. In the modeling studies, the SOM took up very little water and was a single organic-rich phase at low RH values. At high RH, the SOM underwent LLPS to form an organic-rich phase and a water-rich phase, consistent with the laboratory studies. The presence of LLPS at high RH values can have consequences for the cloud condensation nuclei (CCN) activity of SOM particles. In the simulated Köhler curves for SOM particles, two local maxima were observed. Depending on the composition of the SOM, the first or second maximum can determine the critical supersaturation for activation. Recently researchers have observed inconsistencies between measured CCN properties of SOM particles and hygroscopic growth measured below water saturation (i.e., hygroscopic parameters measured below water saturation were inconsistent with hygroscopic parameters measured above water saturation). Furthermore, the work presented here illustrates that such inconsistencies are expected for systems with LLPS when the water uptake at subsaturated conditions represents the hygroscopicity of an organic-rich phase while the barrier for CCN activation can be determined by the second maximum in the Köhler curve when the particles are water rich.« less

Further evidence for CCN aerosol concentrations determining the height of warm rain and ice initiation in convective clouds over the Amazon basin

NASA Astrophysics Data System (ADS)

Campos Braga, Ramon; Rosenfeld, Daniel; Weigel, Ralf; Jurkat, Tina; Andreae, Meinrat O.; Wendisch, Manfred; Pöschl, Ulrich; Voigt, Christiane; Mahnke, Christoph; Borrmann, Stephan; Albrecht, Rachel I.; Molleker, Sergej; Vila, Daniel A.; Machado, Luiz A. T.; Grulich, Lucas

2017-12-01

We have investigated how aerosols affect the height above cloud base of rain and ice hydrometeor initiation and the subsequent vertical evolution of cloud droplet size and number concentrations in growing convective cumulus. For this purpose we used in situ data of hydrometeor size distributions measured with instruments mounted on HALO aircraft during the ACRIDICON-CHUVA campaign over the Amazon during September 2014. The results show that the height of rain initiation by collision and coalescence processes (Dr, in units of meters above cloud base) is linearly correlated with the number concentration of droplets (Nd in cm-3) nucleated at cloud base (Dr ≈ 5 ṡ Nd). Additional cloud processes associated with Dr, such as GCCN, cloud, and mixing with ambient air and other processes, produce deviations of ˜ 21 % in the linear relationship, but it does not mask the clear relationship between Dr and Nd, which was also found at different regions around the globe (e.g., Israel and India). When Nd exceeded values of about 1000 cm-3, Dr became greater than 5000 m, and the first observed precipitation particles were ice hydrometeors. Therefore, no liquid water raindrops were observed within growing convective cumulus during polluted conditions. Furthermore, the formation of ice particles also took place at higher altitudes in the clouds in polluted conditions because the resulting smaller cloud droplets froze at colder temperatures compared to the larger drops in the unpolluted cases. The measured vertical profiles of droplet effective radius (re) were close to those estimated by assuming adiabatic conditions (rea), supporting the hypothesis that the entrainment and mixing of air into convective clouds is nearly inhomogeneous. Additional CCN activation on aerosol particles from biomass burning and air pollution reduced re below rea, which further inhibited the formation of raindrops and ice particles and resulted in even higher altitudes for rain and ice initiation.

On the characteristics of aerosol indirect effect based on dynamic regimes in global climate models

DOE PAGES

Zhang, Shipeng; Wang, Minghuai; Ghan, Steven J.; ...

2016-03-04

Aerosol–cloud interactions continue to constitute a major source of uncertainty for the estimate of climate radiative forcing. The variation of aerosol indirect effects (AIE) in climate models is investigated across different dynamical regimes, determined by monthly mean 500 hPa vertical pressure velocity ( ω 500), lower-tropospheric stability (LTS) and large-scale surface precipitation rate derived from several global climate models (GCMs), with a focus on liquid water path (LWP) response to cloud condensation nuclei (CCN) concentrations. The LWP sensitivity to aerosol perturbation within dynamic regimes is found to exhibit a large spread among these GCMs. It is in regimes of strongmore » large-scale ascent ( ω 500  <  −25 hPa day −1) and low clouds (stratocumulus and trade wind cumulus) where the models differ most. Shortwave aerosol indirect forcing is also found to differ significantly among different regimes. Shortwave aerosol indirect forcing in ascending regimes is close to that in subsidence regimes, which indicates that regimes with strong large-scale ascent are as important as stratocumulus regimes in studying AIE. It is further shown that shortwave aerosol indirect forcing over regions with high monthly large-scale surface precipitation rate (> 0.1 mm day −1) contributes the most to the total aerosol indirect forcing (from 64 to nearly 100 %). Results show that the uncertainty in AIE is even larger within specific dynamical regimes compared to the uncertainty in its global mean values, pointing to the need to reduce the uncertainty in AIE in different dynamical regimes.« less

A Study of Direct and Cloud-Mediated Radiative Forcing of Climate Due to Aerosols

NASA Technical Reports Server (NTRS)

Yu, Shao-Cai

1999-01-01

The Intergovernmental Panel on Climate Change (IPCC) has reported that in the southeastern US and eastern China, the general greenhouse warming due to anthropogenic gaseous emissions is dominated by the cooling effect of anthropogenic aerosols. To verify this model prediction in eastern China and southeastern US, we analyzed regional patterns of climate changes at 72 stations in eastern China during 1951- 94 (44 years), and at 52 stations in the southeastern US during 1949-94 (46 years) to detect the fingerprint of aerosol radiative forcing. It was found that the mean rates of change of annual mean daily, maximum, minimum temperatures and diurnal temperature range (DTR) in eastern China were 0.8, -0.2, 1.8, and -2.0 C/100 years respectively, while the mean rates of change of annual mean daily, maximum, minimum temperatures and DTR in the southeastern US were -0.2, -0.6, 0.2, and -0.8 C/100 years, respectively. This indicates that the high rate of increase in annual mean minimum temperature in eastern China results in a slightly warming trend of daily temperature, while the high rate of decrease in annual mean maximum temperature and low rate of increase in annual mean minimum temperature lead to the cooling trend of daily temperature in the southeastern US. We found that the warming from the longwave forcing due to both greenhouse gases and aerosols was completely counteracted by the shortwave aerosol forcing in the southeastern US in the past 46 years. A slightly overall warming trend in eastern China is evident; winters have become milder. This finding is explained by hypothesizing that increasing energy usage during the past 44 years has resulted in more coal and biomass burning, thus increasing the emission of absorbing soot and organic aerosols in eastern China. Such emissions, in addition to well-known Asia dust and greenhouse gases, may be responsible for the winter warming trend in eastern China that we have reported here. The sensitivity of aerosol radiative properties to aerosol composition, size distribution, relative humidity (RH) is examined for the following aerosol systems: inorganic and organic ions (Cl-, Br-, NO3 -, SO4 2-, Na+, NH4 +, K+, Ca2+, Mg2+, HCOO-, CH3COO-, CH3CH2COO-, CH3COCOO-, OOCCOO2-, MSA-1); water-insoluble inorganic and organic compounds (elemental carbon, n-alkanes, SiO2, Al2O3, Fe2O3 and other organic compounds). The partial molar refraction method was used to calculate the real part of the refractive index. It was found that the asymmetry factor increased by approximately 48% with the real part varying from 1.40 to 1.65, and the single scattering albedo decreased by 24% with the imaginary part varying from -0.005 to -0.1. The asymmetry factor increased by 5.4 times with the geometric standard deviation varying from 1.2 to 3.0. The radiation transmission is very sensitive to the change in size distribution; other factors are not as significant. To determine the aerosol direct radiative forcing (ADRF), the aerosol optical depth (AOD) values at the three operational wavelengths (415, 500 and 673 nm) were determined at a regionally representative site, namely, Mt. Gibbs (35.78 deg N, 82.29 deg W, elevation 2006 m) in Mt. Mitchell State Park, NC, and a site located in an adjacent valley (Black Mountain, 35.66 deg N, 82.38 deg W, elevation 951 m) in the southeastern US. The two sites are separated horizontally by 10 km and vertically by 1 km. It was found that the representative total AOD values at 500 nm at the valley site for highly polluted (HP), marine (M) and continental (C) air masses were 0.68 +/- 0.33, 0.29 +/- 0.19 and 0.10 +/- 0.04, respectively. A search-graph method was used to retrieve the columnar size distribution (number concentration N, effective radius reff and geometric standard deviation=?g) from the optical depth observations at three operational wavelengths. The ground albedo, single scattering albedo and imaginary part of the refractive index were calculated using a mathematically unique procedure involving a Mie code and a radiative transfer code in conjunction with the retrieved aerosol size distribution, AOD, and diffuse-direct irradiance ratio. It was found that N, r(eff) and sigma(g) were in the ranges of 10 to 1.7 x 10(exp 4)/cubic cm, 0.09 to 0.68 micrometers and 1.12 to 2.95, respectively. The asymmetry factor and single scattering albedo were in the ranges of 0.63 to 0.75 and 0.74 to 0.97 respectively. The ground albedo for the forested terrain and imaginary part of refractive index were found to be in the ranges of 0.06 to 0.29 and 0.005 to 0.051 respectively. On the basis of these aerosol radiative properties obtained at the research sites and computations using the Column Radiation Model (CRM) of National Center of Atmospheric Research (NCAR) Community Climate Model (CCM3), it was found that the average cloud-free 24-hour ADRF values were -13 +/- 8, -8 +/- 3, -33 +/- 16 W/square m for marine, continental, and polluted air masses, respectively. On the assumption that the fractional coverage of clouds is 0.61, it was estimated that the annual mean ADRF was 7 +/- 2 W/square m in the southeastern US. The review with respect to the current knowledge of organic acids shows that aerosol formate and acetate concentrations range from 0.02 to 5.3 nmol/cubic m and from 0.03 to 12.4 nmol/cubic m respectively, and that between 34% to 77% of formate and between 21% to 66% of acetate are present in the fine fraction of aerosols. It was found that although most (98-99%) of these volatile organic acids were present in the gas phase, their concentrations in the aerosol particles were sufficient to make them a good candidate for cloud condensation nuclei (CCN). It is hypothesized that organic acids are at least one of the primary sources of CCN in the atmosphere due to their ubiquitous presence in the troposphere, especially over the continental forested areas. The results of our measurements at Palmer Station, Antarctica show that the daily average CCN concentrations at 0.3% and 1% supersaturations ranged from 0.3 to 160/cubic cm and from 4 to 168/cubic cm, respectively, during the period from 17 January to 26 February, 1994. New evidence for substantial and definitive CCN enhancement near and within cloud has been observed at Mt. Mitchell, North Carolina. The results show that the average monthly CCN concentrations were 460 +/- 217, 386 +/- 286, 429 +/- 228 and 238 +/- 134/cubic cm for in-cloud, overcast, clear and rainy conditions, respectively. The typical CCN spectra show that there were a lot of small CCN produced and the ion concentrations (especially H+ and SO4 2-) were very high during the CCN enhancement period. The significantly positive correlation between black carbon (BC) and CCN at 1% supersaturation indicates that a percentage of the BC measured at the site may be in the form of an internal mixture and participated in the formation of CCN.

Impact of mixing state and hygroscopicity on CCN activity of biomass burning aerosol in Amazonia

NASA Astrophysics Data System (ADS)

Sánchez Gácita, Madeleine; Longo, Karla M.; Freire, Julliana L. M.; Freitas, Saulo R.; Martin, Scot T.

2017-02-01

Smoke aerosols prevail throughout Amazonia because of widespread biomass burning during the dry season, and external mixing, low variability in the particle size distribution and low particle hygroscopicity are typical. There can be profound effects on cloud properties. This study uses an adiabatic cloud model to simulate the activation of smoke particles as cloud condensation nuclei (CCN) for three hypothetical case studies, chosen as to resemble biomass burning aerosol observations in Amazonia. The relative importance of variability in hygroscopicity, mixing state, and activation kinetics for the activated fraction and maximum supersaturation is assessed. For a population with κp = 0.04, an overestimation of the cloud droplet number concentration Nd for the three selected case studies between 22.4 ± 1.4 and 54.3 ± 3.7 % was obtained when assuming a hygroscopicity parameter κp = 0.20. Assuming internal mixing of the aerosol population led to overestimations of up to 20 % of Nd when a group of particles with medium hygroscopicity was present in the externally mixed population cases. However, the overestimations were below 10 % for external mixtures between very low and low-hygroscopicity particles, as seems to be the case for Amazon smoke particles. Kinetic limitations were significant for medium- and high-hygroscopicity particles, and much lower for very low and low-hygroscopicity particles. When particles were assumed to be at equilibrium and to respond instantly to changes in the air parcel supersaturation, the overestimation of the droplet concentration was up to ˜ 100 % in internally mixed populations, and up to ˜ 250 % in externally mixed ones, being larger for the higher values of hygroscopicity. In addition, a perceptible delay between the times when maximum supersaturation and maximum aerosol activated fraction are reached was noticed and, for aerosol populations with effective hygroscopicity κpeff higher than a certain threshold value, the delay in particle activation was such that no particles were activated at the time of maximum supersaturation. Considering internally mixed populations, for an updraft velocity W = 0.5 m s-1 this threshold of no activation varied between κpeff = 0.35 and κpeff = 0.5 for the different case studies. However, for low hygroscopicity, kinetic limitations played a weaker role for CCN activation of particles, even when taking into account the large aerosol mass and number concentrations. For the very low range of hygroscopicities, the overestimation of the droplet concentration due to the equilibrium assumption was lowest and the delay between the times when maximum supersaturation and maximum activated fraction were reached was greatly reduced or no longer observed (depending on the case study). These findings on uncertainties and sensitivities provide guidance on appropriate simplifications that can be used for modeling of smoke aerosols within general circulation models. The use of medium values of hygroscopicity representative of smoke aerosols for other biomass burning regions on Earth can lead to significant errors compared to the use of low hygroscopicity for Amazonia (between 0.05 and 0.13, according to available observations). Also in this region, consideration of the biomass burning population as internally mixed will lead to small errors in the droplet concentration, while significantly increasing the computational burden. Regardless of the large smoke aerosol loads in the region during the dry season, kinetic limitations are expected to be low.

Hygroscopicity of dicarbonyl-amine secondary organic aerosol products investigated with HTDMA

NASA Astrophysics Data System (ADS)

Hawkins, L. N.; de Haan, D. O.

2010-12-01

Recent studies have shown the importance of amine-dicarbonyl chemistry as a secondary organic aerosol (SOA) formation pathway, producing imines, imidazoles, and N-containing oligomers. Preliminary work in our group has suggested that some of these products may be surface active. Therefore, the presence of these products may result in important changes to submicron particle hygroscopicity that affect aerosol scattering and cloud condensation nuclei (CCN) activity, especially in regions with significant amine-containing particles. To investigate their hygroscopicity, we have designed a hygroscopicity tandem differential mobility analyzer (HTDMA) system around a 300 L Teflon chamber that allows for longer humidification times needed for some organic aerosol components that are only slightly hygroscopic. This modification provides a range of residence times from 2.5 minutes up to 1 hour, unlike previously published systems that vary from 2-30 seconds. Using the modified hygroscopicity tandem differential mobility analyzer (HTDMA), we have measured the hygroscopic growth factor (HGF) of SOA formed from reactions of glyoxal (and methylglyoxal) with methylamine, ammonium sulfate, and several amino acids. Changes to inorganic aerosol HGF in response to the presence of SOA products are also investigated.

Clouds in GEOS-5

NASA Technical Reports Server (NTRS)

Bacmeister, Julio; Rienecker, Michele; Suarez, Max; Norris, Peter

2007-01-01

The GEOS-5 atmospheric model is being developed as a weather-and-climate capable model. It must perform well in assimilation mode as well as in weather and climate simulations and forecasts and in coupled chemistry-climate simulations. In developing GEOS-5, attention has focused on the representation of moist processes. The moist physics package uses a single phase prognostic condensate and a prognostic cloud fraction. Two separate cloud types are distinguished by their source: "anvil" cloud originates in detraining convection, and large-scale cloud originates in a PDF-based condensation calculation. Ice and liquid phases for each cloud type are considered. Once created, condensate and fraction from the anvil and statistical cloud types experience the same loss processes: evaporation of condensate and fraction, auto-conversion of liquid or mixed phase condensate, sedimentation of frozen condensate, and accretion of condensate by falling precipitation. The convective parameterization scheme is the Relaxed Arakawa-Schubert, or RAS, scheme. Satellite data are used to evaluate the performance of the moist physics packages and help in their tuning. In addition, analysis of and comparisons to cloud-resolving models such as the Goddard Cumulus Ensemble model are used to help improve the PDFs used in the moist physics. The presentation will show some of our evaluations including precipitation diagnostics.

Functional Group Analysis of Biomass Burning Particles Using Infrared Spectroscopy

NASA Astrophysics Data System (ADS)

Horrell, K.; Lau, A.; Bond, T.; Iraci, L. T.

2008-12-01

Biomass burning is a significant source of particulate organic carbon in the atmosphere. These particles affect the energy balance of the atmosphere directly by absorbing and scattering solar radiation, and indirectly through their ability to act as cloud condensation nuclei (CCN). The chemical composition of biomass burning particles influences their ability to act as CCN, thus understanding the chemistry of these particles is required for understanding their effects on climate and air quality. As climate change influences the frequency and severity of boreal forest fires, the influence of biomass burning aerosols on the atmosphere may become significantly greater. Only a small portion of the organic carbon (OC) fraction of these particles has been identified at the molecular level, although several studies have explored the general chemical classes found in biomass burning smoke. To complement those studies and provide additional information about the reactive functional groups present, we are developing a method for polarity-based separation of compound classes found in the OC fraction, followed by infrared (IR) spectroscopic analysis of each polarity fraction. It is our goal to find a simple, relatively low-tech method which will provide a moderate chemical understanding of the entire suite of compounds present in the OC fraction of biomass burning particles. Here we present preliminary results from pine and oak samples representative of Midwestern United States forests burned at several different temperatures. Wood type and combustion temperature are both seen to affect the composition of the particles. The latter seems to affect relative contributions of certain functional groups, while oak demonstrates at least one additional chemical class of compounds, particularly at lower burning temperatures, where gradual solid-gas phase reactions can produce relatively large amounts of incompletely oxidized products.

Fine Mode Aerosol over the United Arab Emirates

NASA Astrophysics Data System (ADS)

Ross, K. E.; Piketh, S. J.; Reid, J. S.; Reid, E. A.

2005-12-01

The aerosol loading of the atmosphere over the Arabian Gulf region is extremely diverse and is composed not only of dust, but also of pollution that is derived largely from oil-related activities. Fine mode pollution particles are most efficient at scattering incoming solar radiation and have the potential to act as cloud condensation nuclei (CCN), and may therefore have implications for climate change. The smaller aerosols may also pose a health hazard if present in high concentrations. The United Arab Emirates Unified Aerosol Experiment (UAE2) was designed to investigate aerosol and meteorological characteristics over the region using ground-based, aircraft and satellite measurements, and was conducted in August and September 2004. Aerosol chemical composition has been obtained from filters that were collected at the site of the Mobile Atmospheric Aerosol and Radiation Characterization Observatory (MAARCO) on the coast of the UAE between Abu Dhabi and Dubai. Filter samples were also collected on an airborne platform in order to assess how aerosol chemical composition varies across the region and throughout the depth of the boundary layer. Results of the analysis of the PM2.5 coastal samples show that ammonium sulphate is the most prevalent constituent of the fine mode aerosol in the region (>50% of the mass), followed by organic matter, alumino-silicates, calcium carbonate and black carbon. Source apportionment indicates that most of the fine aerosol mass is derived from fossil fuel combustion, while mineral dust and local vehicle emissions also contribute to the fine aerosol loading. The organic carbon-to-total carbon ratio of the aerosol is 0.65, which is typical of fossil fuel combustion. The dominance of sulphates means that the fine mode aerosol in the region is probably responsible for a negative radiative forcing, and that the polluting emissions significantly elevate the concentration of CCN.

Aerosol Size, CCN, and Black Carbon Properties at a Coastal Site in the Eastern U.S.

NASA Astrophysics Data System (ADS)

Royalty, T. M.; Petters, M. D.; Grieshop, A. P.; Meskhidze, N.; Reed, R. E.; Phillips, B.; Dawson, K. W.

2015-12-01

Atmospheric aerosols play an important role in regulating the global radiative budget through direct and indirect effects. To date, the role of sea spray aerosols in modulating climate remains poorly understood. Here we present results from measurements performed at the United States Army Corps of Engineers' Field Research Facility in Duck, North Carolina, USA. Aerosol mobility size distributions (10-600 nm), refractory black carbon (rBC) and scattering particle size distributions (200-620 nm), and size resolved cloud condensation nuclei distributions (.07% - .6% supersaturation) were collected at the end of a 560m pier. Aerosol characteristics associated with northerly, high wind speed (15+ m s-1) flow originating from an oceanic trajectory are contrasted with aerosol properties observed during a weak to moderate westerly flow originating from a continental trajectory. Both marine and continental air masses had aerosol with bi-modal number size distributions with modes centered at 30nm and 140nm. In the marine air-mass, the CCN concentration at supersaturation of 0.4%, total aerosol number, surface, and volume concentration were low. rBC number concentration (D > 200 nm) associated with the marine air-mass was an order of magnitude less than continental number concentration and indicative of relatively unpolluted air. These measurements are consistent with measurements from other coastal sites under marine influence. The relative proportion of Aitken mode size particles increased from 1:2 to 2:1 while aerosol surface area was < 25 μm2 cm-3, suggesting that conditions upwind were potentially conducive to new particle formation. Overall, these results will contribute a better understanding to composition and size variation of marine aerosols.

The Effect of Particle Composition on Hygroscopicity and Droplet Formation at CARES

NASA Astrophysics Data System (ADS)

Cziczo, D. J.; Pekour, M. S.; Hiranuma, N.; Nelson, D.

2010-12-01

During the June, 2010 Carbonaceous Aerosol and Radiative Effects Study (CARES) a custom made humidity controlled nephelometer, hereafter termed a ‘humidograph’, was deployed with a commercial cloud condensation nucleus counter (CCNC) and the particle analysis by laser mass spectrometry (PALMS) instrument. Other ancillary measurements, such as particle size distributions, were made continuously during the month. The CARES field study took place in the Sacramento, CA area. Early June was characterized by cool, wet weather with predominantly northerly flow and very low particle loading. Very little biomass burning took place and the aerosol was largely sulfate neutralized by ammonia. Later in the month a more typical flow pattern from the Sacramento urban area toward the foothills developed. During this period more biomass burning occurred and organics from anthropogenic and urban sources were present on particles. The aforementioned instruments were located in the town of Cool, CA in the Sierra foothills, approximately 50 kilometers north east of cool. This site was chosen as being on the typical summertime daily flow some hours downstream of the Sacramento urban plume. Using these instruments we were able to correlate water uptake and droplet formation with particle composition. The early period of CARES was characterized by a clear deliquescence of the aerosol at ~80% relative humidity which correlated with an ammonium neutralized sulfate aerosol composition. Few CCN were present although these activated at low supersaturations and represented a large fraction of the total aerosol over ~70 nanometers in diameter. Later in the month deliquescence was not clearly indicated for a more organic-rich and biomass burning influenced aerosol. More CCN were present although activation generally required much higher saturations.

Intercomparison of aerosol-cloud-precipitation interactions in stratiform orographic mixed-phase clouds

NASA Astrophysics Data System (ADS)

Muhlbauer, A.; Hashino, T.; Xue, L.; Teller, A.; Lohmann, U.; Rasmussen, R. M.; Geresdi, I.; Pan, Z.

2010-04-01

Anthropogenic aerosols serve as a source of both cloud condensation nuclei (CCN) and ice nuclei (IN) and affect microphysical properties of clouds. Increasing aerosol number concentrations is hypothesized to retard the cloud droplet collision/coalescence and the riming in mixed-phase clouds, thereby decreasing orographic precipitation. This study presents results from a model intercomparison of 2-D simulations of aerosol-cloud-precipitation interactions in stratiform orographic mixed-phase clouds. The sensitivity of orographic precipitation to changes in the aerosol number concentrations is analyzed and compared for various dynamical and thermodynamical situations. Furthermore, the sensitivities of microphysical processes such as collision/coalescence, aggregation and riming to changes in the aerosol number concentrations are evaluated and compared. The participating models are the Consortium for Small-Scale Modeling's (COSMO) model with bulk-microphysics, the Weather Research and Forecasting (WRF) model with bin-microphysics and the University of Wisconsin modeling system (UWNMS) with a spectral ice-habit prediction microphysics scheme. All models are operated on a cloud-resolving scale with 2 km horizontal grid spacing. The results of the model intercomparison suggest that the sensitivity of orographic precipitation to aerosol modifications varies greatly from case to case and from model to model. Neither a precipitation decrease nor a precipitation increase is found robustly in all simulations. Qualitative robust results can only be found for a subset of the simulations but even then quantitative agreement is scarce. Estimates of the second indirect aerosol effect on orographic precipitation are found to range from -19% to 0% depending on the simulated case and the model. Similarly, riming is shown to decrease in some cases and models whereas it increases in others which implies that a decrease in riming with increasing aerosol load is not a robust result. Furthermore, it is found that neither a decrease in cloud droplet coalescence nor a decrease in riming necessarily implies a decrease in precipitation due to compensation effects by other microphysical pathways. The simulations suggest that mixed-phase conditions play an important role in reducing the overall susceptibility of clouds and precipitation with respect to changes in the aerosols number concentrations. As a consequence the indirect aerosol effect on precipitation is suggested to be less pronounced or even inverted in regions with high terrain (e.g., the Alps or Rocky Mountains) or in regions where mixed-phase microphysics climatologically plays an important role for orographic precipitation.

Aerosols, clouds, and precipitation in the North Atlantic trades observed during the Barbados aerosol cloud experiment - Part 1: Distributions and variability

NASA Astrophysics Data System (ADS)

Jung, Eunsil; Albrecht, Bruce A.; Feingold, Graham; Jonsson, Haflidi H.; Chuang, Patrick; Donaher, Shaunna L.

2016-07-01

Shallow marine cumulus clouds are by far the most frequently observed cloud type over the Earth's oceans; but they are poorly understood and have not been investigated as extensively as stratocumulus clouds. This study describes and discusses the properties and variations of aerosol, cloud, and precipitation associated with shallow marine cumulus clouds observed in the North Atlantic trades during a field campaign (Barbados Aerosol Cloud Experiment- BACEX, March-April 2010), which took place off Barbados where African dust periodically affects the region. The principal observing platform was the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter (TO) research aircraft, which was equipped with standard meteorological instruments, a zenith pointing cloud radar and probes that measured aerosol, cloud, and precipitation characteristics.The temporal variation and vertical distribution of aerosols observed from the 15 flights, which included the most intense African dust event during all of 2010 in Barbados, showed a wide range of aerosol conditions. During dusty periods, aerosol concentrations increased substantially in the size range between 0.5 and 10 µm (diameter), particles that are large enough to be effective giant cloud condensation nuclei (CCN). The 10-day back trajectories showed three distinct air masses with distinct vertical structures associated with air masses originating in the Atlantic (typical maritime air mass with relatively low aerosol concentrations in the marine boundary layer), Africa (Saharan air layer), and mid-latitudes (continental pollution plumes). Despite the large differences in the total mass loading and the origin of the aerosols, the overall shapes of the aerosol particle size distributions were consistent, with the exception of the transition period.The TO was able to sample many clouds at various phases of growth. Maximum cloud depth observed was less than ˜ 3 km, while most clouds were less than 1 km deep. Clouds tend to precipitate when the cloud is thicker than 500-600 m. Distributions of cloud field characteristics (depth, radar reflectivity, Doppler velocity, precipitation) were well identified in the reflectivity-velocity diagram from the cloud radar observations. Two types of precipitation features were observed for shallow marine cumulus clouds that may impact boundary layer differently: first, a classic cloud-base precipitation where precipitation shafts were observed to emanate from the cloud base; second, cloud-top precipitation where precipitation shafts emanated mainly near the cloud tops, sometimes accompanied by precipitation near the cloud base. The second type of precipitation was more frequently observed during the experiment. Only 42-44 % of the clouds sampled were non-precipitating throughout the entire cloud layer and the rest of the clouds showed precipitation somewhere in the cloud, predominantly closer to the cloud top.

Aerosol, cloud, and precipitation interactions in Eastern North Atlantic

NASA Astrophysics Data System (ADS)

Wang, J.; Wood, R.; Dong, X.

2017-12-01

With their extensive coverage, marine low clouds greatly impact global climate. Presently, marine low clouds are poorly represented in global climate models, and the response of marine low clouds to changes in atmospheric greenhouse gases and aerosols remains the major source of uncertainty in climate simulations. The Eastern North Atlantic (ENA) is a region of persistent but diverse subtropical marine boundary layer clouds, whose albedo and precipitation are highly susceptible to perturbations in aerosol properties. In addition, ENA is periodically impacted by anthropogenic aerosol both from North American and from continental Europe, making it an excellent location to study the CCN budget in a remote marine region periodically perturbed by anthropogenic emissions, and to investigate the impacts of long-range transport of aerosols on remote marine clouds. Aerosol and Cloud Experiments in Eastern North Atlantic (ACE-ENA), funded by DOE Atmospheric Radiation Measurement (ARM) program, is designed to improve the understanding of marine boundary CCN budget, cloud and drizzle microphysics, and the impact of aerosol on marine low cloud and precipitation in the ENA by combining airborne observations and long term surface based measurements. The study has two airborne deployments. The first deployment took place from June 15 to July 25, 2017, and the second one will take place from January 10 to February 20, 2018. Flights during the first deployment were carried out in the Azores, near the ARM ENA site on Graciosa Island. The long term measurements at the ENA site provide important Climatological context for the airborne observations during the two deployments, and the cloud structures provided by the scanning radars at the ENA site put the detailed in-situ measurements into mesoscale and cloud lifecycle contexts. Another important aspect of this study is to provide high quality in-situ measurements for validating and improving ground-based retrieval algorithms at the ENA site. This presentation will describe the setup and strategies of the study, early results from the first deployment on vertical structures and horizontal variabilities of aerosol properties, cloud and drizzle microphysics, and insights into the processes that drive the properties and interactions of aerosol and marine low clouds.

Prebiotic chemistry in clouds

NASA Technical Reports Server (NTRS)

Oberbeck, Verne R.; Marshall, John; Shen, Thomas

1991-01-01

The chemical evolution hypothesis of Woese (1979), according to which prebiotic reactions occurred rapidly in droplets in giant atmospheric reflux columns was criticized by Scherer (1985). This paper proposes a mechanism for prebiotic chemistry in clouds that answers Scherer's concerns and supports Woese's hypothesis. According to this mechanism, rapid prebiotic chemical evolution was facilitated on the primordial earth by cycles of condensation and evaporation of cloud drops containing clay condensation nuclei and nonvolatile monomers. For example, amino acids supplied by, or synthesized during entry of meteorites, comets, and interplanetary dust, would have been scavenged by cloud drops containing clay condensation nuclei and would be polymerized within cloud systems during cycles of condensation, freezing, melting, and evaporation of cloud drops.

The Impact of Aerosols on Cloud and Precipitation Processes: Cloud-Resolving Model Simulations

NASA Technical Reports Server (NTRS)

Tao, Wei-Kuo; Li, Xiaowen; Khain, Alexander; Matsui, Toshihisa; Lang, Stephen; Simpson, Joanne

2012-01-01

Recently, a detailed spectral-bin microphysical scheme was implemented into the Goddard Cumulus Ensemble (GCE) model. Atmospheric aerosols are also described using number density size-distribution functions. A spectral-bin microphysical model is very expensive from a computational point of view and has only been implemented into the 2D version of the GCE at the present time. The model is tested by studying the evolution of deep tropical clouds in the west Pacific warm pool region and summertime convection over a mid-latitude continent with different concentrations of CCN: a low clean concentration and a high dirty concentration. The impact of atmospheric aerosol concentration on cloud and precipitation will be investigated.

Vertical profiling of aerosol particles and trace gases over the central Arctic Ocean during summer

NASA Astrophysics Data System (ADS)

Kupiszewski, P.; Leck, C.; Tjernström, M.; Sjogren, S.; Sedlar, J.; Graus, M.; Müller, M.; Brooks, B.; Swietlicki, E.; Norris, S.; Hansel, A.

2013-04-01

Unique measurements of vertical size resolved aerosol particle concentrations, trace gas concentrations and meteorological data were obtained during the Arctic Summer Cloud Ocean Study (ASCOS, http://www.ascos.se), an International Polar Year project aimed at establishing the processes responsible for formation and evolution of low-level clouds over the high Arctic summer pack ice. The experiment was conducted from onboard the Swedish icebreaker Oden, and provided both ship- and helicopter-based measurements. This study focuses on the vertical helicopter profiles and onboard measurements obtained during a three-week period when Oden was anchored to a drifting ice floe, and sheds light on the characteristics of Arctic aerosol particles and their distribution throughout the lower atmosphere. Distinct differences in aerosol particle characteristics within defined atmospheric layers are identified. Near the surface (lowermost couple hundred meters), transport from the marginal ice zone (MIZ), if sufficiently short (less than ca. 2 days), condensational growth and cloud-processing develop the aerosol population. During two of the four representative periods defined in this study, such influence is shown. At altitudes above about 1 km, long-range transport occurs frequently. However, only infrequently does large-scale subsidence descend such air masses to become entrained into the mixed layer in the high Arctic, and therefore they are unlikely to directly influence low-level stratiform cloud formation. Nonetheless, long-range transport plumes can influence the radiative balance of the PBL by influencing formation and evolution of higher clouds, as well as through precipitation transport of particles downwards. New particle formation was occasionally observed, particularly in the near-surface layer. We hypothesize that the origin of these ultrafine particles can be from biological processes, both primary and secondary, within the open leads between the pack ice and/or along the MIZ. In general, local sources, in combination with upstream boundary layer transport of precursor gases from the MIZ, are suggested to constitute the origin of CCN particles and thus be of importance for the formation of interior Arctic low level clouds during summer, and subsequently, through cloud influences, on the melting and freezing of sea ice.

Marine Cloud Brightening: regional applications to the weakening of hurricanes and reduction in coral bleaching

NASA Astrophysics Data System (ADS)

Gadian, A.; Hauser, R.; Kleypas, J. A.; Latham, J.; Parkes, B.; Salter, S.

2013-12-01

This study examines the potential to cool ocean surface waters in regions of hurricane genesis and early development. This would be achieved by seeding, with copious quantities of seawater cloud condensation nuclei (CCN), low-level maritime stratocumulus clouds covering these regions or those at the source of incoming currents. Higher cloud droplet density would increase these clouds' reflectivity to incoming sunlight, and possibly their longevity. This approach is a more localized application of the Marine Cloud Brightening (MCB) geoengineering technique promoting global cooling. By utilizing a climate ocean/atmosphere coupled model, HadGEM1, and by judicious seeding of maritime stratocumulus clouds, we demonstrate that we may be able to significantly reduce sea surface temperatures (SSTs) in hurricane development regions. Thus artificial seeding may reduce hurricane intensity; but how well the magnitude of this effect is yet to be determined. Increases in coral bleaching events over the last few decades have been largely caused by rising SSTs, and continued warming is expected to cause even greater increases through this century. Using thr same Global Climate Model to examine the potential of MCB to cool oceanic surface waters in three coral reef provinces. Our simulations indicate that under doubled CO2 conditions, the substantial increases in coral bleaching conditions from current values in three reef regions (Caribbean, French Polynesia, and the Great Barrier Reef) were eliminated when MCB was applied, which reduced the SSTs at these sites roughly to their original values. In this study we also illustrate how even regional application of MCB can affect the planetary meridional heat flux and the reduction in poleward heat transfer. (a) Change in annual average sea surface temperature, Celsius, between the 2xCO2 and CONTROL simulations. (b) Change in annual average sea surface temperature, Celsius, between the CONTROL and 2xCO2+MCB simulations. The dashed black boxes in both panels represent the three coral reef regions. In the Southern north Atlantic, the warmer SSTs in (a) is reduced to the current "control" temperatures, weakening hurricane formation.

Aerosol concentration and size distribution measured below, in, and above cloud from the DOE G-1 during VOCALS-REx

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kleinman L. I.; Daum, P. H.; Lee, Y.-N.

2012-01-04

During the VOCALS Regional Experiment, the DOE G-1 aircraft was used to sample a varying aerosol environment pertinent to properties of stratocumulus clouds over a longitude band extending 800 km west from the Chilean coast at Arica. Trace gas and aerosol measurements are presented as a function of longitude, altitude, and dew point in this study. Spatial distributions are consistent with an upper atmospheric source for O{sub 3} and South American coastal sources for marine boundary layer (MBL) CO and aerosol, most of which is acidic sulfate. Pollutant layers in the free troposphere (FT) can be a result of emissionsmore » to the north in Peru or long range transport from the west. At a given altitude in the FT (up to 3 km), dew point varies by 40 C with dry air descending from the upper atmospheric and moist air having a boundary layer (BL) contribution. Ascent of BL air to a cold high altitude results in the condensation and precipitation removal of all but a few percent of BL water along with aerosol that served as CCN. Thus, aerosol volume decreases with dew point in the FT. Aerosol size spectra have a bimodal structure in the MBL and an intermediate diameter unimodal distribution in the FT. Comparing cloud droplet number concentration (CDNC) and pre-cloud aerosol (D{sub p} > 100 nm) gives a linear relation up to a number concentration of {approx}150 cm{sup -3}, followed by a less than proportional increase in CDNC at higher aerosol number concentration. A number balance between below cloud aerosol and cloud droplets indicates that {approx}25 % of aerosol with D{sub p} > 100 nm are interstitial (not activated). A direct comparison of pre-cloud and in-cloud aerosol yields a higher estimate. Artifacts in the measurement of interstitial aerosol due to droplet shatter and evaporation are discussed. Within each of 102 constant altitude cloud transects, CDNC and interstitial aerosol were anti-correlated. An examination of one cloud as a case study shows that the interstitial aerosol appears to have a background, upon which is superimposed a high frequency signal that contains the anti-correlation. The anti-correlation is a possible source of information on particle activation or evaporation.« less

Aerosol concentration and size distribution measured below, in, and above cloud from the DOE G-1 during VOCALS-REx

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kleinman, L.I.; Daum, P. H.; Lee, Y.-N.

2011-06-21

During the VOCALS Regional Experiment, the DOE G-1 aircraft was used to sample a varying aerosol environment pertinent to properties of stratocumulus clouds over a longitude band extending 800 km west from the Chilean coast at Arica. Trace gas and aerosol measurements are presented as a function of longitude, altitude, and dew point in this study. Spatial distributions are consistent with an upper atmospheric source for O{sub 3} and South American coastal sources for marine boundary layer (MBL) CO and aerosol, most of which is acidic sulfate in agreement with the dominant pollution source being SO{sub 2} from Cu smeltersmore » and power plants. Pollutant layers in the free troposphere (FT) can be a result of emissions to the north in Peru or long range transport from the west. At a given altitude in the FT (up to 3 km), dew point varies by 40 C with dry air descending from the upper atmospheric and moist air having a BL contribution. Ascent of BL air to a cold high altitude results in the condensation and precipitation removal of all but a few percent of BL water along with aerosol that served as CCN. Thus, aerosol volume decreases with dew point in the FT. Aerosol size spectra have a bimodal structure in the MBL and an intermediate diameter unimodal distribution in the FT. Comparing cloud droplet number concentration (CDNC) and pre-cloud aerosol (Dp > 100 nm) gives a linear relation up to a number concentration of {approx}150 cm{sup -3}, followed by a less than proportional increase in CDNC at higher aerosol number concentration. A number balance between below cloud aerosol and cloud droplets indicates that {approx}25% of aerosol in the PCASP size range are interstitial (not activated). One hundred and two constant altitude cloud transects were identified and used to determine properties of interstitial aerosol. One transect is examined in detail as a case study. Approximately 25 to 50% of aerosol with D{sub p} > 110 nm were not activated, the difference between the two approaches possibly representing shattered cloud droplets or unknown artifact. CDNC and interstitial aerosol were anti-correlated in all cloud transects, consistent with the occurrence of dry in-cloud areas due to entrainment or circulation mixing.« less

Top-down and bottom-up aerosol-cloud closure: towards understanding sources of uncertainty in deriving cloud shortwave radiative flux

NASA Astrophysics Data System (ADS)

Sanchez, Kevin J.; Roberts, Gregory C.; Calmer, Radiance; Nicoll, Keri; Hashimshoni, Eyal; Rosenfeld, Daniel; Ovadnevaite, Jurgita; Preissler, Jana; Ceburnis, Darius; O'Dowd, Colin; Russell, Lynn M.

2017-08-01

Top-down and bottom-up aerosol-cloud shortwave radiative flux closures were conducted at the Mace Head Atmospheric Research Station in Galway, Ireland, in August 2015. This study is part of the BACCHUS (Impact of Biogenic versus Anthropogenic emissions on Clouds and Climate: towards a Holistic UnderStanding) European collaborative project, with the goal of understanding key processes affecting aerosol-cloud shortwave radiative flux closures to improve future climate predictions and develop sustainable policies for Europe. Instrument platforms include ground-based unmanned aerial vehicles (UAVs)1 and satellite measurements of aerosols, clouds and meteorological variables. The ground-based and airborne measurements of aerosol size distributions and cloud condensation nuclei (CCN) concentration were used to initiate a 1-D microphysical aerosol-cloud parcel model (ACPM). UAVs were equipped for a specific science mission, with an optical particle counter for aerosol distribution profiles, a cloud sensor to measure cloud extinction or a five-hole probe for 3-D wind vectors. UAV cloud measurements are rare and have only become possible in recent years through the miniaturization of instrumentation. These are the first UAV measurements at Mace Head. ACPM simulations are compared to in situ cloud extinction measurements from UAVs to quantify closure in terms of cloud shortwave radiative flux. Two out of seven cases exhibit sub-adiabatic vertical temperature profiles within the cloud, which suggests that entrainment processes affect cloud microphysical properties and lead to an overestimate of simulated cloud shortwave radiative flux. Including an entrainment parameterization and explicitly calculating the entrainment fraction in the ACPM simulations both improved cloud-top radiative closure. Entrainment reduced the difference between simulated and observation-derived cloud-top shortwave radiative flux (δRF) by between 25 and 60 W m-2. After accounting for entrainment, satellite-derived cloud droplet number concentrations (CDNCs) were within 30 % of simulated CDNC. In cases with a well-mixed boundary layer, δRF is no greater than 20 W m-2 after accounting for cloud-top entrainment and up to 50 W m-2 when entrainment is not taken into account. In cases with a decoupled boundary layer, cloud microphysical properties are inconsistent with ground-based aerosol measurements, as expected, and δRF is as high as 88 W m-2, even high (> 30 W m-2) after accounting for cloud-top entrainment. This work demonstrates the need to take in situ measurements of aerosol properties for cases where the boundary layer is decoupled as well as consider cloud-top entrainment to accurately model stratocumulus cloud radiative flux. 1The regulatory term for UAV is remotely piloted aircraft (RPA).

Cloud condensation nucleus-sulfate mass relationship and cloud albedo

NASA Technical Reports Server (NTRS)

Hegg, Dean A.

1994-01-01

Analysis of previously published, simultaneous measurements of cloud condensation nucleus number concentration and sulfate mass concentration suggest a nonlinear relationship between the two variables. This nonlinearity reduces the sensitivity of cloud albedo to changes in the sulfur cycle.

Investigation of the evolution of atmospheric particles with integration of the stochastic particle-resolved model partmc-mosaic and atmospheric measurements

NASA Astrophysics Data System (ADS)

Tian, Jian

With the recently-developed particle-resolved model PartMC-MOSAIC, the mixing state and other physico-chemical properties of individual aerosol particles can be tracked as the particles undergo aerosol aging processes. However, existing PartMC-MOSAIC applications have mainly been based on idealized scenarios, and a link to real atmospheric measurement has not yet been established. In this thesis, we extend the capability of PartMC-MOSAIC and apply the model framework to three distinct scenarios with different environmental conditions to investigate the physical and chemical aging of aerosols in those environments. The first study is to investigate the evolution of particle mixing state and cloud condensation nuclei (CCN) activation properties in a ship plume. Comparisons of our results with observations from the QUANTIFY Study in 2007 in the English channel and the Gulf of Biscay showed that the model was able to reproduce the observed evolution of total number concentration and the vanishing of the nucleation mode consisting of sulfate particles. Further process analysis revealed that during the first hour after emission, dilution reduced the total number concentration by four orders of magnitude, while coagulation reduced it by an additional order of magnitude. Neglecting coagulation resulted in an overprediction of more than one order of magnitude in the number concentration of particles smaller than 40 nm at a plume age of 100 s. Coagulation also significantly altered the mixing state of the particles, leading to a continuum of internal mixtures of sulfate and black carbon. The impact of condensation on CCN concentrations depended on the supersaturation threshold at which CCN activity was evaluated. Nucleation was observed to have a limited impact on the CCN concentration in the ship plume we studied, but was sensitive to formation rates of secondary aerosol. For the second study we adapted PartMC to represent the aerosol evolution in an aerosol chamber, with the intention to use the model as a tool to interpret and guide chamber experiments in the future. We added chamber-specific processes to our model formulation such as wall loss due to particle diffusion and sedimentation, and dilution effects due to sampling. We also implemented a treatment of fractal particles to account for the morphology of agglomerates and its impact on aerosol dynamics. We verified the model with published results of self-similar size distributions, and validated the model using experimental data from an aerosol chamber. To this end we developed a fitting optimization approach to determine the best-estimate values for the wall loss parameters based on minimizing the l2-norm of the model errors of the number distribution. Obtaining the best fit required taking into account the non-spherical structure of the particle agglomerates. Our third study focuses on the implementation of volatility basis set (VBS) framework in PartMC-MOSAIC to investigate the chemical aging of organic aerosols in the atmosphere. The updated PartMC-MOSAIC model framework was used to simulate the evolution of aerosols in air trajectories initialized from CARES field campaign conducted in California in June 2010. The simulation results were compared with aircraft measurement data during the campaign. PartMC-MOSAIC was able to produce gas and aerosol concentrations at similar levels compared to the observation data. Moreover, the simulation with VBS enabled produced consistently more secondary organic aerosols (SOA). The investigation of particle mixing state revealed that the impact of VBS framework on particle mixing state is sensitive to the daylight exposure time. (Abstract shortened by ProQuest.).

Aerosol mixingstate, hygroscopic growth and cloud activation efficiency during MIRAGE 2006

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lance, Sara; Raatikainen, T.; Onasch, Timothy B.

2013-05-15

Observations of aerosol hygroscopic growth and CCN activation spectra for submicron particles are reported for the T1 ground site outside of Mexico City during the MIRAGE 2006 campaign. K¨ohler theory is used to evaluate the characteristic water uptake coefficient, k*, for the CCN active aerosol population using both size-resolved HTMDA and size-resolved CCNc measurements. Organic mass fractions, (forg), are evaluated from size-resolved aerosol mass spectrometer (AMS) measurements, from which kAMS is inferred and compared against k*. Strong diurnal profiles of aerosol water uptake parameters and aerosol composition are observed. We find that new particle formation (NPF) events are correlated withmore » an increased k* and CCN-active fraction during the daytime, with greater impact on smaller particles. During NPF events, the number concentration of 40 nm particles acting as CCN can surpass by more than a factor of two the concentrations of 100 nm particles acting as CCN, at supersaturations of 0.51% +/- 0.06%. We also find that at 0600-0800 in the morning throughout the campaign, fresh traffic emissions result in substantial changes to the chemical distribution of the aerosol, with on average 65% externally-mixed fraction for 40 nm particles and 30% externally-mixed fraction for 100 nm particles, whereas at midday nearly all particles of both sizes can be described as “internally-mixed”. Average activation spectra and growth factor distributions are analyzed for different time periods characterizing the daytime (with and without NPF events), the early morning “rush hour”, and the entire campaign. We show that k* derived from CCNc measurements decreases as a function of size during all time periods, while the CCN-active fraction increases as a function of size. Size-resolved AMS measurements do not predict the observed trend for k* versus particle size, which can be attributed to unresolved mixing-state and the presence of refractory material not measured by the AMS. Measured k* typically ranges from 0.2 to 0.35, and organics typically make up 60-85% of the aerosol mass in the size range studied. Despite some disagreement between kAMS and kCCNc, we show that kAMS is able to describe CCN concentrations reasonably well, especially at the highest CCN concentrations. This is consistent with other CCN studies carried out in urban environments, and is partly due to the fact that the highest CCN concentrations occur during the daytime when the aerosol is internally-mixed and the organic fraction is relatively low. During the early morning rush hour, however, failing to account for the aerosol mixing state results in systematic overestimation of CCN concentrations by 50-100%.« less

Measurement-model comparison of stabilized Criegee intermediate and highly oxygenated molecule production in the CLOUD chamber

NASA Astrophysics Data System (ADS)

Sarnela, Nina; Jokinen, Tuija; Duplissy, Jonathan; Yan, Chao; Nieminen, Tuomo; Ehn, Mikael; Schobesberger, Siegfried; Heinritzi, Martin; Ehrhart, Sebastian; Lehtipalo, Katrianne; Tröstl, Jasmin; Simon, Mario; Kürten, Andreas; Leiminger, Markus; Lawler, Michael J.; Rissanen, Matti P.; Bianchi, Federico; Praplan, Arnaud P.; Hakala, Jani; Amorim, Antonio; Gonin, Marc; Hansel, Armin; Kirkby, Jasper; Dommen, Josef; Curtius, Joachim; Smith, James N.; Petäjä, Tuukka; Worsnop, Douglas R.; Kulmala, Markku; Donahue, Neil M.; Sipilä, Mikko

2018-02-01

Atmospheric oxidation is an important phenomenon which produces large quantities of low-volatility compounds such as sulfuric acid and oxidized organic compounds. Such species may be involved in the nucleation of particles and enhance their subsequent growth to reach the size of cloud condensation nuclei (CCN). In this study, we investigate α-pinene, the most abundant monoterpene globally, and its oxidation products formed through ozonolysis in the Cosmic Leaving OUtdoor Droplets (CLOUD) chamber at CERN (the European Organization for Nuclear Research). By scavenging hydroxyl radicals (OH) with hydrogen (H2), we were able to investigate the formation of highly oxygenated molecules (HOMs) purely driven by ozonolysis and study the oxidation of sulfur dioxide (SO2) driven by stabilized Criegee intermediates (sCIs). We measured the concentrations of HOM and sulfuric acid with a chemical ionization atmospheric-pressure interface time-of-flight (CI-APi-TOF) mass spectrometer and compared the measured concentrations with simulated concentrations calculated with a kinetic model. We found molar yields in the range of 3.5-6.5 % for HOM formation and 22-32 % for the formation of stabilized Criegee intermediates by fitting our model to the measured sulfuric acid concentrations. The simulated time evolution of the ozonolysis products was in good agreement with measured concentrations except that in some of the experiments sulfuric acid formation was faster than simulated. In those experiments the simulated and measured concentrations met when the concentration reached a plateau but the plateau was reached 20-50 min later in the simulations. The results shown here are consistent with the recently published yields for HOM formation from different laboratory experiments. Together with the sCI yields, these results help us to understand atmospheric oxidation processes better and make the reaction parameters more comprehensive for broader use.

Three millimeter molecular line observations in Sagittarius B2. 1: Full synthesis mapping study of HNO, CCS, and HC(13)CCN

NASA Technical Reports Server (NTRS)

Kuan, Yi-Jehng; Snyder, Lewis E.

1994-01-01

We present the first full synthesis maps of the small molecules HNO, CCS, and HC(13)CCN in Sgr B2. We have observed the 3.8 mm continuum, the HNO J(sub K(sub -1)K(sub 1)) = 1(sub O1)-0(sub OO), the CCS J(sub N) = 7(sub 6)-6(sub 5), and the HC(13)CCN J = 9-8 transitions in the core of the Sgr B2 molecular cloud, using the Berkeley Illinois Maryland Association (BIMA) millimeter array and the NRAO 12 m telescope. We have found that HNO exists in five major gas clumps in the Sgr B2 region, which we have labeled HNO(N), HNO(NW), HNO(E), HNO(M), and HNO(S). Of particular interest is HNO(M), a major molecular gas concentration approximately 15 sec west of Sgr B2(M) in a region of young star formation. HNO is found to be closely associated with the ionized gas and might be depleted around bright H II complexes. In general, the peak intensity of the HNO emission is found to be offset from the peak of the continuum emission. We found evidence for some chemical differentiation among the three species, HNO, CCS, and HC(13)CCN, but the abundance ratios are in fair agreement with theoretical models. Two unidentified lines, U81420 and U81518, were observed, and a previously unknown compact dust source was detected. Our HNO data indicate the presence of a rotating approximately (2.2-4.4) x 10(exp 3)solar mass gas envelope surrounding Sgr B2(N), a possible bipolar gas outflow in HNO(M), and possibly a large (approximately 4.2 x 10(exp 4)solar mass) extended rotating disk associated with HNO(S). In addition, the CCS and HC(13)CCN data approximately outline the extended component of Sgr B2 and clearly show that the southern continuum source Sgr B2(S) is actually a major molecular source as well. Consequently, the kinematics of the Sgr B2 molecular cloud is quite complex, but in moving from the northwest to south, the LSR velocity generally changes from 79 to 46 km/s.

Condensed-Phase Nitric Acid in a Tropical Subvisible Cirrus Cloud

NASA Technical Reports Server (NTRS)

Popp, P. J.; Marcy, T. P.; Watts, O. A.; Gao, R. S.; Fahey, D. W.; Weinstock, E. M.; Smith, J. B.; Herman, R. L.; Tropy, R. F.; Webster, C. r.;

Impact of natural and anthropogenic aerosols on stratocumulus and precipitation in the Southeast Pacific: a regional modelling study using WRF-Chem

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Q.; Gustafson, W. I.; Fast, J. D.

2012-09-28

Cloud-system resolving simulations with the chemistry version of the Weather Research and Forecasting (WRF-Chem) model are used to quantify the relative impacts of regional anthropogenic and oceanic emissions on changes in aerosol properties, cloud macro- and microphysics, and cloud radiative forcing over the Southeast Pacific (SEP) during the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) (15 October–16 November 2008). Two distinct regions are identified. The near-coast polluted region is characterized by low surface precipitation rates, the strong suppression of non-sea-salt particle activation due to sea-salt particles, a predominant albedo effect in aerosol indirect effects, and limited impact of aerosols associated withmore » anthropogenic emissions on clouds. Opposite sensitivities to natural marine and anthropogenic aerosol perturbations are seen in cloud properties (e.g., cloud optical depth and cloud-top and cloud-base heights), precipitation, and the top-of-atmosphere and surface shortwave fluxes over this region. The relatively clean remote region is characterized by large contributions of aerosols from non-regional sources (lateral boundaries) and much stronger drizzle at the surface. Under a scenario of five-fold increase in regional anthropogenic emissions, this relatively clean region shows large cloud responses, for example, a 13% increase in cloud-top height and a 9% increase in albedo in response to a moderate increase (25% of the reference case) in cloud condensation nuclei (CCN) concentration. The reduction of precipitation due to this increase in anthropogenic aerosols more than doubles the aerosol lifetime in the clean marine boundary layer. Therefore, the aerosol impacts on precipitation are amplified by the positive feedback of precipitation on aerosol, which ultimately alters the cloud micro- and macro-physical properties, leading to strong aerosol-cloud-precipitation interactions. The high sensitivity is also related to an increase in cloud-top entrainment rate (by 16% at night) due to the increased anthropogenic aerosols. The simulated aerosol-cloud-precipitation interactions due to the increased anthropogenic aerosols have a stronger diurnal cycle over the clean region compared to the near-coast region with stronger interactions at night. During the day, solar heating results in more frequent decoupling of the cloud and sub-cloud layers, thinner clouds, reduced precipitation, and reduced sensitivity to the increase in anthropogenic emissions. This study shows the importance of natural aerosols in accurately quantifying anthropogenic forcing within a regional modeling framework. Finally, the results of this study also imply that the energy balance perturbations from increased anthropogenic emissions are larger in the more susceptible clean environment than in already polluted environment and are larger than possible from the first indirect effect alone.« less

High summertime aerosol organic functional group concentrations from marine and seabird sources at Ross Island, Antarctica, during AWARE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Jun; Dedrick, Jeramy; Russell, Lynn M.

Observations of the organic components of the natural aerosol are scarce in Antarctica, which limits our understanding of natural aerosols and their connection to seasonal and spatial patterns of cloud albedo in the region. From November 2015 to December 2016, the ARM West Antarctic Radiation Experiment (AWARE) measured submicron aerosol properties near McMurdo Station at the southern tip of Ross Island. Submicron organic mass (OM), particle number, and cloud condensation nuclei concentrations were higher in summer than other seasons. The measurements included a range of compositions and concentrations that likely reflected both local anthropogenic emissions and natural background sources. We isolated themore » natural organic components by separating a natural factor and a local combustion factor. The natural OM was 150 times higher in summer than in winter. The local anthropogenic emissions were not hygroscopic and had little contribution to the CCN concentrations. Natural sources that included marine sea spray and seabird emissions contributed 56 % OM in summer but only 3 % in winter. The natural OM had high hydroxyl group fraction (55 %), 6 % alkane, and 6 % amine group mass, consistent with marine organic composition. In addition, the Fourier transform infrared (FTIR) spectra showed the natural sources of organic aerosol were characterized by amide group absorption, which may be from seabird populations. Finally, carboxylic acid group contributions were high in summer and associated with natural sources, likely forming by secondary reactions.« less

High summertime aerosol organic functional group concentrations from marine and seabird sources at Ross Island, Antarctica, during AWARE

DOE PAGES

Liu, Jun; Dedrick, Jeramy; Russell, Lynn M.; ...

2018-01-18

Observations of the organic components of the natural aerosol are scarce in Antarctica, which limits our understanding of natural aerosols and their connection to seasonal and spatial patterns of cloud albedo in the region. From November 2015 to December 2016, the ARM West Antarctic Radiation Experiment (AWARE) measured submicron aerosol properties near McMurdo Station at the southern tip of Ross Island. Submicron organic mass (OM), particle number, and cloud condensation nuclei concentrations were higher in summer than other seasons. The measurements included a range of compositions and concentrations that likely reflected both local anthropogenic emissions and natural background sources. We isolated themore » natural organic components by separating a natural factor and a local combustion factor. The natural OM was 150 times higher in summer than in winter. The local anthropogenic emissions were not hygroscopic and had little contribution to the CCN concentrations. Natural sources that included marine sea spray and seabird emissions contributed 56 % OM in summer but only 3 % in winter. The natural OM had high hydroxyl group fraction (55 %), 6 % alkane, and 6 % amine group mass, consistent with marine organic composition. In addition, the Fourier transform infrared (FTIR) spectra showed the natural sources of organic aerosol were characterized by amide group absorption, which may be from seabird populations. Finally, carboxylic acid group contributions were high in summer and associated with natural sources, likely forming by secondary reactions.« less

Marine sources influence fog bioaerosol composition in Namibia and Maine

NASA Astrophysics Data System (ADS)

Evans, S. E.; Dueker, E.; Logan, J. R. V.; Weathers, K. C.

2017-12-01

Organic aerosol particles act as condensation nuclei for fogs and clouds (CCN) and are main determinants of fog evolution, chemical processing, and overall aerosol-fog-cloud interactions. Recent work has confirmed the presence of marine bioaerosols, but little is known about their sources, transport, taxonomic diversity or viability. The few studies that have characterized bioaerosols in fog have been limited to culture-based approaches that capture only a fraction of microbial diversity. We characterized fungal and bacterial communities in the fog in two iconic fog systems, the Coast of Maine (USA) and the Namib Desert (Namibia). The biology of fog in both systems was diverse and distinct, by geography, from dry aerosols, and from local sources. The local environment had a dominant influence on fog in both the Namib and Maine; in particular, the biology of fog in Maine, which was collected near the coast, was more similar to microbial communities from the ocean surface. In both systems, differences between pre- and post-fog aerosol communities suggest that fog events can significantly alter microbial aerosol diversity and composition. This insight into the microbial composition of fog indicates that its origin and frequency has the potential to influence the number and diversity of microorganisms that settle in a given environment, and the composition of microbial aerosol communities in ambient or clear conditions. Here we suggest that fog microbes can possess specific traits that enhance nucleation, altering the transport and deposition of marine- and soil-derived organic matter in terrestrial systems.

Intercomparison of aerosol-cloud-precipitation interactions in stratiform orographic mixed-phase clouds

NASA Astrophysics Data System (ADS)

Muhlbauer, A.; Hashino, T.; Xue, L.; Teller, A.; Lohmann, U.; Rasmussen, R. M.; Geresdi, I.; Pan, Z.

2010-09-01

Anthropogenic aerosols serve as a source of both cloud condensation nuclei (CCN) and ice nuclei (IN) and affect microphysical properties of clouds. Increasing aerosol number concentrations is hypothesized to retard the cloud droplet coalescence and the riming in mixed-phase clouds, thereby decreasing orographic precipitation. This study presents results from a model intercomparison of 2-D simulations of aerosol-cloud-precipitation interactions in stratiform orographic mixed-phase clouds. The sensitivity of orographic precipitation to changes in the aerosol number concentrations is analysed and compared for various dynamical and thermodynamical situations. Furthermore, the sensitivities of microphysical processes such as coalescence, aggregation, riming and diffusional growth to changes in the aerosol number concentrations are evaluated and compared. The participating numerical models are the model from the Consortium for Small-Scale Modeling (COSMO) with bulk microphysics, the Weather Research and Forecasting (WRF) model with bin microphysics and the University of Wisconsin modeling system (UWNMS) with a spectral ice habit prediction microphysics scheme. All models are operated on a cloud-resolving scale with 2 km horizontal grid spacing. The results of the model intercomparison suggest that the sensitivity of orographic precipitation to aerosol modifications varies greatly from case to case and from model to model. Neither a precipitation decrease nor a precipitation increase is found robustly in all simulations. Qualitative robust results can only be found for a subset of the simulations but even then quantitative agreement is scarce. Estimates of the aerosol effect on orographic precipitation are found to range from -19% to 0% depending on the simulated case and the model. Similarly, riming is shown to decrease in some cases and models whereas it increases in others, which implies that a decrease in riming with increasing aerosol load is not a robust result. Furthermore, it is found that neither a decrease in cloud droplet coalescence nor a decrease in riming necessarily implies a decrease in precipitation due to compensation effects by other microphysical pathways. The simulations suggest that mixed-phase conditions play an important role in buffering the effect of aerosol perturbations on cloud microphysics and reducing the overall susceptibility of clouds and precipitation to changes in the aerosol number concentrations. As a consequence the aerosol effect on precipitation is suggested to be less pronounced or even inverted in regions with high terrain (e.g., the Alps or Rocky Mountains) or in regions where mixed-phase microphysics is important for the climatology of orographic precipitation.

Seasonal variability of aerosol vertical profiles over east US and west Europe: GEOS-Chem/APM simulation and comparison with CALIPSO observations

NASA Astrophysics Data System (ADS)

Ma, Xiaoyan; Yu, Fangqun

2014-04-01

In this study, we employed 5 years (2007-2011) of the CALIPSO level-3 monthly aerosol extinction product to compare with the GEOS-Chem/APM simulations for the same time period over two major industrial regions (east US and west Europe). The objective is to understand which aerosol types or species significantly determine the vertical profiles by comparing the seasonal variability between the simulations and observations. Our study shows that the model successfully produces the magnitude of aerosol extinction, profile shape, and their seasonal variability observed by CALIPSO over both east US (EUS) and west Europe (WEU). The extinctions below 1 km make up 44-79% to the total, from either the model simulations or satellite retrievals, with larger percentages in winter seasons (62-79%) and smaller percentages in summer seasons (44-57%) associated with the strength of vertical transport. The shape of the vertical profiles has, therefore, a distinct seasonal variability, with a more like quasi-exponential shape in DJF (December, January, and February) and SON (September, October, and November) than in MAM (March, April, and May) and JJA (June, July, and August), which have been discerned from both measurements and simulations. Analysis of modeled aerosol species indicates that secondary particles (SP), containing sulfate, ammonia, nitrate, and secondary organic aerosols (SOAs), predominantly determine the total aerosol vertical profiles while black carbon (BC), primary organic carbon (OC), and sea salt (SS), only account for a small fraction and are also limited near the surface. Mineral dust (DS) contributes more to the total extinction over WEU than over EUS, particularly in MAM, a result of being adjacent to the North Africa desert. Secondary inorganic aerosol (SIA, i.e. sulfate, ammonia, and nitrate) contributes most of the total SP mass in DJF and SON while SOA is particularly important in MAM and JJA when the emissions from leafed plants are active. Our study also indicates that, compared to aerosol extinction, the number concentration of particles larger than 10 nm (CN10) exhibits a different seasonal variation and vertical profile, but Cloud Condensation Nuclei (CCN) concentration at supersaturation of 0.4% (CCN0.4) presents a consistent seasonal variation and similar vertical profile. Therefore, aerosol extinction could be a good indicator for CCN0.4 with regard to seasonal variations of vertical profiles.

Marine biogeochemical influence on primary sea spray aerosol composition in the Southern Ocean: predictions from a mechanistic model

NASA Astrophysics Data System (ADS)

McCoy, D.; Burrows, S. M.; Elliott, S.; Frossard, A. A.; Russell, L. M.; Liu, X.; Ogunro, O. O.; Easter, R. C.; Rasch, P. J.

2014-12-01

Remote marine clouds, such as those over the Southern Ocean, are particularly sensitive to variations in the concentration and chemical composition of aerosols that serve as cloud condensation nuclei (CCN). Observational evidence indicates that the organic content of fine marine aerosol is greatly increased during the biologically active season near strong phytoplankton blooms in certain locations, while being nearly constant in other locations. We have recently developed a novel modeling framework that mechanistically links the organic fraction of submicron sea spray to ocean biogeochemistry (Burrows et al., in discussion, ACPD, 2014; Elliott et al., ERL, 2014). Because of its combination of large phytoplankton blooms and high wind speeds, the Southern Ocean is an ideal location for testing our understanding of the processes driving the enrichment of organics in sea spray aerosol. Comparison of the simulated OM fraction with satellite observations shows that OM fraction is a statistically significant predictor of cloud droplet number concentration over the Southern Ocean. This presentation will focus on predictions from our modeling framework for the Southern Ocean, specifically, the predicted geographic gradients and seasonal cycles in the aerosol organic matter and its functional group composition. The timing and location of a Southern Ocean field campaign will determine its utility in observing the effects of highly localized and seasonal phytoplankton blooms on aerosol composition and clouds. Reference cited: Burrows, S. M., Ogunro, O., Frossard, A. A., Russell, L. M., Rasch, P. J., and Elliott, S.: A physically-based framework for modelling the organic fractionation of sea spray aerosol from bubble film Langmuir equilibria, Atmos. Chem. Phys. Discuss., 14, 5375-5443, doi:10.5194/acpd-14-5375-2014, 2014. Elliott, S., Burrows, S. M., Deal, C., Liu, X., Long, M., Ogunro, O., Russell, L. M., and Wingenter O.. "Prospects for simulating macromolecular surfactant chemistry at the ocean-atmosphere boundary." Environmental Research Letters 9, no. 6 (2014): 064012.

Slower CCN growth kinetics of anthropogenic aerosol compared to biogenic aerosol observed at a rural site

NASA Astrophysics Data System (ADS)

Shantz, N. C.; Chang, R. Y.-W.; Slowik, J. G.; Vlasenko, A.; Abbatt, J. P. D.; Leaitch, W. R.

2010-01-01

Growth rates of water droplets were measured with a static diffusion cloud condensation chamber in May-June 2007 at a rural field site in Southern Ontario, Canada, 70 km north of Toronto. The observations include periods when the winds were from the south and the site was impacted by anthropogenic air from the U.S. and Southern Ontario as well as during a 5-day period of northerly wind flow when the aerosol was dominated by biogenic sources. The growth of droplets on anthropogenic size-selected particles centred at 0.1 μm diameter and composed of approximately 40% organic and 60% ammonium sulphate (AS) by mass, was delayed by on the order of 1 s compared to a pure AS aerosol. Simulations of the growth rate on monodisperse particles indicate that a lowering of the water mass accommodation coefficient from αc=1 to an average of αc=0.04 is needed (assuming an insoluble organic with hygroscopicity parameter, κorg, of zero). Simulations of the initial growth rate on polydisperse anthropogenic particles agree best with observations for αc=0.07. In contrast, the growth rate of droplets on size-selected aerosol of biogenic character, consisting of >80% organic, was similar to that of pure AS. Simulations of the predominantly biogenic polydisperse aerosol show agreement between the observations and simulations when κorg=0.2 (with upper and lower limits of 0.5 and 0.07, respectively) and αc=1. Inhibition of water uptake by the anthropogenic organic applied to an adiabatic cloud parcel model in the form of a constant low αc increases the number of droplets in a cloud compared to pure AS. If the αc is assumed to increase with increasing liquid water on the droplets, then the number of droplets decreases which could diminish the indirect climate forcing effect. The slightly lower κorg in the biogenic case decreases the number of droplets in a cloud compared to pure AS.

Fresh clouds: A parameterized updraft method for calculating cloud densities in one-dimensional models

NASA Astrophysics Data System (ADS)

Wong, Michael H.; Atreya, Sushil K.; Kuhn, William R.; Romani, Paul N.; Mihalka, Kristen M.

2015-01-01

Models of cloud condensation under thermodynamic equilibrium in planetary atmospheres are useful for several reasons. These equilibrium cloud condensation models (ECCMs) calculate the wet adiabatic lapse rate, determine saturation-limited mixing ratios of condensing species, calculate the stabilizing effect of latent heat release and molecular weight stratification, and locate cloud base levels. Many ECCMs trace their heritage to Lewis (Lewis, J.S. [1969]. Icarus 10, 365-378) and Weidenschilling and Lewis (Weidenschilling, S.J., Lewis, J.S. [1973]. Icarus 20, 465-476). Calculation of atmospheric structure and gas mixing ratios are correct in these models. We resolve errors affecting the cloud density calculation in these models by first calculating a cloud density rate: the change in cloud density with updraft length scale. The updraft length scale parameterizes the strength of the cloud-forming updraft, and converts the cloud density rate from the ECCM into cloud density. The method is validated by comparison with terrestrial cloud data. Our parameterized updraft method gives a first-order prediction of cloud densities in a “fresh” cloud, where condensation is the dominant microphysical process. Older evolved clouds may be better approximated by another 1-D method, the diffusive-precipitative Ackerman and Marley (Ackerman, A.S., Marley, M.S. [2001]. Astrophys. J. 556, 872-884) model, which represents a steady-state equilibrium between precipitation and condensation of vapor delivered by turbulent diffusion. We re-evaluate observed cloud densities in the Galileo Probe entry site (Ragent, B. et al. [1998]. J. Geophys. Res. 103, 22891-22910), and show that the upper and lower observed clouds at ∼0.5 and ∼3 bars are consistent with weak (cirrus-like) updrafts under conditions of saturated ammonia and water vapor, respectively. The densest observed cloud, near 1.3 bar, requires unexpectedly strong updraft conditions, or higher cloud density rates. The cloud density rate in this layer may be augmented by a composition with non-NH4SH components (possibly including adsorbed NH3).

Shipborne measurements of aerosol number size distribution and hygroscopicity over the North Pacific Ocean

NASA Astrophysics Data System (ADS)

Royalty, T. M.; Phillips, B.; Dawson, K. W.; Reed, R. E.; Meskhidze, N.

2016-12-01

We report aerosol number size distribution and hygroscopicity data collected over the Pacific Ocean near the Hawaii Ocean Timeseries (HOT) Station ALOHA (centered near 22°N, 158°W). From June 25 to July 3, 2016 our hygroscopicity tandem differential mobility analyzer (HTDMA)/scanning mobility particle sizer (SMPS) system was deployed onboard of NOAA Ship Hi'ialakai that participated in mooring operations associated with the Woods Hole Oceanographic Institution WHOTS project. The ambient aerosol data was collected during the ship's planned operations. The inlet was located at the bow of the ship and the air samples were drawn (using 3/8 inch stainless steel tubing) inside a dry, air-conditioned lab. The region north of Oahu was very clean, with total particle number approximately 200 cm-3, occasionally dropping below 100 cm-3. We compare our particle number size distribution and hygroscopicity data with previously reported estimates. Our measurements contribute to process-level understanding of the role of sea spray aerosol in marine boundary layer cloud condensation nuclei (CCN) budget and provide crucial information to the community interested in studying and projecting climate change using Earth System Models.

Measurements of IN and BIO-IN with the fast ice nucleus chamber FINCH at Mt. Zugspitze, Mt. Puy de Dôme and Jungfraujoch during fall and winter

NASA Astrophysics Data System (ADS)

Nillius, B.; Frank, F.; Bingemer, H.; Curtius, J.; Bundke, U.

2013-05-01

In this work we present IN measurements at Mt. Zugspitze, Germany, 2650 m.a.s.l., Mt. Puy de Dôme, France, 1464 m.a.s.l. and Jungfraujoch, Switzerland, 3580 m a.s.l during fall and winter 2012 with the instrument FINCH HALO (Fast Ice Nucleus Chamber for the High Altitude and LOng range research aircraft HALO). In this device the temperature and super saturation for activation of Ice Nuclei (IN) and the growth to ice crystals is obtained by mixing three gas flows of different temperatures and moisture. After the growth of IN and Cloud Condensation Nuclei (CCN) to macroscopic ice crystals and super-cooled water droplets in the development chamber, they are counted using an optical detector. The discrimination between ice and water is made by measuring the circular depolarization ratio of the backscattered laser light of each individual particle. IN are classified as biological particles by measuring their individual intrinsic-fluorescence during the winter campaigns in average 30-40 % of the IN show an intrinsic fluorescence and are supposed to be of biological origin.

Increased ionization supports growth of aerosols into cloud condensation nuclei.

PubMed

Svensmark, H; Enghoff, M B; Shaviv, N J; Svensmark, J

2017-12-19

Ions produced by cosmic rays have been thought to influence aerosols and clouds. In this study, the effect of ionization on the growth of aerosols into cloud condensation nuclei is investigated theoretically and experimentally. We show that the mass-flux of small ions can constitute an important addition to the growth caused by condensation of neutral molecules. Under atmospheric conditions the growth from ions can constitute several percent of the neutral growth. We performed experimental studies which quantify the effect of ions on the growth of aerosols between nucleation and sizes >20 nm and find good agreement with theory. Ion-induced condensation should be of importance not just in Earth's present day atmosphere for the growth of aerosols into cloud condensation nuclei under pristine marine conditions, but also under elevated atmospheric ionization caused by increased supernova activity.

New particle formation in the free troposphere: from the Alps to the Everest Base Camp.

NASA Astrophysics Data System (ADS)

Bianchi, F.; Junninen, H.; Kontkanen, J.; Marinoni, A.; Bonasoni, P.; Sellegri, K.; Laj, P.; Dommen, J.; Worsnop, D. R.; Baltensperger, U.

2016-12-01

Atmospheric aerosols can affect the climate by absorbing or scattering incoming radiation and also by acting as cloud condensation nuclei (CCN). A recent study estimates that the major fraction of CCN comes from gas to particle conversion (Merikanto et al., 2009). During the last decade, several nucleation studies have been published based on field observations mainly in the planetary boundary layer. Therefore, we have only little information about the free tropospheric case. The aim of these studies is to understand what species contribute to new particle formation at high altitude. In order to characterize NPF processes, advanced instrumentation was deployed at the Swiss station Jungfraujoch (3580 m asl - Bianchi et al., 2016) and at the Himalayan Nepal Climate Observatory Pyramid site, not far from Everest base camp (5079 m asl). Previous studies have already showed that at both of these locations NPF takes place frequently. However, no chemical information of the vapours was retrieved. At the Nepal Observatory, we deployed an atmospheric pressure interface time-of-flight mass spectrometer (APi-TOF), a particle size magnifier (PSM) and a neutral cluster and air ion spectrometer (NAIS). The APi-TOF measured the chemical composition of either the positive or negative ions during the nucleation events and when equipped with a chemical ionization source it provided information on the chemical composition of the neutral species. Figure 1 shows the first APi-TOF mass spectrum running in negative mode recorded above 5000 m asl during a nucleation event. The main ions that have been identified so far are all deprotonated acids: sulfuric acid, nitric acid, malonic acid, methanesulfonic acid and iodic acid. Larger ions are formed by different combinations of these acids (i.e. H2SO4°HSO4-, CH3SO3H°HSO4-, etc.). We will present a detailed analysis of the particle evolution during NPF and also the chemical composition of the small clusters measured with these advanced mass spectrometers. We will also show that even at this altitude highly oxidised molecules (HOM) have been detected, confirming the CLOUD laboratory experiments (Kirkby et al., 2016). Bianchi, F., et al. (2016) Science, 6289, 1109-1112.Kirkby, J., et al. (2016) Nature, 10.1038/nature17953. Merikanto, J., et al. (2009) Atmos. Chem. Phys. 9 (21), 8601-8616.

Helicopter-borne observations of the continental background aerosol in combination with remote sensing and ground-based measurements

NASA Astrophysics Data System (ADS)

Düsing, Sebastian; Wehner, Birgit; Seifert, Patric; Ansmann, Albert; Baars, Holger; Ditas, Florian; Henning, Silvia; Ma, Nan; Poulain, Laurent; Siebert, Holger; Wiedensohler, Alfred; Macke, Andreas

2018-01-01

This paper examines the representativeness of ground-based in situ measurements for the planetary boundary layer (PBL) and conducts a closure study between airborne in situ and ground-based lidar measurements up to an altitude of 2300 m. The related measurements were carried out in a field campaign within the framework of the High-Definition Clouds and Precipitation for Advancing Climate Prediction (HD(CP)2) Observational Prototype Experiment (HOPE) in September 2013 in a rural background area of central Europe.The helicopter-borne probe ACTOS (Airborne Cloud and Turbulence Observation System) provided measurements of the aerosol particle number size distribution (PNSD), the aerosol particle number concentration (PNC), the number concentration of cloud condensation nuclei (CCN-NC), and meteorological atmospheric parameters (e.g., temperature and relative humidity). These measurements were supported by the ground-based 3+2 wavelength polarization lidar system PollyXT, which provided profiles of the particle backscatter coefficient (σbsc) for three wavelengths (355, 532, and 1064 nm). Particle extinction coefficient (σext) profiles were obtained by using a fixed backscatter-to-extinction ratio (also lidar ratio, LR). A new approach was used to determine profiles of CCN-NC for continental aerosol. The results of this new approach were consistent with the airborne in situ measurements within the uncertainties.In terms of representativeness, the PNSD measurements on the ground showed a good agreement with the measurements provided with ACTOS for lower altitudes. The ground-based measurements of PNC and CCN-NC are representative of the PBL when the PBL is well mixed. Locally isolated new particle formation events on the ground or at the top of the PBL led to vertical variability in the cases presented here and ground-based measurements are not entirely representative of the PBL. Based on Mie theory (Mie, 1908), optical aerosol properties under ambient conditions for different altitudes were determined using the airborne in situ measurements and were compared with the lidar measurements. The investigation of the optical properties shows that on average the airborne-based particle light backscatter coefficient is 50.1 % smaller for 1064 nm, 27.4 % smaller for 532 nm, and 29.5 % smaller for 355 nm than the measurements of the lidar system. These results are quite promising, since in situ measurement-based Mie calculations of the particle light backscattering are scarce and the modeling is quite challenging. In contrast, for the particle light extinction coefficient we found a good agreement. The airborne-based particle light extinction coefficient was just 8.2 % larger for 532 nm and 3 % smaller for 355 nm, for an assumed LR of 55 sr. The particle light extinction coefficient for 1064 nm was derived with a LR of 30 sr. For this wavelength, the airborne-based particle light extinction coefficient is 5.2 % smaller than the lidar measurements. For the first time, the lidar ratio of 30 sr for 1064 nm was determined on the basis of in situ measurements and the LR of 55 sr for 355 and 532 nm wavelength was reproduced for European continental aerosol on the basis of this comparison. Lidar observations and the in situ based aerosol optical properties agree within the uncertainties. However, our observations indicate that a determination of the PNSD for a large size range is important for a reliable modeling of aerosol particle backscattering.

Observations of the boundary layer, cloud, and aerosol variability in the southeast Pacific near-coastal marine stratocumulus during VOCALS-REx

NASA Astrophysics Data System (ADS)

Zheng, X.; Albrecht, B.; Jonsson, H. H.; Khelif, D.; Feingold, G.; Minnis, P.; Ayers, K.; Chuang, P.; Donaher, S.; Rossiter, D.; Ghate, V.; Ruiz-Plancarte, J.; Sun-Mack, S.

2011-09-01

Aircraft observations made off the coast of northern Chile in the Southeastern Pacific (20° S, 72° W; named Point Alpha) from 16 October to 13 November 2008 during the VAMOS Ocean-Cloud- Atmosphere-Land Study-Regional Experiment (VOCALS-REx), combined with meteorological reanalysis, satellite measurements, and radiosonde data, are used to investigate the boundary layer (BL) and aerosol-cloud-drizzle variations in this region. On days without predominately synoptic and meso-scale influences, the BL at Point Alpha was typical of a non-drizzling stratocumulus-topped BL. Entrainment rates calculated from the near cloud-top fluxes and turbulence in the BL at Point Alpha appeared to be weaker than those in the BL over the open ocean west of Point Alpha and the BL near the coast of the northeast Pacific. The cloud liquid water path (LWP) varied between 15 g m-2 and 160 g m-2. The BL had a depth of 1140 ± 120 m, was generally well-mixed and capped by a sharp inversion without predominately synoptic and meso-scale influences. The wind direction generally switched from southerly within the BL to northerly above the inversion. On days when a synoptic system and related mesoscale costal circulations affected conditions at Point Alpha (29 October-4 November), a moist layer above the inversion moved over Point Alpha, and the total-water mixing ratio above the inversion was larger than that within the BL. The accumulation mode aerosol varied from 250 to 700 cm-3 within the BL, and CCN at 0.2 % supersaturation within the BL ranged between 150 and 550 cm-3. The main aerosol source at Point Alpha was horizontal advection within the BL from south. The average cloud droplet number concentration ranged between 80 and 400 cm-3. While the mean LWP retrieved from GOES was in good agreement with the in situ measurements, the GOES-derived cloud droplet effective radius tended to be larger than that from the aircraft in situ observations near cloud top. The aerosol and cloud LWP relationship reveals that during the typical well-mixed BL days the cloud LWP increased with the CCN concentrations. On the other hand, meteorological factors and the decoupling processes have large influences on the cloud LWP variation as well.

Clouds in Super-Earth Atmospheres: Chemical Equilibrium Calculations

NASA Astrophysics Data System (ADS)

Mbarek, Rostom; Kempton, Eliza M.-R.

2016-08-01

Recent studies have unequivocally proven the existence of clouds in super-Earth atmospheres. Here we provide a theoretical context for the formation of super-Earth clouds by determining which condensates are likely to form under the assumption of chemical equilibrium. We study super-Earth atmospheres of diverse bulk composition, which are assumed to form by outgassing from a solid core of chondritic material, following Schaefer & Fegley. The super-Earth atmospheres that we study arise from planetary cores made up of individual types of chondritic meteorites. They range from highly reducing to oxidizing and have carbon to oxygen (C:O) ratios that are both sub-solar and super-solar, thereby spanning a range of atmospheric composition that is appropriate for low-mass exoplanets. Given the atomic makeup of these atmospheres, we minimize the global Gibbs free energy of formation for over 550 gases and condensates to obtain the molecular composition of the atmospheres over a temperature range of 350-3000 K. Clouds should form along the temperature-pressure boundaries where the condensed species appear in our calculation. We find that the composition of condensate clouds depends strongly on both the H:O and C:O ratios. For the super-Earth archetype GJ 1214b, KCl and ZnS are the primary cloud-forming condensates at solar composition, in agreement with previous work. However, for oxidizing atmospheres, K2SO4 and ZnO condensates are favored instead, and for carbon-rich atmospheres with super-solar C:O ratios, graphite clouds appear. For even hotter planets, clouds form from a wide variety of rock-forming and metallic species.

Idealized simulation of the Colorado hailstorm case: comparison of bulk and detailed microphysics

NASA Astrophysics Data System (ADS)

Geresdi, I.

One of the purposes of the Fourth Cloud Modeling Workshop was to compare different microphysical treatments. In this paper, the results of a widely used bulk treatment and five versions of a detailed microphysical model are presented. Sensitivity analysis was made to investigate the effect of bulk parametrization, ice initiation technique, CCN concentration and collision efficiency of rimed ice crystal-drop collision. The results show that: (i) The mixing ratios of different species of hydrometeors calculated by bulk and one of the detailed models show some similarity. However, the processes of hail/graupel formation are different in the bulk and the detailed models. (ii) Using different ice initiation in the detailed models' different processes became important in the hail and graupel formation. (iii) In the case of higher CCN concentration, the mixing ratio of liquid water, hail and graupel were more sensitive to the value of collision efficiency of rimed ice crystal-drop collision. (iv) The Bergeron-Findeisen process does not work in the updraft core of a convective cloud. The vapor content was always over water saturation; moreover, the supersaturation gradually increased after the appearance of precipitation ice particles.

Numerical simulations of Jupiter’s moist convection layer: Structure and dynamics in statistically steady states

NASA Astrophysics Data System (ADS)

Sugiyama, K.; Nakajima, K.; Odaka, M.; Kuramoto, K.; Hayashi, Y.-Y.

2014-02-01

A series of long-term numerical simulations of moist convection in Jupiter’s atmosphere is performed in order to investigate the idealized characteristics of the vertical structure of multi-composition clouds and the convective motions associated with them, varying the deep abundances of condensable gases and the autoconversion time scale, the latter being one of the most questionable parameters in cloud microphysical parameterization. The simulations are conducted using a two-dimensional cloud resolving model that explicitly represents the convective motion and microphysics of the three cloud components, H2O, NH3, and NH4SH imposing a body cooling that substitutes the net radiative cooling. The results are qualitatively similar to those reported in Sugiyama et al. (Sugiyama, K. et al. [2011]. Intermittent cumulonimbus activity breaking the three-layer cloud structure of Jupiter. Geophys. Res. Lett. 38, L13201. doi:10.1029/2011GL047878): stable layers associated with condensation and chemical reaction act as effective dynamical and compositional boundaries, intense cumulonimbus clouds develop with distinct temporal intermittency, and the active transport associated with these clouds results in the establishment of mean vertical profiles of condensates and condensable gases that are distinctly different from the hitherto accepted three-layered structure (e.g., Atreya, S.K., Romani, P.N. [1985]. Photochemistry and clouds of Jupiter, Saturn and Uranus. In: Recent Advances in Planetary Meteorology. Cambridge Univ. Press, London, pp. 17-68). Our results also demonstrate that the period of intermittent cloud activity is roughly proportional to the deep abundance of H2O gas. The autoconversion time scale does not strongly affect the results, except for the vertical profiles of the condensates. Changing the autoconversion time scale by a factor of 100 changes the intermittency period by a factor of less than two, although it causes a dramatic increase in the amount of condensates in the upper troposphere. The moist convection layer becomes potentially unstable with respect to an air parcel rising from below the H2O lifting condensation level (LCL) well before the development of cumulonimbus clouds. The instability accumulates until an appropriate trigger is provided by the H2O condensate that falls down through the H2O LCL; the H2O condensate drives a downward flow below the H2O LCL as a result of the latent cooling associated with the re-evaporation of the condensate, and the returning updrafts carry moist air from below to the moist convection layer. Active cloud development is terminated when the instability is completely exhausted. The period of intermittency is roughly equal to the time obtained by dividing the mean temperature increase, which is caused by active cumulonimbus development, by the body cooling rate.

Emissions from Ships with respect to Their Effects on Clouds.

NASA Astrophysics Data System (ADS)

Hobbs, Peter V.; Garrett, Timothy J.; Ferek, Ronald J.; Strader, Scott R.; Hegg, Dean A.; Frick, Glendon M.; Hoppel, William A.; Gasparovic, Richard F.; Russell, Lynn M.; Johnson, Douglas W.; O'Dowd, Colin; Durkee, Philip A.; Nielsen, Kurt E.; Innis, George

2000-08-01

Emissions of particles, gases, heat, and water vapor from ships are discussed with respect to their potential for changing the microstructure of marine stratiform clouds and producing the phenomenon known as `ship tracks.' Airborne measurements are used to derive emission factors of SO2 and NO from diesel-powered and steam turbine-powered ships, burning low-grade marine fuel oil (MFO); they were 15-89 and 2-25 g kg1 of fuel burned, respectively. By contrast a steam turbine-powered ship burning high-grade navy distillate fuel had an SO2 emission factor of 6 g kg1.Various types of ships, burning both MFO and navy distillate fuel, emitted from 4 × 1015 to 2 × 1016 total particles per kilogram of fuel burned (4 × 1015-1.5 × 1016 particles per second). However, diesel-powered ships burning MFO emitted particles with a larger mode radius (0.03-0.05 m) and larger maximum sizes than those powered by steam turbines burning navy distillate fuel (mode radius 0.02 m). Consequently, if the particles have similar chemical compositions, those emitted by diesel ships burning MFO will serve as cloud condensation nuclei (CCN) at lower supersaturations (and will therefore be more likely to produce ship tracks) than the particles emitted by steam turbine ships burning distillate fuel. Since steam turbine-powered ships fueled by MFO emit particles with a mode radius similar to that of diesel-powered ships fueled by MFO, it appears that, for given ambient conditions, the type of fuel burned by a ship is more important than the type of ship engine in determining whether or not a ship will produce a ship track. However, more measurements are needed to test this hypothesis.The particles emitted from ships appear to be primarily organics, possibly combined with sulfuric acid produced by gas-to-particle conversion of SO2. Comparison of model results with measurements in ship tracks suggests that the particles from ships contain only about 10% water-soluble materials. Measurements of the total particles entering marine stratiform clouds from diesel-powered ships fueled by MFO, and increases in droplet concentrations produced by these particles, show that only about 12% of the particles serve as CCN.The fluxes of heat and water vapor from ships are estimated to be 2-22 MW and 0.5-1.5 kg s1, respectively. These emissions rarely produced measurable temperature perturbations, and never produced detectable perturbations in water vapor, in the plumes from ships. Nuclear-powered ships, which emit heat but negligible particles, do not produce ship tracks. Therefore, it is concluded that heat and water vapor emissions do not play a significant role in ship track formation and that particle emissions, particularly from those burning low-grade fuel oil, are responsible for ship track formation. Subsequent papers in this special issue discuss and test these hypotheses.

Clouds Composition in Super-Earth Atmospheres: Chemical Equilibrium Calculations

NASA Astrophysics Data System (ADS)

Kempton, Eliza M.-R.; Mbarek, Rostom

2015-12-01

Attempts to determine the composition of super-Earth atmospheres have so far been plagued by the presence of clouds. Yet the theoretical framework to understand these clouds is still in its infancy. For the super-Earth archetype GJ 1214b, KCl, Na2S, and ZnS have been proposed as condensates that would form under the condition of chemical equilibrium, if the planet’s atmosphere has a bulk composition near solar. Condensation chemistry calculations have not been presented for a wider range of atmospheric bulk composition that is to be expected for super-Earth exoplanets. Here we provide a theoretical context for the formation of super-Earth clouds in atmospheres of varied composition by determining which condensates are likely to form, under the assumption of chemical equilibrium. We model super-Earth atmospheres assuming they are formed by degassing of volatiles from a solid planetary core of chondritic material. Given the atomic makeup of these atmospheres, we minimize the global Gibbs free energy of over 550 gases and condensates to obtain the molecular composition of the atmospheres over a temperature range of 350-3,000 K. Clouds should form along the temperature-pressure boundaries where the condensed species appear in our calculations. The super-Earth atmospheres that we study range from highly reducing to oxidizing and have carbon to oxygen (C:O) ratios that are both sub-solar and super-solar, thereby spanning a diverse range of atmospheric composition that is appropriate for low-mass exoplanets. Some condensates appear across all of our models. However, the majority of condensed species appear only over specific ranges of H:O and C:O ratios. We find that for GJ 1214b, KCl is the primary cloud-forming condensate at solar composition, in agreement with previous work. However, for oxidizing atmospheres, where H:O is less than unity, K2SO4 clouds form instead. For carbon-rich atmospheres with super-solar C:O ratios, graphite clouds additionally appear. At higher temperatures, clouds are formed from a variety of materials including metals, metal oxides, and aluminosilicates.

Cloud Microphysics Budget in the Tropical Deep Convective Regime

NASA Technical Reports Server (NTRS)

Li, Xiao-Fan; Sui, C.-H.; Lau, K.-M.; Einaudi, Franco (Technical Monitor)

2001-01-01

Cloud microphysics budgets in the tropical deep convective regime are analyzed based on a 2-D cloud resolving simulation. The model is forced by the large-scale vertical velocity and zonal wind and large-scale horizontal advections derived from TOGA COARE for a 20-day period. The role of cloud microphysics is first examined by analyzing mass-weighted mean heat budget and column-integrated moisture budget. Hourly budgets show that local changes of mass-weighted mean temperature and column-integrated moisture are mainly determined by the residuals between vertical thermal advection and latent heat of condensation and between vertical moisture advection and condensation respectively. Thus, atmospheric thermodynamics depends on how cloud microphysical processes are parameterized. Cloud microphysics budgets are then analyzed for raining conditions. For cloud-vapor exchange between cloud system and its embedded environment, rainfall and evaporation of raindrop are compensated by the condensation and deposition of supersaturated vapor. Inside the cloud system, the condensation of supersaturated vapor balances conversion from cloud water to raindrop, snow, and graupel through collection and accretion processes. The deposition of supersaturated vapor balances conversion from cloud ice to snow through conversion and riming processes. The conversion and riming of cloud ice and the accretion of cloud water balance conversion from snow to graupel through accretion process. Finally, the collection of cloud water and the melting of graupel increase raindrop to compensate the loss of raindrop due to rainfall and the evaporation of raindrop.

Evaluating the feasibility of global climate models to simulate cloud cover effect controlled by Marine Stratocumulus regime transitions

NASA Astrophysics Data System (ADS)

Goren, Tom; Muelmenstaedt, Johannes; Rosenfeld, Daniel; Quaas, Johannes

2017-04-01

Marine stratocumulus clouds (MSC) occur in two main cloud regimes of open and closed cells that differ significantly by their cloud cover. Closed cells gradually get cleansed of high CCN concentrations in a process that involves initiation of drizzle that breaks the full cloud cover into open cells. The drizzle creates downdrafts that organize the convection along converging gust fronts, which in turn produce stronger updrafts that can sustain more cloud water that compensates the depletion of the cloud water by the rain. In addition, having stronger updrafts allow the clouds to grow relatively deep before rain starts to deplete its cloud water. Therefore, lower droplet concentrations and stronger rain would lead to lower cloud fraction, but not necessary also to lower liquid water path (LWP). The fundamental relationships between these key variables derived from global climate model (GCM) simulations are analyzed with respect to observations in order to determine whether the GCM parameterizations can represent well the governing physical mechanisms upon MSC regime transitions. The results are used to evaluate the feasibility of GCM's for estimating aerosol cloud-mediated radiative forcing upon MSC regime transitions, which are responsible for the largest aerosol cloud-mediated radiative forcing.

An aircraft-based case study of new particle formation and growth in the summertime Arctic

NASA Astrophysics Data System (ADS)

Willis, M. D.; Abbatt, J.; Burkart, J.; Bozem, H.; Koellner, F.; Schneider, J.; Hoor, P. M.; Herber, A. B.; Leaitch, W. R.

2015-12-01

Motivated by the changing climate of the Arctic and decreasing summer sea-ice extent, we aim to better understand how atmospheric composition will impact, or be impacted by, climate and environmental change in this region. Much attention has been paid to springtime Arctic aerosol owing to significant anthropogenic influence on this remote environment, but the cleaner, more locally influenced summertime Arctic is not well characterized. We present results of vertically resolved, particle number, aerosol size distributions, submicron aerosol composition from an aerosol mass spectrometer (AMS), and cloud condensation nuclei (CCN) concentrations from the NETCARE 2014 Polar 6 aircraft campaign. The campaign was based in the high Arctic, at Resolute Bay, Nunavut, Canada (74°N, 94°W), allowing measurements from 60 to 2900 meters over ice, open water and near the ice-edge. The focus of this case study is a new particle formation and growth event observed at the eastern end of Lancaster Sound (74°N, 81°W) on July 12, 2014 under clear sky conditions. During this flight Polar 6 travelled to the end of Lancaster Sound at 2900 m and subsequently descended to 60-70 m above the surface heading due west, with winds from the west. At the lowest altitude we observed a significant increase in particles > 4 nm, between 20 - 100 nm, and > 100 nm, indicating the presence of small particles between 4 - 20 nm and growth to larger sizes. In addition, CCN concentrations were enhanced up to ~ 200/cm3 from background levels of ≤ 100/cm3. Concurrently, the AMS indicated enhanced levels of methane sulfonic acid (MSA) and marine-like organic aerosol (OA) correlated in time with the presence of larger particles, as well as an iodide signal which correlated with the presence of small particles. These observations suggest that iodine oxides could be one contributor to particle formation, and that marine-like OA and MSA could contribute to particle growth in the summertime Arctic.

Observation of nitrate coatings on atmospheric mineral dust particles

NASA Astrophysics Data System (ADS)

Li, W. J.; Shao, L. Y.

2009-03-01

Nitrate compounds have received much attention because of their ability to alter the hygroscopic properties and cloud condensation nuclei (CCN) activity of mineral dust particles in the atmosphere. However, very little is known about specific characteristics of ambient nitrate-coated mineral particles on an individual particle scale. In this study, sample collection was conducted during brown haze and dust episodes between 24 May and 21 June 2007 in Beijing, northern China. Sizes, morphologies, and compositions of 332 mineral dust particles together with their coatings were analyzed using transmission electron microscopy (TEM) coupled with energy-dispersive X-ray (EDX) microanalyses. Structures of some mineral particles were verified using selected-area electron diffraction (SAED). TEM observation indicates that approximately 90% of the collected mineral particles are covered by visible coatings in haze samples whereas only 5% are coated in the dust sample. 92% of the analyzed mineral particles are covered with Ca-, Mg-, and Na-rich coatings, and 8% are associated with K- and S-rich coatings. The majority of coatings contain Ca, Mg, O, and N with minor amounts of S and Cl, suggesting that they are possibly nitrates mixed with small amounts of sulfates and chlorides. These nitrate coatings are strongly correlated with the presence of alkaline mineral components (e.g., calcite and dolomite). CaSO4 particles with diameters from 10 to 500 nm were also detected in the coatings including Ca(NO3)2 and Mg(NO3)2. Our results indicate that mineral particles in brown haze episodes were involved in atmospheric heterogeneous reactions with two or more acidic gases (e.g., SO2, NO2, HCl, and HNO3). Mineral particles that acquire hygroscopic nitrate coatings tend to be more spherical and larger, enhancing their light scattering and CCN activity, both of which have cooling effects on the climate.

The oleic acid-ozone heterogeneous reaction system: products, kinetics, secondary chemistry, and atmospheric implications of a model system - a review

NASA Astrophysics Data System (ADS)

Zahardis, J.; Petrucci, G. A.

2007-02-01

The heterogeneous processing of organic aerosols by trace oxidants has many implications to atmospheric chemistry and climate regulation. This review covers a model heterogeneous reaction system (HRS): the oleic acid-ozone HRS and other reaction systems featuring fatty acids, and their derivatives. The analysis of the commonly observed aldehyde and organic acid products of ozonolysis (azelaic acid, nonanoic acid, 9-oxononanoic acid, nonanal) is described. The relative product yields are noted and explained by the observation of secondary chemical reactions. The secondary reaction products arising from reactive Criegee intermediates are mainly peroxidic, notably secondary ozonides and α-acyloxyalkyl hydroperoxide oligomers and polymers, and their formation is in accord with solution and liquid-phase ozonolysis. These highly oxygenated products are of low volatility and hydrophilic which may enhance the ability of particles to act as cloud condensation nuclei (CCN). The kinetic description of this HRS is critically reviewed. Most kinetic studies suggest this oxidative processing is either a near surface reaction that is limited by the diffusion of ozone or a surface based reaction. Internally mixed particles and coatings represent the next stage in the progression towards more realistic proxies of tropospheric organic aerosols and a description of the products and the kinetics resulting from the ozonolysis of these proxies, which are based on fatty acids or their derivatives, is presented. Finally, the main atmospheric implications of oxidative processing of particulate containing fatty acids are presented. These implications include the extended lifetime of unsaturated species in the troposphere facilitated by the presence of solids, semi-solids or viscous phases, and an enhanced rate of ozone uptake by particulate unsaturates compared to corresponding gas-phase organics. Ozonolysis of oleic acid enhances its CCN activity, which implies that oxidatively processed particulate may contribute to indirect forcing of radiation.

CLOUDS IN SUPER-EARTH ATMOSPHERES: CHEMICAL EQUILIBRIUM CALCULATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mbarek, Rostom; Kempton, Eliza M.-R., E-mail: mbarekro@grinnell.edu, E-mail: kemptone@grinnell.edu

Recent studies have unequivocally proven the existence of clouds in super-Earth atmospheres. Here we provide a theoretical context for the formation of super-Earth clouds by determining which condensates are likely to form under the assumption of chemical equilibrium. We study super-Earth atmospheres of diverse bulk composition, which are assumed to form by outgassing from a solid core of chondritic material, following Schaefer and Fegley. The super-Earth atmospheres that we study arise from planetary cores made up of individual types of chondritic meteorites. They range from highly reducing to oxidizing and have carbon to oxygen (C:O) ratios that are both sub-solarmore » and super-solar, thereby spanning a range of atmospheric composition that is appropriate for low-mass exoplanets. Given the atomic makeup of these atmospheres, we minimize the global Gibbs free energy of formation for over 550 gases and condensates to obtain the molecular composition of the atmospheres over a temperature range of 350–3000 K. Clouds should form along the temperature–pressure boundaries where the condensed species appear in our calculation. We find that the composition of condensate clouds depends strongly on both the H:O and C:O ratios. For the super-Earth archetype GJ 1214b, KCl and ZnS are the primary cloud-forming condensates at solar composition, in agreement with previous work. However, for oxidizing atmospheres, K{sub 2}SO{sub 4} and ZnO condensates are favored instead, and for carbon-rich atmospheres with super-solar C:O ratios, graphite clouds appear. For even hotter planets, clouds form from a wide variety of rock-forming and metallic species.« less

A one-dimensional sectional aerosol model integrated with mesoscale meteorological data to study marine boundary layer aerosol dynamics

NASA Astrophysics Data System (ADS)

Caffrey, Peter F.; Hoppel, William A.; Shi, Jainn J.

2006-12-01

The dynamics of aerosols in the marine boundary layer are simulated with a one-dimensional, multicomponent, sectional aerosol model using vertical profiles of turbulence, relative humidity, temperature, vertical velocity, cloud cover, and precipitation provided by 3-D mesoscale meteorological model output. The Naval Research Laboratory's (NRL) sectional aerosol model MARBLES (Fitzgerald et al., 1998a) was adapted to use hourly meteorological input taken from NRL's Coupled Ocean-Atmosphere Prediction System (COAMPS). COAMPS-generated turbulent mixing coefficients and large-scale vertical velocities determine vertical exchange within the marine boundary layer and exchange with the free troposphere. Air mass back trajectories were used to define the air column history along which the meteorology was retrieved for use with the aerosol model. Details on the integration of these models are described here, as well as a description of improvements made to the aerosol model, including transport by large-scale vertical motions (such as subsidence and lifting), a revised sea-salt aerosol source function, and separate tracking of sulfate mass from each of the five sources (free tropospheric, nucleated, condensed from gas phase oxidation products, cloud-processed, and produced from heterogeneous oxidation of S(IV) on sea-salt aerosol). Results from modeling air masses arriving at Oahu, Hawaii, are presented, and the relative contribution of free-tropospheric sulfate particles versus sea-salt aerosol from the surface to CCN concentrations is discussed. Limitations and benefits of the method are presented, as are sensitivity analyses of the effect of large-scale vertical motions versus turbulent mixing.

Investigating the connectivity between emissions of BVOC and rainfall formation in Amazonia using Genetic Programming

NASA Astrophysics Data System (ADS)

Von Randow, Celso; Sanches, Marcos B.; Santos, Rosa Maria N.; Chamecki, Marcelo; Fuentes, Jose D.

2017-04-01

A detailed field experiment measuring turbulent properties, trace gases and BVOCs was carried out from April 2014 to January 2015 within and above a central Amazonian rainforest, with the objective of understanding the role of emissions and reactions of BVOCs, formation and transport of aerosols out of the boundary layer on cloud formation and precipitation triggers. Our measurements show two-way aspects of connectivity: mesoscale convective systems transport ozone down from the middle troposphere, enriching the atmospheric boundary layer as well as the forest canopy and surface layer, and, through multiple chemical transformations, an ozone-enriched atmospheric surface layer that can oxidize rainforest-emitted hydrocarbons and generate aerosols that subsequently activate into cloud condensation nuclei, thereby possibly influencing the formation of new convective precipitation. Qualitatively, we address the connectivity between emissions of BVOCs near the surface and rainfall generation, using the technique of Genetic Programing (GP), introduced by Koza (1992), based on the concepts of natural selection and genetics. The technique involves finding a mathematical expression that fits a given set of data, and constructing a population of mathematical models from different combinations of variables, constants and operators. An advantage of GP is that it can flexibly incorporate multivariate non-linear relations, and obtained numeric solutions are possibly interpreted and checked for physical consistency. A number of state variables (for example, surface fluxes, meteorological conditions, boundary layer stability conditions, BVOC and Ozone vertical profiles, etc), representing possible influences on BVOC emissions and their interrelations along the way through secondary organic aerosol and CCN formation to rainfall will be used.

Introductory lecture: atmospheric organic aerosols: insights from the combination of measurements and chemical transport models.

PubMed

Pandis, Spyros N; Donahue, Neil M; Murphy, Benjamin N; Riipinen, Ilona; Fountoukis, Christos; Karnezi, Eleni; Patoulias, David; Skyllakou, Ksakousti

2013-01-01

The formation, atmospheric evolution, properties, and removal of organic particulate matter remain some of the least understood aspects of atmospheric chemistry despite the importance of organic aerosol (OA) for both human health and climate change. Here, we summarize our recent efforts to deal with the chemical complexity of the tens of thousands of organic compounds in the atmosphere using the volatility-oxygen content framework (often called the 2D-Volatility Basis Set, 2D-VBS). Our current ability to measure the ambient OA concentration as a function of its volatility and oxygen to carbon (O:C) ratio is evaluated. The combination of a thermodenuder, isothermal dilution and Aerosol Mass Spectrometry (AMS) together with a mathematical aerosol dynamics model is a promising approach. The development of computational modules based on the 2D-VBS that can be used in chemical transport models (CTMs) is described. Approaches of different complexity are tested against ambient observations, showing the challenge of simulating the complex chemical evolution of atmospheric OA. The results of the simplest approach describing the net change due to functionalization and fragmentation are quite encouraging, reproducing both the observed OA levels and O : C in a variety of conditions. The same CTM coupled with source-apportionment algorithms can be used to gain insights into the travel distances and age of atmospheric OA. We estimate that the average age of OA near the ground in continental locations is 1-2 days and most of it was emitted (either as precursor vapors or particles) hundreds of kilometers away. Condensation of organic vapors on fresh particles is critical for the growth of these new particles to larger sizes and eventually to cloud condensation nuclei (CCN) sizes. The semivolatile organics currently simulated by CTMs are too volatile to condense on these tiny particles with high curvature. We show that chemical aging reactions converting these semivolatile compounds to extremely low volatility compounds can explain the observed growth rates of new particles in rural environments.

The Arctic Summer Cloud-Ocean Study (ASCOS): overview and experimental design

NASA Astrophysics Data System (ADS)

Tjernström, M.; Leck, C.; Birch, C. E.; Brooks, B. J.; Brooks, I. M.; Bäcklin, L.; Chang, R. Y.-W.; Granath, E.; Graus, M.; Hansel, A.; Heintzenberg, J.; Held, A.; Hind, A.; de la Rosa, S.; Johnston, P.; Knulst, J.; de Leeuw, G.; Di Liberto, L.; Martin, M.; Matrai, P. A.; Mauritsen, T.; Müller, M.; Norris, S. J.; Orellana, M. V.; Orsini, D. A.; Paatero, J.; Persson, P. O. G.; Gao, Q.; Rauschenberg, C.; Ristovski, Z.; Sedlar, J.; Shupe, M. D.; Sierau, B.; Sirevaag, A.; Sjogren, S.; Stetzer, O.; Swietlicki, E.; Szczodrak, M.; Vaattovaara, P.; Wahlberg, N.; Westberg, M.; Wheeler, C. R.

2013-05-01

The climate in the Arctic is changing faster than anywhere else on Earth. Poorly understood feedback processes relating to Arctic clouds and aerosol-cloud interactions contribute to a poor understanding of the present changes in the Arctic climate system, and also to a large spread in projections of future climate in the Arctic. The problem is exacerbated by the paucity of research-quality observations in the central Arctic. Improved formulations in climate models require such observations, which can only come from measurements in-situ in this difficult to reach region with logistically demanding environmental conditions. The Arctic Summer Cloud-Ocean Study (ASCOS) was the most extensive central Arctic Ocean expedition with an atmospheric focus during the International Polar Year (IPY) 2007-2008. ASCOS focused on the study of the formation and life cycle of low-level Arctic clouds. ASCOS departed from Longyearbyen on Svalbard on 2 August and returned on 9 September 2008. In transit into and out of the pack ice, four short research stations were undertaken in the Fram Strait; two in open water and two in the marginal ice zone. After traversing the pack-ice northward an ice camp was set up on 12 August at 87°21' N 01°29' W and remained in operation through 1 September, drifting with the ice. During this time extensive measurements were taken of atmospheric gas and particle chemistry and physics, mesoscale and boundary-layer meteorology, marine biology and chemistry, and upper ocean physics. ASCOS provides a unique interdisciplinary data set for development and testing of new hypotheses on cloud processes, their interactions with the sea ice and ocean and associated physical, chemical, and biological processes and interactions. For example, the first ever quantitative observation of bubbles in Arctic leads, combined with the unique discovery of marine organic material, polymer gels with an origin in the ocean, inside cloud droplets suggest the possibility of primary marine organically derived cloud condensation nuclei in Arctic stratocumulus clouds. Direct observations of surface fluxes of aerosols could, however, not explain observed variability in aerosol concentrations and the balance between local and remote aerosols sources remains open. Lack of CCN was at times a controlling factor in low-level cloud formation, and hence for the impact of clouds on the surface energy budget. ASCOS provided detailed measurements of the surface energy balance from late summer melt into the initial autumn freeze-up, and documented the effects of clouds and storms on the surface energy balance during this transition. In addition to such process-level studies, the unique, independent ASCOS data set can and is being used for validation of satellite retrievals, operational models, and reanalysis data sets.

Cloud Condensation in Titan's Lower Stratosphere

NASA Technical Reports Server (NTRS)

Romani, Paul N.; Anderson, Carrie M.

2011-01-01

A 1-D condensation model is developed for the purpose of reproducing ice clouds in Titan's lower stratosphere observed by the Composite Infrared Spectrometer (CIRS) onboard Cassini. Hydrogen cyanide (HCN), cyanoacetylene (HC3N), and ethane (C2H6) vapors are treated as chemically inert gas species that flow from an upper boundary at 500 km to a condensation sink near Titan's tropopause (-45 km). Gas vertical profiles are determined from eddy mixing and a downward flux at the upper boundary. The condensation sink is based upon diffusive growth of the cloud particles and is proportional to the degree of supersaturation in the cloud formation regIOn. Observations of the vapor phase abundances above the condensation levels and the locations and properties of the ice clouds provide constraints on the free parameters in the model. Vapor phase abundances are determined from CIRS mid-IR observations, whereas cloud particle sizes, altitudes, and latitudinal distributions are derived from analyses of CIRS far-IR observations of Titan. Specific cloud constraints include: I) mean particle radii of2-3 J.lm inferred from the V6 506 cm- band of HC3N, 2) latitudinal abundance distributions of condensed nitriles, inferred from a composite emission feature that peaks at 160/cm , and 3) a possible hydrocarbon cloud layer at high latitudes, located near an altitude of 60 km, which peaks between 60 and 80 cm l . Nitrile abundances appear to diminish substantially at high northern latitudes over the time period 2005 to 2010 (northern mid winter to early spring). Use of multiple gas species provides a consistency check on the eddy mixing coefficient profile. The flux at the upper boundary is the net column chemical production from the upper atmosphere and provides a constraint on chemical pathways leading to the production of these compounds. Comparison of the differing lifetimes, vapor phase transport, vapor phase loss rate, and particle sedimentation, sheds light on temporal stability of the clouds.

Global impact of mineral dust on cloud droplet number concentration

NASA Astrophysics Data System (ADS)

Karydis, Vlassis A.; Tsimpidi, Alexandra P.; Bacer, Sara; Pozzer, Andrea; Nenes, Athanasios; Lelieveld, Jos

2017-05-01

The importance of wind-blown mineral dust for cloud droplet formation is studied by considering (i) the adsorption of water on the surface of insoluble particles, (ii) particle coating by soluble material (atmospheric aging) which augments cloud condensation nuclei (CCN) activity, and (iii) the effect of dust on inorganic aerosol concentrations through thermodynamic interactions with mineral cations. The ECHAM5/MESSy Atmospheric Chemistry (EMAC) model is used to simulate the composition of global atmospheric aerosol, while the ISORROPIA-II thermodynamic equilibrium model treats the interactions of K+-Ca2+-Mg2+-NH4+-Na+-SO42--NO3--Cl--H2O aerosol with gas-phase inorganic constituents. Dust is considered a mixture of inert material with reactive minerals and its emissions are calculated online by taking into account the soil particle size distribution and chemical composition of different deserts worldwide. The impact of dust on droplet formation is treated through the unified dust activation parameterization that considers the inherent hydrophilicity from adsorption and acquired hygroscopicity from soluble salts during aging. Our simulations suggest that the presence of dust increases cloud droplet number concentration (CDNC) over major deserts (e.g., up to 20 % over the Sahara and the Taklimakan desert) and decreases CDNC over polluted areas (e.g., up to 10 % over southern Europe and 20 % over northeastern Asia). This leads to a global net decrease in CDNC by 11 %. The adsorption activation of insoluble aerosols and the mineral dust chemistry are shown to be equally important for the cloud droplet formation over the main deserts; for example, these effects increase CDNC by 20 % over the Sahara. Remote from deserts the application of adsorption theory is critically important since the increased water uptake by the large aged dust particles (i.e., due to the added hydrophilicity by the soluble coating) reduce the maximum supersaturation and thus cloud droplet formation from the relatively smaller anthropogenic particles (e.g., CDNC decreases by 10 % over southern Europe and 20 % over northeastern Asia by applying adsorption theory). The global average CDNC decreases by 10 % by considering adsorption activation, while changes are negligible when accounting for the mineral dust chemistry. Sensitivity simulations indicate that CDNC is also sensitive to the mineral dust mass and inherent hydrophilicity, and not to the chemical composition of the emitted dust.

Radiative Impacts of Cloud Heterogeneity and Overlap in an Atmospheric General Circulation Model

NASA Technical Reports Server (NTRS)

Oreopoulos, L.; Lee, D.; Sud, Y. C.; Suarez, M. J.

2012-01-01

The radiative impacts of introducing horizontal heterogeneity of layer cloud condensate, and vertical overlap of condensate and cloud fraction are examined with the aid of a new radiation package operating in the GEOS-5 Atmospheric General Circulation Model. The impacts are examined in terms of diagnostic top-of-the-atmosphere shortwave (SW) and longwave (LW) cloud radiative effect (CRE) calculations for a range of assumptions and parameter specifications about the overlap. The investigation is conducted for two distinct cloud schemes, the one that comes with the standard GEOS-5 distribution, and another which has been recently used experimentally for its enhanced GEOS-5 distribution, and another which has been recently used experimentally for its enhanced cloud microphysical capabilities; both are coupled to a cloud generator allowing arbitrary cloud overlap specification. We find that cloud overlap radiative impacts are significantly stronger for the operational cloud scheme for which a change of cloud fraction overlap from maximum-random to generalized results to global changes of SW and LW CRE of approximately 4 Watts per square meter, and zonal changes of up to approximately 10 Watts per square meter. This is because of fewer occurrences compared to the other scheme of large layer cloud fractions and of multi-layer situations with large numbers of atmospheric being simultaneously cloudy, conditions that make overlap details more important. The impact on CRE of the details of condensate distribution overlap is much weaker. Once generalized overlap is adopted, both cloud schemes are only modestly sensitive to the exact values of the overlap parameters. We also find that if one of the CRE components is overestimated and the other underestimated, both cannot be driven towards observed values by adjustments to cloud condensate heterogeneity and overlap alone.

Laser-filamentation-induced condensation and snow formation in a cloud chamber.

PubMed

Ju, Jingjing; Liu, Jiansheng; Wang, Cheng; Sun, Haiyi; Wang, Wentao; Ge, Xiaochun; Li, Chuang; Chin, See Leang; Li, Ruxin; Xu, Zhizhan

2012-04-01

Using 1 kHz, 9 mJ femtosecond laser pulses, we demonstrate laser-filamentation-induced spectacular snow formation in a cloud chamber. An intense updraft of warm moist air is generated owing to the continuous heating by the high-repetition filamentation. As it encounters the cold air above, water condensation and large-sized particles spread unevenly across the whole cloud chamber via convection and cyclone like action on a macroscopic scale. This indicates that high-repetition filamentation plays a significant role in macroscopic laser-induced water condensation and snow formation.

Satellite remote sensing of aerosol and cloud properties over Eurasia

NASA Astrophysics Data System (ADS)

Sogacheva, Larisa; Kolmonen, Pekka; Saponaro, Giulia; Virtanen, Timo; Rodriguez, Edith; Sundström, Anu-Maija; Atlaskina, Ksenia; de Leeuw, Gerrit

2015-04-01

Satellite remote sensing provides the spatial distribution of aerosol and cloud properties over a wide area. In our studies large data sets are used for statistical studies on aerosol and cloud interaction in an area over Fennoscandia, the Baltic Sea and adjacent regions over the European mainland. This area spans several regimes with different influences on aerosol cloud interaction such as a the transition from relative clean air over Fennoscandia to more anthropogenically polluted air further south, and the influence maritime air over the Baltic and oceanic air advected from the North Atlantic. Anthropogenic pollution occurs in several parts of the study area, and in particular near densely populated areas and megacities, but also in industrialized areas and areas with dense traffic. The aerosol in such areas is quite different from that produced over the boreal forest and has different effects on air quality and climate. Studies have been made on the effects of aerosols on air quality and on the radiation balance in China. The aim of the study is to study the effect of these different regimes on aerosol-cloud interaction using a large aerosol and cloud data set retrieved with the (Advanced) Along Track Scanning Radiometer (A)ATSR Dual View algorithm (ADV) further developed at Finnish Meteorological Institute and aerosol and cloud data provided by MODIS. Retrieval algorithms for aerosol and clouds have been developed for the (A)ATSR, consisting of a series of instruments of which we use the second and third one: ATSR-2 which flew on the ERS-2 satellite (1995-2003) and AATSR which flew on the ENVISAT satellite (2002-2012) (both from the European Space Agency, ESA). The ADV algorithm provides aerosol data on a global scale with a default resolution of 10x10km2 (L2) and an aggregate product on 1x1 degree (L3). Optional, a 1x1 km2 retrieval products is available over smaller areas for specific studies. Since for the retrieval of AOD no prior knowledge is needed on surface properties, the surface reflectance can be independently retrieved using the AOD for atmospheric correction. For the retrieval of cloud properties, the SACURA algorithm has been implemented in the ADV/ASV aerosol retrieval suite. Cloud properties retrieved from AATSR data are cloud fraction, cloud optical thickness, cloud top height, cloud droplet effective radius, liquid water path. Aerosol and cloud properties are applied for different studies over the Eurasia area. Using the simultaneous retrieval of aerosol and cloud properties allows for study of the transition from the aerosol regime to the cloud regime, such as changes in effective radius or AOD (aerosol optical depth) to COT (cloud optical thickness). The column- integrated aerosol extinction, aerosol optical depth or AOD, which is primarily reported from satellite observations, can be used as a proxy for cloud condensation nuclei (CCN) and hence contains information on the ability of aerosol particles to form clouds. Hence, connecting this information with direct observations of cloud properties provides information on aerosol-cloud interactions.

Reducing Errors in Satellite Simulated Views of Clouds with an Improved Parameterization of Unresolved Scales

NASA Astrophysics Data System (ADS)

Hillman, B. R.; Marchand, R.; Ackerman, T. P.

2016-12-01

Satellite instrument simulators have emerged as a means to reduce errors in model evaluation by producing simulated or psuedo-retrievals from model fields, which account for limitations in the satellite retrieval process. Because of the mismatch in resolved scales between satellite retrievals and large-scale models, model cloud fields must first be downscaled to scales consistent with satellite retrievals. This downscaling is analogous to that required for model radiative transfer calculations. The assumption is often made in both model radiative transfer codes and satellite simulators that the unresolved clouds follow maximum-random overlap with horizontally homogeneous cloud condensate amounts. We examine errors in simulated MISR and CloudSat retrievals that arise due to these assumptions by applying the MISR and CloudSat simulators to cloud resolving model (CRM) output generated by the Super-parameterized Community Atmosphere Model (SP-CAM). Errors are quantified by comparing simulated retrievals performed directly on the CRM fields with those simulated by first averaging the CRM fields to approximately 2-degree resolution, applying a "subcolumn generator" to regenerate psuedo-resolved cloud and precipitation condensate fields, and then applying the MISR and CloudSat simulators on the regenerated condensate fields. We show that errors due to both assumptions of maximum-random overlap and homogeneous condensate are significant (relative to uncertainties in the observations and other simulator limitations). The treatment of precipitation is particularly problematic for CloudSat-simulated radar reflectivity. We introduce an improved subcolumn generator for use with the simulators, and show that these errors can be greatly reduced by replacing the maximum-random overlap assumption with the more realistic generalized overlap and incorporating a simple parameterization of subgrid-scale cloud and precipitation condensate heterogeneity. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND NO. SAND2016-7485 A

Precipitating Condensation Clouds in Substellar Atmospheres

NASA Technical Reports Server (NTRS)

Ackerman, Andrew S.; Marley, Mark S.; Gore, Warren J. (Technical Monitor)

2000-01-01

We present a method to calculate vertical profiles of particle size distributions in condensation clouds of giant planets and brown dwarfs. The method assumes a balance between turbulent diffusion and precipitation in horizontally uniform cloud decks. Calculations for the Jovian ammonia cloud are compared with previous methods. An adjustable parameter describing the efficiency of precipitation allows the new model to span the range of predictions from previous models. Calculations for the Jovian ammonia cloud are found to be consistent with observational constraints. Example calculations are provided for water, silicate, and iron clouds on brown dwarfs and on a cool extrasolar giant planet.

Modeling the surface tension of complex, reactive organic-inorganic mixtures

NASA Astrophysics Data System (ADS)

Schwier, A. N.; Viglione, G. A.; Li, Z.; McNeill, V. F.

2013-01-01

Atmospheric aerosols can contain thousands of organic compounds which impact aerosol surface tension, affecting aerosol properties such as cloud condensation nuclei (CCN) ability. We present new experimental data for the surface tension of complex, reactive organic-inorganic aqueous mixtures mimicking tropospheric aerosols. Each solution contained 2-6 organic compounds, including methylglyoxal, glyoxal, formaldehyde, acetaldehyde, oxalic acid, succinic acid, leucine, alanine, glycine, and serine, with and without ammonium sulfate. We test two surface tension models and find that most reactive, complex, aqueous organic mixtures which do not contain salt are well-described by a weighted Szyszkowski-Langmuir (S-L) model which was first presented by Henning et al. (2005). Two approaches for modeling the effects of salt were tested: (1) the Tuckermann approach (an extension of the Henning model with an additional explicit salt term), and (2) a new implicit method proposed here which employs experimental surface tension data obtained for each organic species in the presence of salt used with the Henning model. We recommend the use of method (2) for surface tension modeling because the Henning model (using data obtained from organic-inorganic systems) and Tuckermann approach provide similar modeling fits and goodness of fit (χ2) values, yet the Henning model is a simpler and more physical approach to modeling the effects of salt, requiring less empirically determined parameters.