A33G-01 

Tropical Marine Clouds: Sinks, Sources and Transformers of CCN

* Clarke, A (tclarke@soest.hawaii.edu), University of Hawaii, Department of Oceanodraphy, 1000 Pope Rd., MSB501, Honolulu, HI 96822, United States Howell, S (showell@soest.hawaii.edu), University of Hawaii, Department of Oceanodraphy, 1000 Pope Rd., MSB501, Honolulu, HI 96822, United States Freitag, S (SteffenFreitag@web.de), University of Hawaii, Department of Oceanodraphy, 1000 Pope Rd., MSB501, Honolulu, HI 96822, United States Blomquist, B (blomquis@hawaii.edu), University of Hawaii, Department of Oceanodraphy, 1000 Pope Rd., MSB501, Honolulu, HI 96822, United States Blomquist, B (blomquis@hawaii.edu), Drexel University, Department of Chemistry, 3141 Chestnut Street, Philadelphia, PA 19104, United States Bandy, A (bandyar@drexel.edu), Drexel University, Department of Chemistry, 3141 Chestnut Street, Philadelphia, PA 19104, United States Mauldin, L (mauldin@ucar.edu), NCAR/ACD, 1850 Table Mesa POB 3000, Boulder, CO 80303-3000, United States Anderson, R (rca@ucar.edu), NCAR/ACD, 1850 Table Mesa POB 3000, Boulder, CO 80303-3000, United States

During August of 2007 the Pacific Atmospheric Sulfur Experiment (PASE) investigated the sulfur cycle using 13 NCAR C-130 aircraft missions based out of Christmas Is. (2N, 157W). Part of this study examined the origin and evolution of aerosol in the cloudy equatorial marine boundary layer, MBL, and their relation to effective cloud condensation nuclei, CCN. These data confirm that most of these particles originate through nucleation in the free troposphere FT, and are entrained into the MBL where they establish most of the MBL particle number. No homogeneous nucleation of particles was observed in the MBL. A separate mode is generated at the ocean surface as sea-salt with a number peak below about 0.1 μm that also grows heterogeneously. Most particles in the equatorial FT appear to be volatile sulfates generated in cloud outflow. A smaller number fraction with refractory (stable at 300C) cores co-vary with ozone and appear to be related to the long range transport of particles in the FT. All FT particles were measured as a monomodal number distribution that subside and then evolve into bimodal number distributions in response to cloud processing in the buffer (cloud) layer and subsequently in the MBL. Here particles increased their mass through heterogeneous gas to particle conversion primarily linked to the sulfur cycle. Measurements confirmed that non-precipitating clouds in the MBL act as a chemical factory for gas-to-particle conversion. This process results in the development in a Hoppel minima near 0.08 um and preferentially adds mass to the larger sizes activated as CCN. When such clouds grow into precipitating Cu with tops above about 4km they act to scavenge the larger aerosol through precipitation. Active precipitation in these regions was also associated with a reduction in CCN concentrations and aerosol mass. However, the outflow and anvil regions of these clouds revealed that CCN sizes were scavenged via precipitation but this air included enhanced SO2 and sulfuric acid pumped aloft where they coincided with regions of new particle formation. Hence, clouds in the tropical MBL act to convert most of the sulfur mass originating from DMS onto existing aerosol at CCN sizes and also serve to remove this mass when they precipitate. Depleted particle number can also be replenished aloft by precipitating clouds dependent upon the details of the scavenging, gas phase sources, photochemisty and thermodynamic considerations near the outflow regions.

A33G-02 

An Overview of the Cumulus Humilis Aerosol Processing Study

* Berkowitz, C M (carl.berkowitz@pnl.gov AF: AF: AF:

The U.S. Department of Energy's (DOE) Atmospheric Science Program (ASP) conducted a field campaign to investigate the processing of aerosols by fields of shallow cumuli in the vicinity of Oklahoma City during June 2007. This study, called the Cumulus Humilis Aerosol Processing Study (CHAPS) involved two research aircraft. One aircraft, the ASP Gulfstream 1, was used for in-situ sampling of aerosol size, composition and optical properties, below, within, and immediately above the cloud layers. A sampling system was devised that used two aerosol inlets, an isokinetic inlet and an inlet equipped with a Counter Flow Virtual Impactor (CVI). The CVI is designed to allow only cloud drops to enter the inlet and evaporate, allowing us to examine the composition of the residual mass within the cloud drops. Aerosols from each inlet were directed into nearly identical sets of instruments. The second aircraft, the NASA Langley King Air, carried the NASA High Spectral Resolution Lidar (HRSL) that was used to obtain profiles of aerosol backscattering and extinction. In addition to the two aircraft, data were also collected at a surface site just north of Oklahoma City. The coordinated G-1 and King Air flight patterns and instrumentation will be described. Data analysis has started, and our data processing techniques and preliminary results will be presented. http://asp.labworks.org/

A33G-03 INVITED 

Secondary Organic Aerosol Formation in Clouds: A Synthesis of Data From Four Field Campaigns

* Sorooshian, A (armin@caltech.edu), Departments of Chemical Engineering and Environmental Science and Engineering, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, United States Brechtel, F J (fredbmi@sbcglobal.net), Departments of Chemical Engineering and Environmental Science and Engineering, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, United States Brechtel, F J (fredbmi@sbcglobal.net), Brechtel Manufacturing Inc., 1789 Addison Way, Hayward, CA 94544, United States Lu, M (julialu@caltech.edu), Departments of Chemical Engineering and Environmental Science and Engineering, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, United States Feingold, G (Graham.Feingold@noaa.gov), Earth System Research Laboratory/Chemical Sciences Division, National Oceanic and Atmospheric Administration, 325 Broadway, Boulder, CA 80305, United States Ervens, B (Barbara.Ervens@noaa.gov), Earth System Research Laboratory/Chemical Sciences Division, National Oceanic and Atmospheric Administration, 325 Broadway, Boulder, CA 80305, United States Ervens, B (Barbara.Ervens@noaa.gov), Atmospheric Science Department, Colorado State University, 200 West Lake Street, Fort Collins, CA 80523, United States Jonsson, H (hjonsson@nps.navy.mil), Center for Interdisciplinary Remotely Piloted Aircraft Studies, Naval Postgraduate School, 3200 Imjin Rd., Hangar 507, Marina, CA 93933, United States Flagan, R C (flagan@caltech.edu), Departments of Chemical Engineering and Environmental Science and Engineering, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, United States Seinfeld, J H (seinfeld@caltech.edu), Departments of Chemical Engineering and Environmental Science and Engineering, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, United States

There is growing evidence, based on laboratory and ambient measurements, that secondary organic aerosol (SOA) is formed by aqueous-phase reactions in cloud droplets. Owing to the low volatility and water-soluble nature of organic acids, these species constitute a significant fraction of SOA mass. Airborne particle-into-liquid sampler (PILS-coupled to ion chromatography) measurements made on the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter are presented from four separate field campaigns representing urban and marine atmospheres: International Consortium for Atmospheric Research on Transport and Transformation (ICARTT 2004), Marine Stratus/Stratocumulus Experiment I and II (MASE 2005, 2007), Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS 2006). Sulfate and oxalate are strongly correlated in ambient aerosols, especially evaporated cloud droplet residual particles. Since their chemical formation mechanisms are not directly linked, this correlation can be explained by a common medium necessary for production: droplets. Enhanced organic acid aerosol layers have been observed directly above cloudtops in both marine and urban atmospheres; as derived from large eddy simulations of stratocumulus under the conditions of MASE, both Lagrangian trajectory analysis and diurnal cloudtop evolution provide evidence that a significant fraction of the aerosol mass concentration above cloud can be accounted for by evaporated droplet residual particles. Predictions from a chemical cloud parcel model considering the aqueous-phase production of organic acids and sulfate show good agreement with ambient data for the relative magnitude of sulfate and organic acid growth in clouds and also the evolution of oxalic acid and its aqueous-phase precursors with increasing altitude in cloud.

A33G-04 

SOA Formation by Chemical Processes in Cloud Droplets

* Ervens, B (barbara.ervens@noaa.gov), Colorado State University, 200 West Lake Street, Fort Collins, CO 80523, United States * Ervens, B (barbara.ervens@noaa.gov), ESRL NOAA, 325 Broadway, Boulder, CO 80305, United States Carlton, A G (carlton.annmarie@epamail.epa.gov), ASMD ARL NOAA, Mail Drop E-243-01, Res. Triangle Park, NC 27711, United States Turpin, B J (turpin@envsci.rutgers.edu), Department of Environmental Sciences, Rutgers University, 71 Dudley Road, New Brunswick, NJ 08901, United States Altieri, K E (altieri@marine.rutgers.edu), Institute of Marine and Coastal Sciences, Rutgers University, 71 Dudley Road, New Brunswick, NJ 08901, United States Kreidenweis, S M (sonia@atmos.colostate.edu), Colorado State University, 200 West Lake Street, Fort Collins, CO 80523, United States Feingold, G (graham.feingold@noaa.gov), ESRL NOAA, 325 Broadway, Boulder, CO 80305, United States

While there is a growing understanding from laboratory studies of aqueous-phase chemical processes that lead to secondary organic aerosol (SOA) formation in cloud droplets ('SOAdrop'), the extent of which in-cloud chemistry contributes to atmospheric SOA burden and modifies the composition and size distribution of pre-existing aerosol populations by cloud-processing is not quantified yet. Using a parcel model including a multiphase chemical mechanism, we show that SOAdrop yields (Yc) from several precursors (e.g., isoprene and water- soluble oxidation products) (i) depend strongly on the initial volatile organic carbon (VOC)/NOx ratio; (ii) increase in longer-lived clouds; (iii) are not greatly affected by cloud liquid water content, pH, and droplet number and (iv) change little within realistic variability of gas-particle partitioning of semivolatile organics outside of clouds. We will present parameterized expressions of SOAdrop yields that can be easily applied to air quality and climate models as is done with SOA formed on/in haze particles ('SOAhaze').

A33G-05 INVITED 

The Impact of Deep Convection on the Mid- and Upper Tropospheric Aerosol Size Distribution

* Ekman, A M (annica@misu.su.se), Stockholm University, Department of Meteorology, Stockholm, 10691, Sweden Engstrom, A (anderse@misu.su.se), Stockholm University, Department of Meteorology, Stockholm, 10691, Sweden Krejci, R (radek@misu.su.se), Stockholm University, Department of Meteorology, Stockholm, 10691, Sweden Strom, J (johan@itm.su.se), Stockholm University, Department of Applied Environmental Science, Stockholm, 10691, Sweden Wang, C (wangc@mit.edu), Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, United States

A cloud-resolving model is used in combination with observations of aerosol size distributions from the LBA- CLAIRE and INDOEX campaigns in order to better understand aerosol transport and processing within deep convective clouds. It is shown that deep convective clouds are an important source of accumulation mode aerosols (~>100 nm) to the mid-troposphere (altitudes between approximately 5 and 9 km). In this region, heterogeneous freezing results in strong mixing at the lateral boundaries of the cloud that in turn generates evaporation and re-suspension of aerosols to the air outside of the cloud. These aerosols are important for the lifetime and development of the convective cloud. For the upper tropospheric aerosol distribution, the study confirms that the outflow region is a source of small particles formed by nucleation. These aerosols grow into the Aitken mode (~>30 nm) and are together with direct transport from the boundary layer the main source of Aitken mode aerosols at this altitude. For the LBA-CLAIRE region, the model underestimates the observed nucleation and Aitken mode aerosol concentration. We discuss possible explanations to this discrepancy and also analyze the importance of using a correct mixing state of the aerosols when simulating aerosol transport within convective clouds.

A33G-06 INVITED 

The ECPP Hybrid Approach for Aerosols and Trace Gases in MMF Models

* Gustafson, W I (william.gustafson@pnl.gov), Pacific Northwest National Laboratory, P.O. Box 999, MSIN K9-30, Richland, WA 99352, United States Easter, R C (richard.easter@pnl.gov), Pacific Northwest National Laboratory, P.O. Box 999, MSIN K9-30, Richland, WA 99352, United States Berg, L K (larry.berg@pnl.gov), Pacific Northwest National Laboratory, P.O. Box 999, MSIN K9-30, Richland, WA 99352, United States Ghan, S J (steve.ghan@pnl.gov), Pacific Northwest National Laboratory, P.O. Box 999, MSIN K9-30, Richland, WA 99352, United States

The Multiscale Modeling Framework (MMF) poses opportunities to significantly improve the handling of cloud- aerosol interactions in global climate models (GCMs). In traditional GCMs the aerosols are transported at the grid resolution with subgrid vertical transport, scavenging and aqueous chemistry represented using cloud parameterizations. With MMF, physically-based subgrid scale information is available through the replacement of the cloud parameterizations by an embedded cloud-resolving model. The Explicit-Cloud Parameterized-Pollutant (ECPP) approach is a technique for using the statistics of the cloud and motion fields within the cloud-resolving model to more accurately parameterize subgrid vertical transport, wet scavenging, and aqueous chemistry for species resolved at the GCM resolution. As a step towards implementing the ECPP technique in the MMF enabled Community Atmosphere Model (CAM), Super-CAM, initial development and tests are being performed using the chemistry version of the Weather Research and Forecasting model (WRF-Chem). Idealized 3-dimensional WRF-Chem simulations based on large-scale forcing from the Kwajalein Experiment (KWAJEX) field campaign with 2-km grid spacing serve as a benchmark for cloud-aerosol interactions. Cloud and motion statistics from the 3-D simulation are then used to drive a single column ECPP version of WRF-Chem, analogous to how the cloud-resolving model feeds information back to the GCM grid column in MMF. Results from the ECPP within this WRF-Chem framework will be compared with the 3-D simulation and with simulations by the single column version of CAM.

A33G-07 

Aerosol Scavenging by Cirrus Clouds: Evidence from Polarization Lidar Measurements

* Sassen, K (ksassen@gi.alaska.edu), University of Alaska Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775, United States Zhu, J (jzhu@gi.alaska.edu), University of Alaska Fairbanks, 903 Koyukuk Drive, Fairbanks, AK 99775, United States

Under some conditions polarization lidar observations of ice clouds suggest the depletion of aerosol particles in the vicinity of the cloud margins and just below cloud base. This is particularly evident for cirrus that form in connection with transported desert dust layers, because these dust particles can be relatively large and hence strongly backscattering and depolarizing. Indications of aerosol scavenging primarily through the ice nucleation and gravitational capture processes, as well as phoretic forces where ice crystals are evaporating, can then produce a noticeable decrease in lidar backscattering and depolarization in clear (but recently cloudy) air. (In contrast, aerosol loss due to Brownian diffusion may not be as noticeable because these generally smaller particles are relatively weak backscatterers.) Presumably, previously cloudy air with its depleted interstitial aerosol is disclosed by variable fallstreak production and evaporation effects. The action of clouds is of great importance to the redistribution and removal (through precipitation) of aerosols suspended in the atmosphere. Polarization lidar examples will be given of aerosol-depleted halos surrounding cirrus cloud elements and backscatter troughs just below the base of undulating cirrus layers.

A33G-08 

Evaluating atmospheric aerosol removal processes through integration of global modeling and satellite data

* Lough, G C (glynislough@gmail.com), University of Illinois Urbana-Champaign, Department of Civil and Environmental Engineering Newmark Civil Engineering Laboratory, MC-250 205 N Mathews Ave, Urbana, IL 61801, United States Bond, T C (yark@uiuc.edu), University of Illinois Urbana-Champaign, Department of Civil and Environmental Engineering Newmark Civil Engineering Laboratory, MC-250 205 N Mathews Ave, Urbana, IL 61801, United States Rasch, P J (pjr@ucar.edu), National Center for Atmospheric Research, 1850 Table Mesa Dr, Boulder, CO 80307-5000, United States

Aerosols can influence the energy balance of the Earth-Atmosphere system with profound effect on regional climate. Emissions affect the quantity and location of aerosols, while atmospheric processes govern aerosol lifetimes and transport. Here we evaluate the ability of a global atmospheric model to represent the atmospheric processes regulating the global distribution of aerosols and magnitude of aerosol radiative forcing. We focus on anthropogenic sulfur and carbonaceous species, which comprise 50% to more than 90% of fine mode aerosols in continental outflows, but exclude plumes dominated by dust in order to focus on industrial emissions. Models are frequently evaluated by comparing model output with observations, but uncertainties in many factors at any given location may contribute to model-observation agreement or discrepancy. To understand aerosol behavior, we identify areas which on some spatial and temporal scales are subject to a limited suite of atmospheric aerosol removal processes, such as convection, scavenging, and wet or dry deposition. The Community Atmosphere Model (CAM) is used to simulate atmospheric aerosol concentrations and identify regions and times in which aerosol atmospheric burden or aerosol optical depth (AOD) is influenced primarily by one of these atmospheric processes. Appropriate regions are identified in a series of sensitivity studies. Limiting the investigation to areas with one dominant atmospheric process allows more robust comparison of model output and observations by reducing the number of factors contributing to uncertainty. For regions identified by CAM where modeled aerosol burden is most sensitive to convection and scavenging in warm and cold clouds, modeled AOD is compared with that retrieved by the Moderate Resolution Imaging Spectroradiometer (MODIS). Additionally, where aerosol burden has a seasonality dominated by a single process, comparison of the amplitude of seasonality between modeled and observed AOD is used to evaluate the modeled representation of that process.

Author(s) (2007), Title, Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract #####-##.