A34A-01 INVITED 

Advances in Quantifying the Radiative Effects of Aerosol Particles on Climate from Airborne Field Studies

* Pilewskie, P (Peter.Pilewskie@lasp.colorado.edu) Schmidt, K S (sebastian.schmidt@lasp.colorado.edu), University of Colorado, Laboratory for Atmospheric and Space Physics, 1234 Innovation Drive, Boulder, CO 80303-7814, United States Coddington, O (Odele.Coddington@lasp.colorado.edu), University of Colorado, Laboratory for Atmospheric and Space Physics, 1234 Innovation Drive, Boulder, CO 80303-7814, United States Bergstrom, R (bergstrom@baeri.org), Bay Area Environmental Research Institute, 560 Third St West, Sanoma, CA 95476, United States Redemann, J (jredemann@mail.arc.nasa.gov), Bay Area Environmental Research Institute, 560 Third St West, Sanoma, CA 95476, United States

In the fourth assessment report of the Intergovernmental Panel on Climate Change, large uncertainties persist in estimates of climate forcing by aerosol particles. One contributor to this uncertainty is the poorly quantified vertical distribution of solar radiation absorbed by aerosol particles, from the regional to global scale. Another is the spectral and spatial variability of surface albedo, an effect that can dominate the top-of-atmosphere perturbations due to aerosol scattering and absorption, particularly over land. Over the past three years a number of intensive airborne field experiments (ICARTT, MILAGRO, GoMACCS) have contributed significantly to our understanding of the impact of pollution outflow from urban-industrial centers on radiative forcing, using spectrally resolved radiometric measurements and novel observationally-based methods to derive forcing efficiency and flux divergence. We present an overview of some of the most significant advances in direct radiative forcing realized by these studies, and recommendations on where the greatest challenges remain. In addition we present findings from these experiments on the influence of aerosol particles on cloud radiative properties, a potentially greater effect but even more uncertain than direct radiative forcing.

A34A-02 INVITED 

Aerosol Physiochemistry in Clean and Polluted Regions: Influences on Optical Properties and CCN

* Clarke, A (tclarke@soest.hawaii.edu), Department of Oceanography, University of Hawaii, 1000 Pope Rd., Honolulu, HI 96822, United States kapustin, V (kapustin@soest.hawaii.edu), Department of Oceanography, University of Hawaii, 1000 Pope Rd., Honolulu, HI 96822, United States Howell, S (showell@soest.hawaii.edu), Department of Oceanography, University of Hawaii, 1000 Pope Rd., Honolulu, HI 96822, United States Shinozuka, Y (yohei@hawaii.edu), Department of Oceanography, University of Hawaii, 1000 Pope Rd., Honolulu, HI 96822, United States McNaughton, C (cameronm@soest.hawaii.edu), Department of Oceanography, University of Hawaii, 1000 Pope Rd., Honolulu, HI 96822, United States Zhou, J (jczhou@hawaii.edu), Department of Oceanography, University of Hawaii, 1000 Pope Rd., Honolulu, HI 96822, United States DeCarlo, P (decarlop@colorado.edu), Dept. of Chemistry & CIRES, UCB 216, Boulder, CO 80309, United States Jimenez, J (jose.jimenez@colorado.edu), Dept. of Chemistry & CIRES, UCB 216, Boulder, CO 80309, United States Roberts, G (gcroberts@ucsd.edu), Scripps Institution of Oceanography, UCSD, 9500 Gilman Drive, La Jolla, CA 92093, United States

Long range transport of aerosol from urban regions and anthropogenic sources is recognized to influence the radiative properties of aerosol and cloud condensation nuclei, CCN, over large portions of the planet. The nature of these influences is determined by the size distributions, concentration and composition of the aerosol and their magnitude relative to natural sources. We have participated in diverse major field studies over the past decade designed to measure and isolate key properties that can be used to characterize various source regions and to provide aerosol parameters to effectively model both "direct" and "indirect" radiative effects. More recently these have expanded to include scales that can assess transformation in both gas and aerosol components as they evolve downwind or get lofted into the free troposphere. These experiments have revealed the importance of primary emissions and secondary emissions and the state of mixing of the aerosol both near the source and after aging downwind. The physiochemical processes that influence aerosol composition, growth, evolution, optical properties and cloud processes differ markedly with size. In this talk we focus on direct radiative effects that depend on sizes that dominate aerosol surface area or mass and on cloud related effects more sensitive to smaller sizes that dominate aerosol number and CCN. Key players of both anthropogenic and natural origin are black carbon (BC), sulfate, nitrate and organic carbon. These frequently evolve into internal mixtures and/or interact with similar natural aerosol such as dust and sea- salt. Hence, the size resolved state-of-mixing of these components determine their influences and also impact the strategies that might be used to mitigate any effects. Recent data highlight the significance of BC to both direct and indirect effects and reveal its multiple roles expressed through its optical properties, its evolution, its relation to light absorbing OC (brown carbon) and role as a condensation sites for other aerosol. Observed variations in mixing state for diverse regions and/or combustion sources also affect other aerosol properties including the humidity dependence of light scattering expressed as f(RH) or gamma. Such aging can vary the mixing ratio of OC in the aerosol which modifies their effectiveness as CCN at a given size. Observations of particle nucleation and growth are now common but its larger significance will depends upon the particle number, relative to primary emissions, that can age and survive to optically effective sizes or CCN. The latter is particularly complex as cloud are sinks, sources and processors of both aerosol and gases that impact the CCN population. A related issue we address is how well satellite retrieval of aerosol radiances can be used to monitor relevant properties such as PM2.5 or the potential to retrieve effective CCN. Examples of these and other size resolved properties revealed in recent campaigns will be presented.

A34A-03 

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

* Quinn, P (patricia.k.quinn@noaa.gov), NOAA PMEL, 7600 Sand Point Way NE, Seattle, WA 98115, Bates, T (tim.bates@noaa.gov), NOAA PMEL, 7600 Sand Point Way NE, Seattle, WA 98115, Coffman, D (derek.coffman@noaa.gov), NOAA PMEL, 7600 Sand Point Way NE, Seattle, WA 98115, Covert, D (dcovert@u.washington.edu), University of Washington, 4909 25th Ave NE, Seattle, WA 98105,

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].

A34A-04 INVITED 

CCN measurements aboard the CIRPAS Twin Otter and the NOAA P3 platforms during TexAQS/GoMACCS

* Athanasios, N (nenes@eas.gatech.edu), Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332, United States * Athanasios, N (nenes@eas.gatech.edu), Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332, United States Asa-Awuku, A A (akua.asaawuku@chbe.gatech.edu), Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332, United States Lance, S (lance@ucar.edu), Earth and Atmospheric Sciences, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332, United States Moore, R (richard.moore@chbe.gatech.edu), Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332, United States Bahreini, R (Roya.Bahreini@noaa.gov), National Oceanic and Atmospheric Administration, 325 Broadway, Boulder, CO 80305, United States Brock, C A (Charles.A.Brock@noaa.gov), National Oceanic and Atmospheric Administration, 325 Broadway, Boulder, CO 80305, United States Flagan, R C (flagan@cheme.caltech.edu), Environmental Science and Engineering, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125, United States Flagan, R C (flagan@cheme.caltech.edu), Chemical Engineering, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125, United States Jonsson, H (hjonsson@nps.edu), CIRPAS, Naval Postgraduate School, Hangar 507, 3200 Imjin Road, Marina, CA 93933, United States Murphy, S (murphy@caltech.edu), Chemical Engineering, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125, United States Seinfeld, J H (seinfeld@caltech.edu), Environmental Science and Engineering, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125, United States Seinfeld, J H (seinfeld@caltech.edu), Chemical Engineering, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125, United States Sorooshian, A (armin@catech.edu), Chemical Engineering, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125, United States Varutbangkul, V (tomtor@caltech.edu), Chemical Engineering, California Institute of Technology, 1200 E California Blvd, Pasadena, CA 91125, United States

We present an overview of Cloud Condensation Nuclei (CCN) measurements for boundary layer clouds sampled over the vicinity of Houston, TX during the GoMACCS/TEXAQS campaign (August-September, 2006). Measurements were obtained aboard the NOAA P3 and the CIRPAS Twin Otter platforms, and polluted air masses in and out of cloudy regions were sampled over a total of 40 flights. Throughout this campaign, we sampled freshly emitted and ageing Houston aerosol, aerosol from the Houston ship channel and the heavily industrialized area in the vicinity. The vast range of CCN concentration, aerosol composition and aging/mixing state makes this a particularly valuable dataset for constraining uncertainties associated with prediction of CCN concentration and cloud droplet number for polluted clouds. We will focus on numerous aspects related CCN closure and growth kinetics, with the focus on improving parameterizations of aerosol-cloud interactions.

A34A-05 

CCN Studies at Different Locations: Relative Importance of Aerosol Composition, Hygroscopicity and Mixing State

Cubison, M), Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado, 216 UCB, Boulder, CO 80309, United States * Ervens, B (barbara.ervens@noaa.gov), Colorado State University, Atmospheric Science Department, Fort Collins, CO 80523, United States * Ervens, B (barbara.ervens@noaa.gov), NOAA Earth Research System Laboratory, 325 Broadway, Boulder, CO 80309, United States Andrews, E), Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado, 216 UCB, Boulder, CO 80309, United States Andrews, E), NOAA Earth Research System Laboratory, 325 Broadway, Boulder, CO 80309, United States Feingold, G), NOAA Earth Research System Laboratory, 325 Broadway, Boulder, CO 80309, United States Ogren, J), NOAA Earth Research System Laboratory, 325 Broadway, Boulder, CO 80309, United States Jimenez, J L), Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado, 216 UCB, Boulder, CO 80309, United States Jimenez, J L), University of Colorado Dept. of Chemistry, UCB 216, Boulder, CO 80309, United States DeCarlo, P), Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado, 216 UCB, Boulder, CO 80309, United States DeCarlo, P), University of Colorado Dept. of Atmospheric and Oceanic Sciences, UCB 311, Boulder, CO 80309, United States Nenes, A), Georgia Institute of Technology, Dept. of Earth and Atmospheric Sciences, Atlanta, GA 30332, United States Coe, H), University of Manchester, School of Earth, Atmospheric and Environmental Science, Manchester, GBR M13 9PL, Allan, J), University of Manchester, School of Earth, Atmospheric and Environmental Science, Manchester, GBR M13 9PL, Docherty, K), Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado, 216 UCB, Boulder, CO 80309, United States Ulbrich, I), Cooperative Institute for Research in the Environmental Sciences (CIRES), University of Colorado, 216 UCB, Boulder, CO 80309, United States Denkenberger, K), University of California, San Diego, Department of Chemistry and Biochemistry, La Jolla, CA 92093, United States Prather, K), University of California, San Diego, Department of Chemistry and Biochemistry, La Jolla, CA 92093, United States Snyder, D C), University of Wisconsin, Dept of Civil and Environmental Engineering, Madison, WI 53706, United States Schauer, J J), University of Wisconsin, Dept of Civil and Environmental Engineering, Madison, WI 53706, United States

The level of understanding of the effect of aerosol particles on clouds, via their ability to act as cloud condensation nuclei (CCN), is low. Further analysis of the physical and chemical parameters influencing CCN activation is required in order to quantify these effects and allow parameterizations of these processes in large scale models. Using results from several recent field campaigns in both marine and urban environments, we explore the relationship between aerosol particles and their CCN activity. The data sets analyzed were acquired at Chebogue Point/Nova Scotia (ICARTT 2004), Riverside/California (SOAR 2005), and Point Reyes/California (MACE 2005). We discuss the extent to which detailed (size-resolved) information on aerosol composition, hygroscopic properties, and mixing state are required in order to predict CCN number concentration at a range of supersaturation levels. In addition to CCN predictions, we apply a cloud parcel model that is initialized with measured aerosol size distributions and the different composition descriptions developed for the Riverside data set. We use the cloud model results to evaluate how differences in aerosol composition and mixing state typical of an urban area translate into differences in cloud droplet concentrations and cloud optical properties.

A34A-06 

Are There Aerosol Indirect Effects on Buoyancy and Entrainment in Shallow Cumulus Clouds?

* Small, J D (jsmall@es.ucsc.edu), University of California Santa Cruz, Earth and Planetary Sciences 1156 High Street, Santa Cruz, CA 95064, United States Chuang, P Y (pchuang@es.ucsc.edu), University of California Santa Cruz, Earth and Planetary Sciences 1156 High Street, Santa Cruz, CA 95064, United States Feingold, G (graham.feingold@noaa.gov), NOAA Earth System Research Laboratory, Chemical Sciences Division 325 Broadway, Boulder, CO 80305, United States Jiang, H (hongli.jiang@noaa.gov), NOAA Earth System Research Laboratory, Chemical Sciences Division 325 Broadway, Boulder, CO 80305, United States

During the Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS) project, the microphysical structure of non-precipitating shallow cumulus was observed using the Artium Flight Phase Doppler Interferometer (F/PDI) under a range of aerosol conditions during 11 research flights. We examine here the nature of buoyancy and entrainment in such clouds, with the goal of understanding whether aerosol affects these processes, and, therefore, the radiative impacts of such clouds. Jiang et al. (GRL 2006) report model calculations showing vertical buoyancy profiles that vary with aerosol concentration. Modeled polluted clouds exhibit greater negative and positive buoyancy, which in turn enhances entrainment and therefore reduces cloud lifetime. We utilize GoMACCS F/PDI measurements to examine whether such an effect can be observed. If so, how do these observations compare with the model results? What are the implications for cloud entrainment/detrainment and, therefore, cloud lifetime? The nature of entrainment in clouds, and specifically its impact on cloud microphysical properties, has been the subject of much interest. Two end-member entrainment models, homogeneous and inhomogeneous, have been proposed, where real entrainment falls somewhere in the continuum in between. Where an actual entrainment event falls on this continuum depends on two time scales: (a) the time scale of mixing of saturated and unsaturated air and (b) the time scale for drop evaporation. Because the latter is drop size-dependent, one might expect that any changes to the cloud drop size distribution, such as that caused by changes in aerosol concentration, can ultimately change the nature of entrainment. We examine this question using the GoMACCS F/PDI data set. Implications of any observed aerosol indirect effect on entrainment for the cloud radiative properties are also explored.

A34A-07 

Comparison of statistical properties of simulated and observed cumulus clouds during GoMACCS

* Jiang, H (hongli.jiang@noaa.gov), NOAA Earth System Research Laboratory, 325 Broadway, Boulder, CO 80305, United States Feingold, G (graham.feingold@noaa.gov), NOAA Earth System Research Laboratory, 325 Broadway, Boulder, CO 80305, United States Jonsson, H (hjonsson@nps.edu), Naval Postgraduate School, 1 University circle, Monterey, CA 93943, Lu, M (julialu@caltech.edu), California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125, United States Chuang, P Y (pchuang@pmc.ucsc.edu), University of California, Santa Cruz, 1156 High St, Santa Cruz, CA 95064, United States Flagan, R C (flagan@cheme.caltech.edu), California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125, United States Seinfeld, J H (seinfeld@caltech.edu), California Institute of Technology, 1200 E. California Blvd, Pasadena, CA 91125, United States

We present comparisons of the statistical properties of clouds generated by Large Eddy Simulations (LES) with aircraft observations of non-precipitating, warm cumulus clouds made during the Gulf of Mexico Atmospheric Composition and Climate Study (GoMACCS). Aircraft data were sampled with the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter airplane. Five flights that are most suitable for studying aerosol-cloud interactions are selected. The model simulations are initiated with observed environmental profiles. The simulations are used to generate an ensemble of thousands of cumulus clouds for statistically meaningful evaluations. Comparison focuses on the statistical properties of a set of dynamical and thermodynamical variables: cloud liquid water content, number mixing ratio of cloud droplets, drop effective radius, updraft velocity, and the distribution of cloud sizes. In general, good agreement between the simulated and observed clouds is achieved, despite big differences in sample size between the model output and the aircraft data. These comparisons, together with the excellent agreement between observed and simulated cloud size distributions, suggest that the LES is able to successfully generate the cumulus cloud populations that were present during GoMACCS.

A34A-08 

Impact of aerosol and clouds on 3D irradiance fields during the GoMACCS experiment

* Schmidt, S (sebastian.schmidt@lasp.colorado.edu), University of Colorado, LASP Campus Box 392, Boulder, CO 80309-0392, Feingold, G (graham.feingold@noaa.gov), NOAA, Earth System Research Laboratory 325 Broadway, Boulder, CO 80305, Pilewskie, P (peter.pilewskie@lasp.colorado.edu), University of Colorado, LASP Campus Box 392, Boulder, CO 80309-0392, Jiang, H (Hongli.Jiang@noaa.gov), NOAA, Earth System Research Laboratory 325 Broadway, Boulder, CO 80305,

The GoMACCS field experiment in the heavily polluted industrial Houston area was specifically designed to study the microphysical and macrophysical transformations that clouds may undergo when influenced by aerosol. Solar spectral irradiance is dependent not only on the optical properties of clouds and aerosol but also on their spatial distribution as well as the surface albedo. A radiative signature from aerosol can only be found by clearly separating 3D, surface, and aerosol effects. To this end, we simulated fields of convective clouds based on soundings in the Houston area using a large eddy simulation (LES) with size-resolved microphysics. We then modeled the irradiance fields associated with these clouds using the 3D drop effective radius and water content and 3D aerosol properties as input, and compared with the measured data from an airborne Solar Spectral Flux Radiometer (SSFR). This constitutes a rigorous test of the ability of the LES to simulate the radiative response of clouds to perturbations by aerosol. We discuss the extent to which the irradiance field associated with the LES cloud simulations compares to the observed irradiance field and its spatial and temporal variability, as well as combined aerosol, cloud and 3D effects.

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