Interactions of Aerosol Particles and Marine Stratocumulus Clouds

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The objective of this project is to characterize the chemical and physical characteristics of aerosol particles above, in, and below stratocumulus clouds. The study will be carried out as part of the DYCOMS-II project (Dynamics and Chemistry of Marine Stratocumulus), off the California coast in July 2001. The interaction of aerosol and cloud particles will be evaluated by comparing the size distributions and chemical composition of particles measured within cloud with those outside the cloud. Measurements of the cloud droplet size distribution will be used to investigate the effects of aerosol particles on cloud microphysical properties. Instrumentation includes particle spectrometers for the size range 0.005 to 6400 micrometers. Electron microscopy of aerosol samples will be used to identify chemical functional groups, including organic species, and elements. The residue of cloud droplets collected by counterflow virtual impaction will be analyzed the same way. The data will give insight on the following scientific problems: (1) the chemical composition of particles incorporated into cloud droplets; (2) the effects of different aerosol chemical types and size distributions on cloud microphysics; (3) the degree of chemical processing of the aerosols by cloud; (4) the extent to which the observations can be approximated by physical and chemical cloud models. The ultimate goal of the research is to improve the ability to parameterize the radiative, dynamic, and thermodynamic effects of clouds in large-scale models of atmospheric circulation and climate.