Individual-particle Aerosol Experiments in the Marine Troposphere

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Aerosol particles in the marine boundary layer and free troposphere impact the global solar radiation balance, both directly through radiation backscatter and indirectly as cloud condensation nuclei. This project will use individual-particle methods to examine tropospheric processes that affect aerosol- particle size distribution, concentrations, and chemical compositions. Primary focus will be on the marine boundary layer and stratocumulus clouds that cap that layer in the remote areas of the South Pacific. Analyses will be performed with automated electron-beam instruments, especially the new scanning electron microscope. Methods developed by this research group over the past decade allow the study of large numbers of particles by quantitative determination of composition and morphology. The data from this research will be used to address current issues in atmospheric aerosol research, including (a) the generation, fractionation, and reaction of marine aerosol particles; (b) production of natural, non-sea-salt sulfate particles; (c) partitioning of aerosol particles between droplets and interstitial air in marine stratocumulus clouds; (d) cloud processing of aerosol particles; and (e) evolution of aerosols during long-range transport in the marine troposphere. As a ancillary task, the structure and composition of complex supermicron to submicron particles will be investigated a high spatial resolutions using transmission electron microscopy, both by imaging and by chemical analysis. Transmission electron microscopy also makes possible the examination of reactions involving nitrate and ammonia in submicron individual particles. The proposed studies, taken together, will provide fine-scale data about a wide range of particle types that occur in the marine troposphere and that affect radiation backscatter and the microphysical properties of clouds.