Heterogeneous Reaction Rate of Cloud and Fog Droplets

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Heterogeneous reaction pathways involving water droplets in clouds and fogs are increasingly seen as important conduits for chemical transformation of atmospheric trace gases. One of the basic parameters which determines the transfer rate of trace gases into atmospheric droplets is the mass accommodation or "sticking" coefficient for trace gas molecules on aqueous surfaces. This continuation research project, initiated under grant ATM-8400748, is designed to study certain heterogeneous chemical processes of atmospheric importance. In particular, the variation of sticking coefficients with droplet physical parameters such as temperature and size and chemical parameters including hydrocarbon surface layers and droplet chemical composition will be investigated. These studies will broaden the applicability of our measurements to the natural atmosphere. Chemical reaction kinetics at the droplet surface will also be measured using this technique in order to determine whether bulk aqueous reaction rates are appropriate for modeling heterogeneous processes in clouds and fogs. Techniques for real-time droplet surface analysis such as stimulated Raman scattering and laser induced fluorescence will be developed.