9321496 Davis Oxidation products of organics in the atmosphere can be expected to affect the thermodynamics of cloud droplets and the rates of droplet growth and evaporation. Automobile emissions of olefins yield secondary organic aerosols such as glutaric, adipic and phthalic acids, and a-pinene emissions from tree foliage produce pinonaldehyde and pinonic acid upon oxidation. Recent experiments in this laboratory indicate that such difunctional organic oxygenates are surface active and significantly alter the physical and chemical properties of the surface on an aqueous solution droplet. This proposal addresses the surface chemistry and the effects of the surface chemistry on evaporation/condensation rate processes of aerosol droplets containing organic solutes. Preliminary experiments with aqueous solution droplets of adipic and phthalic acids show that evaporation rates are lowered by more than an order of magnitude eompared with water droplets at the same ambient conditions of temperature and relative humidity. These large effects have not been explored before, but their impact on cloud physics can be expected to be significant. The work plan includes surface tension measurements of aqueous solutions for a wide range of concentrations and evaporation/condensation rate measurements of electrodynamically trapped aerosol droplets. The droplet size will be measured as a function of time by light-scattering techniques, and the light- scattering data will be analyzed to determine the refractive index of the droplet. Facilities are also available to Measure inelastic scattering (Raman scattering) by the droplets, which can be used to chemically characterize the droplets. ***
