Kinetic analysis of the ozone processing of an unsaturated organic monolayer as a model of an aerosol surface

It has been suggested that an organic aerosol containing unsaturated organic compounds at the surface would likely be processed by atmospheric ozone. The ozonolysis of oleic acid gives rise to the formation of products having shorter chain lengths than the starting molecule, and are consequently more water soluble than oleic acid. Hence, the exposure of a monolayer of oleic acid to ozone should lead to a decrease in surface activity at the air-water interface. A model system is used for real-time measurements of surface tension changes due to ozone exposure of a pendant drop that is coated by a fatty acid monolayer. The surface tension is measured based on an analysis of the shape pro. le of acquired images of the drop. A study of the kinetics of the gas-surface reaction is presented. Assuming that the uptake of ozone is dominated by the reaction at the surface, the measured reactive uptake coefficient of ozone gamma(meas) is estimated to be (2.6 +/- 0.1) x 10(-6).