Processing of unsaturated organic acid films and aerosols by ozone

For any organic-containing aerosol, the species present at the particleʹs surface are extremely susceptible to oxidation by atmospheric oxidants, such as OH, halogen atoms, ozone and nitrogen trioxide. In this work, thin films and pure organic aerosols were investigated as proxies for these surface organic compounds. The mechanisms of processing by ozone of unsaturated carboxylic acids, specifically 2-octenoic acid and 10-undecenoic acid, in a thin film are compared to that on pure aerosols. The organic acids utilized were chosen to investigate the effect of substitution on the ozonolysis mechanism. The gas-phase and condensed-phase products were probed via a combination of infrared spectroscopy and mass spectrometry. A significant change was measured in the chemical composition of both the thin films and the aerosols following ozonolysis, and some of the products formed have been identified. Consequences of this chemical processing of aerosols to atmospheric chemistry, climate and transport will be discussed.