Reactive uptake of ozone by proxies for organic aerosols: Surface-bound and gas-phase products

Gas-phase and surface-bound products were determined for the reaction of ozone with self assembled monolayers of alkanes and terminal alkenes serving as proxies for atmospheric organic aerosols. The organic surfaces were characterized using infrared (IR) spectroscopy (direct absorption and attenuated total reflection) as well as contact angle measurements with water before and after the reaction with ozone. The contact angle of the organic surfaces was reduced by similar to 20 degrees owing to the reaction. Following the reaction, IR absorption due to the presence of carbonyls and carboxylic acids was observed on the surface. Gas-phase products were determined using infrared spectroscopy immediately above the reaction surface. Under dry conditions, gas-phase formaldehyde yields of 0.5+/-0.1 for organic monolayers of allyltrichlorosilane (C-3(=)) and octenyltrichlorosilane (C-8(=)) terminal alkenes were observed, in good agreement with the yields observed for gas phase ozonolysis of terminal alkenes. Surfaces of n-octane (C-8) as well as processed alkene surfaces were nonreactive toward ozone. The reaction mechanism of ozone with the surface alkenes is discussed. Finally, the possible implications for the chemistry of organic aerosols are discussed and studied using a box model and realistic atmospheric scenarios.