Organic compounds trapped inside and on surfaces of atmospheric particles are readily accessible to actinic radiation from the sun. While the gas-phase photochemistry of organic compounds is relatively well understood, the rates and mechanisms of photochemical transformations of organic compounds in particles are poorly known. This presentation will describe our recent experiments that characterize the production of small volatile organic compounds (VOC) from various types of secondary organic aerosols (SOA). We generate model SOA by oxidation of VOC in a smog chamber and/or flow tube, collect SOA on an inert substrate, irradiate them with tunable UV radiation, and examine the amount of photoproduced VOC in gas-phase by cavity-ring down spectroscopy and proton transfer reaction mass spectrometry. The resulting UV wavelength dependence of the VOC emission rate, i.e., an action spectrum, can be used to estimate the lifetime of photochemically active organic compounds in SOA with respect to the solar photolysis. Special attention is paid to the emission of formic acid, which is currently under predicted by atmospheric models, possibly because of the neglect of the photochemical reactions that are examined in this work.

Photolysis of secondary organic aerosol material as a source of small oxygenated volatile organic compounds

249th National Meeting (2015)

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