Conventional wisdom assumes that organic compounds inside atmospheric particles are reasonably protected from further oxidation by gas-phase oxidants. However, these compounds are still accessible to actinic radiation from the sun. Furthermore, the environment found inside organic particles has unique chemical (a complex mixture of diverse organic compounds) and physical (a highly viscous fluid) attributes that may promote unique photochemical reactions. This presentation will describe our recent experiments on condensed-phase photochemistry in different types of secondary organic aerosols (SOA). We generate model SOA by oxidation of volatile organic compounds (VOC) in a batch or flow reactor, collect SOA material on an inert substrate, irradiate it with UV radiation, and examine the composition of the emitted gaseous products as well as condensed-phase products remaining in the material. Interesting findings include: an unexpected photostability of SOA produced from aromatic VOC precursors; an observation of impeding effects of viscosity on the rate of photochemical reactions in the organic particles; a production of a wide range of VOC in the photodegradation of SOA; changes in the optical absorption properties of the SOA material induced by the solar radiation. The take-home point of this presentation will be that the condensed-phase photochemical processes in atmospheric organic particles occur on relevant time scales and lead to readily observable chemical composition changes.

Condensed-phase photochemical reactions in atmospheric organic aerosol

251st National Meeting (2016)

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