Photochemistry of Secondary Organic Aerosol

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The focus of this project is on providing a molecular level understanding of photochemical reactions occurring inside secondary organic aerosol (SOA) particles. SOA contributes to both direct and indirect radiative forcing of climate, and affects air quality in the urban and remote atmosphere. The primary goal of this research is to understand the photochemical processing of SOA derived from the oxidation of isoprene and selected monoterpenes by ozone or the nitrate radical (NO3). To achieve this goal, model SOA will be prepared and the absorption spectra and photodissociation spectra of the resulting SOA material will be investigated using the method of aerosol photodissociation spectroscopy. In parallel, the composition of model terpene SOA will be analyzed in detail using ultrahigh-resolution mass spectrometry before and after the SOA is exposed to simulated solar radiation. In addition, absolute quantum yields for photolysis of several model carbonyls embedded in SOA-like materials will be measured. This information will be used to estimate rates of photochemical reactions occurring inside atmospheric SOA particles.The interaction between solar radiation and organic materials is directly relevant to several areas of research, including the photodegradation of organic polymers and coatings, photochemistry of soil organics and dissolved organic matter, organic photochemistry, and water purification. This research will also provide information useful for predicting the health effects of aged organic particulate matter. Two graduate students will be supported through this award.