Photochemistry in Organic Aerosols

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Secondary Organic Aerosols (SOA) contribute to radiative forcing on climate both directly and indirectly and also affect urban air quality. The main goals of this award are: (1) To investigate the mechanism and significance of direct and indirect photolysis processes occurring in SOA and (2) to investigate aqueous photochemistry involving water-soluble SOA during cloud-processing. Model SOA will be generated in a smog chamber and exposed to simulated solar radiation in various states: Dry SOA at low relative humidity (RH), hydrated SOA at high RH, SOA dissolved in water at concentrations relevant to clouds and fogs, and SOA in frozen aqueous extracts. The molecular composition of SOA will characterized by high-resolution mass spectrometry and other analytical methods before and after exposure to the simulated solar radiation. In a parallel set of experiments, photodissociation action spectra of SOA will be measured using unique spectroscopic and mass-spectrometric tools developed in the PI's laboratory. The absolute photodissociation quantum yields and detailed mechanisms of photolysis will be determined for several representative carbonyl compounds embedded in SOA-like materials. This information will be used to estimate rates of photochemical reactions occurring inside atmospheric SOA particles and inside cloud droplets containing dissolved SOA.This project will provide molecular-level understanding of photochemical reactions in SOA and in aqueous solutions of SOA material. Results will also contribute to related disciplines investigating (1) health effects of aged organic matter in air and (2) processes involving interactions between solar radiation and complex organic mixtures in other media (e.g., photodegradation of organic polymers and coatings, photochemistry of soil organics, photodegradation of dissolved organic matter, and water purification). The project will support two graduate students and findings will be widely disseminated through presentations at major conferences and peer-reviewed publications. The principal investigator and student will also communicating the importance and excitement of fundamental research to the general public through ongoing educational and outreach activities including a two-week long summer workshop that provides hands-on laboratory training for high school science teachers and presentations, lab tours, and educational seminars for the general public.