Collaborative Research: Heterogeneous Photocatalytic Transformation of Isoprene: Relevance to Secondary Organic Aerosol Formation

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The hypothesis to be tested in this project is that atmospheric heterogeneous photocatalysis of isoprene may play an important role in secondary organic aerosol (SOA) formation. The atmospheric relevance of transition metal-based particulate semiconductors in the photochemical oxidation of isoprene to low volatility products will be investigated. Photocatalysts will include atmospherically-relevant transition metal oxide particles, desert sand, and volcanic ash in the 0.1 to 10 micrometer size range. Liquid-solid photocatalytic reactions will be studied in terms of the organic substrate (isoprene and the primary products of isoprene gas-phase photochemical oxidation, methacrolein and methyl vinyl ketone), the presence of a sacrificial electron donor (e.g., acetate), oxygen concentration, and pH. The potential for photochemical Diels-Alder reactions to occur between isoprene (a diene) and a range of relevant dienophiles will be investigated, followed by analysis for oligomeric products. The research will be overseen by senior investigators from CalTech and the Oak Crest Institute of Science.These studies will potentially advance the field of aerosol research by guiding future smog chamber studies; identifying chemical markers characteristic of heterogeneous photooxidation pathways; and investigating the polymerization products, which may account for a significant portion of the SOA mass. The research will be carried out by a post-doctoral scholar, and a graduate student at Caltech, as well as community college students and high school teachers working in teams with high school students via Oak Crest. These efforts will help to broaden the participation of underrepresented groups in scientific research.