Atmospheric organic aerosol affects human health and climate, but understanding of organic aerosol chemistry is far from complete. We discuss a new pathway that forms epoxide in organic aerosol via catalytic photo-sensitized oxidation of alkenes by molecular oxygen in the presence of a-dicarbonyls. We identify reaction products of different alkenes and report the reaction kinetics. Yields as high as 100% in 30 minutes of exposure to a solar simulator are observed. Based on a statistical estimate of a-dicarbonyl concentration in secondary organic aerosol, we estimate that this type of reaction will be highly effective under ambient conditions. The high rate constants determined in our experiments suggest that this reaction may limit the lifetime of alkenes in the organic phase. The formation of epoxides also has implications for formation of aerosol components, such as polyalcohols, oligomers and organosulfates and will increase hygroscopicity of pure organic phase particles.

Organic-phase photo-catalytic epoxidation of alkenes by α-dicarbonyls and atmospheric implications

244th National Meeting (2012)

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