Photochemical aging of α-pinene secondary organic aerosol: effects of OH radical sources and photolysis.

Center for Atmospheric Particle Studies, Department of Chemical Engineering, Carnegie Mellon University, 5000 Forbes Ave, Pittsburgh, Pennsylvania, 15213 United States.

The journal of physical chemistry. A 2012 Jun 21

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This study addresses photochemical aging of secondary organic aerosol (SOA) produced from α-pinene ozonolysis. The SOA is aged via hydroxyl radical (OH) reactions with first-generation vapors and UV photolysis. OH radicals are created through tetramethylethylene ozonolysis, HOOH photolysis, or HONO photolysis, sources that vary in OH concentration and the presence or absence of UV illumination. Aging strongly influences observed SOA mass concentrations, but the behavior is complex. In the dark or with high concentrations of OH, vapors are functionalized, lowering their volatility, resulting in an increase in OA by a factor of 2-3. However, with lower concentrations of OH under UV illumination SOA mass concentrations decrease over time. We attribute this decrease to evaporation driven by photolysis of the highly functionalized second-generation products. The photolysis rates are rapid, a few percent of the NO(2) photolysis frequency, and can thus be highly competitive with other aging mechanisms in the atmosphere.

Citation

Kaytlin M Henry, Neil M Donahue. Photochemical aging of α-pinene secondary organic aerosol: effects of OH radical sources and photolysis. The journal of physical chemistry. A. 2012 Jun 21;116(24):5932-40