AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Effective Absorption Cross Sections and Photolysis Rates of Model Secondary Organic Aerosol
DIAN ROMONOSKY, Nujhat Ali, Mariyah Saiduddin, Sergey Nizkorodov, University of California, Irvine
Abstract Number: 31 Working Group: Aerosol Chemistry
Abstract Prevalent mechanisms for secondary organic aerosol (SOA) aging involve heterogeneous oxidation and fog photochemical processes involving the OH radical as well as various other oxidants in the atmosphere. In addition to condensed phase oxidation, SOA can also age in the atmosphere upon exposure to radiation. To estimate the time scales of these condensed-phase photochemical processes, this study focuses on the optical properties of SOA produced by flow-tube ozonolysis and smog chamber photooxidation, during both low- and high-NO$_x oxidation conditions. The volatile organic compound precursors for these SOA samples include isoprene, alpha-pinene, beta-pinene, beta-myrcene, d-limonene, linalool, ocimene, farnesene, p-xylene, 1-methylpyrrole, 2-methylpyrrole, guaiacol, and imidazole. Mass absorption coefficient values were measured for all SOA samples created, and then converted into effective molecular absorption cross sections. Photolysis rates of the SOA compounds were calculated by assuming that the SOA compounds have the photolysis quantum yields of H$_2O$_2 (unity, providing the upper limit for the photochemical rates) or acetone (wavelength dependent, providing a more realistic estimate) and convoluting the absorption cross section data with time-dependent solar flux density. Results of this study suggest that the condensed phase photolysis of SOA can occur with effective lifetimes ranging from minutes to hours, and therefore represents a potentially important aging mechanism for SOA.