(70g) CCN and Morphology Imaging of Numerous Oxidized VOCs In a Smog Chamber

Biogenic sources emit approximately 1150 Tg C/yr in the form of thousands of volatile organic compounds (VOCs) [1]. VOCs nucleate to form secondary organic aerosol (SOA), which participate in atmospheric processes such as the absorption and scattering of radiation, activation as cloud droplets, and other heterogeneous reactions. We have constructed a small, indoor smog chamber for use in studying SOA formation and properties. We generated SOA through the oxidation of VOC directly with injected ozone and indirectly via the photochemical production of ozone from NOx precursors. We studied the time-dependent size distribution and cloud condensation nucleus (CCN) activation potential of aerosol generated from both biogenic and anthropogenic VOCs, including common terpenes such as alpha- and beta-pinene and d-limonene and industrial byproducts such as benzene and toluene. We find that the VOCs nucleate rapidly and the resultant aerosol activates at low supersaturations of water vapor, though the generated SOA is found to be less CCN active than inorganic salts such as sodium chloride and ammonium sulfate. CCN activity is observed to increase with aerosol age, and may influence cloud properties through enhancement of CCN number concentration. The evolution of the SOA size distribution has been found dependent on the initial reactant species, with mixtures of VOC displaying an average of the individual species' distributions. Aerosol particles produced from different reactants are in the process of being characterized by Atomic Force Microscopy. Early microscopy results indicate that the SOA particle shape is not consistent across all reactant species. Our research suggests that models of cloud formation should not neglect contributions and enhancements to total CCN activity from the oxidation of VOCs.

[1] Goldstein and Galbally, ES&T, March 2007.