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Published May 15, 2007 | public
Journal Article

Reactions of Semivolatile Organics and Their Effects on Secondary Organic Aerosol Formation


Secondary organic aerosol (SOA) constitutes a significant fraction of total atmospheric particulate loading, but there is evidence that SOA yields based on laboratory studies may underestimate atmospheric SOA. Here we present chamber data on SOA growth from the photooxidation of aromatic hydrocarbons, finding that SOA yields are systematically lower when inorganic seed particles are not initially present. This indicates that concentrations of semivolatile oxidation products are influenced by processes beyond gas-particle partitioning, such as chemical reactions and/or loss to chamber walls. Predictions of a kinetic model in which semivolatile compounds may undergo reactions in both the gas and particle phases in addition to partitioning are qualitatively consistent with the observed seed effect, as well as with a number of other recently observed features of SOA formation chemistry. The behavior arises from a kinetic competition between uptake to the particle phase and reactive loss of the semivolatile product. It is shown that when hydrocarbons react in the absence of preexisting organic aerosol, such loss processes may lead to measured SOA yields lower than would occur under atmospheric conditions. These results underscore the need to conduct studies of SOA formation in the presence of atmospherically relevant aerosol loadings.

Additional Information

© 2007 American Chemical Society. Received for review August 28, 2006. Revised manuscript received November 21, 2006. Accepted February 28, 2007. This research was funded by the U.S. Environmental Protection Agency Science to Achieve Results (STAR) Program grant RD-83107501-0, managed by EPA's Office of Research and Development (ORD), National Center for Environmental Research (NCER), and by U.S. Department of Energy Biological and Environmental Research Program DE-FG02-05ER63983; this work has not been subjected to the EPA's required peer and policy review and therefore does not necessarily reflect the views of the Agency and no official endorsement should be inferred.

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