ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-9505-2012 Multi-generation gas-phase oxidation, equilibrium partitioning, and the formation and evolution of secondary organic aerosol Cappa C. D. 1 Wilson K. R. 2 Department of Civil and Environmental Engineering, University of California, Davis, CA 95616, USA Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA 22 10 2012 12 20 9505 9528 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/9505/2012/acp-12-9505-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/9505/2012/acp-12-9505-2012.pdf

A new model of secondary organic aerosol (SOA) formation is developed that explicitly takes into account multi-generational oxidation as well as fragmentation of gas-phase compounds, and assumes equilibrium gas-particle partitioning. The model framework requires specification of a limited number of tunable parameters to describe the kinetic evolution of SOA mass, the average oxygen-to-carbon atomic ratio and the mean particle volatility as oxidation proceeds. These parameters describe (1) the relationship between oxygen content and volatility, (2) the probability of fragmentation and (3) the amount of oxygen added per reaction. The time-evolution and absolute value of the simulated SOA mass depends sensitively on all tunable parameters. Of the tunable parameters, the mean O : C is most sensitive to the oxygen/volatility relationship, exhibiting only a weak dependence on the other relationships. The model mean particle O : C produced from a given compound is primarily controlled by the number of carbon atoms comprising the SOA precursor, with some sensitivity to the specified oxygen/volatility relationship. The model is tested against laboratory measurements of time-dependent SOA formation from the photooxidation of &alpha;-pinene and <i>n</i>-pentadecane and performs well (after tuning). The model can also accurately simulate the carbon-number dependence of aerosol yields previously observed for oxidation of straight-chain alkanes. This model may provide a generalized framework for the interpretation of laboratory SOA formation experiments in which explicit consideration of multiple-generations of products is required, which is true for all photo-oxidation experiments.

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