Kinetic and physic models of secondary organic aerosol formation and their application to Houston conditions

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Dechapanya, Wipawee

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Atmospheric reactions of volatile organic compounds can produce low volatility species that condense onto atmospheric particles (secondary organic aerosol), and these particles have significant impact on public health. This work develops quantitative kinetic and physical phase partitioning models of secondary organic aerosol (SOA) formation. These mechanisms were integrated into a state of the art mechanism for gas phase reactions (SAPRC). Using the resulting model, a series of sensitivity analyses were performed. Analyses of the sensitivity of SOA formation to several parameters (e.g., VOC/NOx ratio, rate parameters) were performed. Results indicated that aerosol yield (SOA formed per amount of hydrocarbons reacted) depends on the extent of conversion of parent hydrocarbons, partitioning coefficient (Kom), initial aerosol mass concentration (Mint), and rate parameters. Based on the sensitivity studies, empirical models for SOA yield were developed for both individual and lumped hydrocarbon species. The models were used to examine a number of case studies relevant to the formation of SOA in Houston. In general, the analyses indicated that strategies effective in reducing ozone concentrations will also be effective in reducing SOA. Emission reductions that reduce ozone mixing ratios by O.1 ppm reduces SOA concentration by approximately 2.5 µg/m3 . The models developed in this study are effective prognostic tools for analyzing SOA production under a variety of conditions, and these models can be readily implemented into 3D air quality models, and modified easily if more experimental data on SOA formation become available.