While the heterogeneous oxidation of atmospheric organic aerosols influences their effects on climate, air quality, and visibility, a more detailed understanding of the chemical mechanisms in heterogeneous oxidation is crucial for improving models of their chemical evolution in the atmosphere. Previous experimental work in our lab has shown two general reaction pathways for organic aerosol upon oxidation: functionalization, which adds additional oxygen functional groups to the carbon skeleton, and fragmentation, which leads to C-C bond scission and lower molecular weight oxidized products. Furthermore, these pathways were also found to be dependent on molecular structure, with more branched or oxidized hydrocarbons undergoing more fragmentation than less branched or oxidized hydrocarbons. However, while the mechanisms of hydrocarbon oxidation have been studied extensively in the gas phase, to what extent the gas phase mechanisms of hydrocarbon oxidation can be reliably applied to heterogeneous or bulk oxidation in aerosol remains unclear.To investigate the role of the condensed phase and molecular structure in the mechanism of heterogeneous organic aerosol oxidation, stochastic kinetics models are developed and compared to measurements of the products in the oxidation of both highly reduced and highly oxidized hydrocarbon aerosols. Within the aerosol bulk, condensed phase rate coefficients and product branching ratios for peroxy reactions lead to different product distributions than those expected from gas phase peroxy reactions due to the presence of the liquid radical cage at the reaction site. As a result, tertiary alcohols and ketones were found to be the predominate products in the oxidation of squalane as observed in experiments. For oxidized aerosols, elimination of CO2 from acyl peroxy radicals was also found to be an important fragmentation pathway in addition to and in conjunction with �-scission of alkoxy radicals.

Using kinetics modeling to investigate the role of structure and phase on the functionalization and fragmentation of hydrocarbons in the heterogeneous oxidation by OH

248th National Meeting (2014)

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