Heterogeneous Oxidation of Sulfur Dioxide by Organic Peroxides in 1,3,5-Trimethylbenzene-derived Secondary Organic Aerosol: Kinetics and Formation of Inorganic and Organic Sulfates

The heterogeneous oxidation of sulfur dioxide (SO 2 ) by organic peroxides (POs) in aerosol represents an important pathway for atmospheric sulfate formation. However, the reactivity of SO 2 with POs arising from anthropogenic sources and the resulting sulfate formation characteristics remain poorly understood. Here, we investigate the heterogeneous reaction of SO 2 with secondary organic aerosol (SOA) derived from the photooxidation of 1,3,5-trimethylbenzene (1,3,5-TMB), one of major precursors of anthropogenic SOA. The reactive uptake coefficient (γ SO2 ) of SO 2 on 1,3,5-TMB-derived SOA was determined to be on the order of 10 −4 , depending markedly on aerosol liquid water content and particulate PO concentration. The second-order reaction rate constant ( k obs ) between 1,3,5-TMB-derived POs and dissolved SO 2 is estimated to range between 352 and 3.3×10 4 M −1 s −1 at pH of 3 to 5, which are comparable to the k obs values previously determined for monoterpene-derived POs under similar conditions. Furthermore, 1,3,5-TMB-derived peroxides efficiently convert S(IV) into inorganic sulfate (30-88%) and organosulfates (12-70%). This study reveals the heterogeneous reactivity of anthropogenic SOA and POs towards SO 2 and allows for a more accurate assessment of the role of PO-SO 2 interactions in the formation and aging of secondary aerosol.