Atmospheric fate of organosulfates through gas-phase and aqueous-phase reactions with hydroxyl radicals: Implications for inorganic sulfate formation

Abstract

Organosulfates are important tracers for aerosol particles, yet their influence on aerosol chemical composition remains poorly understood. This study uses quantum chemical calculations based on density functional theory to explore the reactions of some prevalent organosulfates, specifically methyl sulfate and glycolic acid sulfate, with hydroxyl radicals (HO•) in the gas phase and aqueous phase. Results indicate that all reactions initiate with hydrogen abstraction by HO• from CH3- in methyl sulfate and from -CH2- and -COOH in glycolic acid sulfate, followed by the further reaction of the resulting radicals through self-decomposition, interaction with O2 and, possibly, O3. We found that the hydrogen abstraction from the -COOH group in glycolic acid sulfate could lead to decarboxylation and eventually form similar products as methyl sulfate. The primary reaction products are inorganic sulfate, carbonyl compounds, and formic sulfuric anhydride. Rate constants of 1.14×10-13 and 6.17×10-12 cm3 molec.-1 s-1 at 298.15 K were determined for the gas-phase reactions of methyl sulfate and glycolic acid sulfate, respectively. The former value is consistent with a previous experimental report. Additionally, besides O2 as the primary oxidant in the fragmentation of organosulfates, this study unveils that O3 may be a complementary oxidant in this process, especially in environments enriched with ozone. Overall, this study elucidates mechanisms for HO•-initiated transformation of organosulfates and highlights the potential role of chemical substitution, thereby enhancing our understanding of their atmospheric chemistry and implications for inorganic sulfate formation, which are vital for evaluating their impact on aerosol properties and climate processes.