Atmospheric fate of organosulfates through gas-phase and aqueous-phase reaction with hydroxyl radicals: implications in inorganic sulfate formation

Abstract. Organosulfates are important tracers for aerosol particles, yet their influence on aerosol chemical composition remains poorly understood. This study explores the reactions of some prevalent organosulfates, specificaly methyl sulfate and glycolic acid sulfate, with hydroxyl radicals (HO•) in both gas-phase and aqueous-phase environments. Results indicate that all reactions initiate with hydrogen abstraction by HO• from CH₃- or -CH₂- groups adjacent to the sulfate group, followed by the further reaction of the resulting radical through self-decomposition or interactions with O₂ and O₃. While glycolic acid sulfate is unfriendly towards decomposition in the gas-phase, methyl sulfate requires clustering with at least two water molecules for effective decomposition. In the aqueous-phase, the decomposition of glycolic acid sulfate is the least extensive, likely due to the presence of the carboxyl group that stabilizes the radical resulting from hydrogen abstraction. The primary reaction products are inorganic sulfate and carbonyl compounds. The rate constant of 1.14×10^-13 cm³ molecule^-1 s^-1 at 298.15 K was determined for the gas-phase reaction of methyl sulfate, consistent with previous experimental data. Additionally, while prior studies suggested O₂ as primary oxidant in the fragmentation of organosulfates, this study highlight unveils O₃ as a key oxidant in the intermediate steps of this process. 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 implication for inorganic sulfate formation, which are vital for evaluating their impact on aerosol properties and climate processes.