Unraveling a Novel Formation Pathway of Hydroxymethanesulfonate (HMS) in the Marine Atmosphere

Abstract Hydroxymethanesulfonate (HMS, CH 2 (OH)SO 3 − ) is an important contributor to organosulfates with the potential to impact the biogeochemical sulfur cycle and global climate. However, its characteristics in the marine atmosphere have rarely been investigated. This study investigated the abundances of HMS over the Yellow and East China Seas based on island and cruise observations, showing weak seasonal variations but significant spatial patterns. Aerosol pH was diagnosed as the limiting factor governing the production rates of HMS via the traditional aqueous processing. However, the disparities between the theoretical formation rates and observed concentrations implied the possibility of a new formation mechanism for HMS. Strong correlations were found between methanesulfonate (MSA) and HMS, with machine learning simulation indicating MSA as the most pivotal contributor. Through the density functional theory calculations, HMS can be generated by gas‐phase organic reactions between the •OOCH 2 SO 3 H radical (formed from the isomerization of methylsulfonoxyl radical (CH 3 SO 3 •) and oxidation) and NO or CH 3 OO• radical, leading to the cogeneration of HMS and MSA. The HMS production rate via the gas phase process was 3.7–55 times larger than that of aqueous processing, which extends the understanding of formation mechanisms of atmospheric organosulfur compounds.