Modification of the Conversion of Dimethylsulfide to Methanesulfonic Acid by Anthropogenic Pollution as Revealed by Long-Term Observations

Since the CLAW hypothesis was proposed approximately three decades ago, aerosols derived from dimethyl-sulfide (DMS) conversion have been intensively investigated. In this study, long-term observations were conducted for methane-sulfonic acid (MSA), the oxidation product of DMS, from 2008 to 2016 in the marine boundary layer of the Bering Sea. We found that (1) the increase in sea surface temperatures led to increased DMS emissions and MSA concentrations; however, (2) air masses from different sources caused significant differences in the conversion efficiencies of DMS to MSA; and (3) air masses with high O-3 and NO2, low relative humidity, temperature, and cloud liquid water path from the northwest Pacific, which were influenced by anthropogenic activities, together inhibited the conversion of DMS to MSA. Among them, O-3, T2M, and RH were the principal factors. Conversely, air masses, with contrasting atmospheric environments, from the Arctic Ocean promoted the conversion of DMS to MSA.