Efficient Production of Hydroperoxymethyl Thioformate in the Nitrate Radical Oxidation of Dimethyl Sulfide

The oxidation of dimethyl sulfide (DMS), emitted from the surface ocean, contributes to aerosol particle formation and growth in the marine atmosphere. DMS is primarily oxidized by the hydroxyl radical (•OH), leading to the formation of stable intermediates such as hydroperoxymethyl thioformate (HPMTF). The subsequent gas-phase and multiphase chemistry of these intermediates dictate the production rates of sulfuric acid, methanesulfonic acid, and sulfate aerosol. At night, DMS is oxidized by the nitrate radical (NO3•), where nitric acid and the methylthiomethyl peroxy radical (MTMP) are formed following H-abstraction from DMS. The subsequent fate of the MTMP at night is not known. Here, we use measurements in an environmental chamber to investigate the nocturnal chemistry of DMS. We show that under typical atmospheric conditions, HPMTF is formed in unit yield in the NO3•-oxidation of DMS and that the chemical lifetime of HMPTF with respect to oxidation by NO3• is much longer than the length of night. Our results highlight that HPMTF is formed in high yield in the nocturnal marine boundary layer and is likely to accumulate at night due to the slow subsequent oxidation by NO3•.