Organic Sulfur Products and Peroxy Radical Isomerization in the OH Oxidation of Dimethyl Sulfide

The atmospheric oxidation of dimethyl sulfide (DMS) represents a large natural source of sulfate particles and thus is a major contributor to the global radiative effect of aerosols; however, its underlying chemical mechanism remains poorly constrained. In particular, DMS oxidation generates a variety of intermediate organic sulfur species, whose fate and kinetics govern the ultimate amount and distribution of sulfate aerosol. There is thus a need to understand the production and chemistry of such intermediates, including the recently discovered hydroperoxymethyl thioformate, formed from the isomerization of the methylthiomethylperoxy radical (CH3SCH2OO). Here, chamber experiments were performed to measure product formation from the OH-initiated oxidation of DMS. Three real-time mass spectrometers were used to measure the formation and evolution of a broad suite of gas- and aerosol-phase sulfur-containing compounds, including nearly all the closed-shell organic sulfur species included in current mechanisms; some additional species not predicted by such mechanisms are detected as well. The rapid decay of many of the more oxidized organic sulfur species suggests that aerosol uptake and loss to surfaces can be important processes under the conditions of this study. In addition, the isomerization rate constant of the CH3SCH2OO radical was experimentally determined to be 0.09 s-1 (0.03-0.3 s-1, 1σg), in broad agreement with results from other studies.