Characterizing aqueous-phase oxidation of dimethyl sulfide using chemical ionization mass spectrometry

The oxidation of dimethyl sulfide (DMS), the largest natural source of sulfur to the atmosphere, represents an important source of non-sea salt sulfate aerosol. Oxidation of DMS (and its reaction intermediates) may occur in both the gas and aqueous phase, necessitating a full chemical understanding of these mechanisms across multiple phases. Recent mass spectrometric studies have elucidated new pathways in the gas-phase oxidation mechanism; however aqueous-phase oxidation has received relatively little recent attention. Here, we examine aqueous-phase DMS chemistry using NH4+ and H3O+ time-of-flight chemical ionization mass spectrometry to simultaneously monitor the reactants and products. We apply these techniques in the laboratory to study the oxidation of dimethyl sulfide, as well as the chemistry of oxidation products such as dimethyl sulfoxide and methane sulfinic acid. Measurements of product distributions and temporal trends provide insight into the detailed reaction mechanism, and enable comparisons with the corresponding gas-phase oxidation process.