Laboratory Characterization of the Aqueous-Phase Oxidation of Dimethyl Sulfide (DMS) and Its Oxidation Products

SEAMUS FREY, Lexy LeMar, Jesse Kroll, MIT

     Abstract Number: 170
     Working Group: Aerosol Chemistry

Abstract
The oxidation of dimethyl sulfide (DMS) and its products represents a major natural source of sulfate aerosols in the atmosphere. This multi-generational oxidation therefore has major implications for the global sulfate budget both in the pre-industrial times, the present day, and in future atmospheres. While such oxidation processes may occur in both the gas and aqueous phases, previous studies have primarily explored DMS oxidation in the gas phase only, with far fewer studies focusing on aqueous-phase DMS oxidation. As a result, the product distributions, mechanism, and impact of DMS oxidation in the atmospheric aqueous phase (i.e., deliquesced aerosol particles and cloud droplets) remain highly uncertain. Here, we address this uncertainty via laboratory studies of the aqueous-phase oxidation of DMS and its various oxidation products. Organosulfur species (DMS, dimethyl sulfoxide, methylsulfinic acid, and methylsulfonic acid) were oxidized in a new bulk-aqueous-phase reactor, and their products were analyzed in near-real time using electrospray ionization-Orbitrap mass spectrometry (ESI-Orbitrap-MS). Product distributions from oxidation of these sulfur-containing compounds in the aqueous phase were compared to those of the gas phase, enabling identification of differences in branching ratios and in mechanisms across phases. Results from this study enable the development of an improved DMS oxidation mechanism, which in turn can be used for improved predictions of sulfate aerosol in 3D (chemical transport and Earth system) models.