FT-IR product study of the photo-oxidation of dimethyl sulfide: Temperature and O-2 partial pressure dependence

The products of the OH-radical initiated oxidation of dimethyl sulfur (DMS) have been investigated under NO, free conditions using the photolysis of H 2O2 as the OH radical source and FT-IR spectroscopy to monitor reactants an d products at 1000 mbar total pressure (N-2 + O-2). The products were inves tigated as a function of the temperature (284, 295 and 306 +/- 2 K) and the O-2 partial pressure (20, 200 and 500 mbar). Dimethyl sulfoxide (DMSO), SO 2 and methane sulfonic acid (MSA: CH3SO3H) were the major sulfur-containing products and evidence has been found for the formation of methane sulfinic acid (MSIA: CH3S(O)OH) in considerable yield. The variation of the formati on of DMSO and SO2 with temperature and O-2 partial pressure is consistent with a mechanism involving bath addition and abstraction channels. The mola r formation yields of DMSO support that a major fraction of the OH-DMS addu ct formed in the addition channel reacts with O-2 to form DMSO. Due to the uncertainty in the literature rate coefficients used for the corrections in the formation yield of DMSO the possibility of other channels cannot be co mpletely excluded. High overall molar formation yields of SO2 have been mea sured, suggesting that further oxidation of the products in both the additi on and abstraction channels result mainly in SO2 production under the NOx f ree conditions employed in the experiments. Consideration is made of the im plications of the results for the atmospheric oxidation of DMS under condit ions of low NOx such as occur in the remote marine boundary layer.