Role of adducts in the atmospheric oxidation of dimethyl sulfide

Abstract

Based on the results from recent laboratory studies and field observations, we suggest that adduct formation may play a key role in the atmospheric oxidation of dimethyl sulfide (DMS). Experimental evidence for the formation of the DMS · OH and CH₃SO_x· O₂ adducts are described and used in a simple ‘box model’ to calculate the ratio of [MSA]/[SO₄^2–] observed in the atmosphere. These calculated ratios are compared with those inferred from field measurements. Based on these comparisons, we suggest that the changes with temperature in the mechanism of the OH + DMS reaction, one of the primary initiation steps in atmospheric DMS oxidation, are unlikely to be the source of the variation in the [MSA]/[SO₄^2–] ratio with temperature. We suggest that the competition between the thermal decomposition of adducts such as CH₃SO₂ and their bimolecular reactions with atmospheric species is the likely cause of the variation. Finally, a few observations needed to better our understanding of the DMS oxidation are identified.