Laboratory yields of hydroperoxymethyl thioformate, sulfur dioxide, carbonyl sulfide from the low NOx oxidation of dimethyl sulfide

Abstract:

Dimethyl sulfide (DMS), emitted from the surface ocean, contributes to aerosol particle formation and growth in the pristine marine atmosphere. DMS is primarily oxidized by the hydroxyl radical ultimately forming methane sulfonic acid and sulfuric acid. Current models of atmospheric sulfur chemistry often assume that 0.7% of DMS emitted from the ocean is oxidized to carbonyl sulfide (OCS), an abundant trace gas that contributes to the stratospheric sulfate aerosol load. The OCS branching fraction was originally determined in a quartz-glass photoreactor conducted under high RO₂ and NO_x concentrations that are not representative of the marine boundary layer. Recently, a ubiquitous autoxidation product of the OH-initiated H-abstraction of DMS, hydroperoxymethyl thioformate (HPMTF), has been detected in the marine environment. The ubiquity of HPMTF and its formation under low RO₂ and NO_x environments leads us to reexamine DMS oxidation product yields with a focus on HPTMF oxidation as a potential pathway to OCS formation. Here, we report the yield of HPMTF, SO₂ and OCS from OH-initiated oxidation of DMS conducted under conditions representative of the marine boundary layer. The HPTMF experiments were performed in a dark environmental chamber using alkene ozonolysis as the primary source of OH generation under NO_x free conditions.