Sulfate and Carbonyl Sulfide Production in Aqueous Reactions of Hydroperoxymethyl Thioformate

The oxidation products of dimethyl sulfide (DMS) contribute to the production and growth of cloud condensation nuclei (CCN) in the marine boundary layer. Laboratory and field measurements have demonstrated that DMS is oxidized by hydroxyl radicals (OH) forming the stable intermediate hydroperoxymethyl thioformate (HPMTF) in high yield. HPMTF is both globally ubiquitous and efficiently lost to multiphase processes in the marine atmosphere. At present, there are no experimental measurements of the products of aqueous reactions of HPMTF. Prior modeling studies have assumed that HPMTF is irreversibly lost to aqueous interfaces arresting carbonyl sulfide (OCS) and sulfur dioxide (SO2) production and forming sulfate at unit yield. Here, we use a custom-built bubbler apparatus combined with chemical ionization mass spectrometry (CIMS) for detection of gas-phase HPMTF, a commercial quantum cascade laser system for detection of OCS, and ion chromatography for measurement of condensed phase products. We show that the molar yield of OCS and sulfate (SO42–) from the hydrolysis of HPMTF is <1.2% and 122 ± 46%, respectively. The results suggest that sulfate is formed in near unit yield in the cloud processing of HPMTF, and we discuss both the chemical mechanism for sulfate formation and potential for reactive solutes to alter this reaction mechanism.