Impacts of Hydroperoxymethyl Thioformate on the Global Marine Sulfur Budget

Hydroperoxymethyl thioformate (HPMTF) is a newly identified major oxidation product of dimethyl sulfide (DMS). It is speculated that it could act as a major reservoir of marine sulfur, but its fate in the atmosphere is currently unknown. In this study, we have investigated the formation of HPMTF through the oxidation of DMS by OH, NO3 and Cl radicals and its losses through photolysis, OH oxidation, dry deposition, and wet deposition using the global 3-dimensional chemical transport model, STOCHEM-CRI. The model results suggest that the distribution of loss processes for HPMTF are photolysis (46%) and wet deposition (31%) with additional contributions from dry deposition (13%) and OH oxidation (10%). The global burden and the tropospheric lifetime of HPMTF are found to be 0.052 Tg and 0.5 days, respectively. The model integrations agree well with both aircraft derived measurements of HPMTF over the ocean surface between 80 degrees N and 85 degrees S latitudes and ground-based measurements made in the central Amazon. These ground-based data reveal a clear diurnal cycle with a maximum during midday, consistent with other recently reported data and possibly due to the dominance of the photochemical production rather than the photolytic loss. Accounting for HPMTF chemistry results in a significant decrease in boundary layer levels of SO2 and H2SO4 but increases in sulfate aerosol in the upper troposphere. We suggest that these changes could have important consequences on preindustrial to present-day radiative forcing from sulfate aerosol.