| Summary: | Dimethyl sulfide (DMS) is the major sulfur species emitted from the ocean. The gas-phase oxidation of DMS by hydroxyl radicals proceeds through the stable, soluble intermediate hydroperoxymethyl thioformate (HPMTF), eventually forming carbonyl sulfide (OCS) and sulfur dioxide (SO2). Recent work has shown that HPMTF is efficiently lost to marine boundary layer (MBL) clouds, thus arresting OCS and SO2 production and their subsequent contribution to new particle formation and growth events. However, to date, no long-term field studies exist to assess the extent to which frequent cloud processing impacts the fate of HPMTF. Here we present six weeks of measurements of cloud fraction and the marine sulfur species, methanethiol, DMS, and HPMTF, made at the ARM Research Facility on Graciosa Island, Azores, Portugal. Using an observationally constrained chemical box model, we determine that cloud loss is the dominant sink of HPMTF in this region of the MBL over the six study weeks, accounting for 78-92% of HPMTF loss on average. When accounting for HPMTF uptake to clouds, we calculate a campaign average reduction in DMS-derived MBL SO2 and OCS of 46-54% and 79-93% for the study period. Using yearly measurements of site- and satellite-measured 3-dimensional cloud fraction and DMS climatology, we infer that HPMTF cloud loss is the dominant sink of HPMTF in the Eastern North Atlantic during all seasons, and occurs on timescales faster than what is currently prescribed in global chemical transport models. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research, Atmospheric System Research (ASR) under Award Number DE-SC0021985. This research used resources of the Atmospheric Radiation Measurement (ARM) User Facility, which is a DOE Office of Science User Facility, under Award Number AFC010011.
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