Rapid cloud removal of dimethyl sulfide oxidation products short circuits new particle formation in the marine boundary layer

Abstract:

Oceans emit large quantities of dimethyl sulfide (DMS) to the marine atmosphere. The atmospheric oxidation of DMS results in the production and growth of cloud condensation nuclei (CCN) with consequent effects on Earth’s radiation balance. Quantitative assessment of the impact of DMS emissions on CCN concentrations necessitates a detailed description of the oxidation of DMS in the presence of aerosol and clouds. The DMS oxidation pathway affects oxidative loading and sulfate aerosol formation. Current literature reports a wide range of sulfur dioxide (SO₂) yields (31 – 98%) from DMS oxidation.Recent observations have demonstrated that in the pristine marine atmosphere, DMS is efficiently oxidized to hydroperoxymethyl thioformate (HPMTF), a stable intermediate in the chemical trajectory towards SO₂ and ultimately sulfate aerosol. Using direct airborne flux measurements, we demonstrate that irreversible loss of HPMTF to clouds in the marine boundary layer dominates HPMTF loss rates (t_HPMTF < 2 hours) and terminates DMS oxidation and CCN production in the cloudy marine boundary layer. New laboratory kinetic studies show the lifetime of HPMTF to oxidation by OH is on the order of 1 day, which is comparable to dry deposition and which together are the primary loss terms in clear-sky conditions. Globally, we show that the inclusion of HPMTF chemistry and subsequent cloud processing reduces the fraction of DMS oxidized to sulfate aerosol and more generally, we describe a quantitative approach for assessing the role of clouds in disrupting the connection between volatile emissions, oxidative cycling, and aerosol production that is likely applicable to continental regions.