Photochemical assessment of oceanic emissions of DMS and its oxidation to sulfur dioxide based on airborne field observations

Sea-to-air dimethylsulfide (DMS) fluxes have preferentially been evaluated based on sea-air exchange models using seawater DMS concentrations. In this study, the sea-to-air DMS flux and its contribution to SO₂ levels in the marine boundary layer (MM) have been estimated using airborne field observations recorded during the first Aerosol Characterization Experiment (ACE 1). The method used to analyze the sea-to-air DMS flux and the assessment of the SO₂ yield was based on the maw balance/photochemical modeling approach (MBPCM). This study yielded DMS fluxes for the Southern Ocean that ranged from 0.4 to 7.0 μmoles/m2/day with a mean value of 2.6 ± 1.8. These flux values over the Southern Ocean were further subdivided into three regions of decreasing DMS flux: subtropical convergence zone. (40°–43°S), intermediate zone (43°–49°S), and Antarctic zone (<49°S). In addition, the DMS flux was evaluated for the tropical Pacific regions and found to range from 1.0 to 7.4 μmoles/m 2/day with a mean value of 4.2 ± 2.3. A comparison of the MBPCM method with other flux approaches (e.g., seawater DMS based air-sea exchange model and atmospheric DMS based methods) was unable to quantify any significant systematic differences between the approaches. Results from this study have clearly demonstrated that SO₂ over the Southern Ocean as well as over the tropical Pacific regions can be explained in terms of DMS oxidation.