Atmospheric DMS and its role in new aerosol formation

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Dimethylsulphide (DMS) oxidation and its role in generating new aerosols that have the potential to influence cloud formation, persistence and albedo is a key area of study for climate research. This is particularly true in the Arctic and at high latitudes as the surface oceans that ultimately generate atmospheric DMS are expected to experience more temperature variation than at the equator due to radiative forcing. Higher DMS gradients in ocean surface waters as a result of changing in surface water temperatures are generally expected to increase DMS mixing ratios in the atmosphere but the dynamics of sea-air exchange are also factors that need to be considered. Sea-air exchange of DMS typically increases with sea surface roughness and is expressed as an empirical function of wind speed and sea surface temperature. However, ocean surface characteristics not related to roughness are postulated to promote sea-air exchange for compounds participating in new aerosol formation in the Arctic (Leck and Bigg, 2005). Many studies use DMS measurements in surface waters to estimate DMS flux and a fixed branching ratio for methanesulphonic acid (MSA) to biogenic sulphate to assess the impact of DMS aerosol sulphate formation on cloud condensation nuclei (CCN). New research shows such estimates may grossly under-represent sea to air DMS flux, and/or the DMS oxidation pathways forming sulphur dioxide and sulphate are underestimated at mid to high latitudes particularly during spring and summer. In this study, the isotope characteristics of sulphate aerosols, sulphur dioxide, and MSA, products of DMS oxidation will be used to assess regional scale DMS flux and DMS oxidation pathways in the Arctic and over the North Pacific. Trends in DMS oxidation will be assessed through a series of collaborative and independent field studies to provide quantitative estimates of DMS lifetime, its oxidation pathways, and its potential for forming new aerosol sulphate.