Biogenic Sulphate and Sulphur Dioxide Over the North Atlantic: Spring 2003

Dimethylsulphide (DMS) is released from the ocean surface and is a function of wind speed, photo-oxidation, and phytoplankton productivity. CCN from DMS oxidation are thought to alter the global radiation budget by scattering incoming solar radiation and enhancing cloud albedo. Shipboard measurements of size-segregated and total aerosol sulphate and methanesulphonic acid (MSA) as well as sulphur dioxide from the oxidation of dimethylsulphide (DMS) were measured over the North Atlantic during the spring of 2003. These results are compared to atmospheric DMS concentrations from the same sampling program. Natural sulphur isotope abundance measurements were used to identify the contribution of DMS to sulphur dioxide concentrations since anthropogenic plus volcanogenic and biogenic isotope compositions for this gas are distinct. Unusually light isotope values were found for non sea salt sulphate in all size fractions: a result that has not been described elsewhere for the North Atlantic. These results are compared to MSA and atmospheric DMS concentrations.