Dimethylsulfide (DMS), sulfur dioxide (SO2), dimethylesulfoxide (DMSO), sulfate (SO2-4) and methanesulfonate (MSA) were measured at a coastal site, Pointe de Penmarc’h, over a 25 day period during May and June 1993. Measurements were also performed to estimate the DMS flux from the algal beds around the Penmarc’h lighthouse and from the surrounding sea water. Similar atmospheric measurements were conducted at a second site approximately 2 km inland from Penmarc’h. A comparison between the 2 sites indicates similar patterns of DMS concentration at each site, with values at the inland site being generally 10–15% lower. The concentrations of the aerosol phase products such as methanesulfonic acid and sulfate are examined in the light of air mass origins. The fraction of nss SO2-4 produced from biogenic sources is estimated to be less than 25%. The yield of MSA and DMSO from DMS oxidation are assessed from their relative concentrations and estimates of their atmospheric lifetime.