Seawater, atmospheric dimethylsulfide and aerosol ions in the Pearl River Estuary and the adjacent northern South China Sea

The spatial and temporal distribution of dimethylsulfide (DMS) was investigated in surface seawater and in the marine atmosphere in the Pearl River Estuary and northern South China Sea during three cruises in July 2000, May 2001 and November 2002. Sea-to-air fluxes of DMS were subsequently estimated based upon seawater DMS concentration, temperature of surface seawater and wind speed over sea. The seawater DMS concentration of the three cruises ranged from 0.1 to 52.7 nmol l−1 (n=76). DMS concentrations showed remarkable spatial and temporal distributions and highest values were observed at the mouth of the Pearl River Estuary. Throughout the study area we observed high levels of DMS in the water with great sea-to-air flux and relatively low levels of atmospheric DMS (1.70±1.16 nmol m−3 in May 2001 and 2.25±0.38 nmol m−3 in November 2002). Aerosol components, potentially linked with DMS oxidation, were also measured. The atmospheric concentrations of nss-sulfate and nitrate were much higher in the Pearl River Estuary than in the offshore area, with mean values of 12.11 and 4.45 μg m−3 for nss-sulfate, 4.88 and 2.21 μg m−3 for nitrate. Aerosol mass and components' concentrations decreased from the inner estuary to outer waters. High concentrations of nss-sulfate and nitrate in sea salt particles imply that oxidation of atmospheric DMS is related with anthropogenic sources and heavy ozone, NOx and SO2 pollution in the study area.