Geographic and temporal variations of sulfate aerosols over the Pacific Ocean

To investigate the life cycle of marine sulfate aerosols,chemicophysical characteristics of marine aerosolswere measured during five cruises in the Pacific Ocean.Dimethyl sulfide concentrations in seawater and in the air were also measured.The geographic variation of sulfate-aerosol concentrations was studied in relation to biogenic and anthropogenic sources,transport with air trajectories,and chemical transformations in the atmosphere.The highest concentrations were found near Asian and American ports,indicating anthropogenic pollution is the major sulfate aerosols source.Higher concentrations were observed in the upwelling regions than in the oligotrophic areas.Along the coastal regions,both mass and number concentrations of sulfate aerosols depended on wind direction and wind speed,and land-breeze and sea-breeze oscillations; no clear diurnal variation was detected.In pelagic areas,along the equator,the concentrations of small sulfate particles showed a maximum in the afternoon and the minimum at night.