Seasonal characteristics of organic and inorganic species and their size distributions in atmospheric aerosols over the Northwest Pacific Ocean

In order to investigate the chemical properties of marine aerosols and the long-distance transport of continental aerosols to remote oceanic regions, simultaneous measurements of chemical compounds in atmospheric aerosols, cloud condensation nuclei (CCN) and associated species were conducted from December 1994 to January 1997 at Hahajima, the Ogasawara Islands, in the northwest Pacific Ocean, being located on the lee of the large east Asian polluted region. Clear change of air quality, caused by air mass alternation, are found. Concentrations of CCN and aerosol chemical species, such as non-sea-salt sulfate, nitrate, and oxalate, are low under the marine background conditions, whereas largely increased under the continentally affected conditions. It is ascertained that long-distance transport of these species to the remote ocean continues during half-year periods. Seasonal characteristics and size distributions of particulate organic acids, previously not well understood in earlier studies, are clarified. It is found that formate and acetate could have marine biogenic sources, mostly existing as coarse particles, whereas the oxalate was influenced by continental anthropogenic activity, displaying a relative predominance in the accumulation mode.