Aerial measurement of air pollutants and aerosols during 20–22 March 2001 over the East China Sea

Aerial measurement of atmospheric pollutants was carried out over the East China Sea on 20, 21, and 22 March 2001. High concentrations of not only gaseous species (maximum concentrations of SO 2 > 10 ppb and O 3 > 100 ppb in the marine boundary layer) but also particulate matter (PM) (average concentration of PM 2.5 ∼ 30 μg m −3 and PM 10 ∼ 1000 μg m −3 in the marine boundary layer) were observed on 21March. Such high concentrations were observed only at low altitude. A cold front passing over the Korean Peninsula and extension of a high‐pressure system from central China to the East China Sea were responsible for the transport of pollutants. High concentrations of pollutants were confined to lower altitude by the high‐pressure system. This result is in marked contrast to our previous observation: A highly polluted air mass was transported from central China when a low‐pressure system originating near Taiwan moved northeast to Japan along the south coast of the main islands. Anthropogenic sulfate aerosols were transported ahead of Kosa particles (fine yellow sand dust particles). A humid air mass containing a high concentration of sulfate (>20 μg m −3 ) was followed by a dry air mass containing a high concentration of calcium (>1000 μg m −3 ). Interactions between aerosol components and anthropogenic gaseous species gave insight into the formation process of aerosols over the East China Sea. Nitrate showed a good correlation with calcium except in the highly polluted air mass, indicating that gaseous nitric acid was adsorbed on the surface of coarse particles. No correlation between nitrate and ammonium supported this contention. In contrast, sulfate showed an excellent linear correlation with ammonium, indicating quick neutralization of sulfuric acid by ammonia in the polluted air mass. Exceptions were observed when the calcium concentration was >4 μg m −3 , suggesting that SO 2 gas was adsorbed on the surface of yellow sand dust particles and that oxidation took place on the surface.