Impact of long-range transport of aerosols on the PM_2.5 composition at a major metropolitan area in the northern Kyushu area of Japan

In view of the recent rapid economic growth and accompanying energy consumption in the East Asian region, particularly in China, there is much concern about the effects of emitted particulate pollutants on human health. We have thus investigated the impact of long-range transport of aerosols on urban air quality in the upwind areas of Japan by comparing the PM_2.5 composition collected for multiple years in Fukuoka, a representative metropolis in the Kyushu area, and in Fukue Island, located 190km southwest of Fukuoka. Daily averaged PM_2.5 concentrations in Fukuoka and Fukue were almost identical. PM_2.5 concentrations at these sites were dominated by sulfate and particulate organics, and their fluctuation patterns were similar except for organics in the warm season. In contrast, those of nitrate and elemental carbon differed substantially between the sites. In addition, the ratios of Pb/Zn and Cd/Pb in Fukuoka were close to the reported values in Beijing. Non-sea-salt sulfate concentration in Fukuoka measured in this study and reported in the past measurements apparently coincided with the decadal SO₂ emission change in China reported in a recent emission inventory. Therefore, we conclude that even in a city as large as Fukuoka, the PM_2.5 concentration in the northern part of the Kyushu area is primarily dominated by the inflow of long-range transported aerosols throughout the year, except in the summer, rather than local air pollution emitted at each site.