Influences of long-range transport on PM_2.5 in springtime in Tama area, Tokyo

Abstract

In order to investigate the influences of long-range transport on PM_2.5 in Kanto area, observations of PM_2.5 and its inorganic ions were done from 20 February to 22 April, 2010, in Tama area, Tokyo. PM_2.5 was measured by the Tapered Element Oscillating Microbalance method (TEOM) with moisture control. Daily sampling of PM_2.5 was continuously done for the chemical analysis of the inorganic ions. The mean concentration and maximum concentration of the daily means of PM_2.5 were 13 μg m^-3 and 32 μg m^-3, respectively. The ratio of the inorganic ion components in PM_2.5 averaged 49%, and SO₄^2- was highest among the ions. PM_2.5 rapidly increased on 20 March due to a large-scale Asian dust event. At the same time, the maximum concentrations of Ca²⁺ and SO₄^2- appeared, caused by the long-range transport of Asian dusts and sulfate aerosols such as ammonium sulfate. As a result of back trajectory analysis during the entire observation period, PM_2.5, SO₄^2- and NH₄⁺ in the air mass from the Asian continent were significantly higher than those in other air masses. This indicated that the increases were caused by long-range transport from the Asian continent and western Japan rather than air pollution in Tokyo. The long-range transport of NO₃^- was not significant in these observations.