Abstract
ABSTRACTWe observed the size distributions of mass concentration, ionic composition, and trace metal concentration in aerosols collected at an urban site in Kumamoto Prefecture (KM) and a rural site at Cape Hedo in Okinawa Prefecture (HD) between 2012 and 2015. To evaluate the contribution of transboundary nitrate and locally emitted nitrate in the aerosols at Kumamoto, we distinguished between days of transboundary air pollution from East Asia and days of local air pollution on the basis of a threshold for Pb concentration and the ratio Pb (in 0.5 < projected area diameter (Dp) < 1.0 µm)/Cu (in 2.5 < Dp < 10 µm). Fine nitrate (particulate NH4NO3) did not arrive at HD from the Asian continent even under long-range transport conditions. Fine nitrate emitted in Kumamoto and its vicinity also was not transported to HD, even in an air mass that passed over KM and reached HD within one day. Almost all fine nitrate was converted to coarse nitrate during transport by dissociation of fine nitrate and adsorption of HNO3 on larger aerosol particles. Transboundary nitrate existed largely in the particle size range of 0.5 < Dp < 10 µm, and the contribution of transboundary nitrate in the particle size range of 0.1 < Dp < 0.5 µm was about 20% even under long-range transport conditions. The contribution of transboundary nitrate in particles with Dp < 2.5 µm at KM was approximately 50%, 50%, and 80% in spring, autumn, and winter, respectively.
Highlights
Air quality is deteriorating with rapid industrial development and increases in the number of vehicles in East Asia (Deng et al, 2012)
We observed the size distributions of mass concentration, ionic composition, and trace metal concentration in aerosols collected at an urban site in Kumamoto Prefecture (KM) and a rural site at Cape Hedo in Okinawa Prefecture (HD) between 2012 and 2015
To evaluate the contribution of transboundary nitrate and locally emitted nitrate in the aerosols at Kumamoto, we distinguished between days of transboundary air pollution from East Asia and days of local air pollution on the basis of a threshold for Pb concentration and the ratio Pb (in 0.5 < projected area diameter (Dp) < 1.0 μm)/Cu
Summary
Air quality is deteriorating with rapid industrial development and increases in the number of vehicles in East Asia (Deng et al, 2012). Air masses including Asian dust export air pollutants emitted in the highly industrialized coastal areas of China (Uno et al, 2003; Itahashi et al, 2010; Hatakeyama et al, 2014). The influence of Asian dust and anthropogenic air pollutants is of concern in Western Japan, in Kyushu. Uno et al (2016) estimated that transboundary aerosols contribute 51% of the ammonium and 88% of the sulfate in aerosols in the Kyushu region. They performed a sensitivity analysis on a chemical transport model, their model could not reproduce the concentrations of nitrate in PM2.5 and could not estimate the contribution
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