The Asian region has recently shown a remarkable economic growth which leads to a significant increase in the emissions of air pollutants and greenhouse gases. As a result, the air pollution in Asia is becoming a serious problem. Therefore, urgent and effective mitigation measures to reduce these emissions are needed, which requires detailed information about the structures of the emission sources in the Asian countries. In addition, to understand the relationship between the emissions and pollution levels and to assess the effects of the mitigation measures, an analysis using atmospheric chemistry models based on accurate gridded emission data is essential. In this paper, studies about developing and improving the emission inventories in Asia were reviewed from the view points of a bottom-up approach and inverse modeling. For the studies using the bottom-up approach, the Regional Emission inventory in ASia (REAS) version 2.1 (http://www.nies.go.jp/REAS/) was introduced and based on the results of REAS 2.1, recent trends in the emissions in Asia were described. For the inverse modeling studies, comparisons of the NO_x emissions over China between the results of REAS and inverse modeling based on satellite observed NO₂ vertical column densities were discussed.

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The Intake Fraction (iF) is the ratio of the cumulative mass inhaled by the exposed population to the cumulative emission. It has been proposed as a measure that can facilitate the establishment of the measured and decision making for pollution control, but the iFs for any pollutant have not been estimated in Japan. We estimated the iF for emissions from motor vehicles traveling in each prefecture using ADMER (one of the Gaussian plume and puff formula atmospheric dispersion models called the Atmospheric Dispersion Model for Exposure and Risk Assessment developed by the National Institute of Advanced Industrial Science and Technology (AIST), Japan). The value of iF for benzene and 1,3-butadiene emitted from motor vehicles traveling in each prefecture ranged from 2.7×10^-6 to 130×10^-6 and from 1.8×10^-6 to 84×10^-6, respectively. They were higher than the iFs estimated in other countries. Our study also suggested that more sophisticated grids increase the iF values, and considering the diurnal variation in the emission and meteorology will decrease the iF values, then it will be necessary to clarify the effect of the estimation methods on the iF values.

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We analyzed the influence of the long-range trans-boundary air pollution (transport from the continent) on the long-term trends in the hazardous air pollutant 1,2-dichloroethane in the regions of Kyushu and Yamaguchi. In these regions, the long-term trends at the monitoring sites where low concentrations were observed apparently showed increasing trends from around fiscal 2004. Moreover, the trends in this region showed more increasing trends than those in other regions. Based on the monitoring data of this region categorized by backward trajectory classification, the cases of transport from the continent showed a much higher concentration level than those from other areas, and increasing trends of the concentration level in the later period. Based on these results, we concluded that the long-term trends reflected the increasing trends in the concentration level in the air masses transported from the continent. On the other hand, slightly increasing trends in the cases of transport from the background area suggested the possibility of an increase in the concentration in the troposphere. The authors considered that the long-term trends of the 1,2-dichloroethane concentration were consisted by adding the transport from the continent to base increasing concentration in the troposphere.

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In this study, we discussed the long-term trends of 17–year wet deposition data (1995–2011) in Dazaifu, Fukuoka. The annual pH average was 4.68, with a slight downward trend; however, in recent years, it remained relatively constant. pAi, based on -log (nss-SO₄^2-+NO₃^-), showed a general downward trend, but more recently trending upward, similar to pH. The annual average wet deposition of nss-SO₄^2- (nss; non-sea-salt), NO₃^-, NH₄⁺, and nss-Ca²⁺ were slightly higher than the reference values (based on the average of the acid deposition survey results by the Japan Environmental Laboratories Association). The wet deposition of nss-SO₄^2- increased from 2000 to 2008, thereafter decreasing. This trend was especially prevalent in winter and correlated well with the annual variation of the SO₂ emission in China. Trends in the wet deposition of NO₃^- were similar to annual variation of nss-SO₄^2-. However, the NO₃^-/nss-SO₄^2- ratio showed an increasing trend. Again, this was prevalent in winter. The wet deposition of NH₄⁺ showed a decreasing trend, while that of nss-Ca²⁺ showed an increase in spring. Therefore, the nss-Ca²⁺/NH₄⁺ ratio differed by more than 0.4 in spring after the mid-2000s. It is suggested that the transport of pollutants from East Asia to northern Kyushu is decreasing as indicated by the declining nss-SO₄^2- wet deposition and constant pH in recent years.

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