Atmospheric environmental problems, including fine particle matters (PM_2.5) and dispersion of radioactive materials, have generated significant public concerns over the last several years, and chemical transport models (CTM) are expected to contribute to the understanding and resolution of these problems. This review paper shows the previous studies and future directions of source apportionments and understanding of the behaviors of PM_2.5, model inter-comparison, long-term analyses of nitrogen deposition, and behavior analyses of radioactive materials using CTM.

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Source apportionments of domestic/overseas impacts on non-seasalt sulfate aerosol (nss-SO₄^2-) concentration in Japan were analyzed on the basis of tagged tracer method in regional chemical transport model. The emission source groups were categorized into anthropogenic sources from China, Korea, and Japan, and natural sources from volcanic activity. To investigate the seasonal dependency of source apportionments, the representative months of January, April, July, and October on the year of 2005 were chosen in this analysis. A distinguishable feature of this study is that source apportionments of sulfur dioxide (SO₂), which is a precursor of nss-SO₄^2-, were also investigated. Modeling system with 36 km horizontal resolution well captured the seasonal variability of both SO₂ and nss-SO₄^2-. In Japan, domestic impacts on SO₂ concentration was leading contributor (66.3% on average), however, transboundary air pollution with the contribution from China was dominant throughout seasons for nss-SO₄^2- (50.6% on average). This is because the SO₂ concentration in China was one order of magnitude greater than that in Japan, therefore, nss-SO₄^2- was chemically produced during long-range transport. During summer, SO₂ emitted from China was fully (> 95%) converted into nss-SO₄^2- and affected Japan. Impact from volcanic activity was also identified as the major contributor of nss-SO₄^2- concentration in Japan; they surpassed the anthropogenic Japanese domestic impacts during spring and autumn.

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The Chiba Prefectural government issued an alert based on the provisional standard on November 4^th, 2013, due to the possibility of the daily average of the PM_2.5 mass concentration exceeding 70 μg/m³ at the general ambient air monitoring stations located in Ichihara city, Chiba. This paper presents analytical results to investigate the possible causes of this PM_2.5 episode. From the data of air pollutants obtained at the monitoring stations, and the chemical analysis results of the PM_2.5 components, a high concentration of NH₄NO₃ was measured, which was probably due to the influence of oxidative atmospheric conditions assumed from a high concentration of Ox on November 3^rd. Also, levoglucosan, that is commonly used as the tracer of biomass burning, WSOC and Char-EC tended to exhibit high concentrations during the corresponding period, which demonstrated the high impact of biomass burning. V and Ni were the elemental components that showed relatively higher concentrations on November 4^th, which could be attributed as the effect of oil combustion sources. The prevention of air mass diffusion under the nocturnal inversion layer and high relative humidity led the PM_2.5 mass concentration change. Furthermore, the creation of wind convergence, which includes the concentrated PM_2.5 mass, and that of advection to the Ichihara district contributed to the PM_2.5 episode.

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