Source apportionments of PM_2.5 in Japan on 2010 fiscal year were evaluated based on the air quality model by applying the tagged tracer method. Source groups were divided into the total of 15; 10 domestic anthropogenic source, 3 foreign anthropogenic sources from China, Korea, and other regions, and ships and natural sources. The performances of the air quality model were validated through statistical analysis. Annual mean source apportionments averaged over Japan was the largest with 3.60 μg/m³ (33.9% as relative percentages) from domestic anthropogenic source and the second largest with 3.10 μg/m³ (29.2%) from anthropogenic emissions of China. Domestic source had the impacts in the following order; vehicle (7.4%), manufacturing industry (7.0%), livestock (5.5%), rest of domestic sources (5.4%), fertilization (2.8%), and power plant, machines, business boilers, waste incinerator (approximately 1–2%). From the viewpoint of long- and short-term standards, source apportionments were further evaluated for attainment and non-attainment sites. The results showed that the dominant influence of the transboundary air pollution over the Kyushu region especially for short-term standard. Over the Setouchi region, the impacts from manufacturing industry and ships were large. The attribution from vehicle was also important in the Kinki region. In the Kanto region, both of vehicle and manufacturing industry attributions were important for short-term standard, but vehicle was more significant source for long-term standard.

The chemical composition of the Asian mineral dusts (kosa aerosols) will reflect the mineral composition of the surface soil from which they originate, as well as any subsequent reactions with anthropogenic material occurring during transport. This study was undertaken to identify suitable indicator elements for distinguishing kosa aerosols from mixtures of kosa and materials of other origin, and to investigate the mixing of kosa and anthropogenic substances in the air-mass during transport. Sixteen samples of significant kosa aerosols, minimally contaminated by kosa aerosols of different origin and containing approximately 200 μg/m³, were collected during an 11 year period starting in 2001. A backward trajectory analysis of the air masses associated with kosa events showed that, in all but two cases, they corresponded to sandstorm areas reported by the meteorological observatory. The concentrations of 15 elements, namely, Al, Ba, Ca, Cr, Fe, K, La, Mg, Mn, Na, Ni, P, Sr, Ti and V showed good correlations (r>0.7) with aerosol mass concentrations, resulting from crustal origin of these elements. The relative standard deviation (RSD) of the concentration ratios of Ba, Fe and Mn to the concentration of Al in all 16 samples was small (<10%) indicating that the proportions of these elements differed little in the sample from several different sources. In contrast, the concentrations of SO₄^2-, NO₃^-, Zn and Pb showed no correlation with the aerosol mass concentration, but showed good correlations (r>0.7 in each case) with each other. The concentrations of SO₄^2-, NO₃^-, Pb and Zn in one sample with low concentrations of these chemical species showed a correlation with the minimum height of the air mass estimated by a backward trajectory analysis to have passed over Chinese coastal industrial areas.

Comprehensive regulations to reduce the emissions of volatile organic compounds (VOCs), important O₃ precursors, were introduced in Japan in 2006. Analyses of the effect of the VOC reduction on high concentrations of O₃ have been required. Here, in the first place, we briefly review recently reported data analyses and model simulations relevant to the changes in the VOC and high O₃ concentrations. The O₃ level appears to be reduced, but it does not necessarily prove to be a direct result of the VOC reduction. Therefore, we propose a direct comparison of the change in the O₃ behavior in a group of days with high O₃ events before 2006 and another group of days after 2007 with very similar meteorological patterns to the former group. The result of the analysis for the Tokyo Metropolitan Area and its northern inland shows that, in the case of early sea breeze inflow to the inland area, the O₃ increase in the coastal urban area has become milder and that in the inland areas has not changed. Furthermore, for the late sea breeze, the situations of the O₃ increase have not clearly changed in any areas. If chemical transport models are utilized for an evaluation or an assessment of regulations such as VOC control, results of this kind of data analyses should be taken into consideration for productibility of the meteorological conditions and response to those changes.

Nitrogen dioxide (NO₂) observations have been made using car Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) in Fukuoka, an urban area in Japan, to clarify the spatiotemporal inhomogeneity in NO₂. We developed instruments for Car MAX-DOAS, and NO₂ measurements were conducted on 15 August 2015 and 30 November 2015 on the Fukuoka Urban Expressway, along the closed circular route. For both days, in the morning, the maxima were observed around the city center (in the northeast part of the circular route), whereas in the afternoon, the maxima were observed in the south/southeast part of the circular route (to the south/southeast of the city center). Analysis of the surface wind field indicates that the NO₂ inhomogeneity is strongly related to the inhomogeneity of NO_x sources and to horizontal transport of high concentrations from the city center and low concentrations from the ocean via a land-sea breeze.