Aerosol particles are serious concern for human health effects. Moreover, it is necessary to focus on not only the particle mass but also the chemical composition to characterize their toxicity. We focused on chromium whose toxicity changes depending on the oxidation state. Therefore, we carried out the chromium speciation by the X-ray absorption fine structure (XAFS) method. In this study, fine and coarse particles in the powder form were collected using cyclone at Kanagawa, Saitama and Fukuoka during the four seasons of 2017. In Kanagawa, fine particles were also collected by conventional filter sampling. The XAFS spectra of chromium in the aerosol particles and standards were then obtained. To identify the oxidation state of the chromium, the obtained XAFS spectra were applied to the linear combination fitting. The XAFS spectra obtained from pelletized samples showed a better signal/noise ratio and could be applied to the linear combination fitting. The XAFS analysis indicated that Cr (III) was the dominant oxidation state in most of all the particles. Fine particles included more Cr (III) than the coarse particles. Moreover, the aerosol particles collected in Fukuoka included about 15% more Cr (III) than those collected in the other two locations. Furthermore, a Cr (VI)-containing particle was present in one of the coarse particles.

The Community Multiscale Air Quality Model (CMAQ) was used to evaluate the impact of field biomass burning (BB) in Northeast China on the PM_2.5 transboundary heavy pollution over Northeast Asia (Northeast China in China, and Hokkaido and Tohoku regions in Japan) in early spring of 2019. The Global Fire Assimilation System (GFAS) version 1.2 for the year 2019 was used for the field BB emissions in the base line simulation (Base). Northeast China was affected by both 10℃ higher temperatures than normal which could cause early snowmelt and lead to crop field burning. In fact, unusual hot spots in Northeast China were detected by satellite and helped GFAS to estimate the heavy BB pollutants. CMAQ in the Base case reasonably reproduced the daily mean PM_2.5 mass concentrations in Northeast Asia during the evaluation period (from February to March) except for the end of February to the beginning of March when an intensive field BB occurred in Northeast China. Meanwhile, the other simulation with boosted BB sources from the cropland in Northeast China fairly captured the daily mean PM_2.5 mass concentrations in Northeast Asia during this period. These results implied that the current GFAS emission in Northeast China was underestimated and that PM_2.5 heavy pollution in the Hokkaido region, Japan, was attributed to the field BB from the cropland of Northeast China.

Green infrastructure has been considered as one of the remedies for air pollution. The positive effects of forests on air quality through deposition and uptake and air pollution abatement through aerodynamic effects of roadside trees are often studied, but the aerodynamic effect of forests has not yet been analyzed. This paper aims to investigate the transport of air pollutants in forests from an aerodynamic perspective by means of wind tunnel experiments. The porosity of the model tree was estimated to be roughly 30% from our wind tunnel experiment for a row of model trees and computational fluid dynamics simulations considering the shelterbelt drag force (Wang and Takle, 1997). The wind tunnel experimental results for a sparse forest showed a decrease in the tracer gas concentration from the windward side to the leeward side of the forest. On the other hand, there were minimum concentrations of the tracer gas in the center of a dense forest. This is because the dense forest induces a recirculation zone behind the forest and the tracer gas inflows into the forest from both the windward and leeward sides. It is deduced from turbulence statistics that the mass exchange through the canopy crown of the dense forest is lower than that of the sparse forest.

Continuous monitoring of PM_2.5 was conducted at two sites in Niigata city from 2016 to 2017. Mass concentration and chemical components including organic marker of the PM_2.5 were measured. The highest concentration of Levoglucosan which reported as biomass burning marker was observed in autumn (81.8 ng/m³). The higher ratio of Levoglucosan and Mannosan (L/M) was observed in autumn, which may be affected by both rice straw burning in Japan and open burning in northeast China. In winter, a good correlation was observed between Levoglucosan and As. This result suggests that Niigata city may be affected by transboundary air pollution from northeast China in winter because both coal and biomass fuel are mainly used for household heating in that region. PM_2.5 source apportionment was conducted by PMF (Positive Matrix Factorization) model and 11 sources were identified. As the results of the estimation of each source contributions, PM_2.5 in Niigata city was clarified to be more affected by secondary aerosols than primary aerosols.

A trend analysis of Hazardous Air Pollutants (HAPs) concentrations (21 substances) in Japan during the period from 2001 to 2015 was conducted to investigate temporal variations using monitoring data from the Ministry of the Environment of Japan. The monitoring sites were classified into three categories, i.e., general environment (I), stationary industrial region (H), and road site (E) for all over Japan and 6 regions in Japan. Most of the HAPs concentrations tended to decrease except for several species. The trend analytical value, which is described as [concentrations], was below the environmental standard or guideline values. Except for several species, the total reductions of the [concentrations] were 13‒79% for I, 19‒62% for H, 19‒74% for E. In I, the seasonal variation was categorized as three types; i.e., higher values in the winter/spring seasons resulting from the high contributions of transboundary transport from Northeast Asia, higher values in the summer due to a higher contribution from domestic sources, and the mixed type. The difference in the [concentrations] among the region was greater in the first half of the 2000s and these differences began to decrease in the 2010s. The [Concentrations] of the HAPs in H and E were 1‒3 and 0.9‒1.5 times greater than those in I, respectively.

We investigated the volatile organic compounds in the Tokyo Bay area for the purpose of estimating the source areas of aromatics and alkenes that significantly affect the photochemical reaction in the southern Kanto region. As a result of comparing the distance-weighted emissions by the PRTR data and the concentration ratio of the volatile organic compounds, both data were in good agreement. These results indicated that the concentrations and concentration ratios of the volatile organic compounds were influenced by the nearby sources and wind directions in the Tokyo Bay area. The wind directions with the highest alkene concentration ratio at each point were consistent with the 1,3-butadiene source region. The sources of the 1,3-butadiene exist in the coastal areas of Kawasaki and Ichihara. It was suggested that major alkenes, such as ethylene and propylene, were also emitted from the same area.