The estimated roadside NO₂ concentrations in 2020 at the five worst monitoring stations in Tokyo were based on the monitoring data for 2005, an emission reduction scenario for 2020, an air quality simulation for background and an NO oxidation model. It is predicted that the roadside NO₂ concentrations will decrease to an achievable level of the air quality standard by 2020. For a verification of the prediction, the concentrations in 2010 were calculated using the monitoring data for 2005 and predicted concentrations in 2020. The roadside NO₂ concentrations of the 98th percentile arranged from the lowest daily mean calculated at the stations in 2010 are higher than those of the monitoring results, which is mainly due to the overestimation of the NO₂ concentration for an urban background. The decrease in the amount of fuel oil consumption, which was not considered in the estimation, is one of the reasons for the further decrease in the urban background NO₂ concentration.

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Benzo[a]pyrene (BaP) is listed as a priority hazardous air pollutant by the Ministry of the Environment of Japan, and it exists in particle matters emitted from Japan and those transported from other countries to Japan. In order to study the transport contribution to the BaP level observed over a large city of Kyushu Island, Japan, six intensive field campaigns were conducted between 2009 and 2012. BaP associated with total suspended particles was simultaneously observed at the Fukuoka City (FC) and Fukue Island (FI) sites. The average BaP levels observed at the FC and FI sites were 220±191 pg m^-3 (n=74, n represents the number of samples) and 84±77 pg m^-3 (n=73), respectively. Observations at the FI site confirmed that most BaP molecules exist in PM_2.5. Since the FI site was remote from major emission sources, we assumed that the concentration of BaP transported from East Asian countries such as China and Japan to the Northern Kyushu area is observed at the FI site and that the sum of transported- and local-pollutant levels is observed at the FC site. These assumptions were checked using polycyclic aromatic hydrocarbon isomer ratios and meteorological data. From calculations based on these assumptions, we estimated that 47% of the BaP observed at the FC site was attributed to transport from outside the Northern Kyushu area. This is a first study based on the results of four-year observations to evaluate the transport contribution to the BaP level observed in a Japanese city with a population over one million.

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Ground-based PM_2.5 observations were compared with the space-borne observed aerosol optical depth (AOD). Decadal-scale observations at 5 sites in Japan and the observation by the U.S. embassy at Beijing in China were utilized. Measurements by MODIS onboard Terra and Aqua have been detecting AOD from space since February 2000 and July 2002, respectively. The monthly averaged PM_2.5 and AOD at each site corresponded with correlation coefficients around 0.7 both in the morning and afternoon except for Osaka and Beijing. The coverage threshold of monthly data in MODIS dataset was considered as an important factor to evaluate the correspondence of AOD with ground-based PM_2.5, especially at Beijing. When the threshold value of MODIS monthly coverage was set at 40%, the averaged correlation coefficient at 6 sites in Japan and China showed correlation coefficient of 0.63 with a statistically significance level. PM_2.5 and AOD also had a spatial correlation. As an example of application, on the basis of sound relationships between PM_2.5 and AOD, episodic events of high PM_2.5 concentrations in Beijing occurred during January 2013 were assessed, and the results indicated that a dramatic increase of PM_2.5 around Japan were not found during that episode.

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We collected dew samples on fluorine resin sheets at forest declining and non-declining sites of Mt. Gokurakuji, western Japan, and measured chemicals in these samples. The concentrations of nitrite (HNO₂ and NO₂^-), formate, PO₄^3-, NO₃^-, SO₄^2- and NH₄+ in dew samples were much higher for the declining site than those collected at the non-declining site. In contrast, Ca²⁺, Fe and Al mainly originated from soil, showed small differences between these sampling sites, and deposition amounts were greater at the non-declining site than at the declining site. Based on the concentrations of nitrite, NO₃^- and H₂O₂, we estimated OH radical photoformation rates, and found that the rates were 0.25 μM h^-1 at the declining site and 0.023 μM h^-1 at the non-declining site. These values were approximately 6 to 32 times slower than the dew waters collected from the surface of the Japanese red pine needles at the same site. The results suggested that more OH radicals were formed on the surface of pine needles and that the dry deposition which accumulated on the pine needles probably significantly enhanced the OH formation.

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