We have observed the acid fog on Mt. Oyama in the Tanzawa Mountains since 1988 using active and passive fog samplers. The concentrations of the fog-water components significantly differ in each event due to their many dominating factors, which are air pollution, liquid water content, scavenging effect of canopies, wind, and rain. Frequently observed acid fog is caused by nitric acid, which is formed by the oxidation of nitrogen dioxide advected from the Kanto Plain. The fir and beech trees are declining in the forest where acid fog frequently occurs. We have investigated the exposure experiment involving the seedlings of fir and beech, and clarified the mechanism of the direct effect of acid fog on the seedlings. We have also investigated dew-water chemistry, gases of not only strong acids but also weak acids are absorbed in the dew-water, and severely contaminated dew-water is frequently observed in Yokohama.

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In Japan, the increasing automobile traffic has caused considerable increases in the levels of nitrogen dioxide and suspended particulate matter primarily derived from automobile exhausts in urban areas. In the districts adjacent to trunk roads, the potential effect of these concentrations on the health of residents is a matter of concern. Our epidemiological study in Chiba Prefecture showed that the prevalence and the incidence of asthma were significantly higher among school children who lived in the roadside areas than among school children in the other areas, even after adjustment for potential confounding factors such as the history of allergic diseases. A large-scale cohort study by the Japanese Ministry of the Environment (the SORA project) has also shown the significant relationship between the incidence of asthma in school children and elemental carbon levels, which have been estimated to evaluate exposure to traffic-related air pollution. Regarding the health effects of fine particulate matter (PM_2.5), a short-term exposure to considerably low concentrations of PM_2.5 was associated with a decrease in the pulmonary function and occurrence of wheezing among asthmatic children. In order to clarify the health effects of air pollution including PM_2.5, interdisciplinary approaches should be further conducted.

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Ambient ozone and secondary aerosol components are formed via complex and nonlinear photochemical reactions. A three-dimensional regional air quality simulation, which combines a three-dimensional chemical transport model, a three-dimensional meteorology model, and a precursor emission inventory, is useful to consider effective strategies to reduce them. We have developed simulations for Japan, China, and India, and also over the entire South and East Asian countries. They have been applied to various analyses which aim at developing effective strategies. However, the performance of the current simulations on pollutant concentrations is not sufficient. Several issues remain regarding the emission inventory and models. It is expected that the simulations contribute to developing effective strategies to mitigate loads on the atmospheric environment including not only air pollution, but also climate change while remaining issues in the simulations are solved.

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Airborne particles with diameters less than 2.5 μm (PM_2.5) and particles with diameters less than 50 nm (nanoparticles) has been of great concern because of their potential adverse effects on humans. Therefore, effective countermeasures are needed based on their sources and atmospheric behavior. To this end, information about the particulate chemical composition is useful. However, the sample amount of nanoparticles is usually very small so sensitive analytical methods need to be developed for their analysis. For the organic analysis of particles, the solvent extraction method has been generally used but the method is difficult to detect compounds from a small amount of nanoparticles. Therefore, a significant sensitivity improvement was needed by total volume injection using the thermal desorption technique. In this manuscript, the development history and the applications to nanoparticles by thermal desorption–gas chromatography/mass spectrometry (TD–GC/MS), that we have been studying, were reviewed. In this review, vehicle exhaust nanoparticles were introduced and the following issues were described: TD–GC/MS features, limitations, optimization of analytical condition, advancement by such as GC×GC, and applications to nanoparticles. The sources and behavior of the nanoparticles based on the TD–GC/MS results were also reviewed. Studies on the sources and behavior of fine particles were also briefly explained.

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The appearance of a high concentration area of the photochemical oxidant (Ox) over the Kanto Plain was evaluated in terms of the sea breeze system. The sea breeze days, in a which southerly wind developed in the southern Kanto Plain, were selected during July–August of 1990–2011. A principal component analysis was used to explain the distribution of the daily maximum Ox concentration. The sea breeze days were classified as Type 1 and Type 2, wherein the area of the high Ox concentration developed in the northern and southern regions, respectively. The inland penetration of the sea breeze from Sagami Bay and Tokyo Bay of the Type 1 occurred earlier than that of Type 2. The easterly wind suggested to have originated from Kashimanada developed in the northeast region of Type 2. The high Ox concentration area was located in front of the sea breeze front that was supplied with Ox by the upper air in both types. The Ox advection was negative when the sea breeze front passed. The time of the daily maximum inland Ox concentration tended to be later than that in the southern region for both types. These results indicated that the daily maximum Ox concentration is influenced by the speed of the inland penetration of the sea breeze.

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The summer observational campaign of gaseous elemental mercury (GEM) in the ambient air was performed at the top of Mt. Fuji (3776 m a.s.l.), which is located in the free troposphere, from July 14 to 20 and August 22 to 25, 2014, to clarify the background concentration of GEM and the influence of the long-range transport from East Asia to Japan. We also observed GEM at the southeastern foot of Mt. Fuji (1284 m a.s.l.), Shinjuku (urban site), and Kazo (suburban site). The mean GEM concentration in the daytime was 10.1±7.70 ng/m³ (n=19) at the foot of Mt. Fuji, 3.67±0.744 ng/m³ (n=9) at the top of Mt. Fuji, 2.53±0.895 ng/m³ (n=8) in Shinjuku, and 2.50±0.245 ng/m³ (n=5) in Kazo in the order of decreasing concentration. On the other hand, there were little differences in the GEM concentration in the nighttime between sites, namely 2.58±0.360 ng/m³ (n=11) in Shinjuku, 2.38±0.521 ng/m³ (n=9) at the top of Mt. Fuji, 2.37±0.281 ng/m³ (n=6) in Kazo, and 2.13±1.88 ng/m³ (n=14) at the foot of Mt. Fuji. The GEM concentration clearly showed a day-night variation both at the top and the foot of Mt. Fuji. At the foot of Mt. Fuji, it increased in the daytime along with the air temperature, indicating its evaporation from the local surface soil. The backward trajectory analysis showed that the frequencies of the air mass transported from the Asian continent to the top of Mt. Fuji was higher in July than in August, suggesting that the GEM concentration was strongly affected by the pathway of the air mass at the top of Mt. Fuji.

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Continuous monitoring of the PM_2.5 stared in 2009 in each area of Japan. We can obtain much data from any of the sampling points, but these averages cannot express the characteristics of the points. Therefore, this paper presents a Bayesian hierarchical CAR model for analysis of PM_2.5 daily data. This model is based on the estimated monthly average, effect of area and effect of the measurement point. The effect of area is highest around the Port of Nagoya and Owari region, lowest in the Mikawa region and Gifu. The effect of the sampling point is clarified and compared to that of the area. These effects compared to Local Moran's I and CPF values, and the consistency has been confirmed. The greatest product of effect of the point and area is 1.50, and smallest is 0.67. Although some of the measurement data is out of the 95% credible interval, this is often caused by aberrant measurements or lack of data.

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Airborne particulates were collected in Noge and Kudan, Japan, in the summer and winter from 2006 to 2013 and in Tsukuba, Japan, in the summer and winter from 2010 to 2013. The polycyclic aromatic hydrocarbons (PAHs) and nitropolycyclic aromatic hydrocarbons (NPAHs) were determined by HPLC with fluorescence and chemiluminescence detections, respectively. The decreasing tendencies of the total concentrations of nine PAHs were observed at Noge and Kudan in the winter from 2006 to 2008. The decreasing tendencies of the total concentrations of three NPAHs were observed in both the summer and winter in Noge from 2006 to 2011. The decreasing tendencies of the NPAH concentrations were also observed in Kudan in the winter from 2006 to 2011 and in the summer from 2007 to 2009. The concentration ratio of 1-nitropyrene to pyrene also decreased in Noge and Kudan. As the main reason for the decrease in the urban atmospheric PAH and NPAH concentrations, the Japanese regulation of exhaust gas/particulates from automobiles was considered.

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The routine monitoring data for the hourly PM_2.5 mass concentration in the 2011 fiscal year in Japan was analyzed to evaluate the precision. The appearance of negative data and the first-order self-correlation at a total of 115 sites were examined. Five types of FRM-equivalent monitors with different internal configuration were operated in 2011. The negative values were frequently observed in the data from all types of monitors. Certain types of monitors tended to output more negative value than others, besides, the first-order self-correlation coefficients were lower for the data from such monitors. These results suggested that the precision for hourly PM_2.5 mass concentration might significantly differ by the type of monitors. Thus implied difference in the precision seemed not affect on the prediction and caution for the daily PM_2.5 guideline concentration (70 μg/m³), seemingly because of the highly variable PM_2.5 concentration.

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