Field observations and developments of analytical methods for aerosols in East Asia have been conducted aiming to contribute to the elucidation of the human health impact by the aerosols. In particular, studies on (1) compound-specific stable carbon isotopic analysis for polycyclic aromatic hydrocarbons (PAHs), (2) field observation of aerosols in East Asian region, (3) development of analytical method for aerosols aiming to contribute to pollution control policies in Japan, and (4) elucidation of physical and chemical characteristics of aerosols related to adverse health effects. This paper provides an overview of these studies.

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In recent years, the concentrations of precursors of ozone have been decreasing in Japan, but the ground-level ozone concentrations tend to increase. During the summertime in the Kanto region, anthropogenic emission control in Japan is an important factor for decreasing the ozone concentration. In this study, we conducted an air quality simulation using WRF and CMAQ with the anthropogenic emissions data in 2000 and 2005 to verify the effect of the emission controls between 2000 and 2005 on the ozone concentration in the Kanto region. The NO_x and VOC reductions contribute to the increase in the daytime maximum ozone in the central Tokyo surrounding area but to the decrease in the other areas of the Kanto region. For the NO_x reduction case, the daytime maximum ozone was increased in a wide area of the plains. On the other hand, The VOC reduction effectively works to decrease the ozone concentration in the entire Kanto area. Based on the results of the ozone sensitive analysis for a high concentration day, the NO_x sensitive and mixed sensitive regime account for half of the number of occurrences in inland Kanto area. Howeber, the VOC sensitive regime was the majority in the large city. These results show the effectiveness of the reduction of precursors to the decrease in the ozone concentration in each area of Kanto.

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PANs (peroxyacyl nitrates) and ONs (organic nitrates) have been being observed using a thermal dissociation/cavity attenuated phase shift spectroscopy method since December 2012 at Suzu, the Noto Peninsula. In this article, observational results and analyses for the period from December 2012 to August 2013 are described, focusing on the seasonal variations of the PANs and ONs. Both the PANs and ONs showed seasonal variations with spring maxima and summer minima. The air mass origins arriving at Suzu were classified into the following five groups: Russia, North-East China, Middle China·Korea, Japan and Sea, using backward trajectory analyses. From winter to spring, both the PANs and ONs concentrations from Middle China·Korea were higher than those from the other air mass origins. From the spring to summer, their concentrations were independent of the air mass origins. No definite diurnal variations were observed from winter to spring. Meanwhile, the diurnal variations of the PANs and ONs concentrations had daytime maximum and nighttime minimum values from the spring to summer. We concluded that the PANs and ONs concentrations from winter to spring and those from spring to summer would be governed by the long-range transport and in-situ photochemical generation, respectively.

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Based on the measurements by the Japan Meteorological Agency (JMA), in spite of the fact that the total ozone has been increasing at Sapporo, Tsukuba and Naha since the mid-1990s, the surface UV has not been decreasing. In order to understand this phenomenon, the surface UV spectroscopic data obtained by Brewer spectrophotometers at noon at Sapporo, Tsukuba and Naha were analyzed. The trends in the ratios between the UVA and UV indicies(UVA/UV)were analyzed. As a result, the ratio between the UVA index and UV index (UVA/UV) significantly increased only at Sapporo, and it showed a little change or a slight decrease at Tsukuba and Naha. Therefore, the effect of total ozone on the UV index was shown only at Sapporo. This effect was negligible or hidden by other effects at Tsukuba and Naha. To understand these results, the effects of the airmass factor and changes in the size distribution of the aerosols were discussed.

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Many studies have discussed the air monitoring network optimization methods using the observations from the networks to be optimized where the spatial representativeness of the network is assumed. Therefore, these methods are difficult to apply to the networks under development. In this study, the hybrid genetic algorithm that combines the standard GA and simulated annealing is applied to the simulated values from an air quality model instead of observations for the optimization of the developing PM_2.5 monitoring network in the Kinki region of Japan. The current network is evaluated by comparison to the optimized network. The optimized network is uniformly distributed in general and reproduces the spatial distribution of the simulated concentrations. Although the current network describes the spatial distribution in the high concentration areas, the representativeness of the concentrations of the entire area could be improved by the redistribution of some monitors to the stations monitoring other pollutants. The guideline for the placement of monitors at existing stations is proved to be generally appropriate. The optimization with the weighing factor, based on population, results in a network where more stations are distributed in the higher concentration areas.

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High summertime concentrations of ozone in the central Kanto plain, extending northward from the Tokyo metropolitan area, are prominent phenomena. The behavior of ozone precursors is an important factor dominating them, and has been studied in relation to the meteorological conditions. Ambient concentrations of NMHC, NO_x, and photochemical oxidants (Ox), and wind data, routinely measured at the air quality monitoring stations during July and August of 2000–2011, have been employed. For the screening of sea breeze days, the sunshine duration and wind data from the AMeDAS were referred to.
High Ox events, defined as a daily peak concentration over 120 ppb in the studied areas, occur with a very high probability on the sea breeze days, and are preceded by higher concentrations of the precursors, NMHC and NO_x, in a 3 h average between 06 and 09 h LT than on general days in the central Tokyo (the 23-wards area). In particular, convergence flow under calm conditions before the sea breeze develops in this area raises these precursor concentrations, and tends to induce high Ox over a wide region.
In the later six years of the studied term, however, the NMHC concentrations have been conspicuously reduced as a result of the VOC emission control, and wide high- Ox events scarcely occurred. Instead, high Ox mainly in the northern downwind areas, which tends to occur in a relatively low NMHC regime, has remained even in the later six years.

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In 2005, the study group organized by the Tokyo Metropolitan Government to plan countermeasures against photochemical oxidants (Ox) estimated the effects of the reduction in the precursors, non-methane hydrocarbons and nitrogen oxides, based on the observed relationship between the precursor and Ox concentrations during 2000–2002. The result, and the logic of the estimate is validated using the monitoring data obtained after those years. At the same time, the question, how much is the recent trend of occurrence of high levels of Ox attributed to the reduction of the precursors, is examined.
The estimate method lacks any procedure to exclude the ettect of year-to-year variations in climate, and needs to incorporate some technique to select sample days satisfying a meteorological standard, an example of which is the “sea breeze days”.
The estimate given in 2005 generally well describes the recent state of high-level Ox over the central region of the Kanto plain, meaning that the situation has been improved due to the reduction of the precursors. However, the northern part of the area still remains at high Ox levels for some structural reason.

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