Using the CMAQ modeling system, we analyzed transboundary air pollution episodes that occurred during Spring 2007, with emphasis on the temporal variations of the photochemical ozone (O₃), sulfate (nss-SO₄^2-), and its typical of meteorological conditions.
The CMAQ model simulation well explained the observed temporal variations of episodic high concentrations of O₃. We identified five episodes with high concentrations for both O₃ and sulfate in the northern Kyushu area. Among these episodes, we examined three episodes thought to be typical transboundary air pollution and examined further details. During these theree episodes, a traveling anticyclone was located in the southern East-China Sea. The polluted air mass of Asian-origin is favored to be transported by the westerly winds to Kyushu; the distribution of high concentrations of O₃ agrees well with the high-sulfate region. Backward trajectory analysis results also show that the polluted air mass was transported from the Asian-continent in about 2 days.
To investigate the contribution rate of primary air pollutants emitted from China, sensitivity analysis based on zero emissions from China was performed. Photochemical O3 and sulfate originated from China show a high correlation and slope of regression range 0.8 - 1.3 (ppbv_O₃) / (μg/m³_ nss-SO₄^2-). Results show that when the sulfate concentration is 20 μg/m³, the ozone concentration originating from Chinese emissions reaches 16 - 26 ppbv. Accounting for the inflow lateral boundary O₃ concentration of approximately 50 ppbv assigned to CMAQ, this value represents about 30-50% of high ozone concentration during focused episodes. We concluded that high ozone concentration episodes were strongly influenced by the transboundary pollution from the Asian continent.

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The effects of the regulation to incinerators for the countermeasure against dioxins and the eruption of Miyake-jima volcano on nss-Cl^- deposition in Saitama Prefecture were examined from an observation result of 1987 FY - 2007 FY (except 1999 FY when the influence of the meteorological factors to its atmospheric concentration was strong).
The nss-Cl^- deposition increased after 1987 FY, and decreased afterwards a peak in 1991 FY - 1994 FY. The number of the incinerators was remarkably decreased after 1996 FY for the countermeasure against dioxins. The nss-Cl^- deposition in 1998 FY decreased to about 40 % in 1993 FY. The relationship between nss-Cl^- deposition and dioxin concentration in air was significant, and nss-Cl^- deposition also decreased with the decrease of the dioxin concentration.
Average nss-Cl^- deposition from Miyake-jima volcano which totaled from 2000 FY to 2002 FY was 4.2 meq m^-2. The deposition flux of nss-Cl^- increased, as the distance from Miyake-jima volcano was smaller, and the deposition flux of nss-Cl^- was small at the site which existed in the northern part and in the mountainous area in the western part of the Saitama prefecture.

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In hazardous air pollutants monitoring, one week integrated sampling is a effective technique to obtain estimated annual mean values. Forty eight kinds of volatile organic carbons were studied to compare two sampling methods; one is 24- hour, the other is 1 week integrated sampling method. Monitoring was performed once a month with 24-hour method (12 data for a year) and once for 3 months with 1 week integrated method (4 data for a year). Arithmetic annual mean values calculated from 24-hour method were 1 to 1.5 times higher than those from 1 week method. On the other hand, geometric annual mean values calculated from 24-hour method well agreed with those calculated from 1 week method except a few compounds such as 1,3-dichloropropene and trichloroethylene.

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The input-output balance of nitrogen was studied in a catchment area (4.28 km²) at Mt. Awaga (elevation at the summit: 962 m a.s.l.) in the town of Aogaki, Hyogo Prefecture, Japan. Precipitation (collected using a wet-only sampler) and cloud water, as well as gas and aerosol (HNO₃(g), NH₃(g), NO₃^-(p), and NH₄⁺(p) in ambient air), were considered as agents providing input to the catchment area, while stream water was considered as an agent carrying output from the catchment area. The input amounts of nitrogen by precipitation, cloud water, HNO₃(g), NH₃(g), NO₃^-(p), and NH₄⁺(p) in ambient air were approximately 1400, 6700, 230, 160, 27, and 290 kgN, respectively, during the 7-month survey period (May - November, 1999), equivalent to 4.5, 30.2, 1.3, 0.90, 0.15, and 1.6 kgN/ha/year, respectively. However, the output amount of nitrogen by the stream water was approximately 2600 kgN for the period from April 21, 1999, to April 22, 2000, equivalent to 6.1 kgN/ha/year. The input (38.7 kgN/ha/year) was approximately 6.3 times greater than the output (6.1 kgN/ha/year). The input amount of nitrogen through nitrate was approximately 3400 kgN / 7 months, equivalent to 15.0 kgN/ha/year, while that through ammoniacal nitrogen (NHx = NH₃(g) + NH₄⁺(p)) was approximately 5300 kgN / 7 months, equivalent to 23.7 kgN/ha/year. The input through ammoniacal nitrogen was 1.6 times greater than that through nitrate. The dry deposition through HNO₃(g) was 8.7 times larger than that through NO₃^-(p), while the dry deposition through NH₃(g) was approximately two-thirds that through NH₄⁺(p).

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Fine particles (PM_2.5) and coarse particles were collected at six sites, composed with three pairs of roadside of route 17 in Saitama prefecture and ambient located within 4 km using Multi-nozzle cascade impactor (MCI) samplers. PM_2.5 concentrations with MCI sampler were 5 % higher than those with FRM sampler. Correlation coefficient of PM_2.5 concentration between at roadside and ambient was higher than that of PM_2.5-10. However, PM_2.5 concentration at ambient, especially Kisai located country side, was sometimes higher than that at roadside. It is probably caused by open burning of biomass after harvest. Sea-salt particles in PM_2.5-10 were transported to Kisai located in the distance of 55 km from Tokyo bay in summer. It was cleared that the variation of concentrations of sulfate ion at six sites were extremely similar in summer and winter, by evaluation of coefficient of variation in all sampling periods. It shows that a large -scale pollution of sulfate, for example long distance transportation from Eastern Asia or another emission sources occurs.

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There has been an increasing attention to ozone pollution in East Asia including Japan. Better understanding of factors affecting ozone pollution requires highly precise ozone measurements at ambient levels, hence domestic and international traceability networks based on well-maintained metrological standards are needed. However, national standards for ozone at ambient levels and top-down traceability system do not exist in Japan until now. Here we report stability of the Standard Reference Photometer (SRP) 35 built by National Institute of Standards and Technology, USA, and maintained by National Institute for Environmental Studies (NIES), Japan, during the past four years since installation at NIES. Detailed results from recent upgrade of the SRP35 are also described. Finally we discuss importance of establishing ozone traceability network in Japan for air quality policy.

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