The wet and dry deposition of gaseous and particulate substances in East Asia was presented. The Japanese Archipelago was divided into fifteen climatic regions with 114 mesh grids, and the annual and seasonal average concentrations of major chemical substances were estimated. Wet deposition fluxes were determined from CRIEPI's regional monitoring data over East Asia. Dry deposition fluxes were calculated as the product of the estimated deposition velocities and atmospheric concentrations of gaseous and particulate substances. Man-made emission fluxes were estimated from the preliminary inventory for East Asia by CRIEPI. The volcanic emission fluxes were estimated by combining available spectroscopic measurements data with the empirical volcanic classification.
On the basis of the data collected between October 1987 and September 1996, we analyzed (i) wet and dry depositions of major chemical substances;(ii) seasonal variation and long-term trends of chemical composition;(iii) atmospheric sulfur budget over the Japanese Archipelago; and (iv) role of volcanoes on the quality of air and precipitation. In this paper, I describe the design of CRIEPI's monitoring network, meteorological and geological factors affecting the chemical composition of precipitation, and the present status of acidic deposition in East Asia.

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The toxicity of polycyclic aromatic hydrocarbons (PAHs) as well as dioxins occurs by binding to arylhydrocarbon receptor (AhR) is well known. Biological reactions concerning carcinogenicity and the aspects of involvement of both materials were outlined based on this AhR-dependent mechanism. Besides, methodological approaches for evaluating health risk of PAH mixture coming out until now were summarized. Among these, an approach (Relative Potency Factor Approach), which evaluates it by adding up the individual toxicities of PAHs as already used in health assessment of dioxins, was outlined, and in addition, a health risk assessment technique (Induced Mutagenesis Method) which the authors developed based on the mechanism concerning carcinogenicity is described in detail.

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A prototype dust sampler with a changeable inlet diameter nozzle for measuring dust concentrations was developed with the objective of implementing a new method for isokinetic sampling of particulates contained in exhaust gases. This sampling method is based on both the isokinetic samplingby changing the nozzle diameter and a constant flow rate of sampling gas even when the flow of exhaustgases varies during sample collection. Experiments to assess the applicability and reliability of the new dust sampler were carried out, and the results can be summarized as follows:
1. The dimensions for the changeable nozzle diameter type dust sampler (nozzle head section) investigated here were approximately 6 cm in external diameter and 12 cm in length, making it possible to use this as a Type 1 dust sampler.
2. By turning the operation valve, the diameter of the suction nozzle could be adjusted easily in the range of φ5.0-φ11.0mm.
3. As the nozzle head section is made of aluminum, the maximum allowable temperature for the changeable nozzle diameter type dust sampler is approximately 200°C. The surface was covered with a Tafram oxide film, and good corrosion resistance could be verified at the actual combustion temperature of the exhaust gases.
4. A small leakage was detected at the thin seams of the changeable inlet diameter nozzle when it was used in funnel form. However, there was no effect on the measurement with the suction nozzle in its normal open shape.
5. A comparative study using test powder and actual combustion dust shows the changeable nozzle diameter type dust sampler and the regular type (ordinary and balanced type dust sampler) maintained a good equivalent relationship of approximately 1: 1, confirming the applicability of the isokinetic sampling method.

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In order to research the influence on the Japanese Islands of the volcanic gas emitted from Miyakejima volcano that was reactivated in August of 2000, analyses on atmospheric sulfur compounds were conducted using the data monitored in 10 monitoring sites of the National Acid Deposition Monitoring Network. The 10 sites are located in remote or rural areas in Japan. The target period was set for 2 years from August 1999 to July 2001 including one year before the eruption and one year after the eruption. Deposition velocities were calculated using a resistance model based on Wesely's parameterization to estimate the dry depositions.
Increases of SO₂ concentrations caused by the emission of the volcanic gas correlated with frequencies of air inflows from Miyakejima, and the increase was marked primarily in central Japan, and secondarily in western Japan. Since there is little air inflow to the Hokkaido area, no clear increases of SO₂ concentration in the area were observed, compared with central and western Japan. SO₂ dry deposition at Tanzawa, Happo and Sado-seki located in central Japan increased 3 or more times, in particular 6 or more times at Tanzawa, after the eruption. Concerning wet deposition of nss-sulfate, there were also marked increases in central Japan. Wet deposition of nss-sulfate at Tanzawa, Happo and Sado-seki increased 1.5 or more times after the eruption. The relation between increments of dry/wet deposition and distances from Miyakejima at the 3 sites indicated that the influence on wet deposition distributed to a wider area than that of the dry deposition. A series of monthly-accumulated sulfur depositions indicated that the influence on an area near Miyakejima appeared to be marked for several months after the eruption because of the initial huge SO₂ emission, while the continuously high SO₂ emissions for a year after the eruption produced higher rates of increases in a wide area and over a long period of time.

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Photochemical ozone transported from Tokyo metropolitan area is pointed out to be one of the important causes for the forest decline observed in the Oku-Nikko mountainous area. Therefore, it is necessary to monitor ozone in the mountains of Oku-Nikko. However, long term observation of ozone in the Oku-Nikko area has been quite limited due to lack of electric power supply. In the work reported here we set up an ozone monitor near the top of Mt. Mae-Shirane in Oku-Nikko. Twenty Ni-Cd batteries were set for electric power supply, and 20 solar panels were also set to charge those Ni-Cd batteries during day time. On the basis of three months observation of ozone we could analyze the long term variation of ozone there. The highest concentration in summer was-70 ppb. High concentrations of ozone were recorded in the evening in summer when polluted air mass was transported from the Kanto Plane. High concentration of ozone appeared when the south wind prevailed and solar radiation was strong. On the other hand, in autumn, ozone was very constant around 40 ppb. No significant diurnal variation was observed. The influence of free troposphere was suggested in autumn. The air mass came from the west after passing over the Sea of Japan. It is indicated that the air mass containing Asian background ozone had reached this area in that season.

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