Outline of the transboundary air pollutant transport in Asia is presented. The detailed sulfate transport episode in winter was outlined as a typical anthropogenic pollutant and discussed the relationship between winter monsoon pattern (synoptic weather change) and frequency of transboundary air pollutant transport. As a natural aerosol transport, recent numerical modeling activities of spring yellow sand (Kosa) is also outlined and discuss the further development of chemical weather forecasting and its feasibility.

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In Japan, the sulfur content in light oil has been reduced two times during this decade by governmental regulation, and the decrease of sulfur dioxide (SO₂) level in the ambient air has been often observed throughout Japan. In the air monitoring data for SO₂ during 1990-1999 in Nagoya City, the annual mean concentrations had gradually decreased and were found to have very good correlation with the estimated emission amount of SO₂. The gross spatial dilution volume (V_d-t) covered the whole area of Nagoya urban area was practically calculated from the correlation to be 0.48×106 km³/(326 km²· year), and the spatial dilution volume (Vd) for the unit area to be 4.03 km³/(km²·day). In addition, V_d-t and V_d for Aichiprefecture, surrounding Nagoya area, were estimated for the comparison. From the published data on SO₂ and NOR, V_d-t and V_d for other cities or regions were also calculated. The values of Vd from this and previous studies lie in the range of the 4 times and would be effected by the objective area. The relative higher V_d value would be given in the smaller area because of easy dilution by the airflow around the area. Thus, Vd can be utilized as a coefficient and an index for the estimate of the ambient concentration or the emission amount, or for the dynamics of various pollutants in the air in a certain urban area.

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Exhaust gas from vehicles contains a lot of air pollutants. Exhaust gas is regarded as a serious threat because it influences the atmospheric environment and human health around roadside areas. Therefore, it is important to carry out continuous monitoring of ambient air along roadside as well as to grasp present conditions of air pollution from exhaust gas.
Air samplers have been used for collecting suspended particulates in the air. However, this method has some problems, that is, it is difficult to make samplings at the many spots at the same time, because air samplers need power supplies.
So, we analyzed particles adsorbed on leaves of roadside trees as a convenient air monitoring method at many spots. In this study, we investigated what kinds of leaves were suitable for monitoring air pollution caused by exhaust gas from vehicles. We also investigated whether the leaves of roadside trees could be an index of air pollution.
Investigating the amount of adsorbed particles and benzo (a) pyrene (B (a) P) contents on leaves, azalea (Rhododendron mucronatum) was shown to be the most suitable tree for monitoring the atmospheric environment in Morioka City. Monthly variations in the amounts of adsorbed particles on leaves showed the same tendency as SPM concentrations using an air sampler. The measurement of adsorbed particles on azalea leaves is suggested to be an index of air pollution for several days.

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[in Japanese]

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In order to clarify the long-term variation of photochemical oxidants (O_x) over Japan, we analyzed the O_x concentrations measured at monitoring stations over Japan from 1985 to 1999 fiscal year. We found that the O_x concentration observed at 82% of all stations tended to increase during 15 years and its increase rate averaged over Japan was 0.33 ppb per year (1.1% per year). Especially, the increase of O_x concentration from 1991 to 1996, i.e. about 5ppb, was remarkably large. Furthermore, statistically significant O_x increases have been deduced all over Japan and the increases tend to be slightly large in spring and summer seasons except June. However, it must be noted that the application of an O_x analyzer with auto-washing equipment may have affected the O_x long-term variations.

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