Since 1982, I have been investigating the effects of gaseous air pollutants such as ozone and acid deposition on plants with my supervisors, colleagues and students at Faculty of Agriculture, Tokyo University of Agriculture and Technology. In this memorial review of the prize from the Japan Society for Atmospheric Environment, I summarized the results obtained from experimental studies on the effects of ozone, simulated acid rain, soil acidification due to acid deposition, aluminum (Al) and manganese (Mn), singly and in combination, on growth, physiological functions such as photosynthesis and nutrient status of Japanese crop plants and forest tree species.

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The importance of global environmental problem such as global warming and acid rain as well as local air pollution problem has been recognized worldwide, especially over the last decade. Atmospheric aerosols, especially smaller particles less than 2.5μm (PM2.5) have a key role in those environmental problems. Information on the characteristics of aerosols is essential to understanding their behavior in the atmosphere and the resulting effect on the environment. In this paper, the present state and future assignments of air pollution by aerosols are reviewed and the meaning of innovation of PM2.5 is discussed.

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This paper describes the results of highly time-resolved measurement of Suspended Particulate Matter (SPM) conducted at five sites in the Kanto Plain, Japan, during the early-winter severe pollution episode in 1994. 2-hour averaged SPM samples were collected during the period of December 23-25, when the areal mean SPM concentration in the Kanto Plain was highest in fiscal year 1994. The sum of carbonaceous species (elemental carbon: EC, organic carbon: OC) and inorganic ionic species (Cl^-, NO₃^-, NH₄⁺, and SO₄^2-) accounted for most of the SPM mass concentrations except during the period of high relative humidity. Carbonaceous species contributed to about 50% of SPM mass concentrations. Major ionic species of CI^-, NO₃^-, and NH₄⁺were in the form of NH₄Cl and NH₄NO₃produced from gas-particle equilibrium reactions. In the central and western part of the Plain, the production of NH₄Cl and NH₄NO₃appeared to be controlled by the supply of NH₃. While in the northeastern part of the Plain the supply of HCl and HNO₃ may be the controlling factor in producing these particles.
The contribution of water, another major component of SPM, to the measured concentration by automated SPM monitors (β-ray absorption type) was investigated by operating two SPM monitors simultaneously, one of which was equipped with an aerosol drying tube at the air inlet. Readings from the SPM monitor equipped with the drying tube were systematically lower than those equipped with a dummy tube by up to 20%. To account for the water content in the measured SPM concentrations at the ambient air quality monitoring stations, the applicability of an aerosol swelling model based on Winkler's experimental formula was further examined.

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Three kinds of fallen leaves (keyaki: zelkova serrata, sudazii: castanopsis cuspidata, shirakashi: quercus myrsinaefolia) were incinerated using a domestic incinerator and formation factors were investigated.
Although dioxins concentrations in flue gas of zelkova leaves were high (TEQ value) compared with sudazii and shirakashi, dioxins concentrations in leaves, flue gas, and bottom ash showed little difference among the three kinds of leaves. It is thought that the high dioxins concentrations in flue gas of zelkova leaves are influenced by the chlorine contents in leaves. The chlorine contents of 14 kinds of leaves were investigated at parks and streets in Tokyo. It was shown that the chlorine contents in zelkova leaves were the heighest.
The equation
Y=308X^1.3 (R²=0.9485n=12)
demonstrated the relationship between dioxins concentrations (Y: ng-TEQ/m3N) in flue gas and the chlorine ratio (X:%) in combustible materials. From the equation, dioxins concentrations in flue gas increased 20 times when the ratio of chlorine contents (%) increased 10 times.
Flue gas of zelkova leaves with high chlorine contents contained many low-chlorinated-dioxins.

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The atmospheric concentrations of six polycyclic aromatic hydrocarbons (PAHs) whose carcinogenic activities have been shown by the WHO and determination method shown by U.S.EPA were measured. The PAHs were collected for 24 hours at three sites of a large intersection, a residential area and a mountain area. Temporal variation of the PAHs concentrations and composition ratios of the PAHs were analysed.
The PAHs concentrations in air at the intersection and the residential area were varied between 8-20 fold and 20-50 fold in a week, respectively, and 60-90 fold in a year. Therefore, the mean exposure concentration to residents can not be grasped correctly by measurements for several times a year. The concentrations in winter were higher than those in summer, but the composition ratios of 6PAHs were almost constant, and the concentrations were BbF≥IcdP>BaP≥BaA≥BkF>>DahA in any terms. Hence, it was found that the grade of the relative degradation of each PAH in the ambient air doesn't change greatly through the year.
In comparison with the concentrations in the intersection, the concentrations in the residential area were about 1/2-1/4 and the concentrations in the mountain area were about 1/8-1/30. So it was shown that the PAHs from various emission sources spread extensively. Moreover, in comparison among the composition ratios in these three sites, it was suggested that BaA degraded more easily than the other PAHs in the ambient air.
Carcinogenic risks by 6PAHs were estimated in the order of BaP>>DahA>IcdP≅BbF>BaA>>BkF, and the risk of BaP was especially high. Moreover, it was revealed that the risks by 6PAHs were over 5×10^-5 in the intersection and the residential area and the risk may be near 1×10^-5 even in the mountain area.
Consequently, the results of this study showed that efficient monitoring was necessary immediately to set environmental standards of PAHs and to regulate various emission sources.

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Wind tunnel tests for atmospheric environmental assessment were performed under neutral conditions. It is important to consider variations in atmospheric stability, especially low-height gaseous sources and complex terrain, in order to estimate exhaust gas diffusion correctly. Simulations of atmospheric diffusion processes under various atmospheric stability conditions were carried out in a thermally stratified wind tunnel. We used the Pasquill-Meade Chart as a template of typical plume spread. Simulated plume spreads agreed with characteristic lines of each atmospheric stability condition that was categorized by Pasquill-Meade in the chart. Turbulence intensities were widely distributed in accordance with stability conditions, similar to real atmospheric phenomenon. Experimental turbulence scales of main flow for all stability conditions behaved like field data, and those of vertical velocity varied, similar to turbulence intensities. Variations of velocity u and w implied an the existence of certain functions, each scaled by suitable parameters. We concluded that fundamental plume spread patterns of Pasquill-Meade Stability Classes enable simulation in the thermally stratified wind tunnel. Through our study, we have determined that it is possible to develop wind tunnel experiments for non-neutral environmental assessment.

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The concentration of ammonia in the lower atmosphere was observed at four selected sites, Komae, Kagurazaka, Abiko, and Akagi in the Kanto region during the period from January to December 2000. Concentrations of gaseous ammonia, ammonium salt with diameter larger than 2.5μm (coarse particulate), and ammonium salt with diameter smaller than 2.5μm (fine particulate) were measured separately by means of a diffusion denuder sampler. The seasonal variation and horizontal distribution of concentration of ammonia were analyzed on the basis of the data obtained. Emission sources, formation of fine particles, and long-range transport of ammonia in this region were also discussed.
The concentration of gaseous ammonia showed large variations among each site, and was higher in the summer season and lower in the winter season. These seasonal variations were closely connected with the changes in temperature and ensuing emission rate of ammonia from various sources. It was suggested that the atmospheric concentration of ammonia for urban sites such as Kagurazaka was affected by the emission from anthropogenic sources, and that for rural sites such as Akagi, by the emission from agricultural and livestock sources. The concentration of ammonium salt which existed as coarse particulate was higher in the winter season and lower in the summer season. The behavior of ammonium salt which existed as coarse particulate was suggested to be similar to that of soil particles such as calcium and sea salt particles such as sodium. The concentration of ammonium salt which existed as fine particulate showed no clear pattern of seasonal variation at any sites. It was confirmed that ammonium in fine particles was combined with sulfate, nitrate, and chloride. The concentration levels of gaseous ammonia and ammonium salt were almost the same, and ammonium salt mainly existed as fine particles. A high concentration of ammonium salt which existed as fine particulate was observed over the Kanto region following the eruption of Miyake-jima volcano on August 2000. It was suggested that ammonium sulfate, a reaction product of gaseous ammonia and volcanic sulfur, was transported to the Kanto region.

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