Air pollutants cause various types of damage to plants: the retardation of growth, the promotion of ageing, the abscission of leaves and withering. Air pollutants are absorbed by plants mainly through the stomata of their leaves. The absorbed pollutants produce toxic substances in plants: SO2 produces SO₃^2-, NO₂ produces NO₂^- and all pollutants produce active oxygen species, such as O2-, H₂O₂ and ¹O₂, as secondary toxic substances to some extent. These substances destroy or inactivate various cellular components like proteins and lipids and cause damage to plants. On the other hand, plants have metabolic pathways to scavenge these toxic substances and can avoid damage when the amount of absorbed air pollutant is low.
The degree of damage to plants caused by air pollutants depends on the degree of stomatal opening and the potentials to produce and to scavenge toxic substances in plants. Plants also show dynamic responses to air pollutants: stomata tend to close when plants get contact with air pollutants and various activities to scavenge toxic substances in plants increase with the contact of plants with low concentrations of pollutants. The activities of active-oxygen-scavenging enzymes, superoxide dismutase and catalase, were shown to increase with SO₂ and activities of other such enzymes, ascorbate peroxidase and glutathione reductase increased with O₃. By contrast, the activity of nitrate reductase which produces toxic NO₂^- was shown to decrease with NO₂.
Genetic engineering technique is being used to change the tolerance of plants to air pollutants, based on these findings.

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Extrapolation of animal data of high-dose inhalation of diesel exhaust particles (DEP) into a human risk in low-dose exposure was carried out on the data, which were obtained at the 5 institutions in the world (Table 1).
The incidence rate of lung tumors was extrapolated, at first, from a high-dose to low-dose risk in rats by computer calculation using mathematic models. Among the five models used, the multistage model revealed the narrowest range of the estimated VSD values from 10 0 to 10^-2 (Table 2), which indicates that it is the most applicable model for cancer risk assessment. According to this multistage model, life time risk for life time inhalation of 1 μg/m³ (unit risk) of DEP in rats was calculated to be 2.1-8.4×10^-5.
How to extrapolate an animal risk into a human risk is an unsolved problem. EPA prefers an extrapolation by using a ratio in energy consumption corrected by body surface area between the two species. Unit risk in human for lung cancer by low-dose DEP exposure was calculated in this study to be 5.2-21.1×10^-5, when the ratio of 2.5 was adopted.
Lung cancer incidence in rats correlated better to the lung burden of DEP than to the accumulated inhalation dose. Then, an estimation of lung cancer risk was made both from the amount of deposited carboneous dust in the lungs of Tokyo inhabitants and from the risk of lung cancer due to the deposited DEP in the rats. The risk of lung cancer for 1 mg DEP/gr rat lung was calculated to be 4.4×10^-2 by using the multistage model, and the presumed average amount of DEP deposition in the lungs of Tokyo inhabitants was estimated as 0.19mg/gr lung, accordingly, their lung cancer risk was estimated as 82.7×10^-4.
Then, the rate of deposited amount of particles in the lung due to the lfe time inhalation dose in both species was calculated, and the ratio of the rate in the two species was shown to be approximately 3.5 (Table 3). This was used as another extrapolation coefficient, and by using the two coefficients, 2.5 and 3.5, a unit risk range for human lung cancer due to DEP was estimated, finally, to be 5.2-29.5×10^-5 with the geometric mean value of 12.3×10^-5.

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Recent epidemiological studies have demonstrated a slightly higher risk in the population of those, who were occupationally exposed to diesel exhaust particles (DEP), and some of the data have demonstrated a statistical significance (Table 4). Among several cohort studies, the large scale and long followed study by Garshick showed a significantly higher relative risk of 1.45 for all subjects and 1.72 for the population exposed for 17-17 years. Furthermore, his colleagues studied the exposure level for diesel particles in this occupational environment. When applying the equation relative risk=1+c×d×k (c: exposed dose, d: exposed years, k: coefficient), and when the obtained k value was applied to the annual lung cancer death by gender and age group in Japan, annual excess deaths by lung cancer were estimated to be 648.7 (243.2-1198.2) for the whole population of the country (Table 5), and a life time risk for 1 μg/m³ DEP exposure (unit risk) was estimated to be 4.16 (1.56-7.69)×10^-4.
With the presumed average exposure levels of diesel particles in Tokyo, other cities and in the whole country, the obtained values from the three different calculations were compared (Table 6). The range of unit risk was calculated from the animal data overlapped with that from the epidemiological data, and the risk in Tokyo inhabitants showed a close but higher value than the risk from the epidemiological data. A contributing rate of diesel-related lung cancer to the total lung cancer and an annual risk in Japan were calculated from the animal data (Table 7). The standardized mortality ratios of lung cancer by prefecture in Japan were calculated, and a higher incidence of lung cancer in the prefectures, which include densely populated area were shown (Table 8).
Although uncertainties may be included in these calculations, it can be concluded that DEP may partly cause lung cancer in humans, especially who are living in urbanized area.

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In order to analyze the trends and seasonal cycles of atmospheric methane concentration in Japan, the data of monthly averages of methane concentration between April 1980 and March 1990 at the 23 monitoring stations, which were installed by Japan Environment Agency, were used.
The overall monthly average of methane concentration had increased by 0.011±0.006 (1δ) ppmv/v per year, and the average methane concentration in March 1990 was 1.821±0.046 ppmv/v. All data show the seasonal cycle of methane concentration, which has a maximum value in December and a minimum in August.
The relationship between the initial concentration of mathane in the first month of a year, namely the methane concentrations in April, and each yearly increase of methane concentration shows that the yearly increase of methane concentartion became smaller as the initial methane concentration became larger. Therefore, it seems that the methane concentration in Japan tends to become uniform. From the results of principal factor analysis of monthly averages at the 21 monitoring stations over 10 years, it was obtained that two factors had affected the seasonal cycles of methane concentration. The first factor represents the character that methane concentration becomes lower in summer and higher in winter, and the second factor shows the character that methane concentration becomes higher in summer and lower in winter.

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A study was made on indoor air pollution in school rooms and their effect on students, who were living in limited areas, and were exposed to air pollutants in TOKYO. The actual concentrations of pollutants in school rooms were measured, and the p ersonal exposure were monitored. The results were as follows:
1) The indoor and ourdoor concentrations of NO₂ had a high correlation. The level of outdoor NO₂ was very high, but had a similar pattern with that of indoor NO.
2) Both NO₂ and HCHO concentrations at inside of school rooms and outside were measured by TEA (Triethanolamine) and the FILTER BADGE methods both at fixed locations and by mobile persons and it was established that both methods were very accurate.
3) Students personal exposure levels were same in urban and rural areas.
4) Even though the indoor, NO₂ levels were less than the Ambient Air Quality Standard, very high NO₂exposure levels were recorded by some students. It is thought that the reason is the students were exposed to high NO₂ at homes and on their way to school.
5) HCHO levels in schools were not so high as in residential areas, since schools have less sources of HCHO. Furthermore, the indoor HCHO levels were higher due to indoorsources of HCHO.

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Recently, decline of Sugi trees has been reported on the lowland in the Kinki District. To investigate the cause of the decline, we analyzed degree of Sugi decline and surface soil acidity under Sugi trees in 1987-1991. Studied sites were 274 shrines or temples. And in each site we investigated Sugi trees of old age (over 80 years old) and collected surface soil samples under Sugi trees. Soil pH was measured by means of the glass electrode pH meter.
In some sites surface soils close to trees were very acidic (pH values were below 4.0). In most sites there was a tendency that soil pH value around the stem was lower than that among trees. But there was no correlation between the degree of Sugi decline and the soil acidity.
We also analyzed surface soil acidity under other species, Hinoki (Chamaecyparis obtusa), Akamatsu (Pinus densiflora), Kuromatsu (Pinus thunbergii), Kusunoki (Cinnamomum camphora) and Konara (Quercus serrata). The soil pH was lower in the following order, Hinoki sites<Akamatsu and Kuromatsu sites<Kusunoki and Konara sites. Particularly in Hinoki sites soil pH values around stems were lower than those among trees as in Sugi sites. This pH decrease around the stem is probably correlated to stemflow. We measured the pH of leachates from bark of each tree species. The pH value was lower in the following order, Sugi and Hinoki<Akamatsu and Kuromatsu<Kusunoki and Konara.
These results suggested that the stemflow acidity is specific to the species, and that the acidity of surface soil around stem has been influenced by stemflow. The low surface soil pH around Sugi stems might be a result of the acidic stemflow, and might not be the cause of the decline.

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In Okutama (Tokyo, Japan), the evaluation of air-polluted environment using the open-top chambers was conducted in 1989-1990. Radish plants (Raphanus sativus L. cv. Comet) were used as the indicator plant for ambient O₃.
In the experiments with average daily 8-h (8: 00-46: 00) dose of O₃ above 500 ppb·h·day^-1 during the exposure period, visible foliar injuries, which were similar to those caused by the exposure to O₃, were observed on the cotyledons of the plants cultivated in the non-filtered treatment (NF). In these experiments, leaf areal growth, dry weight growth and net assimilation rate of the plants cultivated in the NF were reduced compared with those of the plants cultivated in the charcoal-filtered treatment (CF). These results suggest that theefficiency of dry matter production of the plants cultivated in the NF was reduced mainly by ambient O3. In the experiments with the dose of O₃ below 300 ppb·h·day^-1, average daily air temperature below 20°C and average daily cumulative solar radiation below 5 MJ·m^-2·day^-1, on the other hand, the growth in leaf area and dry weight of the plants cultivated in the NF were increased compared with those of the plants cultivated in the CF.
The results obtained in this survey suggest that O₃ has adverse effects on plants mainly in the summer season in Okutama. The OTC-method presented in this paper is useful mainly in the seasons with relatively high air tempez ature and high solar radiation.

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The amount of sulfur dioxide emission from volcanoes in Japan was estimated. The annual emissionrates of sulfur dioxide from eruptive and non-eruptive volcanoes were estimated by combining available spectroscopic measurements data from 1976 through 1989 with the empirical volcanic classification. Estimated total emission from volcanoes to the atmosphere was about 1.1 Tg/y, which is almost equal to the recent man-made emission in Japan. Regional emission around the Kyushu Island, one of the most active volcanic areas, exceeds 0.8 Tg/y. This is about 5 times higher in magnitude than the rece nt man-made emission in this area. Among these volcanoes, the contribution of Sakurajima Volcano is the most important.

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[in Japanese]

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