NO₂ concentration in urban areas is still rather high and the pattern is like plateau for more than the last decade. Also, concentration of SPM does not satisfy the environmental standard at many monitoring stations. Control of these air pollution is, therefore, a big problem and diffusion model to support the regulation is required. The model should reflect real environmental circumstances, so that it is necessary to know how and when those concentrations increase. In this paper, relation between meso-scale meteorology and high levelsof air pollution, such as NO_x, NO₂ and SPM in early winter is reviewed.

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Three species of crops, radish, spinach and bush bean, were exposed to simulated acid rain of pH 5.6 (control), 4.0, 3.0 and 2.7 (or 2.5) through the growing periods. Plants were subjected to acid rain treatment three times a week, for an hour with 10 mm of precipitation at a time. Ten to twenty plants were sampled every 1 or 2 weeks during exposure periods, and leaf area and dry weights of separated parts (leaves, stems and roots) of plant were measured. All the plants exposed to simulated acid rain falls of pH 3.0 or below produced visible injury on the leaves. The visible injury on cotyledons of radish and spinach and primary leaves of bush beanexposed to rain of pH 2.7 and 2.5 were severe, which resulted in the growth reduction of the plants at early stage of the growth compared to that of pH 5.6. When radish plants were exposed to simulated rain pf pH 2.5 and pH 2.7, dry weight of hypocotyl decreased compared to that exposed to rain of pH 5.6. Leaf area and dry weights of whole plant of “Viroflay” cultivars of spinach exposed to simulated rain of pH 2.5 were significantly smaller than those of plants exposed to rain of pH 5.6. The pod dry weight of bush bean plants exposed to simulated rain of pH 2.7 was not significantly reduced. In any case in this study, treatment at pH 3.0 or higher did not significantly affect the growth of leaf area and dry weight of whole plants of three species. Based on the results, current ambient levels of rain acidity in Japan, of which annual mean pH value over Japan was about 4.6, may not affect the growth of the three species of crop used in this study.

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To assess of contribution of automobile exhaust to indoor and outdoor levels of NO₂ around major trunk road in Tokyo, NO₂ levels of 200 homes were measured at living rooms, kitchens and outdoor at each season, from the summer of 1986 to the spring of 1987. NO₂ level was measured for four days using diffusion NO₂ dosimeter.
Outdoor NO₂ levels at each season and indoor NO₂ levels at seasons when heaters are not used decreased according to the distance from the readside. The differences between NO₂ levels at zone A (within 20 m from the roadside) and zone C (beyond 50 m) was about 3 ppb. This difference can be contributed by automobile exhaust.
At seasons when heaters are used, at homes equipped with vented heater, indoor NO₂ levels decreased according to the distance from the roadside. However, at homes equipped with unvented heater, there was no correlation between indoor levels and the distance from the roadside.

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Future concentration of CFCs are predicted based on “Montreal Protocol” and their contribution to global warming is estimated by one dimensional radiative-convective equilibrium model. Trace gases to be considered are CO₂, H₂O, O₃, CH₄, N₂O, F11 and F12' Present model is after the Manabe school. The vertical concentration profiles of CH₄ and NO₂ are given by summer mid-latitude model by McClatchy and F 11 and F12 are by Makide et al. The transmittances of the trace gases are estimated by AFGL database. The future concentration of the trace gases are estimated by their concentration and its trend at 1987. The CFCs concentrations in future are chosen from Bach and Janes analysis of Montreal Protocol. The ground level temperature at 2030 is predicted to increase by 1.0 degree for lower scenario and 1.7 for high scenario. The contribution to global warming by each trace gas is almost in the same order as that given by Ramanathan et al. and Hansen et al. The differences are mainly caused by the estimation of transmittance of trace gases.

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To investigate the causes of unusually high concentrations TSP (Total Suspended Particulate) in unpolluted areas, particulate samples were collected at two different sites, rural site and mountain top of 920 m above sealevel. Samples were taken using high-volume air sampler every 24 hours over the period of 1-14 November, 1989, and analyzed.
High concentrations of TSP were observed after the passage of a travelling anticyclone, at the unpolluted sites. However, the sources of TSP were suspected to be different between two sites. Samples under conditions of high TSP concentration from rural site were found to contain high levels of carbonaceous materials and K⁺ ions, while samples taken at the mountain top contained high levels of SiO₂ and Ca.
In the rural unpolluted area high concentrated TSP was found due to the rice straw burning, which is usually conducted in the rice fields. In order to estimate the percentage of TSP from rice straw burning, combustion experiment was carried out. The maximum contribution of TSP levels from straw burning was estimated to be about 50%.
On the other hand, high TSP concentrations at the mountain top were attributed to the effects of the long range transportation of volcanic plume from Mt. Sakurajima. This fact was confirmed from the meteorological data (distribution of atmospheric pressure, upper wind direction, potential temperature and specific humidity) and SO₂ and SPM concentration data at atmospheric monitoring stations in Kumamoto and Fukuoka prefectures.
Maximum contribution of volcanic ashes to the high TSP levels at the mountain top was calculated by calcium content to be about 40%. The large contribution was also observed at the ground level where ashcomprised 20% of TSP mass.

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A large amount of gaseous matters emitted from stationary sources are cooled, condensed in the atmospheric environment, and then changed into solid particulates, so-called condensed dust. It is inferred that authorized measuring method for the source dust prescribed in JIS can not accurately estimate the condensed dusts emitted from sources, which may change to suspended particulate matter (SPM) in environment.
This paper describes the experimental investigations on the measuring method and characterization of the condensed dust in test flue gas from A-heavy oil combustion furnace, and the field survey of the condensed dust at actual stationary sources such as oil boilers, coal boilers, pulp recovery boilers and incinerators.
The main experimental results were as follows: 1. The sampling system for the condensed dust developed on the basis of the Type 2 dust sampler could easily estimate the concentration of the condensed dust which is just released from the exit of stack. 2. The generation of the condensed dust depended on the temperature drop of gas aspirated into the improved Type 2 dust sampler, and the concentration increased with decrease of the gas temperature, and then kept the constant value from certain temperature. 3. The shapes of the condensed dusts were observed to be like droplets of the size about 10μm, and also unshaped agglomerations composed of fine particles of the size below 0.1μm. 4. The main chemical components of the condensed dusts were organic carbon and sulfate which were transformed from the gaseous matters (hydrocarbon and sulfur dioxide) in the flue gas. 5. In the field survey of four stationary sources, it was found that the condensed dust amounted to 40-60% of the total dust emitted from each stacks. 6. The shapes of the condensed dust in the sources were similar, but the chemical components were different.

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Methane is one of the greenhouse gases as well as carbon dioxide (CO₂), nitrous oxide (N₂O) and chlorofluorocarbons (CFCs), which have influence on global warming. Theaverage increase of atmospheric methane during the last decade has bcen estimated at abaut 1% per year.
Methane in soil is usually produced by methane-producing bacteria, and this process is assumed as one of the sources for atmospheric methane in the Tokyo metropolitan area. To measure the concentration of methane by gas chromatograph, we sampled air in the soil of 80 cm in depth at 330 sites which were selected at random. As a result, most of the sites showing the concentration of 500 ppm or more were found in the areas of Sumida, Adachi and Katsushika wards, and also along Tama River. It was also found that the methane concentration in soil was higher in summer (Jyly to september) than in winter (February).

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