To clarify the characteristics of nitrogen dioxide (NO₂) emission from diesel vehicles which are the main source of air pollution in the Tokyo metropolitan area, we tested a diesel truck (engine type: direct injection, carrying weight: 4, 000 kg, equivalent inertia weight: 5, 855 kg) on a chassis dynamometer.
We measured NO_x and NO concentrations in the exhaust gas from the truck using a Constant Volume Sampling (CVS) system and calculated the emission rates of NO_x and NO by the Modal Mass Dilute Method, and obtained the emission rate of NO₂. The NO₂/NO_x (v/v) fractions at idling and at four constant speeds were 31%(idling), 26%(20 km/h), 22%(40 km/h), 25%(60 km/h) and 17%(80 km/h).
Under the driving conditions of the M-15 test pattern, the fractions at acceleration and deceleration ranged between 11-21% and 50-60%, respectively. The integration of NO₂/NO_x fractions and NO₂ emission rates under the driving conditions of the Tokyo Metropolitan Test Driving Pattern No.2, No.5 and No.8 were (24% and 1.23g/km at 8.1km/h (average speed)), (20% and 0.69g/km at 18.2km/h) and (18% and 0.52g/km at 28.8km/h), respectively. In these three test patterns, NO₂ emissions in the acceleration mode were greater than in the other three modes.

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Size distribution, concentration, and chemical composition of suspended particulate matter (SPM) in subway cabins and stations on the Ginza Line in Tokyo were investigated on Saturdays in May, July and August, 1996. At all the subway stations, mass concentrations of SPM estimated with a dust counter were consistently below the level recommended by the Law for Maintenance of Sanitation in Buildings, Japan (<0.15mg/m³). There were marked variations in SPM mass concentrations among the subway stations, and the patterns of the variations were essentially the same on three different measuring days. In contrast, SPM mass concentrations at the corresponding above-ground areas did not vary so markedly, suggesting that the air supply systems at each station may play an important role in maintaining air quality. The relative concentrations of SPM with 0.3 0.5μm diameter were lower at all stations than at the corresponding above-ground areas, especially at the stations with reltaively higher mass concentrations of SPM. On the other hand, the relative concentrations of SPM with 0.5-3.0μm diameter appeared to be higher in the air at the subway stations than at the corresponding above-ground locations. Since similar findings have been observed in large underground shopping areas, this distinctive size distribution may be a common feature of underground SPM. Scanning electron microscopy showed that SPM collected in subways contained a relatively large number of aggregated metal fume-like particles, and that their iron concentration was significantly higher than that of SPM collected above-ground.

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A long-range transport model in East Asia with detailed models for wet deposition processes was developed. The parameters in this model comprised meteorological data, and both in-cloud scavenging process and below-cloud scavenging process with chemical reactions were included in the model. Not only anthropogenic pollutants but natural sulfur compounds such as SO2 from volcanos, DMS from ocean and land soil, and H2S from vegetation were considered as sources of sulfur compounds. We adopted 60 km×60 km grid, oblique-terrain cordinate system, and wind fields were simulated with objective analysis. With the model, atmospheric concentrations and deposition fluxes of SO₂ and SO4^2- in Feb. and Aug. of 1993 were calculated. Estimated deposition fluxes were in good agreement with the observed data.

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The effects of ozone and soil water stress, singly and in combination, on the growth, yield, seed quality and germination rate of soybean plants [Glycine max (L.) Merr. cv. Enrei] were investigated. The plants were exposed to charcoal-filtered air or 60 n1· 1^-1 O₃, and were split in both gas treatments between two watering regimes imposed the potted soil with a pF value of 1.8 (well-watered treatment) or 2.5 (water-stressed treatment) in naturally-lit growth cabinets for 98 days.
The exposure of the plants to O₃ caused reductions in the leaf, root and whole-plant dry weights at thevegetative growth stage, and in the yield. The contents of Mg and K in the seed were significantly increased, but the seed germination rate was significantly reduced by the exposure to O₃.
The soil water stress induced reductions in the whole-plant dry weight and yield of the plants. The contents of grain oil, Ca and Mn in the seed were significantly reduced, but the content of Mg in the seed was significantly increased by the soil water stress. There was no significant effect of soil water stress on the seed germination rate of the plants.
Antagonistic effects of 0₃ and soil water stress were detected in the whole-plant dry weight on the 26th day after sowing, the dry weight of pods with seeds on the 67th day after sowing, the seed number per plant, the weight per 100 seeds and grain protein on the 96th day after sowing. However, the additive effects of 03 and soil water stress were generally observed on the dry matter production of the plants. Therefore, the yields of the plants exposed to both stresses were markedly reduced compared with that of the well-watered plants exposed to charcol-filtered air.

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It is the goal of this study to identify substances that have critical role in the metallic mercury removal from incineration flue gas by the coexistence with activated carbon and to clarify the metallic mercury removal mechanism by the simulated synthetic fly ash.
This synthetic fly ash, which consisted of calcium chloride with 5% activated carbon, showed very high efficiency of over 99% for mercury removal at the temperature of 120t, the moisture of 20% and air atmosphere. It was found that metallic mercury changed into mercury (II) oxychlorate on the surface of activated carbon and an oxychlorination reaction occurred in the synthetic fly ash at the temperature of air pollution control device. The metallic mercury removal mechanism by the synthetic fly ash is considered to be a chemisorption through the following route; metallic mercury-mercury (II) oxide→mercury (II) chloride→mercury (II) oxychlorate.
In order to evaluate the influence of quantity of activated carbon and calcium chloride on metallic mercury removal, the experiments were performed using the synthetic fly ash which consisted of activated carbon, calcium chloride and silicon dioxide. When the calcium chloride content was more than 0.5% in the synthetic fly ash with 5% activated carbon, mercury vapor was completely removed. Whereas, the highest removal efficiencies were obtained when the activated carbon content was ranged from 5 to 7% in the synthetic fly ash with 1% calcium chloride. The mercury removal ability was affected by temperature, if the activated carbon content was very small. Because these phenomena were also observed in the experiments using calcined fly ash with 5% activated carbon, it was supposed that the complex chemical action with activated carbon and calcium chloride was most significant for metallic mercury removal by actual fly ash.

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Air-pollution and meteorological data for three years since April 1994 were analyzed to clarify the severe pollution in the Nobi plain areas with emphasis on its meteorological basis. As in most large urban areas in central Japan, suspended particulate matter (SPM) and nitrogen oxides have long been outstanding problems, particularly occurring November and December. Therefore, the analysis was focused on this season.
concentration level in the region, was selected as a representative one. There were 36 days on which the daily average concentration of SPM at Y exceeded 100μgm^-3 out of the 183 days of the two months×three years, defined as “high SPM days”. Around the industrial zone along the east shore of Chita Bay extending southsoutheastward from Nagoya, high SPM levels equivalent to that at Y occurred, and the time of daily maximum concentration delayed as the location sifted to the south. At the stations in other directions from Nagoya, the SPM concentration levels were considerably lower. These distribution and temporal variations of SPM concentration were considered to result from the convergence of northwesterly winds and northeasterly local flow in the above-mentioned zone along Chita Bay, where the northwesterly is the prevailing wind in this region under nearly calm condition, while the northeasterly is nocternal drainage flow from the highlands in the northeast of the plain.
This process forming the high concentrations of air pollutants in early winter is quite different from that in the Kanto plain, where high concentrations are observed in a wide stagnant region extending over the inland part of the plain rather than Tokyo Bay areas.

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