To investigate the origin and charcteristics of sulfate aerosols in Tokyo, we analyzed the relationship between nss-SO42-concentration in atmosphere and air trajectory. The nss-SO₄^2- concentrations were measured for every seven days continuously during the period of March 1995 to February 1997. Three-day back trajectories were calculated at 850 hPa level for every twelve hours during the same period.
The nss-50₄^2- concentration in Tokyo tended to increase in summer. The nss-SO₄^2-concentration had positive correlations with maximum oxidant concentration in aday, global radiation and relative humidity; a negative correaltion with wind speed.It was indicated that the high nss-SO₄^2- concentration in summer was caused by the activation of SO₂ oxidation to sulfate and the air stagnation, which were brought by the stagnated air flow from the Pacific Ocean. And this nss-SO₄^2- originated in the sources in and around the Knato area. Although twenty-eight persent of the air trajectories flowed from western Japan, Korea and central China, which include huge sourses of sulfur, it was not clear that the air flow increased the nss-SO₄^2- concentration in Tokyo.

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In order to clarify atmospheric NO→NO₂ conversion behavior near the emission duct for NOX emitted from a combustion system, we performed reaction calculations in the previous study (Taiki Kankyou Gakkaishi, 32, 341-359 (1997)), assuming constant temperature and volume of the exhaust gas. In this study, we performed reaction calculations concerning NO→NO₂ conversion, considering the decrease in temperature and expansion in volume of the exhaust gas during advection and diffusion in the atmosphere, and we performed sensitivity analyses in order to clarify main elementary reactions.
The results show that, if the temperature at the emission duct exceeds 573K, presence of CH₄ in exhaust gases containing 0₂ causes rapid NO oxidation through formation of HO₂ and CH₃0₂ radicals, leading to a high NO₂ concentration near the emission duct. In addition, it was shown that, important factors affecting the NO oxidation behavior within the exhaust gas include an increase in CH₄ and 0₂ concentration and temperature which increases the NO₂/NO_X ratio within the exhaust gas. These tendencies were similar to the previous study. In contrast, an increase in atmospheric light intensity decreases the NO₂/NO_X ratio, contrary to the result given in the previous study. This is probably because the reaction between O (³P) (produced during photodissociation of NO₂) and, OH, which was considered important for NO₂ production in the previous study, loses its importance with the decrease in temperature. In addition, only a slight increase in the NO₂/NO_X ratio was observed with an increase in H₂O and CO concentration in exhaust gases, which also differs from the previous study. In the case of H₂O, this is probably because the OH production through reaction between H₂O and 0 (¹D) which was also considered important for NO₂ production in the previous study, loses its importance with the decrease in temperature within the exhaust gas, and in the case of CO, adding CO may have consumed OH radicals needed for CH₄ oxidation.

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The removal effect of gaseous nitrogen oxides (NO_x) by grass and soil of highway roadside was evaluated. This kind of location is under relatively higher exposure of NOR and is supposed to be one of the most important sink for NO_x.
Grass-Soil Complex Deposition Model was made for estimating the NOR deposition effect by roadside grass layer and soil separately.
The following investigations were carried out at the observation point of the roadside: automobile traffic survey to estimate the NO_x emission intensity, NO_x distribution measurement to calculate the NO_x dry deposition flux, direct dry deposition measurement using flux-chamber, precipitation survey as the NO_x wet deposition flux, and monitoring of nitrate (NO₃^-) concentration in roadside soil to estimate the fate of NO_x in soil.
Moreover, roadside soil was exposed by NOx under several controlled conditions: glucose concentration, NO³_- concentration, and headspace gas composition (N₂ or Air). Two experimental method were performed for each sample soils: long-term expoure in which NO_x was inserted at interval of 1 day during 30 days and short-term exposure in which NO_x was inserted at interval of 5 minutes.
Dry deposition flux of NO₂ onto the roadside ecosystem was about 1/1000 as much as NO₂ emission intensity from the road. Dry deposition flux of NO was extremely low, about from 1/200 to 1/20 as much as those of NO₂. Both the Complex Deposition Model analysis and the flux-chamber measurement showed, however, that NO_x deposition effect by roadside soil was equal to or more than those by grass. The experimental result also indicated that the effect by roadside soil increased in the appropriate moisture content. It is highly possible that biological dinitrifying reaction is concerned with gaseous NO_x removal, because anaerobic condition and high concentration of organic compounds promoted NO removal.

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An atmospheric diffusion-reaction model of non-conservation system to elucidate the reactive transport process of an arbitrary number of gaseous and particulate pollutants has been developed and applied to the prediction of the concentrations of benzene and toluene in the atmosphere. The model is founded on the one-dimensional solution of coupled parabolic-type partial differential equations with constant parameters, which has been solved by making use of the Fourier-transform technique combined with the matrix algebra. The steady-state solutions for all the pollutants are also derived from the time-dependent solution. The following three model calculations have been carried out to determine the regional profiles of benzene and toluene in the atmosphere.
The mono-pollutant model has treated the analysis of emission, transport, diffusion, and removal for benzene in air. The Heaviside's step function is employed for the source term, which source area is 2 km in width and the source strength is kept to be 100μgm^-3 hr^-1. The steady-state solution predicts that under this emission condition the maximum concentration of benzene will reach 33μgm^-3 near the source area.
The two-pollutants model allows for us to analyze two atmospheric pollutants accompanied by their transport and mutual reactions. This model has been applied to the toluene/cresol system, suggesting that the profiles of their steady-state concentrations are strongly affected by the competition between the forward reaction rate of toluene and the removal rate of cresol.
The four-pollutants model enables to treat the transport of four pollutants with twelve reaction paths. The chemical conversion from toluene to benzaldehyde involving two intermediate radicals with six reaction rate constants has been analyzed by this model. For this model, a state of dynamic equilibrium is attainablein the regional profiles of the area 30 km-80 km at elapsed time of 10hrs.

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This study was conducted to assess the effects of sulfur and aromatics contents of light oil on diesel exhaust emission. Almost similar components of light oil except sulfur atomatics contents were used for tests with a direct injection diesel engine and a swirl chamber engine operated at Japanese urban driving test cycle (13 mode).
The dilution tunnel method was used in this study. Diesel exhaust particulate and semi-volatile organic matter (VOM) were collected from the diluted exhaust gas with fluorocarbon coated glass fiber filters and Amberlite XAD-2 resin. The filters and resin were extracted with dichloromethane using Soxhlet extraction to collect the soluble organic fraction of particulate matter (SOF) and VOM. SOF and VOM were examined to chemical analysis and mutagenicity test with a modified Ames assay.
Reduction of sulfur content in fuel resulted to the decrease of particulate emission. This result could be attributed to the decrease of particulate matter associated sulfate and bonded water. While, emission of polynuclear aromatic hydrocarbons and mutagenicities of SOF and VOM were not affected by fuel sulfur content. Increasing the aromatic contents resulted to the increase of particulate emission, polynuclear aromatic hydrocarbons and mutagenicities of SOF with direct injection diesel engine.

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This study was conducted to assess the effects of aromatics constituents of light oil on diesel exhaust emission. The test fuel containing different chemical constituents of aromatic compounds was used with a direct injection diesel engine operated steady state conditions. Using the dilution tunnel method, diesel exhaust particulate and semi-volatile organic matter (VOM) were collected from the diluted exhaust gas with fluorocarbon coated glass fiber filters and Amberlite XAD-2 resin, respectively. The filters and resin were extracted with dichloromethane using Soxhlet extraction to collect the soluble organic fraction of particulate (SOF) and VOM. SOF and VOM were characterized with chemical analysis and mutagenicity test with a modified Ames assay.
This study showed that the mono-and di-cyclic aromatic hydrocarbons in the test fuel gave slightly effects on emission of particulate matter, polynuclear aromatic hydrocarbon (PAH) and mutagenicities of SOF. The tri-cyclic aromatic hydrocarbons in the fuel gave significant effects on emission of PM, PAH and mutagenicities of SOF. VOM showed higher mass emission level than PM and were slightly affected by aromatic constituents in the fuel. Hydrocarbons in the SOF were corresponded to the high boilling range fraction of fuel and hydrocarbon in the VOM were corresponded to the low boilling range fraction of test fuel.

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