Some methods have been developed to predict transport and dispersion of air pollutants for environmental impact assessment. First, a Gaussian trajectory model was proposed to identify the gamma exposure rate due to radioactive plumes emitted from nuclear power plants. The calculated exposure rate was one-half to twice the measured exposure rate less the background level. This result reflected the guideline of emergency radiation monitoring. Second, an environmental impact assessment method for fugitive dust caused by coal-handling facilities was proposed. This method has been applied to the prediction of coal dust dispersion for almost all coal-fired power plants in Japan. Third, a Lagrangian particle dispersion model was developed for the environmental impact assessment of thermal power plants, and a method for evaluating topographical effects using this model was proposed. The validity of this method was confirmed on the basis of the results of wind tunnel experiments and field tracer experiments. Lastly, a long-range transport model for East Asia was developed to estimate acid deposition in Japan. The model can predict more than 80% of the observed sulfur deposition. The contribution of both domestic anthropogenic and volcanic sources to the total amount of sulfur deposition in Japan around the year 1990 was estimated to be approximately 60% using the model. Future acid depositions in Japan were also forecasted. The results show that if current and future legislations are observed according to the plan, it is anticipated that acid depositions will have no serious impact on Japan. An effective way to prevent harmful consequences for Japan's environment would likely be to assign priority to steps dealing with emission sources along the Yellow Sea and Bo Hai Bay.

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The Atmospheric Boundary layer (ABL) plays an important role in the transfers of the energy, momentum and trace gases between the surface and the atmosphere. Therefore, investigation of the exchange process and ABL structure should be important not only for the air pollution problems but also for the global environmental issues.
First objective of this study is to clarify the structure of the ABL using the data collected by the airplane and tower. From the airplane measurement, the structure of the ABL under the condition of clear daytime is investigated up to the height, 1500 m. On the contrary, the tower observation is restricted to the lower layer than 300 m, so that our analyses are concentrated to the clarification of the formation process of the stable ABL, and the developing process of mixing layer. Mainly, we discussed the vertical profiles and time variations of the turbulent fluxes of heat and momentum, and balance of the turbulent energy equation.
Second objective is to estimate the uptake rates of CO₂ from the atmosphere to temperate forests in Japan, and to compare the results with uptakes obtained in the East Asia. The uptake rates of CO₂ from October, 1993 to the present were estimated from field measurement using a tower in a temperate deciduous forest at Takayama, Japan. The average of integrated uptake of CO₂ was 1.8 tC/ha/year, but it had notable interannual variation due to the differences of insolation and temperature in each summer. According to the CO₂ fl ux measurements at other forests in Japan, the uptake rates were from 1 to 5 tC/ha/year. These results indicated that the forest ecosystems could be a large sink of CO₂, however, more data of the CO2 flux in the various forests and latitudes are needed to estimate the CO2 uptake on a global scale.

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This review is a summary of a study on atmospheric gaseous substances (S0₂, NO, NO₂ and 0₃) and the elemental composition and mapping of beech leaves conducted in the Shirakami-Sanchi World Heritage Area as part of “Establishment of a monitoring method for forest ecosystem conservation of the Shirakami-Sanchi World Heritage Area and research of a forest management method for harmonization with forest utilization in its surrounding areas.”

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Exhaust gases from vehicle contain many air pollutants. Especially, diesel exhaust particles cause environmental problem in big cities. Therefore, it is necessary to carry out continuous monitoring of the air at various roadside spots representing different traffic conditions to grasp the present condition of air pollution from exhaust gases.
In this paper, a new convenient monitoring method for the atmospheric environment using micro fiber sheets at roadside spots is described. It was found that the micro fiber sheets were suitable for collecting air particles such as SPM. Comparing the amounts of particles and B (a) P collected by micro fiber sheets with those collected by using an air sampler at the same spot at the same time, the correlation coefficients were 0.797 and 0.945 respectively. The monitoring method using this micro fiber sheet is suggested to be an index of air pollution for one week. As a result of continuous monitoring at roadsides with different traffic conditions, the amounts of particles and B (a) P collected at intersections were higher than at straight roads far from intersections. The estimated concentrations of SPM were calculated to exceed 0.10 mg/m³ at highway intersections from January to April, and the estimated concentrations of B (a) P were calculated to be about 0.20 ng/m³ less than the national average in the general atmosphere.

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Replicated measurements of a pollutant regularly repeated over a year are often designed, each of which gives several daily average concentrations. The average of all the measured daily average is an estimate of annual average, but it varies depending on the days the measurements are carried out. The quality of estimated averages, relative to the real annual average has been examined using NO₂ concentrations during 1996 from Tokyo and during 1994-1996 from Aichi areas.
The relative error, defined by the ratio of the standard deviation of the estimated averages to the real annual average, is generally reduced with increased times of measurement, and with number of days in each measurement. However, if the number of days in every measurement is confined to three or four, the relative error in case of three time measurements, in other words, measurements carried out every four months, is often smaller than that in case of four time measurements.
The above results were influenced by periodical variations in meteorology during the examined years, and are not necessarily valid when meteorological conditions vary from year to year.

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The evaluation of dust in communication machine rooms is becoming more and more important because of the increasing numbers of optical devices in information communication. To carry out airborne dust evaluation more cheaply and easily, a method for separating “dust collecting” and “dust evaluation” was adopted. A method for automatically exchanging samples was examined in the collecting function. Moreover, a handy optical method was examined in the evaluation function.
The main examination results are listed as follows:
(1) We enabled airborne dust information to be recorded in the dust collecting filter for long term fixed periods using an “Airborne dust environmental recorder”.
(2) The optical reflection method was examined as a method for evaluating dust. We found a very strong correlation between the amount of dust in the filter and the brightness index. The correlation coefficient was 0.961.
(3) The relation between the amount of suck flow and the correction coefficient of the recorder was clarified. By using this correction coefficient, it is possible to calculate the amount of dust from changes in the brightness index in the filter. The width of the data change in this recorder was estimated to be±5% or less from the simultaneous evaluation results of five recorders.
(4) As a result of setting up the recorder in three NTT machine rooms and the simultaneous evaluation of dust in the environment, it was shown that airborne dust in the environment was significantly different in various parts of the same building. Moreover, it was shown to easily judge the relative superiority or inferiority of airborne dust in the environment.

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Air pollution by automobile exhaust gases is still a serious problem. In order to reduce air pollution caused by automobiles, the emission characteristics of the idling-mode and the reduction of exhaust gas emissions achieved by stopping the engine were investigated. Seven gasoline fueled vehicles and 13 diesel fueled vehicles were tested under the transient test cycle and idling-mode test. The results are as follows:
1. Emission rates (mg/s) and fuel consumption rates (mL/s) were compared between the transient test cycle and idling-mode. In the gasoline vehicles, the idling-mode fuel consumption was 47% of the transient cycle fuel consumption. In the gasoline vehicles equipped with a three-way catalyst, the concentration of NOR emitted during the idling mode was very low. In the diesel vehicles, the idling-mode emissions were 30% of the transient cycle NO_x emissions, and the idling-mode fuel consumption was 28% of the transient cycle fuel consumption.
2. Although the amount of exhaust gases slightly increase when an engine is restarted, we confirmed that stopping the engine for a short time (from several seconds to a few minutes) reduced the fuel consumption of the gasoline vehicles and the amount of all exhaust gases of the diesel vehicles.
3. These results were applied to the operation of light-duty diesel trucks in Tokyo. In this case, it was estimated that the emissions contributed during the idling mode consist of 3.5% NO_x, and 3.1% CO₂ As a result, it was suggested that parked idling vehicles should be investigated as an emission source.

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