Dry deposition estimation is essential for an assessment of the acid deposition and transboundary air pollution in East Asia, for example through ecological impact research and source-receptor relationship analysis. Resent field studies on dry deposition, focusing on surfaces in East Asia, were reviewed. Regarding dry deposition of sulfur dioxide on forests, the enhancement of uptake by wet canopies was remarkable in Japan and Thailand, which have moist climates, and a cuticle resistance scheme (Erisman, 1994), taking the surface wetness into account, performed relatively well to estimate the depositions. In the case of ozone dry deposition, the enhancement of uptake by wet canopies and the aerodynamic effect on surface resistance were found in the Thai forest; therefore, the importance of non-stomatal resistance was suggested. Regarding dry deposition on soil (loess) surfaces in northern China, the enhancement of uptake of sulfur dioxide and ozone by high pH and low relative humidity were indicated respectively. The large contribution of dry deposition of nitrous acid and ammonia as well as nitric acid in the total nitrogen deposition was indicated from experiments in Japanese turf grassland; however, note should be taken of the nitrous acid and ammonia emissions from surfaces. Dry deposition of fine particles on a forest in Japan was much higher than those estimated by an empirical formula because of the complicated structure of the real forest. These results are generally consistent with recent findings on elements of the dry deposition process in Europe and America. Therefore the findings could be applied to the dry deposition estimation in East Asia, taking into account the regional characteristics of climate, vegetation and soil.

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There is a possibility of exposure to ambient nanoparticles. In the atmospheric environment, an increase in nanoparticles, due to traffic was observed in the roadside area during rush hour. Diesel engines release a large number of nanoparticles. Due to their extremely small size, nanoparticles have new chemical, electrical, optical magnetic properties, and a different correspondence to external stimuli (light, heat, voltage, and etc), compared with larger particles. Manufactured nanoparticles are utilized in a variety of industrial fields such as chemistry, electronics, cosmetics, medicine, food, and environmental technology. The possibility of exposure to these nanoparticles in workplaces might increase. However, little has been done regarding exposure assessment and the assessment of health effects of both ambient and manufactured nanoparticles. In this paper, the present status and issues of exposure and an assessments of the health effect of nanoparticles have been taken up as topics. Regarding the exposure assessment, further studies on the possibilities of exposure in atmospheric environment and workplaces, selection of appropriate indices of exposure and development of methods for measurement of the metrics under consideration of life cycles of nanomaterials are needed. For the evaluation of the health effect assessment, behavior and translocation of nanomaterials and toxicological assessment under consideration of physico-chemical properties of nanomaterials and development of exposure methods for assessing the toxicity, are needed.

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Recently, because of regulatory enhancement, together with technological developments, the concentration of pollutants in emission sources are decreasing significantly. Nitrogen oxide concentrations in stack gases of electric power plants are around 10ppm, and for gas combined power plants, sometimes it is less than 10 ppm for facilities constructed in city areas. Therefore, the concentrations at emission sources are less than one hundred times the ambient concentrations in urban areas, in some cases less than ten times. The ventilation towers for road tunnels in urban areas are another typical example. For such low concentration sources, particularly for nitrogen oxide dispersion, the inert gas assumption of the usual plume dispersion model is not suitable, since the dispersion and chemical reactions took place together in the atmosphere. They are the major controlling factors of the diffusion in the atmosphere.
The author has developed an Integrated Plume Dispersion Model for NOx with Chemical Reactions. The model is based on the Gaussian plume dispersion model in integrated forms. The atmospheric diffusion, chemical reactions of NO, NO₂, O₃, O in the plume and ambient atmosphere are considered.
He examined the wide varieties of variable parameters on the ground level concentrations of a non-buoyant source and discussed the effects of the parameters on the ground level concentrations. The tested parameters were wind velocity, atmospheric stability, source height, back ground gas concentrations and NO₂ decomposition speed. The studies showed that the source height, wind velocity, atmospheric stability and back ground concentrations were all primary parameters on NO₂ high concentrations, whereas the effect of NO₂ decomposition speed was secondary. These analysis gave reasonable results and the model has proved to be applicable to the environmental assessment of low NOx emission sources.

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TFH filters (TFH-01 and TFH-47), with non-woven fabric PE (Polyethylene) and PET (Polyethylene terephthalate) backing, have been developed to reinforce the PTFE (Polytetrafluoroethylene) filter. Because the filter is thin and its electric conductivity and hygroscopicity is low, automatic PM2.5 mass measurement by the beta-ray absorption technique equipped with the TFH-01 filter is expected to be more accurate than that equipped with a glass-fiber filter. Moreover, the filter is easy to handle due to its strength. In this study, we performed some experiments to confirm whether the automatic measurement method of PM2.5 by the beta-ray absorption technique equipped with the TFH-01 filter satisfies the standards for the PM2.5 mass monitor. The results include:(1) the monitored values have a good correlation with those obtained by the standard measurement method, (2) the monitor is able to measure a wide range of particle concentrations (2μg/m³-several hundreds μg/m³), and (3) the monitor is able to measure 1-hour averaged particle concentration. Moreover, the TFH-47 filter is found to be useful for the measurement of daily averaged particle concentration. TFH filters are, thus, applicable to PM2.5 automatic monitoring by the beta-ray absorption technique and the PM2.5 standard mass measurement.

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We conducted wind-tunnel experiments to study the effect of the heights and arrangements of roadside buildings on the flow and concentration fields in a street canyon.
For the four building arrangements studied (Figs. 3 and 4), the best transfer of pollutants from street level to the upper air was by a zigzag array of tall and short roadside buildings (Fig. 4, Type 4). In this, for a tall building on the windward side of the canyon, the ascending flow along the roadside (leeward) wall was accelerated. For a tall building on the leeward side of the canyon, the descending flow along the roadside (windward) wall was also accelerated.
These flows were linked together at the bottom of the canyon. Consequently, they formed a three-dimensional flow field in the canyon that efficiently carries air pollutants from the street-canyon bottom to the upper air.

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[in Japanese]

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