This is a review on the researches and developments of estimating the atmospheric diffusion for the scientific purpose and the regulatory use, which were carried out for a long time by the author. The boundary layer theories were applied and many field diffusion expriments were carried out in these studies. The main results are following;
(1) The Monin-Obukhov length corresponding to dispersion coefficients on Pasquill-Gifford chart (PG chart) was semi-theoretically derived by applying of Monin-Obukhov's similarity theories in the surface boundary layer. It proposed a way in using the equations of atmospheric boundary layer for the research on the atmospheric diffusion.
(2) Gaussian plume model for low-level release over the sea with PGT dispersion coefficients modified by the characterisitcs of marine boundary layer was developed. The PGT means Pas quill-Gifford-Turner. This model was verified with the data of the diffusion experiments conducted in coastal or offshore areas in USA and Japan.
(3) The atmospheric diffusion in night time under low wind speed less than 2 m/s were studied in carrying the air tracer diffusion experiments with surface release.The results support the estimation methods of atmospheric dispersion on the meteorological guide for safety analysis of nuclear power reactors of Japan Nuclear Safety Commission.
(4) Fumigation dispersion models in thermal internal boundary layer (TIBL) were examined by using the diffusion experiments data of TOKAI 82-83. The results suport that the fumigation-model on Regulatory Guide 1.145 of U.S. Nuclear Regulatory Commission is oneof the models which are able to apply in Japan for evaluating the short period high level concentration under the condition of fumigation caused by TIBL.
(5) The perfluorcarbon tracers (PFT) which were used for the atmospheric diffusion experiments of long distance, long period or multiple release in abroad were examined. We conducted a small field experiment in releasing the SF₆ and PFT from the same point at the same time and showed the PFT were sufficiently practical for the field experiments in Japan, too.

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The effects of forest canopy on the chemical composition of throughfall were studied on conifer (Cryptomeria Japonica) and deciduous (Sapium Japonicum) forests on Simian Mountain, which is 100 km from an urban area during 1992. 1-1995. 12. A similar study was done in the conifer forest (Pinus Massoniana) at Saqiaogou, which is close to an industrial center and is only 10 km from an urban area during 1994. 3-1995. 2. Moreover, the origins of the chemical compositon in the throughfall at Simian Mountain were estimated based on the budget model and their concentrations in bulk precipitation.
All throughfall was acidified and ion concentrations were enriched due to the leaching and washoff of inorganic and organic matters that had accumulated on the foliage. The total ion concentration in the throughfall at Saqiaogou was higher than that of Simian Mountain, this appears to be caused by different levels of air pollution. It was found that there were higher concentrations of total ions in the throughfall of the conifer than in the deciduous canopy. The measurement results for the throughfall components and the step-sampled precipitation suggested that the contributions from foliage leaching of conifers were 26% for Ca²⁺ and 34% for Mg²⁺, those of deciduous trees were 34% for Ca²⁺ and 39% for Mg²⁺, while SO₄^2- ion was not affected by canopy exchange.
Calculations using a model indicated that the contribution from thefoliage leaching to the total throughfall flux for the conifer forest was 61, 59 and 11%, and 70, 64 and 28% for the deciduous forest for K⁺, Mg²⁺and Ca²⁺, respectively. F^-, Cl^-, NO₃^- and NH₄⁺, however, were absorbed by the canopies. For these reasons, a large supply of N and Cl should affect the nutrient balance of the ecosystem. In particular, a large supply of F negatively affects vegetation and the foliage leaching of K⁺, Mg²⁺ and Ca²⁺ will cause a nutrient imbalance of the ecosystem and bring about the decline of the forests.

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For predicting the future acidification of soil at a forested site due to acid precipita tion, the net input of acid precipitation from the atmosphere has to be estimated. Some analysis of throughfall observation data may be applicable as a method for estimation. In this study, a simple multiple regression model that explains throughfall formation process by assuming ionic species in atmospheric particles which have deposited on foliage and foliar exudation during rainfall event are added to rainwater on a canopy was proposed to estimate the contribution of atmospheric particles to net input.
The application of the proposed model at a bamboo forest to the observation result of the amount of ionic species in rainwater, in throughfall and in aerosol particles for 21 rainfall events between April 1994 and March 1995 gave the multiple regression corfficient of 0.8. From one of the regression parameters obtained, the average deposition velocity of atmospheric particles was calculated to be 3.3 mm s^-1 based on land surface base. Subsequently, the average deposition velocity of SO₂ was calculated to be 3.7 mm s^-1 by assuming all the SO₄^2- ion classified as foliar exudation in our model is originated not in uptake from root but in gaseous absorption of SO₂. These values are adequate compared with previously reported values, and the model is useful to estimate atmospheric input at a forested site from throughfall observation.

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Decline of Cryptomeria japonica has been reported in the suburban areas of Japan and related field surveys suggested that high concentration of photochemical oxidants might be linked with its decline. For assessing combined effects of rain acidity and ozone on the growth of trees, seedlings of Cryptomeria japonica, Chamaecyparis obtusa, and Chamaecyparis pisifera were exposed to simulated acid rain (SAR) and ozone for 23 months in the controlled chambers under the natural light condition. The pH of SAR was 5.6 (deionized water) or 3.0 containing sulfate, nitrate and chloride at the equivalent concentration ratio of 5: 2: 3. Plants were exposed to SAR at a rate of 2.5 mm/hr×8 hr/day, 3 times a week from April to September, and twice a week at a rate of 2.5 mm/hr×8 hr from october to March in the first year and 2.5 mm/hr×4 hr in the second year. Total precipitation was 4300 mm for 23 months. Dairy ozone exposure has conducted at a constant concentration of 0, 60, 120 or 180 ppb between 09: 00 to 15: 00 with no exposure between 16: 00 to 08: 00.
Chamaecyparis obtusa and Chamaecyparis pisifera developed needle chlorosis and early defoliation in the older needles exposed to higher ozone concentrations, however, Cryptomeria japonica did not show any visible symptoms for 23 months exposure to ozone. No visible symptoms by the exposure to SAR at pH 3.0 and 5.6 were observed in these three species.
Plant height and stem diameter in plants exposed to SAR at pH 3.0 were greater than those in plants exposed to SAR at pH 5.6. Dry weight of the plants exposed to SAR at pH 3.0 was greater than that of the plants at pH 5.6. Ozone exposure did not modify the total dry weight of the plants, however, dry weight of leaves in plants exposed to higher ozone concentrations was significantly greater than that of plants exposed to clean air. In contrast, high ozone exposure significantly reduced root dry weights. Thus, top/root dry weight ratio in the plants exposed to higher ozone increased and the exposure to SAR at pH 3.0 enhanced this trend.
These results suggested that higher ozone concentration interfered with carbon allocation and increased rain acidity, probably associated with nitrate, exacerbated this effects. This may lead to increase susceptibility to drought stress in these species. As Cryptomeria japonica is more sensitive to drought stress than Chamaecyparis obtuse, current results may support the hypothesis that high concentration of ozone and high input of nitrogen in suburban areas may have a possible linkage with the decline of Cryptomeria japonica. This study also sggested that changes in dry matter distribution of assimilates might be a good indicator for assessing a long-term chronic effect of ozone on the growth.

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Lead isotope ratio in snow samples, which were collected in Japan from Hokkaido to western Honshu in 1990 and 1992, were measured. Lead in snow samples was dissolved with nitric acid and concentrated. After separation of lead from the concentrated sample solution by electrodeposition, isotope ratios of lead were determined by ICP-MS. The lead isotope ratios observed had large variations. The snow samples were classified into five categories based on the five areas where air mass trajectories passed over. Those are (1) Far Eastern Russia, (2) boundary area between Russia and China, (3) northern China, (4) middle China and the Korean Peninsula and (5) Japan. Lead isotope ratios for the samples from each categorized area indicated characteristic value individually. The snow samples of category (4) had the highest values in ²⁰⁸Pb/²⁰⁶Pb (also ²⁰⁷Pb/²⁰⁶Pb), which were similar characteristics to lead produced in the Korean Peninsula and middle China. Lead isotope ratios for category (1) were similar values to Russian lead reported. In the case of category (5), the values were close to those for Japanese air pollution. Such categorization of snow samples according to air mass trajectory well corresponded to property of lead isotope ratios. The relation between them were very similar to the case of aerosol lead, which were reported previously, in spite that category (2) sometimes showed similar values to Japanese lead (category (5)). Two reasons were considered for that. One is the existence of a lead mine (Tetyukhe) in this area (2), which has similar lead isotope ratios to Japanese lead. Another is contribution from coal fly ash, which could give a lower value in ²⁰⁷Pb/²⁰⁶Pb. Thus, it was concluded that lead isotope ratios in snow could be good tracers to indicate long-range transport of air pollution in the Asian region.

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In Part 2 of the study, the CFD method to predict the exhaust gas diffusion around a building was proposed. The numerical results were compared with the measured results of one case in Part 1, a case with an emission souce at the downwind corner on the rooftop on the cube.
In practical purpose, minimizing the computational cost is important. Therefore, the k-ε model was choosed as a turbulent model.
The required mesh fineness in the neighbor of walls should be smaller than H/24 where H is the model height. The values of eddy dissipation rate at the inflow boundaries were well determined by the consideration to balance the terms of the turbulent energy generation and dissipation. The turbulent intensity of the exhausted gas had small effects on the results. The log-law was better than the 1/4 power-law for the wall boundary conditions. The turbulent Schmidt Number of 0.6 or 0.7 brought the best predictions of the concentration field.
Through the validation, the following characteristics were clarified; The standard k-ε model can reproduce the recirculation flows neither on the rooftop nor by the sidewalls correctly. The reattachment point was 2.1H behind from the model center, which was longer than the measured value 1.6H. The turbulent energy at the downward region of the rooftop and sidewalls were predicted smaller than the measued values.
Concerning the concentration field, the horizontal width of the plume was narrower and the vertical peak position was higher than the measured value. These discrepancies can be explained by the above mentioned inaccuracy of the predictions of the flow fields.
The characteristics of the horizontal peak position and the concentration decay rate with distance are important but difficult to be predicted by the Gaussian diffusion models. In spite of remaining small defects, the proposed CFD method reproduced them well.

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Part 1 of this study investigated the flow and diffusion around a cube in a wind tunnel. The flow around a cube was measured with a split-fiber probe designed for measuring flow velocity in those regions of highly turbulent and reversing flows. The rooftop and wake region concentrations of tracer gas released from two different sources (one at the center and one at the downwind corner of the rooftop) were measured.
In the wake region, the flow reattachment behind the building occurred at 1.6 times the building height from the model center. A high turbulent flow region was observed at roof level and behind the cube in the planes of its sides. The data of the standard deviation of u-component velocity showed that the high, turbulence region persisted throughout the downwind region. The high turbulent regions υ-and ω-components increased in area and heared the ground with respected to the down-wind distance.
In the case of the corner emission source on the rooftop, the peak concentration just behind the building occurred at rooftop level. As the source was on the corner of the roof and not in the center, the position of the peak concentration was to the one side of the building, but moved closer to the center as it moved farther downwind. In the case of the center emission, the degree of concentration near the building was less than that of the corner emission as a result of the initial difference in diffusion.

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The cultivar difference in the sensitivity of Brassica campestris L. to O₃ based on the dry weight growth was investigated using the 10 cultivars. On the 8th, 10th and 12th days after sowing, 10 cultivars were exposed to 130±10nl·l^-1 (ppb) O₃ for 4h per day (10: 00-14: 00) at 29.0±1.0°C, 65±10% R. H. and 400μmol·m^-2·s^-1 PPFD. The control plants were exposed to charcoal-filtered air under the same environmental conditions. On the 15th day after sowing, all the plants were harvested to determine leaf area and dry weight.
The sensitivity of the 10 cultivars to O₃ based on the percent reduction in the total dry weight per plant to the control value was ranked as follows: Misugi>Purara>Shinbansei>Maruba>Bansei=Rakuten>Gozekibansei>Harumi>Natsurakuten>Saori. This ranking could not be explained by the degree of O₃-induced visible foliar injuries, whole-plant growth rate and stomatal density. However, the reduction in the photosynthetic CO₂ uptake per unit amount of O₃ absorbed by the leaf was significantly different among the three cultivars, and was ranked as follows: Misugi>Harumi>Saori. This ranking coincided with that in the sensitivity of whole-plant dry weight growth or net photosynthetic rate to O₃. Therefore, the cultivar difference of Brassica campestris L. in the sensitivity to O₃ based on the dry weight growth is considered to depend mainly on the capacity for physiological detoxification of O₃ in the leaves.

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[in Japanese]

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