Aerosol Concentration observations were conducted every second month from August 1990 to February1992 at Tsushima, Nagasaki Prefecture and Ogori, Fukuoka Prefecture. Data included sulfate, nitrate andother anion and cation species concentrations. Sulfate concentration variations at Tsushima and Ogori hadsimilar changes, and from this fact it can be understood that the life time of sulfate is longer than SO₂, andit is a good index of long-range transport (LRT). While nitrate and anmonium concentrations at Ogorilocated in inland took higher values than those observed in Tsushima located isolated in island.
Extremely high concentration episodes of sulfate were found in June 1991 and February 1992. These twoepisodes were analyzed with the help of backward trajectory analysis. It was revealed that the location ofthe rainy season meso-front played a significant role in the transport of pollutants from continental Asia toJapan in June 1991. In February 1992, it was found that the typical winter monsoon weather conditionplayed an important role for the LRT. High concentration of sulfate were observed just after the passagesof lowpressure systems from the East China Sea to the Pacific Ocean. Backward trajectory analysisexplained the observed typical LRT pattern.
These observational and trajectory analysis indicated that the LRT of sulfate from continental Asia toJapan occurred both under the typical rainy season weather condition in June and the typical wintermonsoon season in February.

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Several overwater plume dispersion models under low level release height condition are designed to contribute to impact-prediction of air pollution caused by exhaust gass emitted from artificial establishment overwater in coastal or offshore region. These models are verified by three separate coastal or offshore diffusion experiments in USA.
Gaussian plume equation is used in the overwater disperision model. Diffusion widths (σ_y, σ_z) on Pasquill-Gifford-Turner's chart (PGT chart) are applied to the overwater dispersion in devising the method of use.
It is noticeable that turbulence intensities over sea surface are about a half of these over a flat short grass plain corresponding to the field of PGT chart, because roughness length (z₀) of sea surface is smaller than the above-mentioned grass plain by about two orders. This is clarified by both of observation and similarity theory in surface boundary layer. This valuable relationship is extended to one of diffusion width over sea surface and such grass plain. Moreover, the gradients of az over sea surface are assumed to be smaller than that over land surface because the thickness of surface boundary layer over sea surface are smaller than that over land surface mainly due to the roughness length. They are the original devices. The following two overwater plume dispersion models are recommended,
(1) The relations of Ls and atmospheric stability categories (A-F) in case of z₀=3cm on Golder (1972)'s chart and L observed by bulk method are combined in this model. Categories ofσ_y, σ_z on PGT chart are respectively shifted by two ranks to more stable ranks except the category F to be shifted by one rank, namely A→C, B→D, C→E, D→F, E→G, F→G. Theσ_y, σ_z of category G are respectively extrapolated on PGT chart;σy (G)= (2/3)·σ_y (F), σ_z (G)= (3/5)·σ_z (F).
(2) In case of no observation of atmospheric stabilities, σ_y'σ_z of category G are always used. It is applicable to the case in which safety tolerance is able to establish especially highly.

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Methode are described to evaluate accuracy of monitored data of atmospheric methane st 15 air monitoring stations in the Okayama prefecture. Methane concentrations in 15: 00-16: 00 hour of day are lowest with the lowest deviations and similar to the background levels at the all stations. The monthly averaged concentrations of atmospheric methane in 15: 00-16: 00 hour may be used as standards to estimate systematic errors over long term at the monitoring stations.
Deviation of methane concentrations from the average in this period may be regarded as a systematic error in the monitoring system.
Difference between hourly atmospheric methane and ones at 15: 00-16: 00 houre could be used to observe local characterization of methane emission sources without influence of the wide spread trends of atmospheric methane concentration.

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A three dimensional Eulerian grid model for a long-range transport of air pollutants with simple physical and chemical processes has developed to evaluate the long-term (annual or seasonal) average acid deposition amounts in East Asia. The calculated results by this model concerning amounts of acid deposition and concentration in precipitation were compared with the observed data in Japan. Furthermore, the evaluation concerning nitrogen oxides was also carried out using this model.
According to the result of the comparison between the calculated values and those of the observed data of SO₄^2-and NO₃^-wet depositions in 5 divided regions in Japan, this model could represent the feature of wet depositions in each region Simulated monthly SO₄^2-and NO₃^- concentrations in precipitation indicate reasonable agreement with the observed values at 16 monitoring points in Japan and this mode could also represent the tendency of monthly concentration patterns except for some extreme peaks. The calculated concentration of air pollutants had the same level as observation, and the calculated monthly variation of SO₂, NO₂ and NO₃^-concentration showed a good agree ment with observations.
In general, this model is capable of reproducing the deposition tendency in a long term such as annual or seasonal.

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A wind tunnel study of the flow and diffusion within model urban canopies was conducted. In the Part 1 of the stidy, the mean flow and turbulence structure within and above canopies were investigated. The model canopies consisted of the cubes of 8 cm high in a diamond array, and the plan-area densitiy of the cubes was changed from 10% to 40%. Streamwise and vertical velocity components were measured with a split fiber probe designed for measuring flow velocity in those regions of highly turbulent and reversing fl ows. Three different types of flow patterns were identified through cross-sections of mean velocity vectors, and transitions between them were determined by the density of cubes. The three flow patterns can be referred to as isolated roughness flow, wake interference flow, and skimming flow, following the nomenclature of Morris (1955, Trans. A. S. M. E., 120, 373-398). As the density of cubes increases, streamwise velocityes within the canopy decay until they reach zero at the case of ρ_z=40%, and streamwise velocity fluctuations due to flow separation on the roof disappear for the cases of ρ_z>20%.

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A wind tunnel study of the flow and diffusion within model urban canopies was conducted. The concentration patterns within and above canopies were investigated in the Part 2 of this study. Diffusion for four different building densitites (ρ_z=10-40%) was tested. Tracer gas was emitted from the rooftop at the center of a model building. For the low building density, the highest rooftop concentrations were observed upwind of the source. For the high building density, on the other hand, the highest rooftop concentrations were measured downwind of the source. These differences in the rooftop concentration patterns can be explained by the different rooftop flow patterns shown in the Part 1 of this study. The modified Wilson's equation is a better repesentation of the concentration of the rooftop dispersion.
At ground-level, the maximum concentration appeared windward of the downwind building. This suggests that the gas was transported to the downwind building, then impinged the downwind building, and fl owed down to the ground by cavity flow. In this case, the maximum concentration can be approximately estimated by Briggs's dispersion parameter.

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An extremely acidic fog of pH 1.95 was observed in Mt. Oyama, Tanzawa Mountains on April 25, 1994. The major ions were H⁺ and Cl^-, and non-sea-salt chloride ion concentration of 12.8 mmol/l was detected. The occurrence of acid fogs containing over 1 mmol/l of non-sea-salt chloride ion was limited to the period between 15: 00 and 19: 00, and the concentration increased rapidly, then decreased again in a short time. The extremely acidic fog event may be caused by a local pollution of hydrogen chloride gas, which was discharged from an incinerator. The ion loading of hydrochloric acid in the extremely acidic fog corresponded to about 2 ppb of hydrogen chloride gas in atmosphere, which was often observed in an urban area in Japan. As a result, fog water pH will reach to an extremely low values again in future in a mountainous site close to an urban area.

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Condensed dust is generated in the process of cooling and mixing with environmental air and gaseous matter emitted from stationary sources. Currently, the real state of the condensed dust emissions has not been grasped yet, and the authorized measuring method also is not available.
Two kinds of the condensed dust sampling systems were proposed in the current authorized measuring methods registered in the Japanese Industrial Standard. One is the Air-Direct cooling type, in which the sample gas aspirated from a duct is cooled by diluted air, and the other is the Water-Indirect cooling type, in which the sample gas is cooled in a condenser without dilution by air.
Investigation using these sampling systems is conducted at the various types of combustion facilities. The results of the experiments are as follows.
(1) The relation between the Air-Direct cooling type (Y) and the Water-Indirect cooling type (X) is shown by the following formula. Y=0.930X-1.623. The result, that Y is less than X, is caused by the fact of passing of condensed dust through the Type 2 dust filter and absorbing of gaseous matter into the generated drain in a cooled bottle.
(2) In the case of municipal waste incinerators with high water content in flue gas and large changes of gas conditions, the air-direct cooling type caused some troubles such as difficulty of adjestment of the dilution air corresponding to the gas conditions and damage due to humidification of Type 2 dust filter by water content in sample gas. The Air-Direct cooling type is more complex and larger in scale than the Water-Indirect cooling type. Therefore, the Water-Indirect cooling type is considered to be more reasonable and applicable for field measurements.
(3) The generation of the condensed dust depended on the cooling temperature of the sample gas. Therefore, the cooling temprature should be kept to be constant.

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