The main purpose of this paper is to examine the phenomena when hazardous dense gases, such as ammonia gas and LNG, are spilled into the atmosphere from a pressurized storage tank. This study is useful to develop an accidental risk assessment method. The characteristic of gases released from the pressurized tank is a mixture cloud of gaseousness and droplets. In papers published in the past, the effect of evaporation of liquid droplets has never been examined. In this paper, we propose a two layer box model in order to predict a concentration considering this effect. This model is useful to estimate concentration of dense gas released instantaneously from a pressurized tank. Furthermore, for continuous dense gas spill, we calculated the average concentration at the downwind distance, treating the two layer box model like puff models. Also, we improved it to be able to predict the vertical concentration distribution, which was not estimated in the conventional model. The calculated result in this model generally corresponds well with the data of the Desert Tortoise Experiment.

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The effect of urea injection (selective non catalytic reduction of NO_x) on N₂O emission was investigated at a municipal solid waste incineration plant in Osaka City. N₂O concentration in the case of urea injection was found to be greater to about fivefold of that in the case of non injection. The change in N₂O concentration was very small or negligible between at the exit of electrostatic precipitator and at that of scrubber with or without urea injection. It is estimated that about 14% of reduced NO_x is converted into N₂O in the present study. It is tentatively assumed that NCO derived from urea may contribute to the reduction of NO_x to form N₂O.

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A convenient method is described to appreciate damage levels of building marble plates caused by acid rain in a relatively short exposure period. The relative lightness and arithmetical average roughness height (Ra) are determined on the surfaces of plates (thickness 5 mm, width 30 mm and length 70 mm) after exposing the sample plates for 1-9 months at both outdoor and indoor sites on a mountain top, on a mountain foot and by a highway.
The lower pH of rain water fell, the more remarkable loss of lightness appeared in a short period on the surface of outdoor samples in 1-3 month exposure tests. Physical change of the plate surface may be estimated by using the lightness change optically measured bacause the Ra is inversely correlated to the relative lightness.
In 3-9 month indoor-exposure tests, differences of the lightness were quantitatively observed, but little differences of the Ra were recognized among the different exposure sites.
Damage levels of the marble plates were 4-11 times higher at outdoor sites by rain water than those at indoor sites by air pollutants in the ambient air.
Thus, the optical method may be useful to appreciate damagelevels of marble building meterials caused by acid-rain water after exposing them for a relatively short period.

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To evaluate ambient particulate sulfate concentrations over a wide region, aerosol samples were collected at nine sites in the Kyushu-Okinawa district between 1 and 11 October 1991.
Particulate sulfate concentration in the Kyushu-Okinawa district was shown to be approximately similar in spatial distribution and daily variation among the sites studied. The concentration of particulate sulfate at Okinawa, located in an unpolluted southern marine area, was 7.7 μg/m³. This level is considered to be relatively high. The daily variations of particulate sulfate in the northern Kyushu region (Nagasaka, Saga, Dazaifu) were similar among the sites. The maximum concentration of particulate sultate in Okinawa was found to be delayed one day from that observed in Kagashima. Particulate sulfate in Okinawa was presumed to be transported from southern Kyushu.
High concentrations of elemental carbon were observed in urban areas, such as Kitakyushu and Kumamoto. Particulate clemental carbon in the kyushu-Okinawa district was shown to differ significantly in spatial distributions and temporal variations among sites.

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