In Japan, the first photochemical air pollution epispde was reported in 1970. These episodes were observed often in middle and high school students in Tokyo andOsaka who exercised in the daytime during the photochemical air pollution season. The observed symptoms were divided into three categories: irritating symptoms of eye, throat and airway; general symptoms such as headache, nausea, dizziness and lastitude, etc., and neurological symptoms such as numbness in the extremities, convulsions, and unconsciousness. The health risk assessment for evaluating the causal relationship between the observed symptoms and air pollutants was made by epidemiological and clinical human exposure studies. The result showed thatthe irritating symptoms of airway were due mainly to exposure to ozone. Althoughthe mechanisms of the general and neurological symptoms other than respiratory irritation could not be determined in these studies, a level of 0.15ppm ozone produced significant respiratory effects when the subj ct undertook light exercise.

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A three-dimensional photochemical air pollution model was developed to simulate the regional scale summer time photochemical oxidants episodes. The numerical model includes transport, diffusion, dry deposition, emission and chemical reaction processes. Dry deposition processes were modeled using resistance theory that depends on land use data. Carbon-Bond Mechanism (CBM-IV) was used as chemical reaction scheme. The Colorado State University Mesoscale Model (CSUMM) with a dynamic initialization and a four-dimensional data assimilation based on observed wind data was used as meteorological driver to generate three-dimensional flow anddiffusion fields.
A model validation study was performed over the summer timeKanto area for 42 hours starting from 0400JST on July 16, 1981. NO_x and NMHC emission intensities (including biogenic HC) estimated from 1 km² data over the Kanto area. Numerical results were then quantitatively compared with the routine surface monitoring stations data and the three-dimensional airborne observation data.
The observed spatial and diurnal variations of 0₃, NO_x and NO₂ concentrations are well simulated by the present model. The predictive performance of thepresent model exceeds the model evaluation criteria recommended by the US-EPA. Furthermore, the present model qualitatively reproduces the three-dimensional behaviors of 0₃, NO_x, NO₂ and NMHC concentrations observed by the aircraft.

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Two-year old seedlings of Cryptomeria japonica and Chamaecyparis obtusa were cultivated to examine the effect of root sphere acidity on the plant growth in the nutrient solution culture, for assessing the soil acidification stress, which may contribute to the conifer decline. Acidity of one fifth Hoagland's nutrient culture solution was adjusted to the pH ranging from 3.5 to 6.0 by HC1 and NaOH.
The results of current cultivation experiment for 15 weeks suggested that the growth performance of both Cryptomeria japonica and Chamaecyparis obtusa was best under the lowest pH level of 3.5-4.0. Both species, however, decreased plant dry weight at high pH level. Total cation contents in the leaves and roots of both species cultivated at pH 3.5-4.0 were highest.
These results suggest that both species have a characterstic adaptability to such a low pH condition. Therefore, potentiality that soil acidification stress in the pH range of 3.5 to 4.0 will induce growth reduction, is an ineffective factor for the growth suppressionof both conifer species.

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We have studied the mechanism of retardation of growth in UV-B irradiated plants. Cucumber seedlings were cultivated under artificial visible light, and irradiated with supplemental UV-B using fluorescent lamps for 12 hr a day. The growth of cucumber seedling first leaves was promoted by fertilization. However, the growth of first leaves of fertilized seedlings was suppressed by UV-B irradiation to a level similar to that of unfertilized seedlings. The growth of first leaves of unfertilized plants did not decline significantly by UV-B irradiation. We found that the photosynthetic activity of first leaves was decreased by UV-B irradiation, especially, in the case of fertilized plants. The activity of ascorbate peroxidase, an enzyme involved in detoxication of active oxygen, in first leaves was increased by UV-B irradiation, suggesting that active oxygen was generated by UV-B irradiation in first leaves. Active oxygen was probably the cause of the observed decrease in photosynthetic activity.
Exogenous benzyladenine, a synthetic cytokinin, promoted the growth of disks excised from the first leaves of plants without exposure to UV-B, especially of those supplied with nutrients. However, the cytokinin did not promote the growth of leaf disks from UV-B irradiated plants. The growth-promoting activity of extracts from first leaves was examined. The activity of the extracts from fertilized, unirradiated plants was high, but the activity of extracts from UV-B irradiated plants was not significant, irrespective of fertilization. These results suggest that grwoth-promoting substances in first leaves were increased by fertilization, but inactivated by UV-B irradiation. Therefore, UV-B induced decrease in the growth of first leaves could be related to decrease in sensitivity to plant hormones and the growth-promoting activity in first leaves.

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To obtain basic data about the effects of soil acidification induced by acid deposition on woody plants growing in the East-Asia, the growth tnd element content of red pine (Pinus densiflora Sieb. et Zucc.) seedlings grown in brown forest soil acidified by adding H₂SO₄ solution were investigated. In the case of soil acidification without leaching of cations from the soil, H+ was added as H₂SO₄ solution to the soil at 10, 30, 60 or 90 meq H⁺·L^-1 air-dried soil. Soil without theadditional supply of H⁺ was used as a control. On the other hand, inthe case of soil acidification with leaching of cations from the soil, the soilwas put in the container after soil acidification by the above-mentioned method. Water of threetimes of the amounts of the volume of the soil was poured to thecontainer. After 3 days, water was gradually pulled out from the bottom of the container. The seedlings were transplanted to the acidified soils or the controlsoil, then they were grown in a greenhouse for 120 days from 2 June to 29 September, 1995.
The Al concentration of soil solution in the acidified soil increased with increasing the amount of H⁺ added to the soil. The total dry weight of the red pine seedlings were decreased by the addition of the H₂SO₄ solution. Increase of Al concentration in the underground part ofthe red pine seedlings decreased the concentration of elements such as Caand Mg in the ground part.
On the other hand, the growth of red pine seedlings was dependent not only on the Al concentration but also on the balance of Al and cations such as Ca, Mg, K in the soil solution. When the (Ca + Mg +K)/Al molar ratio of soil solution becomes less than 7.0, total dry weight decreased obviously, and it decreased to approximately 40% in the case of 1.0 in the molar ratio.
Therefore, while the concentration of plant-harmful metal, Al, in the soil solution is an important factor, in the case of red pine seedlings, the concentrationof plant-required elements such as Ca, Mg, and K are also needed to be considered.

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The fluxes of CO₂ and O₃ were observed using Bowen ratio method in wheat (Triticum aestivum) field to fi nd out the method for evaluating the amount of ozone absorption based on the plant production. The fluxes of CO₂ and O₃ were divided by the atmospheric concentration of CO₂ and 0₃ respectively for calculating the deposition velocity of the gases (K_co2 and K_o3). The average value of ratio of deposition velocity (RK; where RK =K_o3/ K_co2) for the observation period was 8.5. It is assumed that the variation of RK by days is caused mainly by the variation in daily average solar radiation, resulting the change in K_co2.

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For elucidation of the actual state of human exposure to carcinogens and its relative compounds in airborne particles, influence of respiratory depth on the deposition ratio of PAHs to respiratory tract was estimated. The particles in exhalation were collected using Hans Rudolph mask, and those in the outdoor air corresponding to inhaled air were collected using the low volume air sampler of low noise model. The concentrations of PAHs in the collected particles were determined by column concentration HPLC/spectrofluorometric detection method. From the results, the deposition ratio of BaP for intentional deep breathing (58.5±12.7%) was about 10% higher than that for shallow breathing (47.2±12.6%). The deposition ratios for shallow breathing are similar to those for diesel exhaust and indoor air contaminated by side stream of tobacco smoke.

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Seven kinds of soil particles (3 mg) were dispersed in 20 ml of NaHSO₃ (1 mmoll^-1) solution and photoirradiated to investigate their effects on the photooxidation of S (IV). All seven soil particles catalyzed S (IV) oxidation without light. With photoirradiation, six soil particles accelerated the oxidation with oxidation rate ranging from 0.5-2.3×10^-5 moll^-1 min^-1, compared to 0.3-1.5×10^-5 moll^-1 min^-1 without photoirradiation. Fe concentration increased during the oxidation of S (IV).

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