Causes of high photochemical oxidant at Nagahama city, located in the O-mi basin, were examined by using surface meteorological data from the 1992-2001 warm seasons. Long-range transportation of photochemical oxidants from Osaka, Kyoto and Fukui prefecture was not detected in cases where the weather was favorable. There was a possibility of transportation from Gifu prefecture by southeasterly winds associated with migrating high pressure systems and following extra-tropical cyclones. Under conditions where land-breezes are prevalent, Hikone will experience high concentrations of nitrogen oxide during the night and early morning; on such occations there is an increase in the afternoon of photochemical oxidants in Nagahama city. Possible mechanisms of short-range transportation of air pollution affected by the land-lake breeze circulation around the Lake Biwa were discusses.

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We assessed carcinogenic risk from inhalation exposure of 1, 2-dichloroethane, which is one of 22 hazardous air pollutants proposed as 'substances requiring priority action' by the Central Environmental Council of Japan in 1996. We calculated the carcinogenic unit risk by the benchmark dose approach utilizing data from mammary gland tumors of female rats exposed to 1, 2-dichloroethane for two years. Four groups comprising 50 rats each were exposed to 1, 2-Bdichloroethane of the following concentrations: 0 ppm, 10 ppm, 40 ppm, and 160 ppm. The numbers of rats bearing tumors in their mammary glands for the respective groups were 8, 8, 11, and 25. We estimated the concentration corresponding to an excess risk of 0.10 (EC₁₀) and its lower confidence limit (LEC₁₀). For the methods of interspecies extrapolation from rat to human we utilized two approaches, one was a dosimetric method based on the regional gas dose ratio, and the other was an allometric scaling method based on body size. The dosimetric method for gases as 1, 2-dichloroethane, which exhibits its toxic effects outside of the respiratory tract, assumes that the effects observed are related to the arterial blood concentration. By the dosimetric method, the human equivalent benchmark concentration of 1, 2-dichloroethane was calculated using the ratio of the blood: gas partition coefficient of the chemical for the rat to the human value. Its carcinogenic unit risk from inhalation exposure was estimated to be 6.3 ×10^-6 per (μg/m³), and the exposure concentration at the risk level of 10^-5 was calculated to be 1.6 μg/m³. Its unit risk was also estimated to be 7.1 ×10^-6 per (μg/m³) using the allometric scaling method, and it was almost the same value as when estimated using the dosimetric method.

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Weekend effects on photochemical oxidant concentrations in the Kanto and Kansai regions are analyzed for the period 1990 to 2002. The mean daily mean concentrations and the mean daily maximum 1-hour concentrations increase on Sunday at most of the stations. Significant negative correlations are found between the change of oxidant concentrations from weekdays to Sunday and the change of NOx concentrations from weekdays to Sunday. It is supposed that the decrease of the NOx inhibition effect on ozone formation on Sunday brings the increase of ozone under the HC-limited regime. However, by comparisons of Ox concentrations on weekdays and weekends along the percentile axis, a reversal of the weekend effectto the weekend's decrease on the higher percentile is found at many observation sites. Similar reversal of weekend effects are found occurring spatially at fixed percentile points from a weekend increase in source areas to a weekenddecrease in rural areas. These phenomena, occurring highly systematically, are estimated to come from the regime change from a HC-limited to a NOx-limited environment in time and space.

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Weekend increases of photochemical Ox concentrations are found on the lower ozone formation conditions in the Kanto and Kansai regions, and also a reversal of the weekend effect to the weekend decrease is found onhigher ozone formation conditions. Similarly, a spatially occurring reversal of weekend effects are found; from weekend increase in source areas to weekend decrease in rural areas. Composite analyses are practiced to understand the mechanism of the phenomena. Composites of the precursor's concentration data and the meteorological data produced by the classified regional Ox concentration levels are compared for the weekday and weekend. The major findings are that 1) NMHC/ NOx ratio varies spatially, from a highly HC-limited regime in source areas to a NOxlimited regime in remote areas; this also varies temporally, from a highly HC-limited regime in lower ozone formation potential days to a NOx-limited regime in higher ozone formation potential days. 2) The primary cause of the temporally occurring reversal on weekend effects is a change of the ozone formation regime, which brings a change in the NOx function from ozone inhibition to ozone promotion. 3) The primary cause of the spatially occurring reversal of weekend effects is similar to the temporally occurring reversal; however, it occurs in an advection process from source areas to downwind rural areas. Furthermore, boundary NMHC/ NOx values between HC-limited and NOx-limited regimes are estimated by using the phenomena of reversal on weekend effects, as 7-16 in the Kanto region and 6-12 in the Kansai region. As a result, dynamically changing ozoneformation regimes in time and space are verified.

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[in Japanese]

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[in Japanese]

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