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Shinji Wakamatsu, Toshimasa Ohara, and Itsushi Uno

Abstract

In the Osaka area, high concentrations of NO2 are observed in spring. To understand the relative roles and amounts of transported background ozone, photochemical ozone, transported NO2, and primary emitted NO2 in controlling NO2 formation in the Osaka area, a three-dimensional photochemical air pollution simulation model was applied based on the actual meteorological and emission conditions. Simulated results reveal that photochemical reactions play an important role in the formation of the springtime high concentrations of NO2 in Osaka.

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Toshimasa Ohara, Itsushi Uno, and Shinji Wakamatsu

Abstract

The penetration of a land breeze front and its turbulence structure was observed at the center of the Tokyo metropolitan area on 27–28 January 1983. A turbulence sonde, small tethersonde and an acoustic sounder were used for the experiment. The detailed shape of the land breeze head and its flow characteristics were analyzed. The penetration of the land breeze was detected at about 2130 JST, and the advance speed of the land breeze front was estimated to be about 2.4 m s−1. The shape of land breeze head was similar to that of a sea breeze head reported by Simpson et al. (1977). The top height of the land breeze head was 400 m and the depth of the land breeze layer proper was about 200 m. A closed circulation pattern was detected inside the land breeze head. Large velocity fluctuations were observed at the leading edge of the head and the boundary of the large turbulence zone showed a wavy pattern behind the land breeze head. These features coincided with the results of Simpson et al. (1977). A comparison of the advance velocity ratio of the land breeze front also showed good agreement with the laboratory experiment of Simpson and Britter (1980).

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Shinji Wakamatsu, Itsushi Uno, and Toshimasa Ohara

Abstract

High concentrations of nitrogen dioxide are frequently observed in the Osaka area in the spring. To clarify the mechanism of springtime air pollution formation, a series of three-dimensional field observations was conducted in April 1993 covering Osaka and the surrounding area. During the aircraft observations of 19–21 April 1993, high concentrations of photochemical air pollution were observed over the Osaka area under a stagnant meteorological condition. The maximum observed ozone concentration was more than 150 ppb. The vertical distribution of ozone was uniform up to 2400 m in the daytime. At Mt. Ikoma (600 m), the ozone level was almost constant during the afternoons of 19–20 April 1993, ranging from 80 to 100 ppb, and the presence of aged secondary pollutants was detected in the nighttime. The upper ozone concentration above 3000 m was approximately 60 ppb. The observational results, near the surface and aloft, indicate the importance of photochemically produced ozone and transported background ozone in controlling secondary air pollution covering Osaka and the surrounding area in spring.

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Hidemi Kurita, Kazutoshi Sasaki, Hisao Muroga, Hiromasa Ueda, and Shinji Wakamatsu

Abstract

The long-range transport of air pollution on clew days under light gradient wind conditions is investigated from an analysis of all days with high oxidant concentrations in 1979 at locations in central Japan that are far from pollutant sources. Surface-level wind and pressure distributions over a 300×300 km area were analyzed, together with concentration isopleths of oxidants and suspended particles produced by photochemical reactions.

It was found that the transport mechanism consists of. 1) land/sea breezes; 2) a steady onshore wind driven by the diurnal-mean land–sea temperature difference; 3) the generation of a strong thermal low in the inland mountainous region in the daytime; and 4) a subsidence inversion accompanied by a synoptic-scale high pressure system. The last three mechanisms work to combine land/sea breezes and slope and valley winds into one large-scale high-speed wind field that transports pollutants a long distance inland into the mountainous region.

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