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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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John H. Seinfeld, Gregory R. Carmichael, Richard Arimoto, William C. Conant, Frederick J. Brechtel, Timothy S. Bates, Thomas A. Cahill, Antony D. Clarke, Sarah J. Doherty, Piotr J. Flatau, Barry J. Huebert, Jiyoung Kim, Krzysztof M. Markowicz, Patricia K. Quinn, Lynn M. Russell, Philip B. Russell, Atsushi Shimizu, Yohei Shinozuka, Chul H. Song, Youhua Tang, Itsushi Uno, Andrew M. Vogelmann, Rodney J. Weber, Jung-Hun Woo, and Xiao Y. Zhang

Although continental-scale plumes of Asian dust and pollution reduce the amount of solar radiation reaching the earth's surface and perturb the chemistry of the atmosphere, our ability to quantify these effects has been limited by a lack of critical observations, particularly of layers above the surface. Comprehensive surface, airborne, shipboard, and satellite measurements of Asian aerosol chemical composition, size, optical properties, and radiative impacts were performed during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) study. Measurements within a massive Chinese dust storm at numerous widely spaced sampling locations revealed the highly complex structure of the atmosphere, in which layers of dust, urban pollution, and biomass- burning smoke may be transported long distances as distinct entities or mixed together. The data allow a first-time assessment of the regional climatic and atmospheric chemical effects of a continental-scale mixture of dust and pollution. Our results show that radiative flux reductions during such episodes are sufficient to cause regional climate change.

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