Springtime photochemical air pollution in Osaka: Field observation

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.