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. D uring the aircraft observations of 19-21 April 1993, high concentratio ns of photochemical air pollution were observed over the Osaka area un der a stagnant meteorological condition. The maximum observed ozone co ncentration 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 ozo ne level was almost constant during the afternoons of 19-20 April 1993 . ranging from 80 to 100 ppb, and the presence of aged secondary pollu tants was detected in the nighttime. The upper ozone concentration abo ve 3000 m was approximately 60 ppb. The observational results, near th e surface and aloft, indicate the importance of photochemically produc ed ozone and transported background ozone in controlling secondary air pollution covering Osaka and the surrounding area in spring.