Aircraft survey of the secondary photochemical pollutants covering the Tokyo metropolitan area

Abstract

To investigate the photochemical smog formation mechanism over the Kanto Plain, a series of aircraft measurements was conducted from 8 to 12 August 1978 covering the Tokyo Metropolitan area. Various flight patterns were designed to provide appropriate data for determining both the horizontal and vertical pollutant profile. It was found that there is a relationship between the pollutant concentration and the local weather pattern, in particular, the sea-land breeze. 9 August was typical of a sea-land breeze day. In the morning, the sea breeze front formed near the shore, gradually moving inland. The concentration pattern showed two peak regions with the sea breeze front as the dividing line. Using trajectory analysis, it was found that the high concentration zone in the land breeze area is caused by pollutants trapped overnight, and the high concentration zone in the sea breeze region is caused by fresh pollutants. On 12 August 1978, high photochemical smog was observed in the southern part of the Kanto Plain (south of the Tokyo Metropolitan area) caused by just such a complex wind structure. The easterly wind replaced the morning land breeze (northerly wind) during the afternoon. This resulted in a low O 3 concentration zone where the clean easterly wind had penetrated into the northern Kanto region. South of this clean zone, a high O 3 concentration zone stretched from Tokyo to the Yokohama area. These results show the importance of the long-time transportation of polluted air masses and the complex wind field structure in understanding the behaviour of photochemical smog in this area.