An Analysis of Annual Trends of Photochemical Oxidants in the Kanto and Kansai Areas

Abstract

Hourly and annual oxidant (O_x) concentrations measured at monitoring stations in the Kanto and Kansai areas from 1978 through 1990 were statistically analyzed to examine annual trends in photochemical air pollutant behavior. The spatial and temporal annual trends of the daily maximum O_x concentration, and of the NMHC and NO_x cencentrations and the NMHC/NO_x ratio were analyzed. The analysis shows, in relation to the daily maximum O_x concentrations during the period 1978-1990, that:(1) the time of the daily maximum O_x concentration occurs later in a day, and (2) the location of the daily maximum O_x concentration shifts inland away from the major emission areas (Tokyo in the Kanto area and Osaka in the Kansai area). In relation to the NMHC/NO_x ratio the analysis shows that the ratio has decreased over the 13-years period. This decrease may be one explanation for the above-described changes in the daily maximum O_x pattern. Numerical simulation may clarify the link between the daily maximum O_x concentration trends and the NMHC/NO_x ratio.