Abstract
Weekend effects on photochemical oxidant concentrations in the Kanto and Kansai regions are analyzed for the period 1990 to 2002. The mean daily mean concentrations and the mean daily maximum 1-hour concentrations increase on Sunday at most of the stations. Significant negative correlations are found between the change of oxidant concentrations from weekdays to Sunday and the change of NOx concentrations from weekdays to Sunday. It is supposed that the decrease of the NOx inhibition effect on ozone formation on Sunday brings the increase of ozone under the HC-limited regime. However, by comparisons of Ox concentrations on weekdays and weekends along the percentile axis, a reversal of the weekend effectto the weekend's decrease on the higher percentile is found at many observation sites. Similar reversal of weekend effects are found occurring spatially at fixed percentile points from a weekend increase in source areas to a weekenddecrease in rural areas. These phenomena, occurring highly systematically, are estimated to come from the regime change from a HC-limited to a NOx-limited environment in time and space.
