Abstract
Weekend increases of photochemical Ox concentrations are found on the lower ozone formation conditions in the Kanto and Kansai regions, and also a reversal of the weekend effect to the weekend decrease is found onhigher ozone formation conditions. Similarly, a spatially occurring reversal of weekend effects are found; from weekend increase in source areas to weekend decrease in rural areas. Composite analyses are practiced to understand the mechanism of the phenomena. Composites of the precursor's concentration data and the meteorological data produced by the classified regional Ox concentration levels are compared for the weekday and weekend. The major findings are that 1) NMHC/ NOx ratio varies spatially, from a highly HC-limited regime in source areas to a NOxlimited regime in remote areas; this also varies temporally, from a highly HC-limited regime in lower ozone formation potential days to a NOx-limited regime in higher ozone formation potential days. 2) The primary cause of the temporally occurring reversal on weekend effects is a change of the ozone formation regime, which brings a change in the NOx function from ozone inhibition to ozone promotion. 3) The primary cause of the spatially occurring reversal of weekend effects is similar to the temporally occurring reversal; however, it occurs in an advection process from source areas to downwind rural areas. Furthermore, boundary NMHC/ NOx values between HC-limited and NOx-limited regimes are estimated by using the phenomena of reversal on weekend effects, as 7-16 in the Kanto region and 6-12 in the Kansai region. As a result, dynamically changing ozoneformation regimes in time and space are verified.
