Abstract
Recently, it has been reported that the O3 concentrations on the weekend are higher than those during the weekday despite the lower concentrations of the O3 precursors such as NOx and NMHCs in urban areas. This phenomenon is called the “ozone weekend effect” (OWE). We investigated the weekly patterns of O3 and its precursors and the cause of the OWE, using the data observed in Osaka from 2006 to 2008. The weekly patterns for both the ozone and its precursors on the weekdays were similar among the air monitoring stations but varied year to year. On the other hand, the weekday-Saturday-Sunday variations of the precursors were similar for all the examined periods. The main cause of the OWE is the titration of O3 by NO in terms of the comparison between the weekdays and weekends. However, the comparison between the weekdays and Saturday in 2007 suggests that the photochemical ozone production on Saturday would be greater than that on the weekdays. The analyses of NOx and Ox (the sum of O3 and NO2) between the weekdays and Saturday indicated that the ozone production regime in 2006, on the weekdays in 2007 and on Saturdays in 2008 would be the boundary region, NMHCs- and NOx-limited, respectively.
