Analyses of the ozone weekend effect in Tokyo, Japan: Regime of oxidant (O 3 + NO 2) production

Abstract

The ozone weekend effect (OWE) in Tokyo, the capital of Japan, was analyzed from April 2005 to March 2008 with respect to the photochemical ozone production, focusing on the ozone production regime. For most periods, the OWE was confirmed in the wintertime as well as in the summertime. The comparison of O x ([O x] = [O 3] + [NO 2] - 0.1[NO x]) concentrations between weekdays and weekends suggests that there are some periods when the photochemical ozone production on the weekends could be larger than on the weekdays (defined as the POP group). We compared NO x (the sum of NO and NO 2) and O x concentrations on the weekends with those on the weekdays for several distinct ranges of the non-methane hydrocarbons (NMHCs) concentrations, and NO x and O x concentrations on the weekends are significantly lower and higher than those on the weekdays in the POP group. Therefore, the ozone production regime would be NMHC-limited in the POP group. The ozone production regime in the summertime in Tokyo could be in the boundary area between NMHCand NO x-limited in terms of the NMHCs/NO x ratios. The NMHCs/NO x ratios in the NMHC-limited regime are smaller than those in the NO x -limited regime in general. However, the NMHCs/NO x ratios in the POP group were not smaller than those in the non-POP group. © Taiwan Association for Aerosol Research.