||Overview of Policy Actions and Observational Data for PM2.5 and O3 in Japan: A Study of Urban Air Quality Improvement in Asia
Recent topics on PM2.5 and O3 in Japan have been briefly discussed in this paper. In the first part, Japan’s policy measures for PM2.5, including the establishment of Environmental Quality Standards (EQS) and monitoring stations, are described. Additionally, we discuss the monitoring data obtained and the exceedance of EQS in the years 2010-2013. The nationwide averaged data shows that sulfate and EC/OC are the most prominent components of PM2.5 and contribute almost equally to it . Secondly, long-term variation of O3 (Ox) and its precursors, NO2 and NMHC/VOC (non-methane hydrocarbon/volatile organic compound) are presented. The paradox of the increase in the average concentration of O3 in spite of the decrease in ambient concentrations of NO2 and VOC is discussed. The phenomenon was found to reflect three components: (1) a decrease in the NO titration effect, (2) an increase in transboundary transport, and (3) a decrease in in situ photochemical production. It is proposed that the integrated approach to mitigation measures for PM2.5 and O3 pollution should be considered within a framework of the SLCPs (short-lived climate pollutants) co-control policy.