Long-term change in the source contribution to surface ozone over Japan

The relative contributions of various source regions to the long-term (1980-2005) increasing trend in surface ozone (O-3) over Japan were estimated by a series of tracer-tagging simulations using a global chemical transport model. The model simulated the observed increasing trend in surface O-3, including its seasonal variation and geographical features, in Japan well and demonstrated the relative roles of different source regions in forming this trend. Most of the increasing trend in surface O-3 over Japan (similar to 97 %) that was simulated was explained as the sum of trends in contributions of different regions to photochemical O-3 production. The increasing trend in O-3 produced in China accounted for 36% of the total increasing trend and those in the other northeast Asian regions (the Korean Peninsula, coastal regions in East Asia, and Japan) each accounted for about 12-15 %. Furthermore, the contributions of O-3 created in the entire free troposphere and in western, southern, and southeastern Asian regions also increased, and their increasing trends accounted for 16 and 7% of the total trend, respectively. The impact of interannual variations in climate, in methane concentration, and in emission of O-3 precursors from different source regions on the relative contributions of O-3 created in each region estimated above was also investigated. The variation of climate and the increase in methane concentration together caused the increase of photochemical O-3 production in several regions, and represented about 19% of the total increasing trend in surface O-3 over Japan. The increase in emission of O-3 precursors in China caused an increase of photochemical O-3 production not only in China itself but also in the other northeast Asian regions and accounted for about 46% of the total increase in surface O-3 over Japan. Similarly, the relative impact of O-3 precursor emission changes in the Korean Peninsula and Japan were estimated as about 16 and 4% of the total increasing trend, respectively. The O-3 precursor emission change in regions other than northeast Asia caused increases in surface O-3 over Japan mainly through increasing photochemical O-3 production in western, southern, and southeast Asia and the free troposphere and accounted for about 16% of the total.