The relative importance of various source regions on East Asian surface ozone
We estimated the source-receptor relationship for surface O3 in East Asia during the early 2000s using a method that tags O3 tracers according to their region of chemical production (tagged tracer method) with a global chemical transport model. The estimation demonstrated the importance of intracontinental transport of O3 inside East Asia as well as of the transport of O3 from distant source regions. The model well simulated the absolute concentration and seasonal variation of surface O3 in East Asia and demonstrated significant seasonal differences in the origin of surface O3. In the cold season (October to March), more than half of surface O3 in East Asia is attributable to the O3 transported from distant sources outside of East Asia. In the warm season (April to September), most of the surface O3 is attributable to O3 created within East Asia in most areas of East Asia. In spring the contribution of domestically created O3 accounted for 20% of the surface O3 in Japan and the Korean Peninsula, 40% in the North China Plain, and around 50% in the southern part of China, and the domestic contribution increased greatly in summer. The contributions of O3 created in China and the Korean Peninsula to O3 in Japan were estimated at about 10% and 5%, respectively. We also demonstrated a large contribution (20%) from China to the Korean Peninsula. In the northern and southern parts of China, large contributions of over 10% from East Siberia and the Indochina Peninsula, respectively, were identified. The contribution from intercontinental transport increased with latitude; it was 21% in Northeast China and 13% in Japan and the Korean Peninsula in spring. As for the hourly mean of surface O3, domestically created O3 was the main contributor in most areas of East Asia, except for the low O3 class (<30 ppbv), and accounted for more than 50% in the very high O3 class (>90 ppbv). The mean relative contribution of O3 created in China to O3 in central Japan was about 10% in every class, but that created in the Korean Peninsula was significant in all except the low O3 class. We identified the substantial impact of foreign sources on Japan's ambient air quality standard in the high O3 class (60–90 ppbv) in spring.