1Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
2Lancaster Environment Centre, Lancaster University, Lancaster, UK
3Asia Center for Air Pollution Research, Niigata, Japan
Received: 16 Dec 2010 – Discussion started: 01 Apr 2011
Abstract. Japan lies downwind of the Asian continent and for much of the year air quality is directly influenced by emissions of ozone precursors over these heavily-populated and rapidly-industrializing regions. This study examines the extent to which oxidant transport from regional and distant anthropogenic sources influences air quality in Japan in springtime, when these contributions are largest. We find that European and North American contributions to surface ozone over Japan in spring are persistent, averaging 3.5±1.1 ppb and 2.8±0.5 ppb respectively, and are greatest in cold continental outflow conditions following the passage of cold fronts. Contributions from China are larger, 4.0±2.8 ppb, and more variable, as expected for a closer source region, and are generally highest near cold fronts preceding the influence of more distant sources. The stratosphere provides a varying but ever-present background of ozone of about 11.2±2.5 ppb during spring. Local sources over Japan and Korea have a relatively small impact on mean ozone, 2.4±7.6 ppb, but this masks a strong diurnal signal, and local sources clearly dominate during episodes of high daytime ozone. By examining the meteorological mechanisms that favour transport from different source regions, we demonstrate that while maximum foreign influence generally does not occur at the same time as the greatest buildup of oxidants from local sources, it retains a significant influence under these conditions. It is thus clear that while meteorological boundaries provide some protection from foreign influence during oxidant outbreaks in Tokyo, these distant sources still make a substantial contribution to exceedance of the Japanese ozone air quality standard in springtime.
Revised: 15 Jul 2011 – Accepted: 22 Jul 2011 – Published: 01 Aug 2011
Yoshitomi, M., Wild, O., and Akimoto, H.: Contributions of regional and intercontinental transport to surface ozone in the Tokyo area, Atmos. Chem. Phys., 11, 7583-7599, doi:10.5194/acp-11-7583-2011, 2011.