Abstract
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.
Highlights
Air pollution is recognized as a global issue occurring over hemispheric scales through the intercontinental transport of air pollutants such as tropospheric ozone (O3), aerosols, mercury, and persistent organic pollutants which have atmospheric lifetimes of greater than a week (Akimoto, 2003; Holloway et al, 2003; TF-HTAP, 2007)
This study aims to determine how local, regional and distant sources contribute to surface O3 over Japan in springtime and the extent to which they influence episodes of high O3 over the Tokyo metropolitan area
We have shown how local, regional and distant sources contribute to surface O3 and CO over Japan in springtime and explored the transport pathways that lead to this influence
Summary
Air pollution is recognized as a global issue occurring over hemispheric scales through the intercontinental transport of air pollutants such as tropospheric ozone (O3), aerosols, mercury, and persistent organic pollutants which have atmospheric lifetimes of greater than a week (Akimoto, 2003; Holloway et al, 2003; TF-HTAP, 2007). The performance of the model during spring 2001 is evaluated with hourly observational data for surface O3 from 10 measurement sites in the Acid Deposition Monitoring Network in East Asia (EANET) (Network Center for EANET, 2005) and with O3 and CO from four World Meteorological Organization/Global Atmosphere Watch (WMO/GAW) stations (Tsutsumi et al, 2006). 141◦12 E 140◦21 E 138◦24 E 137◦48 E 133◦11 E 136◦41 E 131◦48 E 132◦56 E 142◦13 E 128◦15 E 141◦49 E 140◦08 E 123◦01 E 153◦58 E
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