Contributions of regional and intercontinental transport to surface ozone in the Tokyo area

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.

Assessment of cloud condensation nucleus activation of urban aerosol particles with different hygroscopicity and the application to the cloud parcel model

“…More hygroscopic particles may have consisted of secondary-generated OOA and inorganics as has been suggested for urban aerosols (Tokyo) by Mochida et al [2008]. Aerosols from the East Asian continent [Aikawa et al, 2010;Yoshitomi et al, 2011] as well as those from other parts of Japan might have contributed to the observed more hygroscopic particles, as suggested from the 5 day backward air mass trajectories ( Figure S2) passing near the coast of China. This interpretation is also supported by observation that aerosols from China by the long-range Figure 6.…”

Megacity ozone air quality under four alternative future scenarios

“…In the USA between 1990 and 2008, total emissions of toxic pollutants (as defined by the US Clean Air Act) declined by 41 % (EPA, 2010). Efforts to reduce emissions in urbanised areas of the developed world have been so successful that many studies now suggest an influence of regional and long range transport of ozone and its precursors on ozone air quality in these areas (Jacob et al, 1999;Parrish et al, 2010;Yoshitomi et al, 2011). The developing world has yet to catch up to these standards; air quality in the megacities of the developing world can be especially poor .…”

Identification of nitrogen dioxide and ozone source regions for an urban area in Korea using back trajectory analysis

“…In the case of the coastal areas in Japan (E), the local surface ozone concentration was much higher under specific meteorological conditions than those affected by the foreign influences. Hence, under such conditions, trans-boundary pollution of O 3 can be stimulated in the surrounding areas (Yoshitomi et al, 2011). It should be noted that the potential source regions, whether residing in or passing over the Yellow Sea, were influenced by both anthropogenic (industrial and automobile) (Akimoto et al, 2015) and natural sources (formation of sea salt from sea breezes and topography) (Sikder et al, 2011).…”