Contributions of regional and intercontinental transport to surface ozone in the Tokyo area 1Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
01 Aug 2011
2Lancaster Environment Centre, Lancaster University, Lancaster, UK
3Asia Center for Air Pollution Research, Niigata, Japan
Received: 16 December 2010 – Published in Atmos. Chem. Phys. Discuss.: 01 April 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 July 2011 – Accepted: 22 July 2011 – Published: 01 August 2011
Citation: 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.