Significant impact of the East Asia monsoon on ozone seasonal behavior in the boundary layer of Eastern China and the west Pacific region

摘要

The impact of the East Asia monsoon on the seasonal behavior of O inthe boundary layer of Eastern China and the west Pacific region was analyzedfor 2004–2006 by means of full-year nested chemical transport modelsimulations and continuous observational data obtained from three inlandmountain sites in central and eastern China and three oceanic sites in thewest Pacific region. The basic common features of O seasonal behaviorsover all the monitoring sites are the pre- and post-monsoon peaks with asummer trough. Such bimodal seasonal patterns of O are predominantover the region with strong summer monsoon penetration, and become weaker oreven disappear outside the monsoon region. The seasonal/geographicaldistribution of the pre-defined monsoon index indicated that the East Asiasummer monsoon is responsible for the bimodal seasonal O pattern, andalso partly account for the differences in the O seasonal variationsbetween the inland mountain and oceanic sites. Over the inland mountainsites, the O concentration increased gradually from the beginning ofthe year, reached a maximum in June, decreased rapidly to the summer valleyin July or August, and then peaked in September or October, thereafterdecreased gradually again. Over the oceanic sites, O abundance showeda similar increasing trend beginning in January, but then decreasedgradually from the end of March, followed by a wide trough with the minimumin July and August and a small peak in October or November. A sensitivityanalysis performed by setting China-emission to zero revealed that thechemically produced O from China-emission contributed substantially tothe O abundance, particularly the pre- and post-monsoon O peaks,over China mainland. We found that China-emission contributed more than40% to total boundary layer O during summertime (60–70% in July)and accounted for about 40 ppb of each peak value over the inland region ifwithout considering the effect of the nonlinear chemical productions. Incontrast, over the oceanic region in the high monsoon index zone, thecontribution of China-emission to total boundary layer O was alwaysless than 20% (10 ppb), and less than 10% in summer.