Seasonal characteristics of tropospheric ozone production and mixing ratios over East Asia: A global three-dimensional chemical transport model analysis

International audienceWe examine seasonal and geographical distributions of tropospheric ozone production and mixing ratios over East Asia with a global three-dimensional chemical transport model called Model of Ozone and Related Tracers, version 1 (MOZART 1). Net ozone production within the East Asian boundary layer exhibits three distinct seasonal cycles depending on region (north of 20øN, 5-20øN and south of 5øN). North of 20øN, net ozone production over East Asia from spring through autumn is found to have a maximum extending from 25øN-40øN and from central eastern China to Japan, resulting from the strong emission and transport of anthropogenic 03 precursors. In winter, maximum 03 production in this region occurs between 20øN and 30øN. This is a region of long-range transport. Over the Indochina peninsula, between 5øN and 20øN, net 03 production is controlled by the seasonal cycle between wet and dry seasons and has a maximum at the end of the dry season due to emissions from biomass burning. South of 5øN, in the true tropics, 03 mixing ratios are relatively constant throughout the year and do not exhibit a seasonal cycle. A spring-summer maximum of net 03 production is found throughout the troposphere in East Asia. We estimate an annual net 03 production in East Asia of 117 Tg/yr. Both model results and analysis of measurements of O3/CO correlations over East Asia and Japan show strong variability as a function of both photochemical activity and seasonal meteorology, and indicate ozone export off the coast of East Asia in spring. An upper estimate of 03 export from East Asia to the Pacific Ocean in the mid-1980s of 3.3 Gmol/d (58 Tg/yr) is obtained