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

We examine seasonal and geographical distributions of tropospheric ozone pr oduction and mixing ratios over East Asia with a global three-dimensional c hemical transport model called Model of Ozone and Related Tracers, version 1 (MOZART 1). Net ozone production within the East Asian boundary layer exh ibits three distinct seasonal cycles depending on region (north of 20 degre es N, 5-20 degrees N and south of 5 degrees N). North of 20 degrees N, net ozone production over East Asia from spring through autumn is found to have a maximum extending from 25 degrees N-40 degrees N and from central easter n China to Japan, resulting from the strong emission and transport of anthr opogenic O-3 precursors. In winter, maximum O-3 production in this region o ccurs between 20 degrees N and 30 degrees N, This is a region of long-range transport. Over the Indochina peninsula, between 5 degrees N and 20 degree s N, net O-3 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 emission s from biomass burning. South of 5 degrees N, in the true tropics, O-3 mixi ng ratios are relatively constant throughout the year and do not exhibit a seasonal cycle. A spring-summer maximum of net O-3 production is found thro ughout the troposphere in East Asia. We estimate an annual net O-3 producti on in East Asia of 117 Tg/yr, Both model results and analysis of measuremen ts of O-3/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 estima te of O-3 export from East Asia to the Pacific Ocean in the mid-1980s of 3. 3 Gmol/d (58 Tg/yr) is obtained.