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 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 20°N, 5–20°N and south of 5°N). North of 20°N, net ozone production over East Asia from spring through autumn is found to have a maximum extending from 25°N–40°N and from central eastern China to Japan, resulting from the strong emission and transport of anthropogenic O 3 precursors. In winter, maximum O 3 production in this region occurs between 20°N and 30°N. This is a region of long‐range transport. Over the Indochina peninsula, between 5°N and 20°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 emissions from biomass burning. South of 5°N, in the true tropics, O 3 mixing 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 throughout the troposphere in East Asia. We estimate an annual net O 3 production in East Asia of 117 Tg/yr. Both model results and analysis of measurements 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 estimate 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.