Global source attribution of tropospheric ozone: Long-range transport from various source regions

[1] We examine contributions from various source regions to global distributions and budgets of tropospheric ozone (O-3) in the context of intercontinental transport, using tagged tracer simulation with a global chemical transport model. For tagging O-3, we consider regional separation of the model domain on the basis of the distributions of O-3 chemical production. We define 14 polluted source regions ( 14 tracers) in the boundary layer ( North America, Europe, China, etc.) and 8 regions ( 8 tracers) in the free troposphere; O-3 production in the remaining ( remote) tropospheric region and O-3 transport from the stratosphere are also tagged as separate tracers. O-3 transport from the polluted source regions like North America, Europe, and Asia generally accounts for more than 40% of ozone abundances even in remote locations. O-3 exports from boundary layer in China and Asian free troposphere are discerned through much of the Northern Hemisphere, suggesting significant and extensive impacts of eastern Asian pollution. In particular, O-3 from Asian free troposphere plays the most important roles in distribution and seasonal variation of O-3 in the middle-upper troposphere almost globally. In June - September, the model calculates a large O-3 contribution ( 5 - 10 ppbv) from Asian free troposphere in the upper troposphere over the South Pacific associated with long-range interhemispheric transport from Asia to the southern midlatitudes ( via the western Indian Ocean, Africa, and Atlantic) in the upper troposphere. O-3 transported from biomass burning regions such as South America, Africa, and Australia widely distributes in the Southern Hemisphere. Our simulation demonstrates that there is a significant interhemispheric O-3 transport from South America to the northern midlatitudes in the upper troposphere which reaches Japan, North Pacific, and the United States in conjunction with O-3 export from North Africa. Our tagged O-3 simulation estimates that the annual mean global tropospheric O-3 burden, as calculated to be 344 Tg in this study, comes from chemical production in the source regions (48%) and in the remote regions (29%) and from stratosphere-troposphere exchange (23%).