Mitigating China’s escalating surface ozone (O₃) pollution requires quantification of contributions from transboundary transport and domestic volatile organic compounds (VOCs) emissions. Here, we developed an expanded odd oxygen family (O_y) modeling framework to track the full photochemical cycling between O₃ and all of its reservoirs, following the oxidation of VOCs emitted from various sources. We applied this framework to disentangle O₃ sources in China during Fall 2019. Across all parts of China, 55%-85% of surface O₃ originated from transboundary transport, while the remaining domestic O₃ was complexly affected by inter-regional interactions among oxidants, VOCs, and their products. Previous studies have underestimated these transboundary and inter-regional contributions to local O₃ because they lost track of the sources of oxidants after photochemical cycling. We further strategized the mitigation of O₃ pollution based on our new understanding of its sources. In Northeastern China, O₃ pollution should be mitigated through a coordinated effort to reduce anthropogenic VOC emissions across all the northeastern provinces and municipalities. Conversely, in Southeastern China, where there is a surplus of biogenic peroxy radicals in the boundary layer, O₃ pollution could be most effectively mitigated through simultaneous reduction of NO_x emission in both urban and rural areas.
 

ozone pollution,odd oxygen,volatile organic compounds,source attribution,tagged-modeling,transboundary transport