Evolution of Ozone Pollution in China: What Track Will It Follow?

[Image: see text] Increasing surface ozone (O(3)) concentrations has emerged as a key air pollution problem in many urban regions worldwide in the last decade. A longstanding major issue in tackling ozone pollution is the identification of the O(3) formation regime and its sensitivity to precursor emissions. In this work, we propose a new transformed empirical kinetic modeling approach (EKMA) to diagnose the O(3) formation regime using regulatory O(3) and NO(2) observation datasets, which are easily accessible. We demonstrate that mapping of monitored O(3) and NO(2) data on the modeled regional O(3)–NO(2) relationship diagram can illustrate the ozone formation regime and historical evolution of O(3) precursors of the region. By applying this new approach, we show that for most urban regions of China, the O(3) formation is currently associated with a volatile organic compound (VOC)-limited regime, which is located within the zone of daytime-produced O(3) (DPO(3)) to an 8h-NO(2) concentration ratio below 8.3 ([DPO(3)]/[8h-NO(2)] ≤ 8.3). The ozone production and controlling effects of VOCs and NO(x) in different cities of China were compared according to their historical O(3)–NO(2) evolution routes. The approach developed herein may have broad application potential for evaluating the efficiency of precursor controls and further mitigating O(3) pollution, in particular, for regions where comprehensive photochemical studies are unavailable.