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

Increasing surface ozone (O₃) 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 O₃ formation regime and its sensitivity to precursor emissions. In this work, we propose a new transformed empirical kinetic modeling approach (EKMA) to diagnose the O₃ formation regime using regulatory O₃ and NO₂ observation datasets, which are easily accessible. We demonstrate that mapping of monitored O₃ and NO₂ data on the modeled regional O₃-NO₂ relationship diagram can illustrate the ozone formation regime and historical evolution of O₃ precursors of the region. By applying this new approach, we show that for most urban regions of China, the O₃ formation is currently associated with a volatile organic compound (VOC)-limited regime, which is located within the zone of daytime-produced O₃ (DPO₃) to an 8h-NO₂ concentration ratio below 8.3 ([DPO₃]/[8h-NO₂] ≤ 8.3). The ozone production and controlling effects of VOCs and NO_x in different cities of China were compared according to their historical O₃-NO₂ evolution routes. The approach developed herein may have broad application potential for evaluating the efficiency of precursor controls and further mitigating O₃ pollution, in particular, for regions where comprehensive photochemical studies are unavailable.