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

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.