Formation mechanism, precursor sensitivity and control strategies of summertime ozone on the Fenwei Plain, China

Abstract

As one of the most polluted regions in China, the Fenwei Plain has suffered severe summertime ozone (O3) pollution in recent years. However, related studies in this region are still scarce. In this study, a comprehensive observation campaign was conducted in a typical city on the Fenwei Plain. An observation-based model (OBM) was used to investigate the summer O3 formation mechanism, precursor sensitivity and control strategies during O3-polluted and clean periods. Our results showed that O3 pollution was accompanied by increased O3 precursor concentrations (∼15% higher) and unfavorable meteorological conditions. In situ O3 production played a dominant role in the daytime O3 concentration increment in both polluted (+6.0 ppbv/h) and clean (+3.5 ppbv/h) periods. HO2 + NO (65.9%–66.7%) was the most dominant pathway of daytime O3 formation, and OH + NO2 (41.3%–63.1%) was the most dominant pathway of O3 destruction. Regional transport has a certain contribution to the occurrence of polluted days, as well as a diluting effect on clean days. Regional transport had a certain contribution effect on polluted days and a dilution effect on clean days. The southeastern regions were potential source regions of high O3, and the northwestern regions were potential source regions of low O3. When pollution occurred, the O3 formation control regimes transformed from a volatile organic compound (VOC)-limited regime to a transition regime, corresponding to an increase in precursor concentrations and stronger local O3 production. A 30% reduction in VOCs and a 20% reduction in NOx (VOCs/NOx ≈ 1.5) were determined to be the optimal control strategies to achieve the O3 control target (82 ppbv) in summer. VOC reductions should target reactive and O3-sensitive species (Oxygened VOCs, alkenes, aromatics) to effectively alleviate O3 pollution. This study could provide scientific support for local O3 pollution control on the Fenwei Plain.