Evolution of Ozone Formation Sensitivity during a Persistent Regional Ozone Episode in Northeastern China and Its...

In recent years, the magnitude and frequency of regional ozone (O₃) episodes have increased in China. We combined ground-based measurements, observation-based model (OBM), and the Weather Research and Forecasting and Community Multiscale Air Quality (WRF-CMAQ) model to analyze a typical persistent O₃ episode that occurred across 88 cities in northeastern China during June 19-30, 2021. The meteorological conditions, particularly the wind convergence centers, played crucial roles in the evolution of O₃ pollution. Daily analysis of the O₃ formation sensitivity showed that O₃ formation was in the volatile organic compound (VOC)-limited or transitional regime at the onset of the pollution episode in 92% of the cities. Conversely, it tended to be or eventually became a NOx-limited regime as the episode progressed in the most polluted cities. Based on the emission-reduction scenario simulations, mitigation of the regional O₃ pollution was found to be most effective through a phased control strategy, namely, reduction of a high ratio of VOCs to NOx at the onset of the pollution and lower ratio during evolution of the O₃ episode. This study presents a new possibility for regional O₃ pollution abatement in China based on a reasonable combination of OBM and the WRF-CMAQ model.