Evolution of Ozone Formation Sensitivity during a Persistent Regional Ozone Episode in Northeastern China and Its Implication for a Control Strategy

Abstract

In recent years, the magnitude and frequency of regional ozone (O 3 ) 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 O 3 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 O 3 pollution. Daily analysis of the O 3 formation sensitivity showed that O 3 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 NOxlimited regime as the episode progressed in the most polluted cities. Based on the emission-reduction scenario simulations, mitigation of the regional O 3 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 O 3 episode. This study presents a new possibility for regional O 3 pollution abatement in China based on a reasonable combination of OBM and the WRF−CMAQ model.

Unexpected Trade-Offs of Fossil Fuel Reduction on PM2.5 and O3 Pollution Regulation Can Be Offset by Synergistic Control of VOCs Source

“…Another study reported that a 50% reduction in NO x emissions can decrease PM 2.5 by about 14%, in the North China Plain . VOCs and NO x reduction should reduce by about 30% and 15% to achieve O 3 concentration reduction by 10% in reduction . However, controlling NO x emissions is partly counterproductive for O 3 improvement, as NO x reduction could shift the sensitivity of O 3 formation from the VOCs-limited regime to the NO x -limited regime. , A substantial reduction of NO x emissions led to an exacerbation of O 3 pollution in many urban areas. , Therefore, the effectiveness of NO x and VOCs control to effectively reduce PM 2.5 and O 3 depends not only on the decrease in absolute concentrations but also on changing their relative proportions.…”

“…However, controlling NO x emissions is partly counterproductive for O 3 improvement, as NO x reduction could shift the sensitivity of O 3 formation from the VOCs-limited regime to the NO x -limited regime. , A substantial reduction of NO x emissions led to an exacerbation of O 3 pollution in many urban areas. , Therefore, the effectiveness of NO x and VOCs control to effectively reduce PM 2.5 and O 3 depends not only on the decrease in absolute concentrations but also on changing their relative proportions. In addition, previous studies have determined that gaseous pollutants emitted from pollution sources are complex, due to the diversity of sources and their types. ,,, Overall, there has been limited research extending the study of gaseous precursors to pollution sources in the context of PM 2.5 and O 3 co-mitigation. To further advance the control of PM 2.5 and O 3 , a strategy that targets common pollution sources is needed, instead of focusing solely on NO x and VOCs.…”