Understanding the underlying mechanisms governing the linkage between atmospheric oxidative capacity and ozone precursor sensitivity in the Yangtze River Delta, China: A multi-tool ensemble analysis.

Continued exacerbation of ozone (O) pollution in China has driven the urgent need for an emission control strategy that efficiently reduces O levels. Determining O precursor sensitivity (OPS) and its driving factors is a prerequisite for formulating effective O control strategies. In this study, we proposed an atmospheric oxidative capacity-based indicator, HO/OH, and demonstrated its effectiveness in indicating OPS over the Yangtze River Delta (YRD) of China by applying a localized comprehensive air quality model with extensions (CAMx) coupled with the Weather Research and Forecasting (WRF) model. A strong correlation was discovered between HO/OH and OPS, and HO/OH showed the best performance in separating NO- and VOC-limited regimes in comparison with other commonly used indicators. A comprehensive analysis with ensemble diagnostic tools revealed the spatial heterogeneity of NO and VOC emissions and the impact of regional transport controlling the relationship between OPS variations and the HO/OH indicator over the YRD. The process analysis results show that days with higher contributions from horizontal advection favored OPS transitions in Shanghai, Nanjing, Hefei, Suzhou, and Wuhu, while vertical advection caused OPS transitions in Hangzhou and Ningbo. O source apportionment technology analysis indicated that the regional contributions from Zhejiang and Jiangsu/Anhui corresponded well to the NO-limited and VOC-limited regimes, respectively. Our results provide a better understanding of the underlying mechanisms of the relationship between OPS and the HO/OH indicator and can help guide contingency control measures for O despiking over the YRD and other photochemically active regions worldwide.