Analyzing ozone formation sensitivity in a typical industrial city in China: Implications for effective source control in the chemical transition regime.

Volatile organic compounds (VOCs) play a major role in O formation in urban environments. However, the complexity in the emissions of VOCs and nitrogen oxides (NOx) in industrial cities has made it challenging to identify the key factors influencing O formation. This study used observation-based-model (OBM) to analyze O sensitivities to VOCs and NOx during summer in a typical industrial city in China. The OBM model results were coupled with a receptor model to analyze the sources of O. Higher concentrations of O precursors were observed during polluted periods indicating that precursor accumulation contributed to the higher maxima of the net ozone formation rate and HOx concentrations. Analyses of ROx· budgets and relative incremental reactivity (RIR) indicated that O production is in a chemical transition regime and was sensitive to both VOCs and NOx. Results from Positive Matrix Factorization (PMF) analysis indicated that gasoline vehicle emissions, industrial processes, and coal combustion were major sources of O precursors. The sensitivities of O production to these sources depend on if both VOC and NOx sensitivities are considered. If only VOCs sensitivity is considered, in contrast, the contribution of anthropogenic sources to O production was significantly underestimated. This study highlights the importance of accounting for both VOCs and NOx sensitivities when O chemistry is in a transition regime in O production attribution studies.