[Changes in O-VOCs-NO Sensitivity and VOCs Sources at an Urban Site of Nanjing Between 2020 and 2021].

The synergistic control of PM and ozone (O) are the focus of air quality improvement during the 14 Five-Year Plan in China. The production of O shows a highly nonlinear relationship with its precursors volatile organic compounds (VOCs) and nitrogen oxides (NO). In this study, we conducted online observations of O, VOCs, and NO at an urban site in downtown Nanjing from April to September of 2020 and 2021. The average concentrations of O and its precursors between these two years were compared, and then the O-VOCs-NO sensitivity and the VOCs sources were analyzed using the observation-based box model (OBM) and positive matrix factorization (PMF), respectively. The results showed that the mean daily maximum O concentrations, VOCs, and NO concentrations decreased by 7% (=0.031), 17.6% (<0.001), and 14.0% (=0.004) from April to September of 2021 compared with those from the same period in 2020, respectively. The average relative incremental reactivity (RIR) values of NO and anthropogenic VOCs during the O non-attainment days in 2020 and 2021 were 0.17 and 0.14 and 0.21 and 0.14, respectively. The positive RIR values of NO and VOCs indicated that O production was controlled by both VOCs and NO. The O production potential contours (EKMA curves) based on the 50×50 scenario simulations also supported this conclusion. The PMF results showed that industrial and traffic-related emissions were the main sources of VOCs. The five PMF-resolved factors were identified as industrial emissions, including industrial liquefied petroleum gas (LPG) use, the benzene-related industry, petrochemistry, toluene-related industry, and solvent and paint use, which contributed 55%-57% of the average mass concentration of total VOCs. The summed relative contributions of vehicular exhaust and gasoline evaporation were 43%-45%. Petrochemistry and solvent and paint use showed the two highest RIR values, suggesting that VOCs from these two sources should be reduced with priority to control O. With the implementation of VOCs and NO control measures, the O-VOCs-NO sensitivity and VOCs sources have changed, and therefore we still need to follow their variations in the future to timely adjust O control strategies during the 14 Five-Year Plan.