[Analysis of O₃ Pollution Characteristics, Formation Sensitivity, and Transport Impact in Southern Nanjing]

As one of the most important city clusters in China, surface ozone (O₃) pollution in the Yangtze River Delta (YRD) Region has become a prominent air quality problem in recent years. Online observations of ambient O₃, nitrogen oxides (NO), and volatile organic compounds (VOCs) were conducted in southern Nanjing from July-September 2020 and April-May 2021. On this basis, the pollution characteristics of O₃ were analyzed. The O₃-VOCs-NO sensitivity and the transport influence of its precursors were further discussed using models. The frequency statistics of the daily maximum 8-hour moving average (DMA-8h O₃) and hourly concentration (O₃-1h) showed that O₃ pollution in southern Nanjing was more serious than that in urban areas. Three typical O₃ pollution episodes were selected during the whole observation period, which included August 16^th-27^th, 2020; September 3^rd-11^th, 2020; and May 17^th-25^th, 2021. The O₃-VOCs-NO sensitivities in these three pollution episodes were analyzed using the observation-based model (OBM). The results of the relative incremental reactivity (RIR) and empirical kinetics modeling approach (EKMA) showed that the sensitivities of O₃ formation in the three pollution episodes were in the NO-limited regime, the transition regime, and the VOCs-limited regime, respectively. This difference in O₃-VOCs-NO sensitivity reflects that the site may have been influenced by transport. Therefore, the potential source contribution function (PSCF) and the concentration weighted trajectory (CWT) method were further used to analyze the potential source areas of NO, VOCs, and O₃ in these three pollution episodes. The results showed that there were obvious regional transport effects of NO, VOCs, and O₃ in these three pollution episodes. The location of potential sources differed in these three pollution episodes, which were affected by the eastern cities of the Lishui site; the urban area of Nanjing and eastern area of Anhui Province; and the urban area of Nanjing and the middle of the YRD Region, respectively. The impact of transport on O₃ and its precursors also indicated the necessity of regional joint prevention and control of O₃ pollution in the YRD Region.