Based on the observational data of volatile organic compounds （VOCs）, conventional air pollutants, and ERA5 meteorological reanalysis data at three sites, namely, Caochangmen （CCM）, Pukou （PK）, and Xianlin University Town （XL）, in Nanjing from 2015 to 2021, the ozone generation and depletion mechanisms in ozone-polluted days under stable weather conditions were investigated using the observation-based model （OBM-MCM）. The results showed that ① Significant year-by-year differences exist in the frequency of stable weather on ozone-polluted days for the three sites. The maximum number of stable days occurred in 2019, with 46 d （66.7%）, 50 d （64.9%）, and 54 d （69.2%） at the CCM, PK, and XL sites, respectively. ② Significant differences exist between the net O