Abstract: From May to October 2021, volatile organic compounds (VOCs) and conventional continuous online observation data were monitored in typical cities such as Shanghai, Nanjing and Hefei in the Yangtze River Delta region to understand the characteristics and sources of ozone (O₃) pollution. The VOCs components that contribute significantly to O₃ production were identified, and the changes in VOCs component concentrations were compared between ozone polluted and non-polluted days. The positive matrix decomposition model was used to explore the source apportionment of VOCs. The results showed that: (1) The 90^th percentile of daily maximum 8-hour average ozone concentration in Shanghai, Nanjing, and Hefei was 163, 185 and 163 μg/m³, respectively. The number of days exceeding the standard were 20 days, 42 days and 20 days, respectively. The average volume fraction of VOCs were 12.93×10⁻⁹±8.61×10⁻⁹, 14.45×10⁻⁹±7.56×10⁻⁹ and 15.60×10⁻⁹±8.12×10⁻⁹, respectively. The VOCs in all three cities were dominated by alkanes, among which aromatic hydrocarbons in Shanghai, olefins in Nanjing, and alkynes in Hefei account for prominent proportions. (2) The monthly variations of ozone generation potential (OFP) in Nanjing and Hefei showed a trend of first decreasing and then increasing, while the variation in Shanghai was not significant; aromatic hydrocarbons in VOCs in Shanghai and Hefei contributed the most to ozone generation, accounting for above 40% each. Olefins and aromatic hydrocarbons in Nanjing made significant contributions to ozone generation. (3) The daily variation of ozone in the three cities showed a unimodal distribution. The ozone generation rate and amount before 12:00 on polluted days were significantly higher than those on non-polluted days. The precursors VOCs and NO₂ showed similar bimodal distributions. From the perspective of tracer components, Shanghai′s solvent coatings and industrial emissions, Nanjing′s motor vehicle exhaust and solvent coatings, and Hefei′s gasoline volatilization all increased on ozone pollution days. (4) Motor vehicle exhaust and industrial emissions were the main sources of VOCs in the three cities. In addition, the contributions of Shanghai petrochemical and chemical industry sources, Nanjing solvent use sources, and Hefei gasoline volatilization and combustion sources to VOCs in summer cannot be ignored. The results show that higher precursor concentrations and faster precursor consumption rate are important reasons for excessive ozone levels. The sources of atmospheric VOCs control in the Yangtze River Delta region should focus on vehicle exhaust and industrial source emissions.