Ground-level ozone (O
3) has become a critical pollutant impeding air quality improvement in Yangtze River Delta region of China. In this study, we present O
3 pollution characteristics based on one-year online measurements during 2016 at an urban site in Nanjing, Jiangsu Province. Then, the sensitivity of O
3 to its precursors during 2 O
3 pollution episodes in August was analyzed using a box model based on observation (OBM). The relative incremental reactivity (RIR) of hydrocarbons was larger than other precursors, suggesting that hydrocarbons played the dominant role in O
3 formation. The RIR values for NO
X ranged from –0.41%/% to 0.19%/%. The O
3 sensitivity was also analyzed based on relationship of simulated O
3 production rates with reductions of VOC and NO
X derived from scenario analyses. Simulation results illustrate that O
3 formation was between VOCs-limited and transition regime. Xylenes and light alkenes were found to be key species in O
3 formation according to RIR values, and their sources were determined using the Positive Matrix Factorization (PMF) model. Paints and solvent use was the largest contributor to xylenes (54%), while petrochemical industry was the most important source to propene (82%). Discussions on VOCs and NO
X reduction schemes suggest that the 5% O
3 control goal can be achieved by reducing VOCs by 20%. To obtain 10% O
3 control goal, VOCs need to be reduced by 30% with VOCs/NO
X larger than 3:1.
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