Ozone pollution characteristics and sensitivity analysis using an observation-based model in Nanjing, Yangtze River Delta Region of China.

Ground-level ozone (O) has become a critical pollutant impeding air quality improvement in Yangtze River Delta region of China. In this study, we present O pollution characteristics based on one-year online measurements during 2016 at an urban site in Nanjing, Jiangsu Province. Then, the sensitivity of O to its precursors during 2 O 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 formation. The RIR values for NO ranged from -0.41%/% to 0.19%/%. The O sensitivity was also analyzed based on relationship of simulated O production rates with reductions of VOC and NO derived from scenario analyses. Simulation results illustrate that O formation was between VOCs-limited and transition regime. Xylenes and light alkenes were found to be key species in O 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 reduction schemes suggest that the 5% O control goal can be achieved by reducing VOCs by 20%. To obtain 10% O control goal, VOCs need to be reduced by 30% with VOCs/NO larger than 3:1.