A high level of ozone(O3)is frequently observed in the suburbs of Shanghai,the reason for this high level remains unclear.To obtain a detailed insight on the high level of O3 during summer in Shanghai,O3 and its precursors were measured at a suburban site in Shanghai from July 1,2016 to July 31,2016.Using the Hybrid Single-Particle Lagrangian Integrated Trajectory(HYSPLIT)model and concentration weighted trajectories(CWT),we found that Zhejiang province was the main potential source of O3 in suburban Shanghai.When the sampling site was controlled by south-western winds exceeding 2 m/s,the O3-rich air masses from upwind regions(such as Zhejiang province)could be transported to the suburban Shanghai.The propylene-equivalent concentration(PEC)and ozone formation potential(OFP)were further calculated for each VOC species,and the results suggested that propylene,(m+p)-xylene,and toluene played dominant roles in O3 formation.The Ozone Isopleth Plotting Research(OZIPR)model was used to reveal the impact of O3 precursors on O3 formation,and 4 base-cases were selected to adjust the model simulation.An average disparity of 18.20％was achieved between the simulated and observed O3 concentrations.The O3 isopleth diagram illustrated that O3 formation in July 2016 was in VOC-sensitive regime,although the VOC/NOx ratio was greater than 20.By introducing sensitivity(S),a sensitivity analysis was performed for O3 formation.We found that O3 formation was sensitive to propylene,(m+p)-xylene,o-xylene and toluene.The results provide theoretical support for O3 pollution treatment in Shanghai.