Precursors and potential sources of ground-level ozone in suburban Shanghai

A high level of ozone (O-3) 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 O-3 during summer in Shanghai, O-3 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 O-3 in suburban Shanghai. When the sampling site was controlled by south-western winds exceeding 2 m/s, the O-3-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 O-3 formation. The Ozone Isopleth Plotting Research (OZIPR) model was used to reveal the impact of O-3 precursors on O-3 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 O-3 concentrations. The O-3 isopleth diagram illustrated that O-3 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 O-3 formation. We found that O-3 formation was sensitive to propylene, (m + p)-xylene, o-xylene and toluene. The results provide theoretical support for O-3 pollution treatment in Shanghai.