[Ozone Sensitivity Analysis and Control Strategy in Shijiazhuang City in July 2019]

The pollution characteristics of surface ozone and its response to meteorological factors were studied based on monitoring in July 2019 in Shijiazhuang City, China. Furthermore, the WRF-CMAQ model coupled with O₃ isopleths (EKMA curves) were applied to explore the non-linear response relationship of O₃ to precursors VOCs and NO, aiming to identify a suitable precursor control strategy. The results showed that the days with the maximum daily 8-hour average ozone concentration (MDA8 O₃) exceeded the standard by 70.9%. The nonattainment days were usually accompanied by higher temperature, lower relative humidity, and low winds, and the south and southeast winds occurred frequently. The O₃ formation was in the strong VOC-limited regime in the urban area of Shijiazhuang, whereas it was in the NO and VOCs transition regime in suburban areas. As for the urban area, under the condition of single NO emission reduction, O₃ pollution improved when continuous NO emission reduction was higher than 50% during the nonattainment days. By contrast, during the non-polluted days, O₃ concentrations would not rebound when the reduction ratio of NO and VOCs was higher than 1. In conclusion, VOCs reduction should be the priority for emission reduction plans in urban areas, whereas all different NO and VOCs ratios led to a decline in O₃ concentration in the suburban areas, and a VOCs:NO of 1:2 was recommended.