| In recent years, there have been frequent ozone pollution episodes in Dezhou, China. In the summer of 2018 (from June to August), Dezhou experienced serious ozone pollution episodes. The daily 8-hour maximum ozone concentrations exceeded the national standard for 60 days with the standard exceeding ratio of 65%. The average of daily 8-hour maximum ozone concentration was 176 μg ·m-3 over these three months, and the highest value reached was 262 μg ·m-3. In this study, the WRF-CAMx model coupled with the higher-order decoupled direct method (HDDM) was used to analyze the ozone sensitivity and emission control plans in Dezhou during this period. The results showed that ozone formation was in the strong VOC-limited regime in the urban area of Dezhou, while it was in the NOx and VOCs transition regime in suburban areas. VOCs sensitivity values (dO3_V50) were positive every day in summer, which was higher in June (18.7 μg ·m-3 in urban area, 19.7 μg ·m-3 in suburban area) and August (15.3 μg ·m-3 in urban area, 16.4 μg ·m-3 in suburban area) than in July (13.0 μg ·m-3 in urban area, 11.8 μg ·m-3 in suburban area). NOx sensitivity values (dO3_N50) were positive or negative in the urban area, and most days were positive in the suburban area, which were close to the VOCs sensitivity values. For urban areas, VOC reduction should be the priority for emission reduction plans, whereas for suburban areas, NOx：VOCs=1：1 is recommended because the reductions in NOx and VOCs emissions had the same effect on ozone pollution control. |
