[Applying Photochemical Indicators to Analyze Ozone Sensitivity in Handan].

Ozone pollution in Handan has become severe in recent years and in the summer of 2018, the average maximum daily 8-hour average ozone concentration in Handan was 175 µg·m-3 with a maximum of 257 µg·m-3. Ozone concentrations exceeded the National Air Quality Grade Ⅱ Standard in 59% of cases. In this study, the H2O2/HNO3 indicator was applied to analyze summertime ozone sensitivity in Handan using the WRF-CMAQ modeling system. The results showed that H2O2/HNO3 was more appropriate than other ozone indicators, both theoretically and based on simulation outputs. The good simulation effect of CMAQ on H2O2 and HNO3 was attributed to fine emission inventory and grid resolution. The H2O2/HNO3 simulation results showed that the relative importance of a VOCs-limited regime decreased month by month; a VOCs-NOx-mixed-limited regime was dominant in June; and a NOx-limited regime was more dominant in July and August than in June. The remarkable spatial difference in VOCs and NOx emission ratios among the counties of Handan led to differences in ozone sensitivity. The VOCs-limited regime was concentrated in counties where VOCs/NOx emission ratios were lower than 1.7. Southern counties had a NOx-limited regime, where VOCs/NOx emission ratios were higher than 6.9. Counties with VOCs/NOx emission ratios varying from 1.7 to 6.9 were more susceptible to both VOCs and NOx. According to these results, the transition range of HCHO/NO2, O3/HNO3, and O3/NOx ratios were adjusted to 0.35-0.6, 20-35, and 10-25 respectively. Adjusting the transition range of H2O2/(O3+NO2) was not effective, indicating that this indicator may not be applicable to Handan.

[Pollution Characteristics and Sensitivity of Surface Ozone in a Typical Heavy-Industry City of the North China Plain in Summer].

The pollution characteristics of surface ozone and its response to meteorological factors and precursors were studied based on monitoring and Model-3/CMAQ modeling from May to August 2018 in Handan City, China. The monitoring results showed that the maximum daily 8-hour average ozone concentration (MDA8 O3) ranged from 38.0-238.0 µg·m-3, and the nonattainment for ozone reached 44.7% during the studied period, indicating the more severe photochemical pollution in summer in Handan City. The ozone concentration was positively correlated with temperature (R=0.74 on nonattainment days and 0.42 on attainment days), but negatively correlated with relative humidity (R=-0.63 on nonattainment days and -0.58 on attainment days), demonstrating the role of photochemistry in the surface ozone of Handan City. Moreover, the highest ozone level occurred at wind speeds higher than 2.25 m·s-1 or lower than 1.00 m·s-1 during ozone nonattainment days, which indicated that regional transport and local accumulation can both cause serious ozone pollution in the city. Regarding the response of ozone to its precursors (VOCs and NOx), model simulation results based on the brute force method showed the stronger positive sensitivity to VOCs, but a weak negative sensitivity to NOx. Therefore, reduction of anthropogenic VOCs emissions is the key to improving ozone pollution in Handan City. We used the propylene-equivalent method to identify the importance of alkene and aromatic species for ozone pollution during ozone nonattainment days.