Analysis of ozone pollution characteristics and potential sources of ozone pollution in downwind urban areas affected by coking

In order to understand the pollution characteristics and sources of O₃ in downwind urban areas affected by coking, a study was carried out based on the monitoring data of O₃ and meteorological parameters (temperature, etc.) at six national monitoring sites in Linfen City, and VOCs at Beidajie site in 2019. The results showed that the 90th percentile (MDA8-90th) of the maximum daily 8-hour moving average (MDA8) of O₃ was 204 μg/m³ in Linfen City in 2019, ranking first among 11 cities in Shanxi Province. There were 103 days when O₃ concentrations exceeded the standard and were mainly concentrated in May-September; MDA8 began to rise in February, reached the maximum in June, and then decreased month by month; O₃ concentration showed a single-peak diurnal variation, with a peak between 14:00 and 16:00. MDA8 was positively correlated with daily maximum temperature (T_max) and negatively correlated with daily minimum relative humidity (RH_min). When T_max was greater than 22 ℃ or RH_min was less than 55%, O₃ concentration may exceed the standard. The analysis of O₃ formation potential (OFP) of VOCs showed that ethylene had the highest OFP, accounting for 44.5% of the total OFP, which was the key active species leading to O₃ pollution. The emissions from the use of Liquefied petroleum gas (LPG), vehicle exhaust, and coking activities contributed to O₃ pollution in Linfen City. Among the six national monitoring sites, Chengnan and Tangyao Hotel contributed the most of O₃ pollution at all levels in Linfen urban area. At both sites, 77% of O₃ exceeding the standard concentration occurred when the south and southwest wind was blowing, while16.6% of O₃ exceeding the standard concentration at Chengnan site occurred when the wind speed was greater than 3 m/s; the frequency of naphthalene, as a typical tracer of coking, appearing higher than its mean value in the southerly direction was 30.4%, which indicated that the unreasonable industrial layout made the atmosphere in Linfen City affected by the coking area, and O₃ concentration was more likely to exceed the standard when the southerly wind blew. The pollution emission in Xiangfen, Hongdong, Yicheng and Fushan counties contributed to O₃ pollution in Linfen City. The above results showed that O₃ pollution in the urban area of Linfen City was not only affected by the local generation but also by the transportation of polluted air masses containing high concentration of NO_x and VOCs emitted by coking and steel plants in the above four counties. Therefore, joint prevention and control with the upwind areas affected by coking should be paid attention to while strengthening the control of local LPG use and vehicle exhaust emissions in Linfen urban area.