受焦化影响的下风向城区臭氧污染特征及潜在源区分析

为了解受焦化影响的下风向城区臭氧(O₃)的污染特征及来源，基于2019年临汾市6个国控点的O₃浓度、气象参数（气温等）以及北大街站点VOCs监测数据开展研究。结果表明：2019年临汾市O₃日最大8 h滑动平均值（MDA8）的90百分位数（MDA8-90th）为204 μg/m³，在山西省11个地市中排名第一；全年共有103 d O₃浓度超标，且超标天主要集中在5—9月；MDA8从2月开始升高，6月达到最大值，之后逐月下降；O₃小时浓度总体呈14:00—16:00出现峰值的单峰日变化。MDA8与日最高气温（T_max）呈正相关、与日最低相对湿度（RH_min）呈负相关，当T_max>22 ℃或RH_min<55%时，可能发生O₃浓度超标现象。VOCs的O₃生成潜势（OFP）分析结果表明，乙烯的OFP最高，占总OFP的44.5%，乙烯是导致O₃污染的关键VOCs活性物种；液化石油气（LPG）的使用、机动车尾气和炼焦活动等的排放对临汾市O₃污染有重要贡献。6个国控点中，城南和唐尧大酒店对临汾市区所有级别的O₃污染贡献均较大，2个站点均有77%的O₃超标出现在刮南风和西南风时，其中城南有16.6%的O₃超标出现在风速大于3 m/s时，作为焦化典型示踪物的萘在南风向其浓度高于均值的占比为30.4%，表明不合理的工业布局使临汾市区大气受到了焦化区的影响，O₃浓度更易在刮南风时超标。临汾市区O₃污染除受到本地生成影响外，还受到襄汾县、洪洞县、翼城县和浮山县的焦化企业和钢铁企业排放的含高浓度NO_x、VOCs污染气团传输的影响。因此，临汾市在对本地LPG使用和机动车尾气排放进行管控的同时，还要加强与上风向焦化地区的联防联控。

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 (Tmax) and negatively correlated with daily minimum relative humidity (RHmin). When Tmax was greater than 22 ℃ or RHmin 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 NOx 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.