| 2015—2022年我国华北地区冬季PM2.5-O3复合污染及特征分析 |
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| 引用本文： | 候杰,李柯,张丹瑜婷.2015—2022年我国华北地区冬季PM2.5-O3复合污染及特征分析[J].环境科学研究,2023,36(6):1061-1071. |
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| 作者姓名： | 候杰 李柯 张丹瑜婷 |
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| 作者单位： | 南京信息工程大学环境科学与工程学院，江苏 南京 210044 |
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| 基金项目： | 国家自然科学基金项目(No.42205114） |
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| 摘 要： | 以往关于大气PM2.5-O3复合污染的研究主要集中在夏季，尚较缺乏对严峻的冬季复合污染问题的关注，为了解冬季大气PM2.5-O3复合污染过程，该文基于2015—2022年冬季(1—2月)空气质量地面监测、气象数据等资料，结合统计方法分析了我国华北地区冬季大气PM2.5-O3复合污染的特征及驱动因素. 结果表明:2015—2022年冬季，我国南方主要城市复合污染天数呈显著下降趋势(?0.8~?0.2 d/a)，这与我国采取一系列措施降低了PM2.5浓度有关；但在我国北方地区，特别是华北地区冬季大气PM2.5-O3复合污染天数却呈现显著的上升趋势(0.2~0.7 d/a). 针对华北地区较为严峻的复合污染形势，挑选出19 d区域性的复合污染天进行重点分析. 在气象因素方面，复合污染发生时华北上空500 hPa高空存在反气旋环流异常、850 hPa高空存在偏南风异常，地面午后(10:00—18:00)平均温度(0.43~5.27 ℃)偏高、平均风速(?4.19~?0.22 m/s)偏小. 在化学过程方面，冬季华北地区发生复合污染的城市观测站点中PM2.5与O3浓度之间呈显著正相关(R=0.45，P<0.05)，而在非复合污染的城市观测站点则表现为负相关(R=?0.68，P<0.05). 进一步对比华北地区复合污染城市观测站点与非复合污染城市观测站点Ox(Ox=NO2+O3)和NO2浓度的拟合斜率(分别为0.62、0.55)、PM2.5与CO浓度的比值(分别为0.07、0.06)以及Ox的浓度(平均值分别为124.40、113.47 μg/m3)，定性地表明了华北地区冬季O3浓度的升高与活跃的光化学反应有关，同时较高的O3浓度也可能导致了更多的二次PM2.5生成. 研究显示，我国华北地区复合污染呈现加剧的态势且往往伴随着活跃的光化学反应，亟需进一步深入研究厘清复合污染发生时的大气化学过程.
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| 关 键 词： | PM2.5-O3协同控制 冬季O3 PM2.5 华北地区 气象因素 化学过程 |
| 收稿时间： | 2022-10-05 |
Analysis of PM2.5-Ozone Co-Pollution in Winter in North China from 2015 to 2022 |
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| Affiliation: | School of Environmental Science and Engineering, Nanjing University of Information Science & Technology, Nanjing 210044, China |
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| Abstract: | Early studies examined the PM2.5-ozone co-pollution in summer in China. However, less attention has been paid to their spatiotemporal characteristics and driving factors in winter. In order to understand the driving factors of the co-pollution in winter, this study investigated PM2.5-ozone co-pollution days and their meteorological and chemical drivers in winter (January-February) in China, especially in the highly polluted North China Plain (NCP), using statistical methods based on the surface air quality measurement network and meteorological reanalysis dataset (MERRA-2) from 2015 to 2022. Our results showed that southern China experienced a decrease of ?0.8-?0.2 d/a in co-pollution days, which was mainly due to the reduction of PM2.5 concentration because of strict emission reduction by the Chinese government. But in northern China, particularly the NCP, the wintertime co-pollution days increased by 0.2-0.7 d/a from 2015 to 2022. Then, we focused on the NCP and identified 19 days of regional PM2.5-ozone pollution in the NCP for further analysis. In terms of meteorological driving factors, we found that there were anomalous anticyclone at 500 hPa and southerly wind at 850 hPa, accompanied by anomalous higher afternoon average (10:00-18:00) temperature (0.43-5.27 ℃) and lower average wind speed (?4.19-?0.22 m/s) at the surface in these co-pollution days. In terms of chemical drivers, we found that there was a strong positive correlation (R=0.45, P<0.05) between PM2.5 and ozone in the cities with co-pollution but a negative correlation (R=?0.68, P<0.05) in cities without co-pollution. We further examined the relationships of Ox (Ox=NO2+O3) vs. NO2 (k: 0.62 vs. 0.55), and PM2.5 vs. CO (ratio: 0.07 vs. 0.06) and the concentrations of Ox (average: 124.40 μg/m3 vs. 113.47 μg/m3) in observation sites with and without co-pollution days in the North China Plain. Qualitatively, it is found that higher winter O3 concentrations in North China were related to winter photochemistry, which could further drive a faster formation of secondary PM2.5. This together contributed to the occurrence of PM2.5-ozone co-pollution. This study highlights the urgency and severity of PM2.5-ozone co-pollution in the North China Plain, and shows that there is a worsening trend of PM2.5-ozone co-pollution days accompanied by active photochemistry. As such, it calls for a better understanding of the co-pollution days both meteorologically and chemically. |
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