汾渭平原PM_(2.5)-O_(3)复合污染特征及气象成因分析

Characteristics of PM_(2.5)-O_(3)Compound Pollution and Meteorological Impact in Fenwei Plain

PM_(2.5)和O_(3)已经成为汾渭平原城市最主要的污染物,两者之间相互影响,在暖季经常同时出现构成污染,其污染程度与气象条件密切相关。利用2015—2021年汾渭平原12个城市逐日PM_(2.5)和O_(3)浓度、地面气象观测数据以及ERA5高空再分析数据等资料,分析了汾渭平原PM_(2.5)和O_(3)的时空变化特征以及复合污染发生时PM_(2.5)和O_(3)的关系,并研究了局地气象条件和天气形势对复合污染的影响。结果显示,该地区年均PM_(2.5)和日最大8小时O_(3)浓度分别在2017年和2018年开始持续下降,复合污染日数也在2019年后开始持续下降;复合污染主要发生在3—9月,在汾渭平原东部城市出现次数较多,多出现在高温、低湿的环境下;最后利用T-PCA算法(正交主成分分析)将复合污染的天气环流形势分为4种类型,主要呈现出以高空西北气流或偏西气流、低层为暖区偏南风或微风为主的天气特征。研究结果对汾渭平原的大气污染防治提供了参考依据,尤其对于PM_(2.5)和O_(3)污染协同治理具有重要意义。

PM_(2.5)and O_(3)which interact with each other have become the most important pollutants in the cities of Fenwei Plain.The pollution often occurs simultaneously in warm seasons and is closely related to meteorological conditions.Based on the daily PM_(2.5)and O_(3)concentration data,surface meteorological observation data and ERA5 high-altitude reanalysis data of 12 cities in the Fenwei Plain from 2015 to 2021,the spatio-temporal characteristics of PM_(2.5)and O_(3)in the Fenwei Plain,as well as the relationship between PM_(2.5)and O_(3)when compound pollution occurs are analyzed.Besides,the impact of local meteorological conditions and synoptic situation on compound pollution is also studied.The results show that the average annual PM_(2.5)and MDA8 O_(3)(maximum daily 8 h average ozone)concentrations in the Fenwei Plain began to decline continuously in 2017 and 2018,respectively,and the number of compound pollution days also began to decrease continuously after 2019.Compound pollution mainly occurs in March to September,frequently seen in the cities of eastern Fenwei Plain,mostly in condition of high temperature and low humidity.Finally,the synoptic circulation situation of compound pollution is divided into four types by principal component analysis with the T-PCA algorithm,featured with the northwest or westerly air flow in high-altitude and the southerly wind or breeze in the low-level warm zone.These findings could provide some basis for controlling pollution in the Fenwei Plain and are of great significance for cooperative governance of PM_(2.5)and O_(3)pollution.