2021年南京市新冠疫情期间大气污染物变化特征及来源解析

Variation characteristics and source analysis of air pollutants during the COVID-19 pandemic in Nanjing in 2021

为了解2021年南京市新冠疫情期间城市大气污染物浓度的变化和成因,利用南京大学SORPES站点2021年7月1日—2021年8月30日大气污染物在线监测数据,分析疫情前、中、后颗粒物及气态污染物的浓度变化,针对臭氧(O 3)的关键前体物,挥发性有机物(Volatile Organic Compounds,VOCs)采用正定矩阵因子分解法模型(Positive Matrix Factorization,PMF)、拉格朗日粒子输送与扩散模型(Lagrangian Particle Distribution Model,LPDM)分析其污染来源。结果表明:疫情封闭期间,南京市PM 2.5质量浓度较疫情前降低了40%~50%,组分中硝酸盐、有机物质量浓度降幅最为显著,分别下降了34.0%和16.5%。臭氧体积浓度不降反升,城中区域增幅最显著站点可达50%左右。其气态前体物氮氧化物(NO x)及VOCs浓度变化呈相反态势,分别较疫情前降低28%、升高49.6%。模型及卫星遥感结果表明,疫情期间南京市臭氧属于协同偏VOCs控制区。气团溯源结果显示,南京市受本地及周边区域传输的共同影响,疫情封闭期间省外上海方向、省内苏州-无锡-镇江-南通方向的气团贡献增大。PMF解析了南京市本地VOCs主要来源于机动车排放源、植物源、溶剂源、工业生产源以及油气挥发源,其中机动车源占比变幅最大,疫情封闭期间下降了15.1%,疫情后上升了4.3%。其次为油气挥发源、溶剂源,这两项污染源疫情封闭期间分别上升了11.2%、1.7%,疫情后则分别下降了4.8%、4.3%。

This paper investigates the impact of the COVID-19 pandemic lockdown on urban air pollution in Nanjing during the summer of 2021.Using online monitoring data from the SORPES site at Nanjing University,we compared the concentrations of particulate matter and gaseous pollutants before,during,and after the lockdown.Additionally,we used the PMF model and the LPDM model to analyze the sources of volatile organic compounds(VOCs).The results show that,compared to the period before the lockdown,PM 2.5 concentrations in Nanjing decreased by 40%-50%,while nitrate and organic matter concentrations decreased by 34.0%and 16.5%,respectively.Urban areas experienced a significant increase in ozone concentration,approximately 50%.The two gaseous precursors of ozone exhibited opposite trends:NO x concentrations dropped by 28%,while TVOCs increased by 49.6%.The OBM model and satellite data results indicate that ozone formation in Nanjing was in the VOC-limited regime during the lockdown.Air mass tracing results reveal that VOCs in Nanjing were jointly influenced by local and regional transport from surrounding cities,with increased contributions from the Shanghai-Suzhou-Changzhou-Zhenjiang and Tongling-Ma anshan directions during the lockdown.PMF source analysis results demonstrate that local VOCs in Nanjing primarily originate from motor vehicle emissions,plant sources,solvent sources,industrial production,and oil and gas volatile sources.Motor vehicle emissions exhibited the most significant variation among all sources,with a reduction of 15.1%during the lockdown and an increase of 4.3%after the lockdown.Oil and gas volatilization and solvent sources increased by 11.2%and 1.7%,respectively,during the lockdown and decreased by 4.8%and 4.3%,respectively,after the lockdown.