2022年春季南京臭氧污染特征及成因分析

Analysis on the Characteristics and Causes of Ozone Pollution in Nanjing in the Spring of 2022

2022年春季,受新一轮新冠疫情影响,长三角各城市采取了一系列管控措施,使得大气污染物排放水平降低。对2022年春季(3—5月)南京及长三角地区的六项污染物尤其是臭氧(O_(3))的变化特征进行了分析,从气象因素和O_(3)前体物方面,同时利用基于观测的模型(OBM)对南京O_(3)污染变化原因进行了研究,并分析了南京挥发性有机物(VOCs)的关键活性组分和来源。结果表明:2022年春季,南京PM_(2.5)、PM_(10)、NO_(2)和CO均值浓度均同比下降,但O_(3)日最大8 h滑动平均质量浓度(O_(3)-8 h)同比上升19.8%,O_(3)-8 h超标时间同比增加9 d;长三角区域O_(3)-8 h同比上升17.9%,O_(3)-8 h超标天数为2021年同期的2.5倍。南京O_(3)浓度上升的原因:一方面是由于不利的气象条件,另一方面是由于南京O_(3)生成处于VOCs控制区,但氮氧化物(NO_(x))降幅大于VOCs降幅,同时结合O_(3)前体物削减方案的分析结果发现,VOCs和NO_(x)不当的削减比例会导致O_(3)浓度不降反升。南京O_(3)生成的关键VOC活性物种依次为乙醛、丙烯、间/对二甲苯、丙烯醛和乙烯;正定矩阵因子分解(PMF)解析结果显示,机动车尾气是南京城区VOCs的主要来源,其次为液化石油气/天然气使用和石油化工。

Affected by the new round of COVID-19 in the spring of 2022,cities in the Yangtze River Delta adopted a series of control measures,resulting in a reduction in the emission level of air pollutants.The variation characteristics of six pollutants,especially ozone(O_(3)),in Nanjing and Yangtze River Delta in the spring(from March to May)of 2022 were analyzed.From the aspects of meteorological factors and O_(3)precursors,and using observation-based models(OBM),the cause of variation of O_(3)pollution in Nanjing were studied.Key active components and sources of volatile organic compounds(VOCs)of Nanjing were analyzed.The results showed that:compared with that in 2021,the average concentrations of PM_(2.5),PM_(10),NO_(2)and CO all decreased,but O_(3)-8 h concentration increased by 19.8%and days of O_(3)-8 h exceeding standard increased by 9 days in Nanjing,and O_(3)-8 h concentration increased by 17.9%,and the number of days of O_(3)-8 h exceeding standard increased by 1.5 times in the Yangtze River Delta in the spring of 2022.On the one hand,the rise of O_(3)concentration in Nanjing was due to unfavorable meteorological conditions,on the other hand,O_(3)generation in Nanjing was more sensitive to VOCs,but reduction percentage of nitrogen oxides(NO_(x))concentration was more than that of VOCs,and combined with the analysis results of O_(3)precursor emission reduction scheme,it was found that the improper emission reduction ratio of VOCs and NO_(x)could lead to O_(3)concentration rising instead of falling.The key active species of VOC for ozone generation of Nanjing were acetaldehyde,propylene,m/p-xylene,acrolein and ethylene.The results of positive matrix factorization(PMF)showed that vehicle exhaust was the main source of VOCs in Nanjing urban area,followed by LPG/NG use and petrochemistry.