福州2017—2021年环境空气质量变化特征及新冠疫情对其变化的影响

Characteristics of ambient air quality change in Fuzhou from 2017-2021 and the impact of COVID-19

基于福州市2017—2021年大气常规污染物(PM_(10)、PM_(2.5)、SO_(2)、NO_(2)、CO和O_(3))小时观测数据,探讨了不同时间尺度(年度、季度、新冠疫情前后)福州主要污染物变化特征.结果表明:2017—2021年福州市6种大气常规污染物年均浓度整体上均呈下降趋势,年均下降率最大的是NO_(2)(10.3%),其次是SO_(2)(8.3%).由于复杂的生成机制及较高的温度和较强的太阳辐射,福州春季、夏季和秋季O_(3)浓度较高且差异不大.除O_(3)外,其他污染物具有显著季节变化特征(春季>冬季>秋季>夏季).5年间福州空气污染物日均浓度变化幅度趋于平稳,全年大气环境状况愈加优良.新冠疫情发生期间(2020—2021)福州空气质量指数(AQI)年均下降率是疫情前(2017—2019)的2.2倍,疫情管控期间相较管控前PM_(10)、PM_(2.5)、NO_(2)、SO_(2)和CO浓度分别下降了41.1%、37.2%、62.4%、6.7%和22.8%.新冠疫情期间停工导致的“净环境效益”显著加速了福州空气质量的提升.但疫情管控期间O_(3)浓度不降反升,NO_(x)和VOCs的不成比例减排、NO_(x)对O_(3)的滴定作用减小以及不利气象条件是造成这一结果的主要原因.疫情前后多种污染物的相关性分析表明,福州大气环境受二次污染物及其前体物影响显著,加强二次污染物生成机理研究及前体物控制可以进一步推动福州空气质量的提升.

The temporal variations of the concentrations of major air pollutants(PM_(10),PM_(2.5),SO_(2),NO_(2),CO,O_(3))in Fuzhou were investigated at different time scales(interannual,seasonal,before and after the COVID-19 epidemic)based on the hourly observation data from 2017 to 2021.The results showed that the annual average concentrations of the six pollutants in Fuzhou decreased during 2017 to 2021,and the decreasing rate of NO_(2)was the largest(10.3%),followed by that of SO_(2)(8.3%).O_(3)showed higher average concentrations in spring,summer and autumn due to its complex generation mechanism as well as the higher temperature and stronger solar radiation in all the three seasons.PM_(10),PM_(2.5),NO_(2),SO_(2)and CO concentrations had significant seasonal variations(spring>winter>autumn>summer).The daily fluctuation of pollutant concentrations in Fuzhou decreased and the air quality improved during the five years.During the period of COVID-19(2020—2021),the annual decreasing rate of AQI values in Fuzhou was 2.2 times higher than that before the period(2017—2019).The concentrations of PM_(10),PM_(2.5),NO_(2),SO_(2)and CO decreased by 41.1%,37.2%,62.4%,6.7%and 22.8%,respectively,during the lockdown compared with those before the lockdown.The rapid reduction of economic activities and the associated emissions during the COVID-19 lockdown resulted in significant improvements in air quality in Fuzhou.However,O_(3)concentrations increased due to the disproportionate reduction of NO_(x)and VOCs,weakened NO_(x)titration effect and unfavorable meteorological conditions.The correlation analysis of various pollutants in Fuzhou indicated that the air quality was significantly influenced by concentrations of secondary pollutants and their precursors.These suggested the important roles of further research on the generation mechanism of secondary pollutants and precursor emission control in improving air quality in Fuzhou.