Abstract
The lockdown during the coronavirus disease 2019 (COVID-19) pandemic provides a scarce opportunity to assess the efficiency of air pollution mitigation. Herein, the monitoring data of air pollutants were thoroughly analyzed together with meteorological parameters to explore the impact of human activity on the multi-time scale changes of air pollutant concentrations in Guiyang city, located in Southwest China. The results show that the COVID-19 lockdown had different effects on the criteria air pollutants, i.e., PM2.5 (diameter ≤ 2.5 μm), PM10 (diameter ≤ 10 μm), sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), and ozone (O3) concentrations. The lockdown caused a significant drop in NO2 concentration. During the first-level lockdown period, the NO2 concentration declined sharply by 8.41 μg·m−3 (45.68%). The decrease in NO concentration caused the “titration effect” to weaken, leading to a sharp increase in O3 concentration. Although human activities resumed partially and the “titration effect” enhanced certainly during the second-level lockdown period, the meteorological conditions became more conducive to the formation of O3 by photochemical reactions. Atmosphere oxidation was enhanced to promote the generation of secondary aerosols through gas–particle transitions, thus compensating for the reduced primary emission of PM2.5. The implication of this study is that the appropriate air pollution control policies must be initiated to suppress the secondary generation of both PM2.5 and O3.
Highlights
The coronavirus disease 2019 (COVID-19) pandemic has caused unprecedented socioeconomic impact around the world [1]
As compared with the Pre-Lockdown period, the mean concentrations of PM10, NO2, and carbon monoxide (CO) during the Fir-Lockdown period decreased by 2.59 μg·m−3 (6.67%), 8.41 μg·m−3 (45.68%), and 159.09 μg·m−3 (18.82%), respectively, with the mean concentration of NO2 decreasing the most, by nearly 50%
Compared with the Pre-Lockdown period, the mean concentrations of PM10, NO2, and CO decreased during the Fir-Lockdown period by 2.59 μg·m−3 (6.67%), 8.41 μg·m−3 (45.68%), and 159.09 μg·m−3 (18.82%), respectively
Summary
The coronavirus disease 2019 (COVID-19) pandemic has caused unprecedented socioeconomic impact around the world [1]. In order to curb the viral transmission among humans, the State Council of China issued the National Emergency Plan for Public Emergencies, which set out the strictest lockdown measures and almost completely stagnated economic activities related to transportation and movement [2]. The lockdown measures included the partial or total closure of international borders, schools, and non-essential businesses, in addition to the restriction on non-essential movement of citizens [3]. COVID-19 lockdown caused a reduction in the levels of human activities, which is essentially similar to the temporary emission control imposed on pollution sources during major conferences or sporting events. Anthropogenic activities and the emissions from their pollution sources were
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