The impacts of human migration and city lockdowns on specific air pollutants during the COVID-19 outbreak: A spatial perspective

Abstract

The outbreak of COVID-19 continues to bring unprecedented shock to mankind's socioeconomic activities, and to the wider environment. China, as the early epicenter of the pandemic, locked down one-third of its cities in an attempt to prevent the rapid spread of the virus. Human migration patterns have subsequently been radically altered and many regions have seen perceived improvements in air quality during the lockdowns. This study empirically examines the relationship between human migration and air pollution and further evaluates the causal impacts of the lockdowns. A spatial econometric method and a spatial explicit counterfactual framework are employed in this study. The key findings are as follows: i) a considerable amount of variation in AQI, PM 10 , PM 2.5 , and NO 2 concentration can be explained by human migration but we fail to find suggestive evidence in the cases of SO 2 and CO; ii) the implementation of lockdown measures led to a significant reduction in AQI (18.1%), PM 2.5 (22.2%), NO 2 (20.5%), and PM 10 (10.7%), but has no meaningful impacts on SO 2, CO and O 3 levels; iii) further analysis indicates that the impacts of lockdown policies varied by control stringency and by regional heterogeneity. Our findings are of great importance for the Chinese government to create a stronger and more coherent framework in its efforts to tackle air pollution.

Association of population migration with air quality: Role of city attributes in China during COVID-19 pandemic (2019–2021)

“…Air quality improvement is an indirect environmental benefit of lockdown policies in response to the pandemic ( Braga et al, 2020 ; Depellegrin et al, 2020 ; Wang and Su, 2020 ; Zeng and Bao, 2021 ). An annual peak period of returning home and returning to workplaces normally emerges after the Spring Festival holiday.…”

“…The observed decrease in population migration has been attributed to the pandemic outbreaks and traffic restriction policies ( Lau et al, 2021 ). Nonetheless, cities are inherently heterogeneous entities ( Zeng and Bao, 2021 ). Our study found that the classification of city scale, pollution level, and population mobility is consistent with the characteristics of the cluster mappers of the local Moran's I.…”

“…The urban migration boundary adopted an administrative division of the city, including districts, counties, townships, and villages. Population migration was estimated using previously described equations (H. Fang et al, 2020 ; Zeng and Bao, 2021 ) based on the proportional relationship between the Baidu migration index and population: where the WCM represents the within-city migration (1000 people), and ICM represents the inter-city migration (1000 people).…”

“…Because there are obvious differences in climate, population distribution, economic structure, and urbanization process in Chinese regions with a vast territory (H. Wang et al, 2021 ), air pollution variation during the lockdown also has regional characteristics. As shown in Table S1 , only a few studies have identified larger lockdown effects in colder, richer, larger, more industrialized, and more air-polluted cities with previous heterogeneity analysis, suggesting interactions with city attributes ( He et al, 2020 ; Hu et al, 2021 ; Shen et al, 2021 ; H. Wang et al, 2021 ; Zeng and Bao, 2021 ). However, this cannot be deduced in all cases.…”

Short-Term Field Research on Air Pollution within the Boundaries of the Large City in the Baltic Region

“…The performed studies showed that the level of primary pollution causes secondary pollution, which in turn exacerbates the environmental situation (Zheng et al, 2020). Thus, theoretical air pollution models estimating human migration have been developed for comparing the results of eld research (Zeng & Bao, 2021).…”