Does lockdown reduce air pollution? Evidence from 44 cities in northern China

Abstract

Responding to the ongoing novel coronavirus (agent of COVID-19) outbreak, China implemented "the largest quarantine in human history" in Wuhan on 23 January 2020. Similar quarantine measures were imposed on other Chinese cities within days. Human mobility and relevant production and consumption activities have since decreased significantly. As a likely side effect of this decrease, many regions have recorded significant reductions in air pollution. We employed daily air pollution data and Intracity Migration Index (IMI) data form Baidu between 1 January and 21 March 2020 for 44 cities in northern China to examine whether, how, and to what extent travel restrictions affected air quality. On the basis of this quantitative analysis, we reached the following conclusions: (1) The reduction of air pollution was strongly associated with travel restrictions during this pandemic-on average, the air quality index (AQI) decreased by 7.80%, and five air pollutants (i.e., SO₂, PM_2.5, PM₁₀, NO₂, and CO) decreased by 6.76%, 5.93%, 13.66%, 24.67%, and 4.58%, respectively. (2) Mechanism analysis illustrated that the lockdowns of 44 cities reduced human movements by 69.85%, and a reduction in the AQI, PM_2.5, and CO was partially mediated by human mobility, and SO₂, PM₁₀, and NO₂ were completely mediated. (3) Our findings highlight the importance of understanding the role of green production and consumption.

Keywords: Air pollution; COVID-19; Dynamic panel; Human mobility; Travel restriction.

Graphical abstract

Fig. 1

Study area.

Fig. 2

Dates of discovery of COVID-2019, and lockdown timeline of cities in Hubei Province and 44 cities in northern China beginning 31 December 2019.

Fig. 3

Variations of AQI index, SO₂, PM_2.5, PM₁₀, NO₂, and CO concentrations before and after lockdowns.

Fig. 4

Time trends 10 days before and after travel restrictions in Beijing. (The plotted dots are the sum of residuals from estimating Eq. (1). The fitted line represents the time trend.)

Fig. 5

Average variations of IMI index for 44 cities in 2020 (dark blue line) and same periods of 2019 (ochre yellow line), the red dashed line stands for fluxes of human mobility when the travel restrictions are implemented. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. A1

Variations of IMI index for 44 cities in 2020 (dark blue line) and same periods of 2019 (ochre yellow line), the red line stands for fluxes of human mobility when the travel restrictions are implemented.