Air quality improvement from COVID-19 lockdown: evidence from China

Abstract

As we move through 2020, our world has been transformed by the spread of COVID-19 in many aspects. A large number of cities across the world entered "sleep mode" sequentially due to the stay-at-home or lockdown policies. This study exploits the impact of pandemic-induced human mobility restrictions, as the response to COVID-19 pandemic, on the urban air quality across China. Different from the "traditional" difference-in-differences analysis, a human mobility-based difference-in-differences method is used to quantify the effect of intracity mobility reductions on air quality across 325 cities in China. The model shows that the air quality index (AQI) experiences a 12.2% larger reduction in the cities with lockdown. Moreover, this reduction effect varies with different types of air pollutants (PM_2.5, PM₁₀, SO₂, NO₂, and CO decreased by 13.1%, 15.3%, 4%, 3.3%, and 3.3%, respectively). The heterogeneity analysis in terms of different types of cities shows that the effect is greater in northern, higher income, more industrialized cities, and more economically active cities. We also estimate the subsequent health benefits following such improvement, and the expected averted premature deaths due to air pollution declines are around 26,385 to 38,977 during the sample period. These findings illuminate a new light on the role of a policy intervention in the pollution emission, while also providing a roadmap for future research on the pollution effect of COVID-19 pandemic.

Keywords: Air pollution; COVID-19 pandemic; Health benefit; Heterogeneity; Lockdown.

Fig. 1

Daily within-city migration intensity for the national city averages and new locked-down cities in China during the sample period. The green dash line represents the date of official confirmation of the person-to-person transmission of COVID-19 (January 20, 2020), and the red solid line represents the date of Wuhan lockdown (January 23, 2020)

Fig 2

The reduction of AQI before and after lockdowns. This figure reflects the geographic distributions of cities involved in this study and the relative change in the average value of AQI after lockdown compared with that before lockdown in treated cities during the sample period. The non-white area indicates cities that enforce lockdown policies

Fig 3

Event study analysis of city lockdown. These figures present the results of the parallel trend tests based on Eq. (4). The control group is the cities without lockdown. The last group of cities that declared the lockdown policies on February 13, 2020, are all located at Inner Mongolia, as our sample date ranges from January 1 to May 2, 2020. Forty-three days are remaining until they impose the lockdown, while there are 99 days left after Wuhan firstly imposed the lockdown policy on January 23, 2020, during the sample period

Fig. 4

Daily within-city migration intensity for the national city averages in 2020 and the same periods of 2019. The green line represents the date of official confirmation of the person-to-person transmission of COVID-19 (January 20, 2020), and the red solid line represents the date of Wuhan lockdown (January 23, 2020)