Effects of COVID-19 lockdown on global air quality and health

Abstract

The COVID-19 pandemic has put much of the world into lockdown, as one unintended upside to this response, the air quality has been widely reported to have improved worldwide. Existing studies examine the environmental effect of lockdowns at a city- or country-level, few examines it from a global perspective. Using a novel COVID-19 government response tracker dataset, combining the daily air pollution data and weather data across 597 major cities worldwide between January 1, 2020, and July 5, 2020, this study quantifies the causal impacts of 8 types of lockdown measures on changes of a range of individual pollutants based on a difference-in-differences design. The results show that the NO₂ air quality index value falls more precipitously (23-37%) relative to the pre-lockdown period, followed by PM₁₀ (14-20%), SO₂ (2-20%), PM_2.5 (7-16%), and CO (7-11%), but the O₃ increases 10-27%. Furthermore, intra/intercity travel restrictions have a better performance in curbing air pollution. These results are robust to a set of alternative specifications, including different panel sizes, independent variables, estimation strategies. The heterogeneity analysis in terms of different types of cities shows that the lockdown effects are more remarkable in cities from lower-income, more industrialized, and populous countries. We also do a back-of-the-envelope calculation of the subsequent health benefits following such improvement, and the expected averted premature deaths due to air pollution declines are around 99,270 to 146,649 among 76 countries and regions involved in this study during the COVID-19 lockdown. These findings underscore the importance of continuous air pollution control strategies to protect human health and reduce the associated social welfare loss both during and after the COVID-19 pandemic.

Keywords: Air pollution; COVID-19; Difference-in-differences analysis; Health benefits; Lockdown.

Graphical abstract

Fig. 1

The global trend of air pollution: PM_2.5. Notes: The solid red line indicates the date of Wuhan lockdown (January 23, 2020), and the black dash line indicates the date that this novel coronavirus received an official name from WHO (February 11, 2020). Data comes from the aqicn.org (https://aqicn.org/data-platform/covid19/). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 2

Changes in the government response index across the world.

Fig. 3

The geographic distributions of countries and regions involved in this study. Notes: Gray areas denote non-study areas.

Fig. 4

The daily government response index and PM_2.5 individual AQI of 597 cities worldwide involved in this study from March to June 2020. Notes: Both indicators are logarithmically transformed in order to avoid the nonnormality and heteroscedasticity. The red line indicates the trend line, which predicts the overall relationship between PM_2.5 individual AQI and the intensity of the government response index. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 5

Event-study results on PM_2.5. Notes: These figures summarize the results of the parallel trend tests based on Eq. (4). 95% confidence bands. The solid black line indicates the date of one day before the enforcement of lockdown measures; its corresponding dummy variable is omitted from the specifications.