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Effect of air pollution reductions on mortality during the COVID-19 lockdown: A natural experiment study

Principal Investigator: 

Yale University

This multicountry study will evaluate whether changes in mortality are associated with changes in ambient NO2 and PM2.5 levels before, during, and after the lockdown and disentangle the short-term effects of NO2 versus PM2.5 on mortality. The analysis will be conducted in four countries: China, Germany, Italy, and the United States.

Funded under

Poster abstract for HEI Annual Conference 2022

Effect of Air Pollution Reductions on Mortality during the COVID-19 Lockdown: A Natural Experiment Study

Kai Chen1, Massimo Stafoggia2, Susanne Breitner3, Patrick L. Kinney4, Yiqun Ma1, Federica Nobile2, Anne Marb3, Robert Dubrow1

1Yale School of Public Health, New Haven, CT, USA; 2Lazio Region Health Service, Rome, Italy; 3Ludwig-Maximilians-Universität München, Munich, Germany; 4Boston University School of Public Health, Boston, MA, USA

Background. Unprecedented lockdown measures were implemented worldwide to control the COVID-19 pandemic, leading to significant but temporary air pollution reductions. Substantial decreases in nitrogen dioxide (NO2) concentrations were observed during the lockdowns, whereas changes in fine particulate matter (PM2.5) concentrations have been inconsistent, with reductions comparable to those of NO2, smaller reductions, or even increases. These disproportionate changes in ambient NO2 and PM2.5 pollution provide a rare opportunity for a natural experiment to address the causal effects of NO2 and PM2.5 exposure on health.

Objectives. We will first evaluate whether changes in mortality are associated with changes in ambient NO2 and PM2.5 levels before, during, and after the lockdown (Aim 1). Then, we will leverage the unprecedented natural experiment of disproportionate reductions in NO2 and PM2.5 pollution during the COVID-19 lockdowns to disentangle the short-term effects of NO2 versus PM2.5 on mortality (Aim 2), a challenge that has proven difficult in prior research due to the high correlation between these two pollutants.

Methods. To address Aim 1, we will focus on regions that implemented lockdown measures that led to air pollution reduction but were not severely affected by the COVID-19 pandemic during the lockdown period: Jiangsu, China, Central and Southern Italy, Northern and Eastern Germany, and California, U.S. in 2020. To estimate the effect of air pollution reductions on mortality during the lockdowns in these study regions, we will use a variant of the difference-in-difference approach. We will focus on total, nonaccidental, and cardiovascular mortality to reduce the influence of disrupted healthcare systems and changes in diagnostic criteria for COVID-19. For Aim 2, we will first quantify the air pollution changes during the lockdown using a counterfactual modeling approach and then stratify the locations (cities, counties, or municipalities) in each country into a treatment group (considerable reduction in NO2, but little to no reduction in PM2.5) and a control group (comparable reductions in NO2 and PM2.5). We will apply the difference-in-difference approach developed in Aim 1 to estimate the health effects of NO2 in the treatment and control groups separately; and then calculate the difference between these two estimates to capture the effect of NO2 exposure, independent of PM2.5 exposure. Finally, we will quantify the avoided premature mortality attributable to air pollution changes using the estimated associations and reductions in air pollutants during the COVID-19 lockdown.

Results & Conclusion. This study will provide a thorough assessment of the health benefits from air pollution reductions during the COVID-19 lockdowns and causal evidence on the relationship between NO2 air pollution and mortality.