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

This multicountry study will evaluate whether changes in mortality are associated with changes in ambient NO₂ and PM_2.5 levels before, during, and after the lockdown and disentangle the short-term effects of NO₂ versus PM_2.5 on mortality. The analysis will be conducted in four countries: China, Germany, Italy, and the United States.

Poster abstract for HEI Annual Conference 2023

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

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

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. The COVID-19 pandemic has brought substantial excess mortality worldwide. In response, unprecedented lockdown measures were implemented worldwide to control the pandemic, leading to significant but temporary air pollution reductions. This provided a rare opportunity for a natural experiment to assess the effects of air pollution reduction on mortality changes. Focusing on Jiangsu, China, California, U.S., Italy, and Germany, this project aims to first evaluate the associations between ambient NO₂ and PM_2.5 levels and total, nonaccidental, cardiovascular, and excess mortality, and then to disentangle the short-term effects of NO₂ versus PM_2.5 on mortality.

Methods. We applied a two-stage interrupted time-series design to estimate the excess mortality in four study regions. To estimate the effects of air pollution on mortality, we used an interactive fixed effects model, which could control for both measured and unmeasured spatiotemporal confounders. To quantify the air pollution changes purely due to COVID-19 lockdowns, we first applied a meteorological normalization technique to remove the impacts of meteorological factors, and then used a difference-in-differences approach to control for the time trend of air pollution. Using the estimated associations and reductions in air pollutants due to COVID-19 lockdowns, we will perform a health impact assessment to calculate the avoided mortality attributable to air pollution changes. We will apply a variant of the difference-in-differences approach to capture the independent effects of NO₂ and PM_2.5 exposures. To identify potentially sensitive subpopulations, we will assess the mortality responses to air pollution changes in different sex and age groups.

Results. During the intense period of the COVID-19 pandemic in early 2020, the estimated excess deaths were -6,036 (95% empirical confidence interval [eCI]: -11,631, -706) in Jiangsu, China, 6,342 (95% eCI: 4,671, 7,953) in California, U.S., 51,477 (95% eCI: 44,602, 57,970) in Italy, and 6,666 (95% eCI: 4,460, 8,823) in Germany. The estimation of the air pollution-mortality relationship and the quantification of lockdown induced-air pollution changes are close to complete, and the health impact assessment will follow, using those relationships as inputs. Subgroup and cause-specific analyses are still ongoing.

Conclusion. This study will thoroughly assess the health benefits of air pollution reductions during the COVID-19 lockdowns and provide causal evidence on the effects of NO₂ and PM_2.5 on mortality.