August 19, 2022 – In cities that implemented stricter policies to contain COVID-19 during the early months of the pandemic, the air quality was more likely to improve, according to a new global analysis.
The study, published August 14, 2022 in Environmental Science & Technology, was the first comprehensive look at the impact of COVID-19 containment policies on air pollution. Lead author of the study was Heresh Amini, a fellow of the Cyprus Harvard Endowment Program for the Environment and Public Health and assistant professor of environmental epidemiology at the University of Copenhagen, Denmark. Joel Schwartz, professor of environmental epidemiology at Harvard T.H. Chan School of Public Health, was a co-author.
Researchers analyzed data from 1,851 cities in 149 countries from January 1, 2019 through July 31, 2020. They looked at satellite data showing concentrations of NO2, a pollutant mainly emitted from the transportation sector, and compared that with information on COVID-19 containment policies from around the world. The policy information for countries came from Oxford University’s COVID-19 Government Response Tracker, a database that tracked daily policies, such as school and workplace closures, public event cancellations, restrictions on gatherings, stay-at-home requirements, and international travel restrictions across the world. Researchers also considered daily weather conditions in their analysis.
The study found that, overall, NO2 levels decreased significantly—by 5%—in the cities that implemented the most stringent policies to contain COVID-19; did not change much in cities with moderate policies; and even increased by 2.3% under mild policies, possibly due to more people driving to avoid using public transportation, thus increasing vehicle emissions. These changes differed across World Bank regions.
NO2 reduction was larger at the beginning of the pandemic, the study found. In addition, cities with larger populations and more pollution prior to the pandemic had larger air quality improvements during the pandemic.
Noting that air pollution has been linked with increased transmission of SARS-CoV-2, increased mortality due to COVID-19, and increases in all-cause mortality and illness, the researchers wrote that “slight changes in air quality could result in substantial impacts on population health as billions of people are exposed.” They added, “Needless to say that combustion-related NO2 emissions correlate with other pollutants and increased release of CO2; hence, policies may have jeopardized attempts to abate climate change.” They noted that the study’s findings may be useful to regional authorities considering future environmental policy decisions.