Reductions in ground-level nitrogen dioxide (NO2) concentrations during COVID-19 lockdowns varied considerably by region and emission sector with decreases in mean country-level population weighted NO2 levels being about a third larger in countries with stricter COVID-19 lockdown measures, compared to those without restrictions. The findings, published in Nature, improve our knowledge of NO2 exposure estimates and provide an opportunity for advances in air quality health assessment.
NO2 is an important contributor to air pollution and human exposure is associated with adverse health outcomes, including respiratory infections, asthma and lung cancer. Decreases in atmospheric and ground-level NO2 have previously been reported as a result of lockdown measures to reduce the spread of COVID-19. However, questions remain about the relationship between atmospheric NO2 levels, measured using satellite data, and human health-relevant ground-level NO2 concentrations that are often only measured in higher income countries.
Matthew Cooper and colleagues used high-resolution satellite data to derive global ground-level NO2 concentrations and assess individual cities during COVID-19 lockdowns in 2020 compared to 2019. They then used the satellite measurements to quantify the NO2 level changes in over 200 cities, including 65 cities without available ground level monitoring, largely in lower income regions. The authors found that decreases in mean country-level population-weighted NO2 concentrations were about 29% larger in countries with strict lockdown conditions, such as North America and China, than in those without. NO2 decreases during COVID-19 lockdowns were also found to exceed recent annual mean year-to-year decreases from emission controls, comparable to about 15 years of reductions globally.
The results also suggest that the sensitivity of NO2 to lockdowns varies by country and emission sector (power plants or transportation, for example), demonstrating the need for high-resolution satellite-derived information of ground level concentration estimates.
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