Global Fine Scale Changes in Ambient NO2 During COVID-19 Lockdowns

Nitrogen dioxide (NO2) is an important contributor to air pollution and can adversely
affect human health(1–9) . A decrease in NO2 concentrations has been reported as a result of lockdown measures to reduce the spread of COVID-19(10–20). Questions remain, however, regarding the relationship of satellite-derived atmospheric column NO2
data with health-relevant ambient ground-level concentrations, and the representativeness of limited ground-based monitoring data for global assessment.
Here we derive spatially resolved, global ground-level NO2 concentrations from NO2
column densities observed by the TROPOMI satellite instrument at sufficiently fine
resolution (approximately one kilometre) to allow assessment of individual cities
during COVID-19 lockdowns in 2020 compared to 2019. We apply these estimates to
quantify NO2 changes in more than 200 cities, including 65 cities without available
ground monitoring, largely in lower-income regions. Mean country-level
population-weighted NO2 concentrations are 29% ± 3% lower in countries with strict
lockdown conditions than in those without. Relative to long-term trends, NO2
decreases during COVID-19 lockdowns exceed recent Ozone Monitoring Instrument
(OMI)-derived year-to-year decreases from emission controls, comparable to 15 ± 4
years of reductions globally. Our case studies indicate that the sensitivity of NO2 to
lockdowns varies by country and emissions sector, demonstrating the critical need
for spatially resolved observational information provided by these satellite-derived
surface concentration estimates.