COVID-19 lockdowns highlight a risk of increasing ozone pollution in European urban areas

In March 2020, non-pharmaceutical intervention measures in the form of lockdowns were applied across Europe to urgently reduce the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus which causes the COVID-19 disease. The aggressive curtailing of the European economy had widespread impacts on the atmospheric composition, particularly for nitrogen dioxide (NO2) and ozone (O-3). To investigate these changes, we analyse data from 246 ambient air pollution monitoring sites in 102 urban areas and 34 countries in Europe between February and July 2020. Counterfactual, business-as-usual air quality time series are created using machine-learning models to account for natural weather variability. Across Europe, we estimate that NO2 concentrations were 34% and 32% lower than expected for respective traffic and urban background locations, whereas O-3 was 30% and 21% higher (in the same respective environments) at the point of maximum restriction on mobility. To put the 2020 changes into context, average NO2 trends since 2010 were calculated, and the changes experienced across European urban areas in 2020 was equivalent to 7.6 years of average NO2 reduction (or concentrations which might be anticipated in 2028). Despite NO2 concentrations decreasing by approximately a third, total oxidant (O-x) changed little, suggesting that the reductions in NO2 were substituted by increases in O-3. The lockdown period demonstrated that the expected future reductions in NO2 in European urban areas are likely to lead to widespread increases in urban O-3 pollution unless additional mitigation measures are introduced.

Automated summary

Lockdown measures in Europe in March 2020 significantly reduced air pollution levels, with NO2 concentrations decreasing by approximately one-third. However, total oxidant (O-x) remained largely unchanged, indicating that the reduction in NO2 was compensated by an increase in O-3.