Large reductions in satellite-derived and modelled European lower-tropospheric ozone during and after the COVID-19 pandemic (2020–2022)

Abstract. Activity restrictions during the COVID-19 pandemic caused large-scale reductions in ozone (O3) precursor emissions, which in turn substantially reduced the abundance of tropospheric O3 in the Northern Hemisphere. Satellite records of lower-tropospheric column O3 (0–6 km) from the Rutherford Appleton Laboratory (RAL) highlight these large reductions in O3 during the COVID-19 period (2020), which persisted into 2021 and 2022. The European domain average O3 reduction ranged between 2.0 and 3.0 DU (where DU denotes Dobson units) (11.0 %–14.6 %). These satellite results were supported by the TOMCAT chemical transport model (CTM) through several model sensitivity experiments to account for changes in emissions and the impact of the meteorological conditions in 2020. Here, the business-as-usual (BAU) emissions were scaled by activity data (i.e. anonymized mobility data from big tech companies) to account for the reduction in O3 precursor emissions. The model simulated large O3 reductions (2.0–3.0 DU), similar to the satellite records, where approximately 66 % and 34 % of the O3 loss can be explained by emission changes and meteorological conditions, respectively. Our results also show that the reduced flux of stratospheric O3 into the troposphere accounted for a substantial component of the meteorological signal in the overall lower-tropospheric O3 levels during the COVID-19 period.