How did ozone pollution evolve during the COVID-19 lockdown of spring 2020? 

In the boreal spring of 2020, worldwide measures for curbing the spread of the COVID-19 virus have led to unprecedented and abrupt lockdowns in transportation and industry. They have led to sharp decrease of emissions of anthropogenic pollutants that induced significant changes in the composition of the atmosphere from city to hemispheric scale.

Using an unprecedented synergy of satellite observations, in situ measurements and chemistry-transport models, Cuesta et al. (2022) have quantified the changes in ozone pollution in Europe associated with this first lockdown. The satellite observations used in the study are obtained from the IASI+GOME2 multispectral approach, in terms of the differences between 2020 and before the pandemic. Satellite data are adjusted to quantify only the effect of lockdown using simulations of the CHIMERE chemistry-transport model. By confirming the in situ measurements at the surface and increasing the spatial coverage, they highlighted a large reduction in background ozone pollution, associated with the numerous lockdowns in the northern hemisphere. Over the continent, a reduction in ozone pollution is noticed in less urbanized and rural regions, typically characterized by a photochemical regime linked to the abundance of nitrogen oxides. However, an increase in ozone pollution is clearly measured in more urbanized regions, especially in central Europe. This is the accumulation of ozone in areas where the sink of this pollutant has decreased by the reduction of anthropogenic emissions of nitric oxide. These observational estimates of the impact of lockdowns also show the difficulty of models in estimating its amplitude and vertical extent.