Numerical simulation of the impact of COVID-19 lockdown on tropospheric composition and aerosol radiative forcing in Europe

Abstract. Aerosols influence the Earth's energy balance directly by modifying radiation transfer and indirectly altering cloud microphysics. Anthropogenic aerosol emissions dropped considerably when global COVID-19 pandemic resulted in severe restraints on mobility, production, public life spring 2020. We assess effects of these reduced direct indirect radiative forcing over Europe, excluding contributions from contrails. simulate atmospheric composition with ECHAM5/MESSy Atmospheric Chemistry (EMAC) model a baseline (business-as-usual) emission scenario. The results are compared to aircraft observations BLUESKY campaign performed May–June 2020 Europe. agrees well most observations, except for sulfur dioxide, particulate sulfate, nitrate upper troposphere, likely due biased representation stratospheric chemistry missing information about volcanic eruptions. comparison scenario shows that largest relative differences tracers aerosols found around cruise altitude, emissions, while absolute changes present at surface. also find an increase all-sky shortwave 0.21 ± 0.05 W m−2 surface Europe May 2020, solely attributable effect, which is dominated decreased scattering sunlight, followed absorption caused lower concentrations inorganic black carbon troposphere. A further was be much smaller than its variability. Impacts ice crystal concentrations, droplet number effective radii negligible.