10 Dec 2021
10 Dec 2021
Status: a revised version of this preprint is currently under review for the journal ACP.

Impact of reduced emissions on direct and indirect aerosol radiative forcing during COVID–19 lockdown in Europe

Simon Felix Reifenberg1,a, Anna Martin1, Matthias Kohl1, Zaneta Hamryszczak1, Ivan Tadic1, Lenard Röder1, Daniel J. Crowley1, Horst Fischer1, Katharina Kaiser2, Johannes Schneider2, Raphael Dörich1, John N. Crowley1, Laura Tomsche3, Andreas Marsing3, Christiane Voigt3,4, Andreas Zahn5, Christopher Pöhlker6, Bruna Holanda6, Ovid O. Krüger6, Ulrich Pöschl6, Mira Pöhlker6,7,8, Patrick Jöckel3, Marcel Dorf1, Ulrich Schumann3, Jonathan Williams1, Joachim Curtius9, Hardwig Harder1, Hans Schlager3, Jos Lelieveld1,10, and Andrea Pozzer1 Simon Felix Reifenberg et al.
  • 1Max Planck Institute for Chemistry, Atmospheric Chemistry Department, 55128 Mainz, Germany
  • 2Max Planck Institute for Chemistry, Particle Chemistry Department, 55128 Mainz, Germany
  • 3Deutsches Zentrum für Luft– und Raumfahrt, Institute for Atmospheric Physics, Oberpfaffenhofen, 82230 Wessling, Germany
  • 4Johannes Gutenberg–University Mainz, Institute for Physics of the Atmosphere, 55099 Mainz, Germany
  • 5Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, 76344 Karlsruhe, Germany
  • 6Max Planck Institute for Chemistry, Multiphase Chemistry Department, 55128 Mainz, Germany
  • 7Faculty of Physics and Earth Sciences, Leipzig Institute for Meteorology, University of Leipzig, 04318 Leipzig, Germany
  • 8Experimental Aerosol and Cloud Microphysics Department, Leibniz Institute for Tropospheric Research, 04318 Leipzig, Germany
  • 9Goethe–University of Frankfurt, Institute for Atmospheric and Environmental Sciences, 60438 Frankfurt am Main, Germany
  • 10The Cyprus Institute, Climate and Atmosphere Research Center, Nicosia, 1645, Cyprus
  • anow at: MARUM – Center for Marine Environmental Science, University of Bremen, Bremen, Germany

Abstract. Aerosols influence the Earth’s energy balance through direct radiative effects and indirectly by altering the cloud micro-physics. Anthropogenic aerosol emissions dropped considerably when the global COVID–19 pandemic resulted in severe restraints on mobility, production, and public life in spring 2020. Here we assess the effects of these reduced emissions on direct and indirect aerosol radiative forcing over Europe, excluding contributions from contrails. We simulate the atmospheric com- position with the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model in a baseline (business as usual) and a reduced emission scenario. The model results are compared to aircraft observations from the BLUESKY aircraft campaign performed in May/June 2020 over Europe. The model agrees well with most of the observations, except for sulfur dioxide, particulate sulfate and nitrate in the upper troposphere, likely due to a somewhat biased representation of stratospheric aerosol chemistry and missing information about volcanic eruptions which could have influenced the campaign. The comparison with a business as usual scenario shows that the largest relative differences for tracers and aerosols are found in the upper troposphere, around the aircraft cruise altitude, due to the reduced aircraft emissions, while the largest absolute changes are present at the surface. We also find an increase in shortwave radiation of 0.327 ± 0.105 Wm−2 at the surface in Europe for May 2020, solely attributable to the direct aerosol effect, which is dominated by decreased aerosol scattering of sunlight, followed by reduced aerosol absorption, caused by lower concentrations of inorganic and black carbon aerosols in the troposphere. A further in- crease in shortwave radiation from aerosol indirect effects was found to be much smaller than its variability. Impacts on ice crystal- and cloud droplet number concentrations and effective crystal radii are found to be negligible.

Simon Felix Reifenberg et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Review of acp-2021-1005', Anonymous Referee #1, 14 Feb 2022
  • RC2: 'Review of acp-2021-1005', Anonymous Referee #2, 24 Mar 2022

Simon Felix Reifenberg et al.

Simon Felix Reifenberg et al.


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Short summary
In this work we use a combination of observational data from an aircraft campaign and model results to investigate the effect of the European lockdown due to COVID-19 in spring 2020. Using model results, we show that the largest relative changes to the atmospheric composition caused by the reduced emissionsare located in the upper troposphere, around the aircraft cruise altitude, while largest absolute changes are present at the surface.