Cleaner Skies during the COVID-19 Lockdown
Christiane Voigt (University of Mainz, Deutsches Zentrum für Luft- und Raumfahrt (DLR))
Jos Lelieveld (Max Planck Institute of Chemistry)
Hans Schlager (Deutsches Zentrum für Luft- und Raumfahrt (DLR))
Johannes Schneider (Max Planck Institute of Chemistry)
Joachim Curtius (Goethe University)
Birger Bohn (Forschungszentrum Jülich)
Mariano Mertens (TU Delft - Aircraft Noise and Climate Effects, Deutsches Zentrum für Luft- und Raumfahrt (DLR))
Volker Grewe (TU Delft - Aircraft Noise and Climate Effects)
Johannes Lucke (TU Delft - Aircraft Noise and Climate Effects)
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Abstract
During spring 2020, the COVID-19 pandemic caused massive reductions in emissions from industry and ground and airborne transportation. To explore the resulting atmospheric composition changes, we conducted the BLUESKY campaign with two research aircraft and measured trace gases, aerosols, and cloud properties from the boundary layer to the lower stratosphere. From 16 May to 9 June 2020, we performed 20 flights in the early COVID-19 lockdown phase over Europe and the Atlantic Ocean. We found up to 50% reductions in boundary layer nitrogen dioxide concentrations in urban areas from GOME-2B satellite data, along with carbon monoxide reductions in the pollution hot spots. We measured 20%-70% reductions in total reactive nitrogen, carbon monoxide, and fine mode aerosol concentration in profiles over German cities compared to a 10-yr dataset from passenger aircraft. The total aerosol mass was significantly reduced below 5 km altitude, and the organic aerosol fraction also aloft, indicative of decreased organic precursor gas emissions. The reduced aerosol optical thickness caused a perceptible shift in sky color toward the blue part of the spectrum (hence BLUESKY) and increased shortwave radiation at the surface. We find that the 80% decline in air traffic led to substantial reductions in nitrogen oxides at cruise altitudes, in contrail cover, and in resulting radiative forcing. The light extinction and depolarization by cirrus were also reduced in regions with substantially decreased air traffic. General circulation-chemistry model simulations indicate good agreement with the measurements when applying a reduced emission scenario. The comprehensive BLUESKY dataset documents the major impact of anthropogenic emissions on the atmospheric composition.
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