Air traffic and contrail changes over Europe during COVID-19: a model study
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Published:2021-05-18
Issue:10
Volume:21
Page:7429-7450
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ISSN:1680-7324
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Container-title:Atmospheric Chemistry and Physics
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language:en
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Short-container-title:Atmos. Chem. Phys.
Author:
Schumann UlrichORCID, Poll Ian, Teoh Roger, Koelle RainerORCID, Spinielli EnricoORCID, Molloy Jarlath, Koudis George S., Baumann RobertORCID, Bugliaro LucaORCID, Stettler Marc, Voigt ChristianeORCID
Abstract
Abstract. The strong reduction of air traffic during the COVID-19
pandemic provides a unique test case for the relationship between air traffic
density, contrails, and their radiative forcing of climate change. Here, air
traffic and contrail cirrus changes are quantified for a European domain for
March to August 2020 and compared to the same period in 2019. Traffic data
show a 72 % reduction in flight distance compared with 2019. This paper
investigates the induced contrail changes in a model study. The contrail
model results depend on various methodological details as discussed in
parameter studies. In the reference case, the reduced traffic caused a
reduction in contrail length. The reduction is slightly stronger than
expected from the traffic change because the weather conditions in 2020 were
less favorable for contrail formation than in 2019. Contrail coverage over
Europe with an optical depth larger than 0.1 decreased from 4.6 % in 2019
to 1.4 % in 2020; the total cirrus cover amount changed by 28 % to 25 %. The
reduced contrail coverage caused 70 % less longwave and 73 % less
shortwave radiative forcing but, because of various nonlinearities, only 54 % less net forcing in this case. The methods include recently developed
models for performance parameters and soot emissions. The overall propulsion
efficiency of the aircraft is about 20 % smaller than estimated in
earlier studies, resulting in 3 % fewer contrails. Considerable
sensitivity to soot emissions is found, highlighting fuel and engine
importance. The contrail model includes a new approximate method to account
for water vapor exchange between contrails and background air and for
radiative forcing changes due to contrail–contrail overlap. The water vapor
exchange reduces available ice supersaturation in the atmosphere, which is
critical for contrail formation. Contrail–contrail overlap changes the
computed radiative forcing considerably. Comparisons to satellite
observations are described and discussed in a parallel publication.
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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