Preprints
https://doi.org/10.5194/acp-2021-1028
https://doi.org/10.5194/acp-2021-1028

  21 Dec 2021

21 Dec 2021

Review status: this preprint is currently under review for the journal ACP.

Tropospheric ozone production and chemical regime analysis during the COVID-19 lockdown over Europe

Clara M. Nussbaumer1, Andrea Pozzer1, Ivan Tadic1, Lenard Röder1, Florian Obersteiner2, Hartwig Harder1, Jos Lelieveld1,3, and Horst Fischer1 Clara M. Nussbaumer et al.
  • 1Max Planck Institute for Chemistry, Department of Atmospheric Chemistry, 55128 Mainz, Germany
  • 2Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany
  • 3Climate and Atmosphere Research Center, The Cyprus Institute, Nicosia, Cyprus

Abstract. The COVID-19 (Coronavirus disease 2019) European lockdowns have lead to a significant reduction in the emissions of primary pollutants such as NO (nitric oxide) and NO2 (nitrogen dioxide). As most photochemical processes are related to nitrogen oxide (NOx ≡ NO + NO2) chemistry, this event has presented an exceptional opportunity to investigate its effects on air quality and secondary pollutants, such as tropospheric ozone (O3). In this study, we present the effects of the COVID-19 lockdown on atmospheric trace gas concentrations, net ozone production rates (NOPR) and the dominant chemical regime throughout the troposphere based on three different research aircraft campaigns across Europe. These are the UTOPIHAN campaigns in 2003 and 2004, the HOOVER campaigns in 2006 and 2007 and the BLUESKY campaign in 2020, the latter performed during the COVID-19 lockdown. We present in situ observations and simulation results from the ECHAM5/MESSy Atmospheric Chemistry model which allows for scenario calculations with business as usual emissions during the BLUESKY campaign, referred to as "no-lockdown scenario". We show that the COVID-19 lockdown reduced NO and NO2 mixing ratios in the upper troposphere by around 55 % compared to the no-lockdown scenario due to reduced air traffic. O3 production and loss terms reflected this reduction with a deceleration in O3 cycling due to reduced mixing ratios of NOx while NOPRs were largely unaffected. We also study the role of methyl peroxyradicals forming HCHO (αCH3O2) to show that the COVID-19 lockdown shifted the chemistry in the upper troposphere/tropopause region to a NOx limited regime during BLUESKY. In comparison, we find a VOC limited regime to be dominant during UTOPIHAN.

Clara M. Nussbaumer et al.

Status: open (until 01 Feb 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-1028', Anonymous Referee #1, 26 Dec 2021 reply
  • RC2: 'Comment on acp-2021-1028', Anonymous Referee #2, 21 Jan 2022 reply

Clara M. Nussbaumer et al.

Clara M. Nussbaumer et al.

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Short summary
The European COVID-19 lockdowns have significantly reduced the emission of primary pollutants such as NOx which impacts the tropospheric photochemical processes and the abundance of O3. In this study, we present how the lockdowns have affected tropospheric trace gases and ozone production based on in situ observations and modeling simulations. We additionally show that the chemical regime shifted from a transition point to a NOx limitation in the upper troposphere.
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