Arctic Ozone Depletion Event of 2020

by Hannah Bryant

Provenance of the research: 

Title of thesis/research question: The Arctic Ozone Depletion Event of 2020

Type of thesis: Master’s

University affiliation: The University of Cambridge

Faculty: Yusuf Hamied Department of Chemistry

Research Duration: October 2020-April 2021


Ozone loss in the stratosphere is associated with the accumulation of substances that destroy ozone. The Montreal Protocol on Substances that Deplete the Ozone Layer (1987) led to a reduction in these substances and thus a recovery of stratospheric ozone was expected [1]. Despite this, during the spring period of 2020, the most extensive ozone loss on record in the Arctic was observed [2][3]. My work examined the timeline of events that led to this loss in order to explain why this depletion was so extreme compared to previous spring periods. This was undertaken by using a model run from the Met Office Unified Model, United Kingdom Chemistry and Aerosols (UM-UKCA), a chemistry climate model [4].

The work demonstrated that there was a peak local reduction in ozone of 95.4% between January and March at the pole, alongside mixing ratios of the primary ozone depleting chemical, chlorine monoxide, four times greater than the modelled climatology [5]. Ozone depletion occurs within the stratospheric polar vortex and analysis showed that 2020 featured a remarkably strong and long lasting vortex [6]. Mixing of air within the vortex with air outside of the vortex was reduced and this prevented the ozone within the vortex from being replenished [5].

  1. What were the most important or surprising findings of your work?

There is a crucial period of time each year which we demonstrated can help to determine whether there will be significant ozone loss in the Arctic stratosphere. Depletion occurs annually between the late winter and early spring and the critical period was found to occur in March. Predicting the springtime ozone conditions is therefore difficult earlier in the year, as the crucial period is yet to occur. I was also able to show that the conditions in the stratosphere in 2020 were primed for ozone depletion and thus led to the unique chemical loss that was observed.

  1. What did you struggle with during the research and/or writing process, and how did you overcome these issues?

The research was based on a depletion event that had occurred only six months before the project was started and so there were initially very few papers published which directly analysed the Arctic stratosphere in 2020. To overcome this, I instead used literature that analysed Antarctic ozone holes and compared the two hemispheres. In addition to this, my research was undertaken during the pandemic, which meant that I was not able to meet my supervisors and fellow research students in person until after I had handed in my thesis. This sometimes led to feelings of uncertainty as to whether the direction of my research aligned with the aims of my supervisors. I overcame this by regularly meeting online with the rest of the group.

  1. What are you doing now, and what are your plans for the coming year? Did your research impact those plans in any way?

I am now studying for a PhD at the University of Edinburgh in Atmospheric and Environmental Science within the Department of Geosciences. My research here is focused on using computational climate modelling to assess the impacts of hydrogen on our atmosphere. As we move away from using fossil fuels in our energy production and potentially towards a more hydrogen based economy, the emissions of hydrogen will likely increase due to leakage from the system [7]. There are many uncertainties surrounding a rise in atmospheric hydrogen and so my research aims to investigate this process to tackle these unknowns [8].

The research I had undertaken for my master’s thesis led me towards my current PhD research as atmospheric hydrogen can influence stratospheric ozone concentrations [9] and so there is overlap in the concepts both projects explore. In addition to this, I was surrounded by very passionate and intelligent supervisors, Dr James Keeble, Professor John Pyle and Dr Alex Archibald, who inspired me to continue on with research. 

  1. Do you have any advice for people who are undertaking this type of research?

Atmospheric chemistry is a dynamic and interesting field in which to undertake research and combines traditional chemistry with environmental science and computer modelling. It can be overwhelming to begin research in this area because of how interdisciplinary it is, and often this means that you have to quickly learn new skills. As I had come from a background in chemistry, the computational side of my research was new to me and was something I initially had to work hard at to understand. The best advice I can give is to learn as many of these skills as you can, so that you are able to make the most of your research.

Author Bio: Hannah is a PhD student in the Department of Geosciences at the University of Edinburgh where her research focuses on the atmospheric and environmental impacts of hydrogen. She previously studied Natural Sciences at the University of Cambridge which inspired her to continue with climate science research. Hannah has been volunteering for the social media team at ClimaTalk since September 2020.

Reference List:

[1] Bednarz E, Maycock A, Abraham N, Braesicke P, Dessens O, McQuaid J. 2016 Future arctic ozone recovery: The importance of chemistry and dynamics. Atmospheric Chemistry and Physics 16, 12159–12176. (doi:10.5194/acp-16-12159-2016).

[2] Lawrence ZD, Perlwitz J, Butler AH, Manney GL, Newman PA, Lee SH, Nash ER. 2020 The remarkably strong arctic stratospheric polar vortex of winter 2020: Links to record-breaking arctic oscillation and ozone loss. Journal of Geophysical Research: Atmospheres 125, 22, e2020JD033271. (doi:10.1029/2020JD033271).

[3] Wohltmann I, von der Gathen P, Lehmann R, Maturilli M, Deckelmann H, Manney GL, Davies J, Tarasick D, Jepsen N, Kivi R, et al. 2020 Near-complete local reduction of arctic stratospheric ozone by severe chemical loss in spring 2020. Geophysical Research Letters 47, 20, e2020GL089547. (doi:10.1029/2020GL089547).

[4] Archibald A, Connor F, Abraham N, Archer-Nicholls S, Chipperfield M, Dalvi M, Folberth G, Dennison F, Dhomse S, Griffiths P, et al. 2020 Description and evaluation of the ukca stratosphere–troposphere chemistry scheme (strattrop vn 1.0) implemented in ukesm1. Geoscientific Model Development 13, 1223–1266. (doi:10.5194/gmd-13-1223-2020).

[5] Klein U, Wohltmann I, Lindner K, K¨unzi KF. 2002 Ozone depletion and chlorine activation in the arctic winter 1999/2000 observed in ny-?Alesund. Journal of Geophysical Research: Atmospheres 107, D20, SOL 31–1–SOL 31–11. (doi:10.1029/2001JD000543).

[6] Voigt C, Schreiner J, Kohlmann A, Zink P, Mauersberger K, Larsen N, Deshler T, Kr¨oger C, Rosen J, Adriani A, et al. 2001 Nitric acid trihydrate (nat) in polar stratospheric clouds. Science (New York, N.Y.) 290, 1756–8. (doi:10.1126/science.290.5497.1756).

[7] Patterson JD, Aydin M, Crotwell AM, Pétron G, Severinghaus JP, Krummel PB, Langenfelds RL, Saltzman ES. H2 in Antarctic firn air: Atmospheric reconstructions and implications for anthropogenic emissions. Proc Natl Acad Sci U S A. 2021 Sep 7;118(36):e2103335118. (doi: 10.1073/pnas.2103335118. PMID: 34426524; PMCID: PMC8433534.)

[8] Sanderson, M.G., Collins, W.J., Derwent, R.G. et al. Simulation of Global Hydrogen Levels Using a Lagrangian Three-Dimensional Model. Journal of Atmospheric Chemistry 46, 15–28 (2003). (

[9] Tromp TK, Shia RL, Allen M, Eiler JM, Yung YL. Potential environmental impact of a hydrogen economy on the stratosphere. Science. 2003 Jun 13;300(5626):1740-2. (doi: 10.1126/science.1085169. PMID: 12805546.)

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