Preprints
https://doi.org/10.5194/egusphere-2025-3181
https://doi.org/10.5194/egusphere-2025-3181
08 Jul 2025
 | 08 Jul 2025

Challenges in Simulating Ozone Depletion Events in the Arctic Boundary Layer: A Case Study Using ECHAM/MESSy for Spring 2019/20

Stefanie Falk, Luca Reißig, Bianca Zilker, Andreas Richter, and Björn-Martin Sinnhuber

Abstract. Ozone depletion events (ODEs) and bromine explosions (BEs) occur regularly in the springtime polar boundary layer. ODEs alter the oxidation capacity of the polar boundary layer and promote formation of toxic mercury. We investigated Arctic ODEs and BEs in 2019/20 using the chemistry-climate model ECHAM/MESSy v2.55.2, nudged with ERA5 reanalysis data. Model results were evaluated against surface ozone measurements, satellite-derived tropospheric BrO vertical column densities (VCDs), and in situ data from the MOSAiC expedition. The model underestimated boundary layer (BL) height during shallow BL conditions, coinciding with a warm surface temperature bias (2 − 10 K), particularly below −10 °C, likely inherited from ERA5. An updated model configuration, incorporating more realistic multi-year sea ice and relaxed bromine release thresholds, improved agreement with coastal ozone observations (Eureka, Utqiaġvik) but still failed to reproduce strong ODEs observed during MOSAiC. Modeled surface BrO mixing ratios were overestimated, while BrO VCDs were underestimated, suggesting that simply increasing Br2 emissions does not resolve discrepancies. A weaker colocation between modeled BrO VCDs and ODEs aligns with prior airborne studies and may reflect tropospheric chemical and transport processes rather than stratospheric contamination. Despite decreasing Arctic sea ice extent and increasing BrO VCDs, long-term records from Alert, Utqiaġvik, and Zeppelin show a decline in strong ODE frequency since 2000. This suggests that bromine emissions from first-year sea ice (FYSIC) alone may not fully account for observed ODE variability, and that additional climate-sensitive mechanisms may modulate Arctic ozone chemistry. Long-term model integrations are recommended to better understand these trends.

Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Stefanie Falk, Luca Reißig, Bianca Zilker, Andreas Richter, and Björn-Martin Sinnhuber

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Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2025-3181', Anonymous Referee #1, 09 Aug 2025
    • AC1: 'Reply on RC1', Stefanie Falk, 15 Aug 2025
  • RC2: 'Comment on egusphere-2025-3181', Anonymous Referee #2, 24 Aug 2025
Stefanie Falk, Luca Reißig, Bianca Zilker, Andreas Richter, and Björn-Martin Sinnhuber
Stefanie Falk, Luca Reißig, Bianca Zilker, Andreas Richter, and Björn-Martin Sinnhuber

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Short summary
We investigate ozone depletion events (ODEs) and bromine explosions in 2019/20. Model results evaluated against surface ozone measurements, satellite-derived tropospheric BrO vertical column densities, and in situ data from the MOSAiC expedition suggest that increased Br2 emissions do not resolve model discrepancies, Br2 emissions from first-year sea ice may not fully account for observed ODE variability, and additional climate-sensitive mechanisms may modulate Arctic ozone chemistry.
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