16 Feb 2022
16 Feb 2022
Status: this preprint is currently under review for the journal ACP.

Comparison of model and ground observations finds snowpack and blowing snow both contribute to Arctic tropospheric reactive bromine

William F. Swanson1, Chris D. Holmes2, William R. Simpson1, Kaitlyn Confer3, Louis Marelle4,5, Jennie L. Thomas4, Lyatt Jaeglé3, Becky Alexander3, Shuting Zhai3, Qianjie Chen6, Xuan Wang7, and Tomás Sherwen8,9 William F. Swanson et al.
  • 1Department of Chemistry and Biochemistry and Geophysical Institute, University of Alaska Fairbanks, Fairbanks, Alaska
  • 2Department of Earth, Ocean and Atmospheric Science, Florida State University, Tallahassee, Florida
  • 3Department of Atmospheric Sciences, University of Washington, Seattle, Washington
  • 4Institut des Géosciences de l'Environnement (IGE), Institut Polytechnique de Grenoble, Grenoble, France
  • 5Laboratoire Atmosphères Observations Spatiales (LATMOS), Sorbonne Université, Paris, France
  • 6Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hong Kong, China
  • 7School of Energy and the Environment, City University of Hong Kong, Hong Kong, China
  • 8National Centre for Atmospheric Science, University of York, York, UK
  • 9Department of Chemistry, University of York, York, United Kingdom

Abstract. Reactive halogens play a prominent role in the atmospheric chemistry of the Arctic during springtime. Field measurements and models studies suggest that halogens are emitted to the atmosphere from snowpack and reactions on wind-blown snow. The relative importance of snowpack and blowing snow sources is still debated, both at local scales and regionally throughout the Arctic. To understand implications of these halogen sources on a pan-Arctic scale, we simulate Arctic reactive bromine chemistry in the atmospheric chemical transport model GEOS-Chem. Two mechanisms are included: 1) a blowing snow sea salt aerosol formation mechanism and 2) a snowpack mechanism assuming uniform molecular bromine production from all snow surfaces. We compare simulations including neither mechanism, each mechanism individually, and both mechanisms to examine conditions where one process may dominate or the mechanisms may interact. We compare the models using these mechanisms to observations of bromine monoxide (BrO) derived from multiple-axis differential optical absorption spectroscopy (MAX-DOAS) instruments on O-Buoy platforms on the sea ice and at a coastal site in Utqiaġvik, Alaska during spring 2015. Model estimations of hourly and monthly average BrO are improved by assuming a constant yield of 0.1 % molecular bromine from all snowpack surfaces on ozone deposition. The blowing snow mechanism increases BrO by providing more surface area for reactive bromine recycling. The snowpack mechanism led to increased BrO across the Arctic Ocean with maximum production in coastal regions, whereas the blowing snow mechanism increases BrO in specific areas due to high surface windspeeds. Our uniform snowpack source has a greater impact on BrO mixing ratios than the blowing snow source. Model results best replicate several features of BrO observations during spring 2015 when using both mechanisms in conjunction, adding evidence that these mechanisms are both active during the Arctic Spring. Extending our transport model throughout the entire year leads to predictions of enhanced fall BrO that are not supported by observations.

William F. Swanson et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-44', Anonymous Referee #1, 07 Apr 2022
    • AC1: 'Reply on RC1', William Swanson, 21 May 2022
    • AC2: 'Reply on RC1', William Swanson, 21 May 2022
  • RC2: 'Comment on acp-2022-44', Anonymous Referee #2, 09 Apr 2022
    • AC3: 'Reply on RC2', William Swanson, 21 May 2022

William F. Swanson et al.

William F. Swanson et al.


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Short summary
Radical bromine molecules are seen at higher concentrations during the Arctic Spring. We use the global model GEOS-Chem to test whether snowpack and wind-blown snow sources can explain high bromine concentrations. We run this model for the entire year of 2015 and compare results to observations of bromine from floating platforms on the Arctic Ocean and at Utqiaġvik. We find that the model performs best when both sources are enabled but may overestimate bromine production in summer and fall.