EGU22-7516
https://doi.org/10.5194/egusphere-egu22-7516
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Reactive halogen chemistry in the Arctic boundary layer over snow during spring: A 1D modelling case study

Shaddy Ahmed1, Jennie L. Thomas1, Katie Tuite2, Jochen Stutz2, Frank Flocke3, John J. Orlando3, Rebecca S. Hornbrook3, Eric C. Apel3, Louisa K. Emmons3, Detlev Helmig4,5, Patrick Boylan4, L. Gregory Huey6, Samuel R. Hall3, Kirk Ullmann3, Christopher A. Cantrell7,8, and Alan Fried4,9
Shaddy Ahmed et al.
  • 1Université de Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE, Grenoble, France (shaddy.ahmed@univ-grenoble-alpes.fr)
  • 2Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA, United States
  • 3Atmospheric Chemistry Observations & Modeling Laboratory, National Center for Atmospheric Research, Boulder, CO, United States
  • 4Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO, United States
  • 5Boulder A.I.R. LLC, Boulder, CO, United States
  • 6School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, United States
  • 7Department of Atmospheric and Oceanic Sciences (ATOC), University of Colorado, Boulder, CO, United States
  • 8Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), Creteil, France
  • 9Earth Observing Laboratory, National Center for Atmospheric Research, Boulder, CO, United States

Polar halogen chemistry has long been known to be active, especially in spring, and has an important influence on the lifetime of some volatile organics, ozone, and mercury. Reactive chlorine and bromine species, produced from snow and aerosols, can have significant impacts on the oxidative capacity of the polar boundary layer. However, halogen production mechanisms from snow remain highly uncertain, making it challenging to include descriptions of halogen snow emissions in models and to understand the impact on atmospheric chemistry. In this work, we investigate the role of Arctic chlorine and bromine emissions from snow on boundary layer oxidation processes using a one-dimensional atmospheric chemistry and transport model (PACT-1D). We explore the impact of halogen snow emissions and boundary layer dynamics on atmospheric chemistry by modelling primary emissions of Cl2 and Br2 from snow, and heterogeneous recycling reactions on snow and aerosols. We present a two-day case study from the 2009 Ocean-Atmosphere-Sea Ice-Snowpack (OASIS) campaign at Utqiagvik, Alaska. 


The model reproduces both the diurnal cycle and high quantity of Cl2 measured, along with the observed concentrations of Br2, BrO, and HOBr. Due to a combination of chemical emissions, recycling, vertical mixing, and atmospheric chemistry, reactive chlorine is confined to the lowest 15 m of the atmosphere, whilst bromine impacts chemistry up to the boundary layer height. Following the inclusion of halogen emissions and recycling, HOx concentrations (HOx = OH+HO2) increase by as much as a factor of 30 at the surface at mid-day. Consequently, volatile organic compound (VOC) lifetimes are significantly reduced within a shallow layer near the surface, due to chlorine atoms from Cl2 snow emissions and increased HOx attributable to halogen chemistry.

How to cite: Ahmed, S., Thomas, J. L., Tuite, K., Stutz, J., Flocke, F., Orlando, J. J., Hornbrook, R. S., Apel, E. C., Emmons, L. K., Helmig, D., Boylan, P., Huey, L. G., Hall, S. R., Ullmann, K., Cantrell, C. A., and Fried, A.: Reactive halogen chemistry in the Arctic boundary layer over snow during spring: A 1D modelling case study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7516, https://doi.org/10.5194/egusphere-egu22-7516, 2022.

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