Articles | Volume 17, issue 5
Atmos. Chem. Phys., 17, 3401–3421, 2017
Atmos. Chem. Phys., 17, 3401–3421, 2017

Research article 09 Mar 2017

Research article | 09 Mar 2017

Bromine atom production and chain propagation during springtime Arctic ozone depletion events in Barrow, Alaska

Chelsea R. Thompson1,a,b, Paul B. Shepson1,2, Jin Liao3,c,d, L. Greg Huey3, Chris Cantrell4,e, Frank Flocke4, and John Orlando4 Chelsea R. Thompson et al.
  • 1Department of Chemistry, Purdue University, West Lafayette, IN, USA
  • 2Department of Earth and Atmospheric Sciences and Purdue Climate Change Research Center, Purdue University, West Lafayette, IN, USA
  • 3School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
  • 4National Center for Atmospheric Research, Boulder, CO, USA
  • anow at: Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO, USA
  • bnow at: Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO, USA
  • cnow at: Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • dnow at: Universities Space Research Association, Columbia, MD, USA
  • enow at: Department of Atmospheric and Ocean Sciences, University of Colorado Boulder, Boulder, CO, USA

Abstract. Ozone depletion events (ODEs) in the Arctic are primarily controlled by a bromine radical-catalyzed destruction mechanism that depends on the efficient production and recycling of Br atoms. Numerous laboratory and modeling studies have suggested the importance of heterogeneous recycling of Br through HOBr reaction with bromide on saline surfaces. On the other hand, the gas-phase regeneration of bromine atoms through BrO–BrO radical reactions has been assumed to be an efficient, if not dominant, pathway for Br reformation and thus ozone destruction. Indeed, it has been estimated that the rate of ozone depletion is approximately equal to twice the rate of the BrO self-reaction. Here, we use a zero-dimensional, photochemical model, largely constrained to observations of stable atmospheric species from the 2009 Ocean–Atmosphere–Sea Ice–Snowpack (OASIS) campaign in Barrow, Alaska, to investigate gas-phase bromine radical propagation and recycling mechanisms of bromine atoms for a 7-day period during late March. This work is a continuation of that presented in Thompson et al. (2015) and utilizes the same model construct. Here, we use the gas-phase radical chain length as a metric for objectively quantifying the efficiency of gas-phase recycling of bromine atoms. The gas-phase bromine chain length is determined to be quite small, at  <  1.5, and highly dependent on ambient O3 concentrations. Furthermore, we find that Br atom production from photolysis of Br2 and BrCl, which is predominately emitted from snow and/or aerosol surfaces, can account for between 30 and 90 % of total Br atom production. This analysis suggests that condensed-phase production of bromine is at least as important as, and at times greater than, gas-phase recycling for the occurrence of Arctic ODEs. Therefore, the rate of the BrO self-reaction is not a sufficient estimate for the rate of O3 depletion.

Short summary
The generally accepted mechanism leading to ozone depletion events in the Arctic assumes efficient gas-phase recycling of bromine atoms, such that the rate of ozone depletion has often been estimated as the rate that Br atoms regenerate through gas-phase BrO + BrO and BrO + ClO reactions. Using a large suite of data from the OASIS2009 campaign, our modeling results show that the gas-phase regeneration of Br is less efficient than expected and that heterogeneous recycling on surfaces is critical.
Final-revised paper