Articles | Volume 15, issue 16
Atmos. Chem. Phys., 15, 9651–9679, 2015
Atmos. Chem. Phys., 15, 9651–9679, 2015

Research article 28 Aug 2015

Research article | 28 Aug 2015

Interactions of bromine, chlorine, and iodine photochemistry during ozone depletions in Barrow, Alaska

C. R. Thompson1,a,b, P. B. Shepson1,2, J. Liao3,a,c, L. G. Huey3, E. C. Apel4, C. A. Cantrell4,d, F. Flocke4, J. Orlando4, A. Fried4,b, S. R. Hall4, R. S. Hornbrook4, D. J. Knapp4, R. L. Mauldin III4,d, D. D. Montzka4, B. C. Sive5,e, K. Ullmann4, P. Weibring4, and A. Weinheimer4 C. R. Thompson et al.
  • 1Department of Chemistry, Purdue University, West Lafayette, Indiana, USA
  • 2Department of Earth, Atmospheric, and Planetary Sciences and Purdue Climate Change Research Center, Purdue University, West Lafayette, Indiana, USA
  • 3School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia, USA
  • 4National Center for Atmospheric Research, Boulder, Colorado, USA
  • 5Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire, USA
  • anow at: Chemical Sciences Division, Earth System Research Laboratory, NOAA, Boulder, Colorado, USA
  • bnow at: Institute of Arctic and Alpine Research, University of Colorado Boulder, Boulder, Colorado, USA
  • cnow at: Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado Boulder, Colorado, USA
  • dnow at: Atmospheric and Ocean Sciences, University of Colorado Boulder, Boulder, Colorado, USA
  • enow at: National Park Service, Lakewood, Colorado, USA

Abstract. The springtime depletion of tropospheric ozone in the Arctic is known to be caused by active halogen photochemistry resulting from halogen atom precursors emitted from snow, ice, or aerosol surfaces. The role of bromine in driving ozone depletion events (ODEs) has been generally accepted, but much less is known about the role of chlorine radicals in ozone depletion chemistry. While the potential impact of iodine in the High Arctic is more uncertain, there have been indications of active iodine chemistry through observed enhancements in filterable iodide, probable detection of tropospheric IO, and recently, observation of snowpack photochemical production of I2. Despite decades of research, significant uncertainty remains regarding the chemical mechanisms associated with the bromine-catalyzed depletion of ozone, as well as the complex interactions that occur in the polar boundary layer due to halogen chemistry. To investigate this, we developed a zero-dimensional photochemical model, constrained with measurements from the 2009 OASIS field campaign in Barrow, Alaska. We simulated a 7-day period during late March that included a full ozone depletion event lasting 3 days and subsequent ozone recovery to study the interactions of halogen radicals under these different conditions. In addition, the effects of iodine added to our Base Model were investigated. While bromine atoms were primarily responsible for ODEs, chlorine and iodine were found to enhance the depletion rates and iodine was found to be more efficient per atom at depleting ozone than Br. The interaction between chlorine and bromine is complex, as the presence of chlorine can increase the recycling and production of Br atoms, while also increasing reactive bromine sinks under certain conditions. Chlorine chemistry was also found to have significant impacts on both HO2 and RO2, with organic compounds serving as the primary reaction partner for Cl atoms. The results of this work highlight the need for future studies on the production mechanisms of Br2 and Cl2, as well as on the potential impact of iodine in the High Arctic.

Final-revised paper