Articles | Volume 15, issue 18
Atmos. Chem. Phys., 15, 10799–10809, 2015
Atmos. Chem. Phys., 15, 10799–10809, 2015

Research article 29 Sep 2015

Research article | 29 Sep 2015

The NOx dependence of bromine chemistry in the Arctic atmospheric boundary layer

K. D. Custard1, C. R. Thompson1,5,b, K. A. Pratt1,2, P B. Shepson1,3, J. Liao4,5,6, L. G. Huey4, J. J. Orlando7, A. J. Weinheimer7, E. Apel7, S. R. Hall7, F. Flocke7, L. Mauldin7,a, R. S. Hornbrook7, D. Pöhler8, S. General8, J. Zielcke8, W. R. Simpson9, U. Platt8, A. Fried11, P. Weibring11, B. C. Sive10, K. Ullmann7, C. Cantrell7,a, D. J. Knapp7, and D. D. Montzka7 K. D. Custard et al.
  • 1Department of Chemistry, Purdue University, West Lafayette, IN, USA
  • 2Department of Chemistry, University of Michigan, Ann Arbor, MI, USA
  • 3Department of Earth, Atmospheric, and Planetary Sciences & Purdue Climate Change Research Center, Purdue University, West Lafayette, IN, USA
  • 4School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
  • 5Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO, USA
  • 6Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA
  • 7National Center for Atmospheric Research, Boulder, CO, USA
  • 8Institute of Environmental Physics, University of Heidelberg, Heidelberg, Germany
  • 9Geophysical Institute and Department of Chemistry, University of Alaska Fairbanks, Fairbanks, AK, USA
  • 10National Park Service, Air Resources Division, Lakewood, CO, USA
  • 11Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO, USA
  • anow at: Atmospheric and Ocean Sciences, University of Colorado, Boulder, CO, USA
  • bnow at: Chemical Sciences Division, National Oceanic and Atmospheric Administration, Boulder, CO, USA

Abstract. Arctic boundary layer nitrogen oxides (NOx = NO2 + NO) are naturally produced in and released from the sunlit snowpack and range between 10 to 100 pptv in the remote background surface layer air. These nitrogen oxides have significant effects on the partitioning and cycling of reactive radicals such as halogens and HOx (OH + HO2). However, little is known about the impacts of local anthropogenic NOx emission sources on gas-phase halogen chemistry in the Arctic, and this is important because these emissions can induce large variability in ambient NOx and thus local chemistry. In this study, a zero-dimensional photochemical kinetics model was used to investigate the influence of NOx on the unique springtime halogen and HOx chemistry in the Arctic. Trace gas measurements obtained during the 2009 OASIS (Ocean – Atmosphere – Sea Ice – Snowpack) field campaign at Barrow, AK were used to constrain many model inputs. We find that elevated NOx significantly impedes gas-phase halogen radical-based depletion of ozone, through the production of a variety of reservoir species, including HNO3, HO2NO2, peroxyacetyl nitrate (PAN), BrNO2, ClNO2 and reductions in BrO and HOBr. The effective removal of BrO by anthropogenic NOx was directly observed from measurements conducted near Prudhoe Bay, AK during the 2012 Bromine, Ozone, and Mercury Experiment (BROMEX). Thus, while changes in snow-covered sea ice attributable to climate change may alter the availability of molecular halogens for ozone and Hg depletion, predicting the impact of climate change on polar atmospheric chemistry is complex and must take into account the simultaneous impact of changes in the distribution and intensity of anthropogenic combustion sources. This is especially true for the Arctic, where NOx emissions are expected to increase because of increasing oil and gas extraction and shipping activities.

Final-revised paper