Articles | Volume 10, issue 13
Atmos. Chem. Phys., 10, 5823–5838, 2010

Special issue: POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface...

Atmos. Chem. Phys., 10, 5823–5838, 2010

  01 Jul 2010

01 Jul 2010

Chemistry of hydrogen oxide radicals (HOx) in the Arctic troposphere in spring

J. Mao1, D. J. Jacob1,2, M. J. Evans3, J. R. Olson4, X. Ren5, W. H. Brune6, J. M. St. Clair7, J. D. Crounse7, K. M. Spencer7, M. R. Beaver7, P. O. Wennberg8,9, M. J. Cubison10, J. L. Jimenez10, A. Fried11, P. Weibring11, J. G. Walega11, S. R. Hall12, A. J. Weinheimer12, R. C. Cohen13, G. Chen4, J. H. Crawford4, C. McNaughton14, A. D. Clarke14, L. Jaeglé15, J. A. Fisher2, R. M. Yantosca1, P. Le Sager1,*, and C. Carouge1 J. Mao et al.
  • 1School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
  • 2Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
  • 3School of Earth and the Environment, University of Leeds, Leeds, LS2 9JT, UK
  • 4Science Directorate, NASA Langley Research Center, Hampton, VA, USA
  • 5Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL, USA
  • 6Department of Meteorology, Pennsylvania State University, University Park, PA, USA
  • 7Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA
  • 8Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
  • 9Division of Engineering and Applied Science, California Institute of Technology, Pasadena, CA, USA
  • 10Department of Chemistry and Biochemistry and Cooperative Institute for Research in the Environmental Sciences (CIRES),University of Colorado at Boulder, Boulder, CO, USA
  • 11Earth Observing Laboratory, National Center for Atmospheric Research, Boulder, CO, USA
  • 12Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO, USA
  • 13Department of Chemistry and Department of Earth and Planetary Science, University of California Berkeley, Berkeley, CA, USA
  • 14University of Hawaii at Manoa, Honolulu, Hawaii, USA
  • 15Department of Atmospheric Sciences, University of Washington, Seattle, Washington, USA
  • *now at: KNMI, Chemistry and Climate Division, De Bilt, The Netherlands

Abstract. We use observations from the April 2008 NASA ARCTAS aircraft campaign to the North American Arctic, interpreted with a global 3-D chemical transport model (GEOS-Chem), to better understand the sources and cycling of hydrogen oxide radicals (HOx≡H+OH+peroxy radicals) and their reservoirs (HOy≡HOx+peroxides) in the springtime Arctic atmosphere. We find that a standard gas-phase chemical mechanism overestimates the observed HO2 and H2O2 concentrations. Computation of HOx and HOy gas-phase chemical budgets on the basis of the aircraft observations also indicates a large missing sink for both. We hypothesize that this could reflect HO2 uptake by aerosols, favored by low temperatures and relatively high aerosol loadings, through a mechanism that does not produce H2O2. We implemented such an uptake of HO2 by aerosol in the model using a standard reactive uptake coefficient parameterization with γ(HO2) values ranging from 0.02 at 275 K to 0.5 at 220 K. This successfully reproduces the concentrations and vertical distributions of the different HOx species and HOy reservoirs. HO2 uptake by aerosol is then a major HOx and HOy sink, decreasing mean OH and HO2 concentrations in the Arctic troposphere by 32% and 31% respectively. Better rate and product data for HO2 uptake by aerosol are needed to understand this role of aerosols in limiting the oxidizing power of the Arctic atmosphere.

Final-revised paper