Articles | Volume 10, issue 17
Atmos. Chem. Phys., 10, 8353–8372, 2010

Special issue: MILAGRO/INTEX-B 2006

Atmos. Chem. Phys., 10, 8353–8372, 2010

  07 Sep 2010

07 Sep 2010

Trans-Pacific transport of reactive nitrogen and ozone to Canada during spring

T. W. Walker1,*, R. V. Martin1,**, A. van Donkelaar1, W. R. Leaitch2, A. M. MacDonald2, K. G. Anlauf2, R. C. Cohen3, T. H. Bertram4, L. G. Huey5, M. A. Avery6, A. J. Weinheimer7, F. M. Flocke7, D. W. Tarasick2, A. M. Thompson8, D. G. Streets9, and X. Liu10 T. W. Walker et al.
  • 1Department of Physics & Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada
  • 2Environment Canada, Downsview, Ontario, Canada
  • 3College of Chemistry, University of California at Berkeley, Berkeley, California, USA
  • 4Department of Chemistry & Biochemistry, University of California at San Diego, San Diego, California, USA
  • 5School of Earth & Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
  • 6Atmospheric Sciences Division, NASA Langley Research Center, Hampton, Virginia, USA
  • 7National Center for Atmospheric Research, Boulder, Colorado, USA
  • 8Meteorology Department, Pennsylvania State University, University Park, Pennsylvania, USA
  • 9Decision and Information Sciences Division, Argonne National Laboratory, Argonne, IL, USA
  • 10University of Baltimore County (UMBC), Goddard Earth Sciences and Technology (GEST), Baltimore, Maryland, USA
  • *now at: Department of Physics, University of Toronto, Toronto, Ontario, Canada
  • **also at: Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA

Abstract. We interpret observations from the Intercontinental Chemical Transport Experiment, Phase B (INTEX-B) in spring 2006 using a global chemical transport model (GEOS-Chem) to evaluate sensitivities of the free troposphere above the North Pacific Ocean and North America to Asian anthropogenic emissions. We develop a method to use satellite observations of tropospheric NO2 columns to provide timely estimates of trends in NOx emissions. NOx emissions increased by 33% for China and 29% for East Asia from 2003 to 2006. We examine measurements from three aircraft platforms from the INTEX-B campaign, including a Canadian Cessna taking vertical profiles of ozone near Whistler Peak. The contribution to the mean simulated ozone profiles over Whistler below 5.5 km is at least 7.2 ppbv for Asian anthropogenic emissions and at least 3.5 ppbv for global lightning NOx emissions. Tropospheric ozone columns from OMI exhibit a broad Asian outflow plume across the Pacific, which is reproduced by simulation. Mean modelled sensitivities of Pacific (30° N–60° N) tropospheric ozone columns are at least 4.6 DU for Asian anthropogenic emissions and at least 3.3 DU for lightning, as determined by simulations excluding either source. Enhancements of ozone over Canada from Asian anthropogenic emissions reflect a combination of trans-Pacific transport of ozone produced over Asia, and ozone produced in the eastern Pacific through decomposition of peroxyacetyl nitrates (PANs). A sensitivity study decoupling PANs globally from the model's chemical mechanism establishes that PANs increase ozone production by removing NOx from regions of low ozone production efficiency (OPE) and injecting it into regions with higher OPE, resulting in a global increase in ozone production by 2% in spring 2006. PANs contribute up to 4 ppbv to surface springtime ozone concentrations in western Canada. Ozone production due to PAN transport is greatest in the eastern Pacific; commonly occurring transport patterns advect this ozone northeastward into Canada. Transport events observed by the aircraft confirm that polluted airmasses were advected in this way.

Special issue
Final-revised paper