Atmos. Chem. Phys. Discuss., 10, 8717-8764, 2010
© Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 License.
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Trans-Pacific transport of reactive nitrogen and ozone to Canada during spring
T. W. Walker1,*, R. V. Martin1,2, A. van Donkelaar1, W. R. Leaitch3, A. M. MacDonald3, K. G. Anlauf3, R. C. Cohen4, T. H. Bertram5, L. G. Huey6, M. A. Avery7, A. J. Weinheimer8, F. M. Flocke8, D. W. Tarasick3, A. M. Thompson9, D. G. Streets10, and X. Liu11
1Department of Physics & Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada
2Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA
3Environment Canada, Downsview, Ontario, Canada
4College of Chemistry, University of California at Berkeley, Berkeley, CA, USA
5Department of Chemistry & Biochemistry, University of California at San Diego, San Diego, CA, USA
6School of Earth & Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
7Atmospheric Sciences Division, NASA Langley Research Center, Hampton, Virginia, USA
8National Center for Atmospheric Research, Boulder, CO, USA
9Meteorology Department, Pennsylvania State University, University Park, PA, USA
10Decision and Information Sciences Division, Argonne National Laboratory, Argonne, IL, USA
11University of Baltimore County (UMBC), Goddard Earth Sciences and Technology (GEST), Baltimore, Maryland, USA
*now at: Department of Physics, University of Toronto, Toronto, Ontario, Canada

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 Pacific and North American free troposphere 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 is at least 7.2 ppbv for Asian anthropogenic emissions and at least 3.5 ppbv for 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 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%. 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; persistent winds advect this ozone northeastward into Canada. Transport events observed by the aircraft confirm that polluted airmasses were advected in this way.

Citation: Walker, T. W., Martin, R. V., van Donkelaar, A., Leaitch, W. R., MacDonald, A. M., Anlauf, K. G., Cohen, R. C., Bertram, T. H., Huey, L. G., Avery, M. A., Weinheimer, A. J., Flocke, F. M., Tarasick, D. W., Thompson, A. M., Streets, D. G., and Liu, X.: Trans-Pacific transport of reactive nitrogen and ozone to Canada during spring, Atmos. Chem. Phys. Discuss., 10, 8717-8764, doi:10.5194/acpd-10-8717-2010, 2010.
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