Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 9 2 2009 10.5194/acpd-9-7927-2009 http://www.atmos-chem-phys-discuss.net/9/7927/2009/ http://www.atmos-chem-phys-discuss.net/9/7927/2009/acpd-9-7927-2009.html http://www.atmos-chem-phys-discuss.net/9/7927/2009/acpd-9-7927-2009.pdf 7927 7969 2009-03-25 The influence of foreign vs. North American emissions on surface ozone in the US D. R. Reidmiller A. M. Fiore D. A. Jaffe D. Bergmann C. Cuvelier F. J. Dentener B. N. Duncan G. Folberth M. Gauss S. Gong P. Hess J. E. Jonson T. Keating A. Lupu E. Marmer R. Park M. G. Schultz D. T. Shindell S. Szopa M. G. Vivanco O. Wild A. Zuber University of Washington, Department of Atmospheric Sciences, Seattle, WA, USA University of Washington – Bothell, Department of Interdisciplinary Arts and Sciences, Bothell, WA, USA NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA Atmospheric Earth and Energy Division, Lawrence Livermore National Laboratory, Livermore, CA, USA European Commission, Joint Research Centre JRC, Institute for Environment and Sustainability, Ispra, Italy Goddard Earth Sciences {&} Technology Center, UMBC, MD, USA Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland Department of Geosciences, University of Oslo, Oslo, Norway Science and Technology Branch, Environment Canada, Toronto, Canada National Center for Atmospheric Research, Boulder, CO, USA Norwegian Meteorological Institute, Oslo, Norway Office of Policy Analysis and Review, EPA, Washington, DC, USA Center for Research in Earth and Space Science, York University, Canada Atmospheric Chemistry Modeling Group, Harvard University, Cambridge, MA, USA Institut für Chemie und Dynamik der Geosphäre ICG-2, Forschungszentrum Jülich, Jülich, Germany NASA Goddard Institute for Space Studies and Columbia University, New York, NY, USA Laboratoire des Sciences du Clima et de l'Environnement, CEA/CNRS/UVSQ/IPSL, Gif-sur-Yvette, France Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain Lancaster Environment Centre, Lancaster University, UK Environment Directorate General, European Commission, Brussels, Belgium now at: NASA Goddard Space Flight Center, Greenbelt, MD, USA also at: Cornell University, Ithaca, New York, USA now at: Seoul National University, Seoul, Korea As part of the Hemispheric Transport of Air Pollution (HTAP; <a href="http://www.htap.org/" target="_blank">http://www.htap.org/</a>) project, we analyze results from 16 global and hemispheric chemical transport models and compare these to Clean Air Status and Trends Network (CASTNet) observations in the United States (US) for 2001. Using the policy-relevant maximum daily 8-h ozone (MDA8 O₃) statistic, the multi-model ensemble represents the observations well (mean <i>r</i>²=0.57, ensemble bias=+4.1 ppbv for all regions and all seasons) despite a wide range in the individual model results. Correlations are strongest in the NorthEastern US during spring and fall (<i>r</i>²=0.68); and weakest in the Midwestern US in summer (<i>r</i>²=0.46). However, large positive mean biases exist during summer for all Eastern US regions, ranging from 10–20 ppbv, and a smaller negative bias is present in the Western US during spring (~3 ppbv). In most all other regions and seasons, the biases of the model ensemble simulations are &le;5 ppbv. Sensitivity simulations in which anthropogenic O₃-precursor emissions (NO_x+NMVOC+CO+aerosols) were decreased by 20% in each of four source regions: East Asia (EA), South Asia (SA), Europe (EU) and North America (NA) show that the greatest response of MDA8 O₃ to the summed foreign emissions reductions occurs during spring in the West (0.9 ppbv reduction due to 20% reductions from EA+SA+EU). East Asia is the largest contributor to MDA8 O₃ at all ranges of the O₃ distribution for most regions (typically ~0.45 ppbv). The exception is in the NorthEastern US where European emissions reductions had the greatest impact on MDA8 O₃, particularly in the middle of the MDA8 O₃ distribution (response of ~0.35 ppbv between 35–55 ppbv). In all regions and seasons, however, O₃-precursor emissions reductions of 20% in the NA source region decrease MDA8 O₃ the most – by a factor of 2 to nearly 10 relative to foreign emissions reductions. 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