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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 13 | Copyright
Atmos. Chem. Phys., 15, 7685-7702, 2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 14 Jul 2015

Research article | 14 Jul 2015

Estimates of black carbon emissions in the western United States using the GEOS-Chem adjoint model

Y. H. Mao1,2,3, Q. B. Li1,2, D. K. Henze4, Z. Jiang5,a, D. B. A. Jones2,5, M. Kopacz6, C. He1,2, L. Qi1,2, M. Gao1,2, W.-M. Hao7, and K.-N. Liou1,2 Y. H. Mao et al.
  • 1Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, CA 90095, USA
  • 2Joint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles, CA 90095, USA
  • 3State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China
  • 4Department of Mechanical Engineering, University of Colorado, Boulder, CO 80309, USA
  • 5Department of Physics, University of Toronto, Toronto, ON M5S 1A7, Canada
  • 6NOAA Climate Program Office, Silver Spring, Maryland, 20910, USA
  • 7Fire Sciences Laboratory, U.S. Forest Service, Missoula, MT, 59808, USA
  • anow at: Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, 91109, USA

Abstract. We estimate black carbon (BC) emissions in the western United States for July–September 2006 by inverting surface BC concentrations from the Interagency Monitoring of Protected Visual Environments (IMPROVE) network using a global chemical transport model (GEOS-Chem) and its adjoint. Our best estimate of the BC emissions is 49.9 Gg at 2° × 2.5° (a factor of 2.1 increase) and 47.3 Gg at 0.5° × 0.667° (1.9 times increase). Model results now capture the observed major fire episodes with substantial bias reductions (~ 35 % at 2° × 2.5° and ~ 15 % at 0.5° × 0.667°). The emissions are ~ 20–50 % larger than those from our earlier analytical inversions (Mao et al., 2014). The discrepancy is especially drastic in the partitioning of anthropogenic versus biomass burning emissions. The August biomass burning BC emissions are 4.6–6.5 Gg and anthropogenic BC emissions 8.6–12.8 Gg, varying with the model resolution, error specifications, and subsets of observations used. On average both anthropogenic and biomass burning emissions in the adjoint inversions increase 2-fold relative to the respective {a priori} emissions, in distinct contrast to the halving of the anthropogenic and tripling of the biomass burning emissions in the analytical inversions. We attribute these discrepancies to the inability of the adjoint inversion system, with limited spatiotemporal coverage of the IMPROVE observations, to effectively distinguish collocated anthropogenic and biomass burning emissions on model grid scales. This calls for concurrent measurements of other tracers of biomass burning and fossil fuel combustion (e.g., carbon monoxide and carbon isotopes). We find that the adjoint inversion system as is has sufficient information content to constrain the total emissions of BC on the model grid scales.

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