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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 16, issue 7 | Copyright
Atmos. Chem. Phys., 16, 4369-4378, 2016
https://doi.org/10.5194/acp-16-4369-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 07 Apr 2016

Research article | 07 Apr 2016

Sensitivity to grid resolution in the ability of a chemical transport model to simulate observed oxidant chemistry under high-isoprene conditions

Karen Yu1, Daniel J. Jacob1,2, Jenny A. Fisher3,4, Patrick S. Kim2, Eloise A. Marais1, Christopher C. Miller1, Katherine R. Travis1, Lei Zhu1, Robert M. Yantosca1, Melissa P. Sulprizio1, Ron C. Cohen5, Jack E. Dibb6, Alan Fried7, Tomas Mikoviny8, Thomas B. Ryerson9, Paul O. Wennberg10,11, and Armin Wisthaler8,12 Karen Yu et al.
  • 1School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA
  • 2Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
  • 3Centre for Atmospheric Chemistry, School of Chemistry, University of Wollongong, Wollongong, NSW, Australia
  • 4School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW, Australia
  • 5Department of Chemistry, University of California, Berkeley, CA, USA
  • 6Earth System Research Center, University of New Hampshire, Durham, NH, USA
  • 7Institute for Arctic and Alpine Research, University of Colorado, Boulder, CO, USA
  • 8Department of Chemistry, University of Oslo, Oslo, Norway
  • 9Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA
  • 10Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
  • 11Division of Engineering and Applied Sciences, California Institute of Technology, Pasadena, CA, USA
  • 12Institute for Ion Physics and Applied Physics, University of Innsbruck, Innsbruck, Austria

Abstract. Formation of ozone and organic aerosol in continental atmospheres depends on whether isoprene emitted by vegetation is oxidized by the high-NOx pathway (where peroxy radicals react with NO) or by low-NOx pathways (where peroxy radicals react by alternate channels, mostly with HO2). We used mixed layer observations from the SEAC4RS aircraft campaign over the Southeast US to test the ability of the GEOS-Chem chemical transport model at different grid resolutions (0.25° × 0.3125°, 2° × 2.5°, 4° × 5°) to simulate this chemistry under high-isoprene, variable-NOx conditions. Observations of isoprene and NOx over the Southeast US show a negative correlation, reflecting the spatial segregation of emissions; this negative correlation is captured in the model at 0.25° × 0.3125° resolution but not at coarser resolutions. As a result, less isoprene oxidation takes place by the high-NOx pathway in the model at 0.25° × 0.3125° resolution (54%) than at coarser resolution (59%). The cumulative probability distribution functions (CDFs) of NOx, isoprene, and ozone concentrations show little difference across model resolutions and good agreement with observations, while formaldehyde is overestimated at coarse resolution because excessive isoprene oxidation takes place by the high-NOx pathway with high formaldehyde yield. The good agreement of simulated and observed concentration variances implies that smaller-scale non-linearities (urban and power plant plumes) are not important on the regional scale. Correlations of simulated vs. observed concentrations do not improve with grid resolution because finer modes of variability are intrinsically more difficult to capture. Higher model resolution leads to decreased conversion of NOx to organic nitrates and increased conversion to nitric acid, with total reactive nitrogen oxides (NOy) changing little across model resolutions. Model concentrations in the lower free troposphere are also insensitive to grid resolution. The overall low sensitivity of modeled concentrations to grid resolution implies that coarse resolution is adequate when modeling continental boundary layer chemistry for global applications.

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Increasing the spatial resolution of a chemical transport model may improve simulations but can be computationally expensive. Using observations from the SEAC4RS aircraft campaign, we find that at higher spatial resolutions, models are better able to simulate the chemical pathways of ozone precursors, but the overall effect on regional mean concentrations is small. This implies that for continental boundary layer applications, coarse resolution models are adequate.
Increasing the spatial resolution of a chemical transport model may improve simulations but can...
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