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Volume 16, issue 14
Atmos. Chem. Phys., 16, 9019–9045, 2016
https://doi.org/10.5194/acp-16-9019-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 16, 9019–9045, 2016
https://doi.org/10.5194/acp-16-9019-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 22 Jul 2016

Research article | 22 Jul 2016

Los Angeles megacity: a high-resolution land–atmosphere modelling system for urban CO2 emissions

Sha Feng1,2,a, Thomas Lauvaux3,2, Sally Newman4, Preeti Rao2, Ravan Ahmadov5,6, Aijun Deng3, Liza I. Díaz-Isaac3, Riley M. Duren2, Marc L. Fischer7, Christoph Gerbig8, Kevin R. Gurney9, Jianhua Huang9, Seongeun Jeong7, Zhijin Li2, Charles E. Miller2, Darragh O'Keeffe9, Risa Patarasuk9, Stanley P. Sander2, Yang Song9, Kam W. Wong4,2, and Yuk L. Yung4 Sha Feng et al.
  • 1JIFRESSE, University of California, Los Angeles, Los Angeles, CA, USA
  • 2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
  • 3Department of Meteorology and Atmospheric Science, Pennsylvania State University, State College, PA, USA
  • 4Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
  • 5Cooperative Institute for Research in Environmental Sciences, University of Colorado at Boulder, Boulder, CO, USA
  • 6Earth System Research Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO, USA
  • 7Lawrence Berkeley National Laboratory, Berkeley, CA, USA
  • 8Max Planck Institute for Biogeochemistry, Hans-Knöll-Str. 10, 07745 Jena, Germany
  • 9School of Life Science, Arizona State University, Tempe, AZ, USA
  • anow at: Department of Meteorology and Atmospheric Science, Pennsylvania State University, University Park, PA, USA

Abstract. Megacities are major sources of anthropogenic fossil fuel CO2 (FFCO2) emissions. The spatial extents of these large urban systems cover areas of 10 000 km2 or more with complex topography and changing landscapes. We present a high-resolution land–atmosphere modelling system for urban CO2 emissions over the Los Angeles (LA) megacity area. The Weather Research and Forecasting (WRF)-Chem model was coupled to a very high-resolution FFCO2 emission product, Hestia-LA, to simulate atmospheric CO2 concentrations across the LA megacity at spatial resolutions as fine as  ∼  1 km. We evaluated multiple WRF configurations, selecting one that minimized errors in wind speed, wind direction, and boundary layer height as evaluated by its performance against meteorological data collected during the CalNex-LA campaign (May–June 2010). Our results show no significant difference between moderate-resolution (4 km) and high-resolution (1.3 km) simulations when evaluated against surface meteorological data, but the high-resolution configurations better resolved planetary boundary layer heights and vertical gradients in the horizontal mean winds. We coupled our WRF configuration with the Vulcan 2.2 (10 km resolution) and Hestia-LA (1.3 km resolution) fossil fuel CO2 emission products to evaluate the impact of the spatial resolution of the CO2 emission products and the meteorological transport model on the representation of spatiotemporal variability in simulated atmospheric CO2 concentrations. We find that high spatial resolution in the fossil fuel CO2 emissions is more important than in the atmospheric model to capture CO2 concentration variability across the LA megacity. Finally, we present a novel approach that employs simultaneous correlations of the simulated atmospheric CO2 fields to qualitatively evaluate the greenhouse gas measurement network over the LA megacity. Spatial correlations in the atmospheric CO2 fields reflect the coverage of individual measurement sites when a statistically significant number of sites observe emissions from a specific source or location. We conclude that elevated atmospheric CO2 concentrations over the LA megacity are composed of multiple fine-scale plumes rather than a single homogenous urban dome. Furthermore, we conclude that FFCO2 emissions monitoring in the LA megacity requires FFCO2 emissions modelling with  ∼  1 km resolution because coarser-resolution emissions modelling tends to overestimate the observational constraints on the emissions estimates.

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We developed a high-resolution land–atmosphere modelling system for urban CO2 emissions over the LA Basin. We evaluated various model configurations, FFCO2 products, and the impact of the model resolution. FFCO2 emissions outpace the atmospheric model resolution to represent the CO2 concentration variability across the basin. A novel forward model approach is presented to evaluate the surface measurement network, reinforcing the importance of using high-resolution emission products.
We developed a high-resolution land–atmosphere modelling system for urban CO2 emissions over the...
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