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Discussion papers | Copyright
https://doi.org/10.5194/amt-2018-171
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 06 Jun 2018

Research article | 06 Jun 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

Quantifying methane point sources from fine-scale (GHGSat) satellite observations of atmospheric methane plumes

Daniel J. Varon1,2, Daniel J. Jacob1, Jason McKeever2, Dylan Jervis2, Berke O. A. Durak2, Yan Xia3, and Yi Huang3 Daniel J. Varon et al.
  • 1School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
  • 2GHGSat, Inc., Montréal, QC H2W 1Y5, Canada
  • 3Department of Atmospheric and Oceanic Sciences, Montréal, QC H3A 0B9, Canada

Abstract. Anthropogenic methane emissions originate from a large number of relatively small point sources. The planned GHGSat satellite fleet aims to quantify emissions from individual point sources by measuring methane column plumes over selected ~10×10km2 domains with ≤50×50m2 pixel resolution and 1–5% measurement precision. Here we develop algorithms for retrieving point source rates from such measurements. We simulate a large ensemble of instantaneous methane column plumes at 50×50m2 pixel resolution for a range of atmospheric conditions using the Weather Research and Forecasting model (WRF) in large eddy simulation (LES) mode and adding instrument noise. We show that standard methods to infer source rates by Gaussian plume inversion or source pixel mass balance are prone to large errors because the turbulence cannot be properly parameterized on the small scale of instantaneous methane plumes. The integrated mass enhancement (IME) method, which relates total plume mass to source rate, and the cross-sectional flux method, which infers source rate from fluxes across plume transects, are better adapted to the problem. We show that the IME method with local measurements of the 10-m wind speed can infer source rates with error of 0.07–0.17th−1+5–12% depending on instrument precision (1–5%). The cross-sectional flux method has slightly larger errors (0.07–0.26th−1+8–12%) but a simpler physical basis. For comparison, point sources larger than 0.5th−1 contribute more than 75% of methane emissions reported to the U.S. Greenhouse Gas Reporting Program. Additional error applies if local wind speed measurements are not available, and may dominate the overall error at low wind speeds. Low winds are beneficial for source detection but not for source quantification.

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Short summary
Methane is a powerful greenhouse gas emitted by numerous human activities. Spaceborne observation of point sources would be a cost-effective monitoring solution, but the resolution of conventional methane-observing satellites is too coarse to resolve most methane emitters. We simulated fine-resolution (50-meter) satellite observations of methane plumes as would be measured by GHGSat (to be launched in 2019), and show that such data can usefully quantify large methane point sources.
Methane is a powerful greenhouse gas emitted by numerous human activities. Spaceborne...
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