Quantification of methane fluxes from local sites using a combination of a tracer release method, a Gaussian Model and an atmospheric statistical inversion approach
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This document discusses a method to quantify methane fluxes from local sites using a combination of a tracer release method, Gaussian modeling, and statistical inversion. It finds that using this combined approach provides better estimates than the tracer method alone when the tracer and methane sources are not perfectly collocated or there are multiple methane sources. The combined method is tested on a real farm case study and able to estimate total methane emissions and diagnose some individual facility uncertainties.
Quantification of methane fluxes from local sites using a combination of a tracer release method, a Gaussian Model and an atmospheric statistical inversion approach
- 1. Quantification of methane fluxes from local sites using a combination of a tracer release method, a Gaussian Model and an atmospheric statistical inversion approach S. Ars, G. Broquet, C. Yver Kwok, P. Bousquet LSCE – CEA/UVSQ/CNRS, Gif-sur-Yvette, France 1 ICOS Conference – September 28th 2016
- 2. The tracer release method Methane concentrations Acetylene concentrations 1860 ppb 2100 ppb ICOS Conference – September 28th 2016
- 3. The tracer release method Methane concentrations Acetylene concentrations 1860 ppb 2100 ppb ICOS Conference – September 28th 2016
- 4. ICOS Conference – September 28th 2016 The tracer release method Pros Cons • Simple to implement • Enable the estimation of a large number of sites • Non-collocation of the tracer • Multiple sources • Spread sources Wind Methane Acetylene
- 5. ICOS Conference – September 28th 2016 The Gaussian model Wind conditions Emission rates Gaussian model Use of meteorological conditions that are stationary in time and homogeneous in space within the study period and area. Cannot account precisely for the local topography and buildings.
- 6. Polyphemus Gaussian model developped by CEREA Doury Briggs Pasquill Q : source emission rate ū : mean wind speed velocity y : crosswind horizontal direction ys : source coordinate z : vertical coordinate zp : plume height above the ground sy and sz : gaussian plume standard deviations in the horizontal (crosswind) and vertical directions sy & sz ? AGU 2015 – December 15 2015 6 The Gaussian model
- 7. Polyphemus Gaussian model developped by CEREA Briggs Q : source emission rate ū : mean wind speed velocity y : crosswind horizontal direction ys : source coordinate z : vertical coordinate zp : plume height above the ground sy and sz : gaussian plume standard deviations in the horizontal (crosswind) and vertical directions sy & sz ? AGU 2015 – December 15 2015 7 The Gaussian model
- 8. ICOS Conference – September 28th 2016 The Gaussian model Use of the tracer data: Configuration optimization of the model parameterization Assessment of the model uncertainty for the configuration of the observation errors in the statistical inversion
- 9. fa = fb + BHT (HBHT+R)-1 (y0 – Hfb) A = (B-1 + HTR-1H)-1 fa Inverted fluxes fb Prior fluxes y0 Observations A Covariance matrix B Covariance matrix of the prior fluxes error R Covariance matrix of the observations and model errors H Observation operator 9 Statistical inversion ICOS Conference – September 28th 2016
- 10. ICOS Conference – September 28th 2016 Tested configurations: Config. 1: Methane and acetylene collocated (blue) Config. 2: Methane located downwind in comparison with the tracer (orange) Config. 3: Lateral shift between methane and acetylene (green) Config. 4: Two sources of methane with and one source of acetylene (grey) A test case with controlled methane emissions
- 11. ICOS Conference – September 28th 2016 A test case with controlled methane emissions As expected, tracer release method gives better estimates than the combined approach when the tracer and the methane sources are perfectly collocated because the tracer is a better proxy than the model in this case. When the tracer is not perfectly collocated or when there are several sources within a site, the combined approach gives better estimates.
- 12. ICOS Conference – September 28th 2016 A test case with controlled methane emissions
- 13. ICOS Conference – September 28th 2016 Estimate of the tracer mislocation error in an OSSE framework The methane and acetylene concentrations are modeled with the Gaussian model at known emission rates. The emission plumes transects of both gases are integrated and used to calculate the methane emission rate with the same formula than the tracer release technique. The calculated emission rates are compared with the actual methane emission rates used in the Gaussian model. Errors are estimated for a downwind shift (a), an upwind shift (b) and a lateral shift (c).
- 14. ICOS Conference – September 28th 2016 Combined method applied to a concrete case a b The Grignon farm
- 15. ICOS Conference – September 28th 2016 Combined method applied to a concrete case Prior and posterior emission rates from the statistical inversion:
- 16. ICOS Conference – September 28th 2016 Combined method applied to a concrete case Examples of plume transects simulated with prior and posterior emission rates:
- 17. ICOS Conference – September 28th 2016 Conclusions and perspectives The combination of the tracer release method, a Gaussian transport model and a statistical atmospheric inversion approach has been tested with controlled methane emissions and compared to the classic tracer release technique for several configuration of tracer and methane sources. The combined method gives generally better estimates of the global emission rate of a site except in the case of a perfect collocation of the tracer and the methane which is extremely rare in real industrial cases. The combined method is applied to a concrete case in order to estimate methane emissions from a farm. The method gives a good estimate of the total amount of methane emitted but it also diagnoses itself to have some difficulties to target all individual facilities through its diagnostic of the individual uncertainties. However the method still manage to separate some parts of the site.