How a European network may help with estimating methane emissions on the French national scale

Abstract

Abstract. Methane emissions on the national scale in France in 2012 are inferred by assimilating continuous atmospheric mixing ratio measurements from nine stations of the European network ICOS located in France and surrounding countries. To assess the robustness of the fluxes deduced by our inversion system based on an objectified quantification of uncertainties, two complementary inversion set-ups are computed and analysed: (i) a regional run correcting for the spatial distribution of fluxes in France and (ii) a sectorial run correcting fluxes for activity sectors on the national scale. In addition, our results for the two set-ups are compared with fluxes produced in the framework of the inversion intercomparison exercise of the InGOS project. The seasonal variability in fluxes is consistent between different set-ups, with maximum emissions in summer, likely due to agricultural activity. However, very high monthly posterior uncertainties (up to ≈ 65 to 74 % in the sectorial run in May and June) make it difficult to attribute maximum emissions to a specific sector. On the yearly and national scales, the two inversions range from 3835 to 4050 Gg CH 4 and from 3570 to 4190 Gg CH 4 for the regional and sectorial runs, respectively, consistently with the InGOS products. These estimates are 25 to 55 % higher than the total national emissions from bottom-up approaches (biogeochemical models from natural emissions, plus inventories for anthropogenic ones), consistently pointing at missing or underestimated sources in the inventories and/or in natural sources. More specifically, in the sectorial set-up, agricultural emissions are inferred as 66% larger than estimates reported to the UNFCCC. Uncertainties in the total annual national budget are 108 and 312 Gg CH 4 , i.e, 3 to 8 %, for the regional and sectorial runs respectively, smaller than uncertainties in available bottom-up products, proving the added value of top-down atmospheric inversions. Therefore, even though the surface network used in 2012 does not allow us to fully constrain all regions in France accurately, a regional inversion set-up makes it possible to provide estimates of French methane fluxes with an uncertainty in the total budget of less than 10 % on the yearly timescale. Additional sites deployed since 2012 would help to constrain French emissions on finer spatial and temporal scales and attributing missing emissions to specific sectors.

Variational regional inverse modeling of reactive species emissions with PYVAR-CHIMERE

“…Some studies 86 Here, we present the Bayesian variational inverse system PYVAR-CHIMERE, that has reached a 96 good level of maturity (robustness of calculations, clarity, portability, modularity of the code) and 97 that is adapted to reactive species such as CO and NO2. This adaptation for reactive species takes 98 advantage of the previous developments for the quantification of fluxes of long-lived GHG species 99 such as CO2 [Broquet et al, 2011] and CH4 [Pison et al, 2018] at the regional to the local scales, 100 paving the way for monitoring anthropogenic emissions at high spatial resolutions. The PYVAR-101 CHIMERE inverse modeling system is based on the Bayesian variational assimilation code PYVAR 102 [Chevallier et al 2005] and on the regional state-of-the-art CTM CHIMERE, dedicated to the study 103 As shown in Figure 1, the minimization algorithm repeats the forward-adjoint cycle to seek an optimal 159 solution for the control parameters.…”

“…382 This paper presents the Bayesian variational inverse system PYVAR-CHIMERE, which has been 383 adapted to the inversion of reactive species such as CO and NO2, taking advantage of the previous 384 developments for long-lived species such as CO2[Broquet et al, 2011] and CH4[Pison et al, 2018]. 385We show the potential of PYVAR-CHIMERE, with inversions for CO and NO2 illustrated over 386Europe for an example day.…”

A decade of CH<sub>4</sub>, CO and N<sub>2</sub>O in situ measurements at Lauder, New Zealand: assessing the long-term performance of a Fourier transform infrared trace gas and isotope analyser

“…Top-down approaches have already been undertaken to quantify national surface flux inventories of the main greenhouse gases (CO 2 , CH 4 and N 2 O) via national surface in situ networks as in Peters et al (2007), Ganesan et al (2015) and Henne et al (2016), or pan-national inventories using international greenhouse gas monitoring network databases (e.g. Cressot et al, 2016;Bergamaschi et al, 2015Bergamaschi et al, , 2018Pison et al, 2018). There is also a need for increased coverage in the Southern Hemisphere (Thompson et al, 2014;Wells et al, 2015), which is relatively data sparse compared to the Northern Hemisphere.…”

“…The original reason for the establishment of greenhouse gas in situ measurements at Lauder were two-fold. First, with the establishment of a TCCON site at Lauder in 2004(Wunch et al, 2011Pollard et al, 2017) it was an initial requirement that sites have co-located continuous high-precision surface in situ measurements of CO 2 and CH 4 . This was to provide a priori surface concentration constraints for the TC-CON total column dry mole fraction retrievals and provide an independent estimate of boundary layer CO 2 and CH 4 .…”

Continuous atmospheric CO<sub>2</sub>, CH<sub>4</sub> and CO measurements at the OPE station in France from 2011 to 2018

“…The potential of ICOS continuous measurements of CO2 dry air mole fraction to improve Net Ecosystem Exchange estimates at the mesoscale across Europe has been evaluated in Kadygrov et al (2015). Pison et al (2018) addressed the potential of the actual ICOS European network for the methane emission estimation at the French national scale. 25…”