Natural and anthropogenic methane fluxes in Eurasia: a mesoscale quantification by generalized atmospheric inversion

Abstract

Abstract. Eight surface observation sites providing quasicontinuous measurements of atmospheric methane mixing ratios have been operated since the mid-2000's in Siberia. For the first time in a single work, we assimilate 1 year of these in situ observations in an atmospheric inversion. Our objective is to quantify methane surface fluxes from anthropogenic and wetland sources at the mesoscale in the Siberian lowlands for the year 2010. To do so, we first inquire about the way the inversion uses the observations and the way the fluxes are constrained by the observation sites. As atmospheric inversions at the mesoscale suffer from mis-quantified sources of uncertainties, we follow recent innovations in inversion techniques and use a new inversion approach which quantifies the uncertainties more objectively than the previous inversion systems. We find that, due to errors in the representation of the atmospheric transport and redundant pieces of information, only one observation every few days is found valuable by the inversion. The remaining high-resolution quasicontinuous signal is representative of very local emission patterns difficult to analyse with a mesoscale system. An analysis of the use of information by the inversion also reveals that the observation sites constrain methane emissions within a radius of 500 km. More observation sites than the ones currently in operation are then necessary to constrain the whole Siberian lowlands. Still, the fluxes within the constrained areas are quantified with objectified uncertainties. Finally, the tolerance intervals for posterior methane fluxes are of roughly 20 % (resp. 50 %) of the fluxes for anthropogenic (resp. wetland) sources. About 50-70 % of Siberian lowlands emissions are constrained by the inversion on average on an annual basis. Extrapolating the figures on the constrained areas to the whole Siberian lowlands, we find a regional methane budget of 5-28 TgCH 4 for the year 2010, i.e. 1-5 % of the global methane emissions. As very few in situ observations are available in the region of interest, observations of methane total columns from the Greenhouse Gas Observing SATellite (GOSAT) are tentatively used for the evaluation of the inversion results, but they exhibit only a marginal signal from the fluxes within the region of interest.

Methane distribution and oxidation around the Lena Delta in summer 2013

“…Previous examinations of methane released by ebullition did not find any isotopic evidence of oxidation; thus, this methane will almost exclusively be released into the atmosphere (Sapart et al, 2017). However, whether this ebullition really results in elevated atmospheric methane concentrations remains a matter of debate, as this fingerprint has not been detected by others Berchet et al, 2015). Overall, methane emissions from the East Siberian Arctic shelf seem relatively insignificant when compared to methane emissions from wetland and anthropogenic sources in eastern Siberia (Berchet et al, 2015).…”

“…However, whether this ebullition really results in elevated atmospheric methane concentrations remains a matter of debate, as this fingerprint has not been detected by others Berchet et al, 2015). Overall, methane emissions from the East Siberian Arctic shelf seem relatively insignificant when compared to methane emissions from wetland and anthropogenic sources in eastern Siberia (Berchet et al, 2015).…”

Detectability of Arctic methane sources at six sites performing continuous atmospheric measurements

“…Although higher emissions are expected in winter, particularly due to household heating, important emissions also occur in summer, e.g. from seepages from maintenance and welling work (Berchet et al, 2015). In the absence of more precise information, anthropogenic emissions are kept constant all year.…”

Pan-Eurasian Experiment (PEEX): towards a holistic understanding of the feedbacks and interactions in the land–atmosphere–ocean–society continuum in the northern Eurasian region

“…3.5). At the moment, there is a serious gap in our knowledge on tropospheric composition and chemistry over Russia and China, with particularly few observation programs being active over Siberia (Crutzen et al, 1998;Ramonet et al, 2002;Paris et al, 2008;Kozlova et al, 2008;Uttal et al, 2015, Paris et al, 2010aSasakawa et al, 2010;Chi et al, 2013;Saeki et al, 2013;Ding et al, 2013a, b;Berchet et al, 2015;Heimann et al, 2014). There is thus an urgent need for harmonized, coordinated and comprehensive greenhouse gas, trace gas, and aerosol in situ observations over northern Eurasia and China (longterm transport aspect) comparable to European and circumpolar data observations.…”