Isotopic signatures of anthropogenic CH4 sources in Alberta, Canada

Publication date: September 2017
Source:Atmospheric Environment, Volume 164
Author(s): M. Lopez, O.A. Sherwood, E.J. Dlugokencky, R. Kessler, L. Giroux, D.E.J. Worthy
A mobile system was used for continuous ambient measurements of stable CH4 isotopes (¹²CH4 and ¹³CH4) and ethane (C2H6). This system was used during a winter mobile campaign to investigate the CH4 isotopic signatures and the C2H6/CH4 ratios of the main anthropogenic sources of CH4 in the Canadian province of Alberta. Individual signatures were derived from δ¹³CH4 and C2H6 measurements in plumes arriving from identifiable single sources. Methane emissions from beef cattle feedlots (n = 2) and landfill (n = 1) had δ¹³CH4 signatures of −66.7 ± 2.4‰ and −55.3 ± 0.2‰, respectively. The CH4 emissions associated with the oil or gas industry had distinct δ¹³CH4 signatures, depending on the formation process. Emissions from oil storage tanks (n = 5) had δ¹³CH4 signatures ranging from −54.9 ± 2.9‰ to −60.6 ± 0.6‰ and non-detectable C2H6, characteristic of secondary microbial methanogenesis in oil-bearing reservoirs. In contrast, CH4 emissions associated with natural gas facilities (n = 8) had δ¹³CH4 signatures ranging from −41.7 ± 0.7‰ to −49.7 ± 0.7‰ and C2H6/CH4 molar ratios of 0.10 for raw natural gas to 0.04 for processed/refined natural gas, consistent with thermogenic origins. These isotopic signatures and C2H6/CH4 ratios have been used for source discrimination in the weekly atmospheric measurements of stable CH4 isotopes over a two-month winter period at the Lac La Biche (LLB) measurement station, located in Alberta, approximately 200 km northeast of Edmonton. The average signature of −59.5 ± 1.4‰ observed at LLB is likely associated with transport of air after passing over oil industry sources located south of the station.



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