Deuteromethanes: potential fingerprints of the sources of atmospheric methane

The purpose of this paper is to suggest that development of analytical techniques to determine the deuterium substitution pattern of 12C- and 13C-methane might lead to better constraints on the apportionment of source strengths among the major methane source categories. Traditional methods of determining the isotopic composition of methane require both combustion of the molecule to CO 2 for δ 13C analysis and reduction of the concomitant water to H 2 for δD analysis. When only δ 13C-CH 4 and δD-CH 4—and even δ 14C-CH 4—are used, the problem of source attribution is fundamentally underdetermined. There are more source categories than unique tracers for each source category. If isotopic analysis could be accomplished without the combustion step, then there are ten isotopomers (a conjunction of “isotope” and “isomer”) of methane available for fingerprinting the sources of methane in the atmosphere. The tritium content of methane also warrants close examination as another constraint on the apportionment of biogenic and fossil methane.