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A model for 12 CH 2 D 2 and 13 CH 3 D as complementary tracers for the budget of atmospheric CH 4
Author(s) -
Haghnegahdar Mojhgan A.,
Schauble Edwin A.,
Young Edward D.
Publication year - 2017
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1002/2017gb005655
Subject(s) - isotopologue , atmospheric methane , atmospheric chemistry , sink (geography) , methane , isotope , chemistry , atmospheric sciences , analytical chemistry (journal) , environmental chemistry , ozone , physics , nuclear physics , molecule , cartography , organic chemistry , geography
We present a theoretical model to investigate the potential of 13 CH 3 D and 12 CH 2 D 2 , the doubly substituted mass‐18 isotopologues of methane, as tools for tracking atmospheric methane sources and sinks. We use electronic structure methods to estimate kinetic isotope fractionations associated with the major sink reactions of methane in air (reactions with OH and Cl radicals) and combine literature data with reconnaissance measurements of the relative abundances of 13 CH 3 D and 12 CH 2 D 2 to estimate the compositions of the largest atmospheric sources. This model atmospheric budget is investigated with a simplified box model in which we explore both steady state and dynamical (nonsteady state) conditions triggered by changes in emission or sink fluxes. The steady state model predicts that sink reactions will generate a marked (>100‰) clumped isotope excess in atmospheric Δ 12 CH 2 D 2 relative to the net source composition. 12 CH 2 D 2 measurements may thus be useful for tracing both atmospheric source and sink fluxes. The effect of sinks on Δ 13 CH 3 D is much less pronounced, indicating that 13 CH 3 D in air will give a more focused picture of the source composition.