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Isotopic fractionation of methane in the stratosphere and its effect on free tropospheric isotopic compositions
Author(s) -
McCarthy M. C.,
Connell P.,
Boering K. A.
Publication year - 2001
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2001gl013159
Subject(s) - stratosphere , troposphere , atmospheric chemistry , chemistry , atmospheric sciences , kinetic isotope effect , ozone , physics , deuterium , organic chemistry , quantum mechanics
Kinetic isotope effects (KIEs) for the oxidation of CH 4 by OH, Cl, and O(¹D) were incorporated into a 2D model of the atmosphere to examine how sensitive the carbon isotopic composition of CH 4 in the free troposphere is to three influences: realistic stratospheric chemistry and transport, tropospheric Cl chemistry, and use of new, experimentally‐determined KIEs for the OH and O(¹D) sinks. At steady‐state, our results indicate that stratospheric chemistry and transport enrich tropospheric δ 13 CH 4 by 0.5 to 0.6‰, tropospheric Cl chemistry as modeled enriches δ 13 CH 4 by ∼0.3‰, and the new KIE for the OH sink depletes modeled global δ 13 CH 4 by >1‰. Ignoring the stratosphere (and Cl chemistry in general) in models therefore happens to partially compensate for use of the previously accepted KIE for OH when comparisons with observations of free tropospheric δ 13 CH 4 are made. In contrast, including only one of these influences increases the error relative to including none. Thus, all 3 effects are of sufficient magnitude to warrant their inclusion in inverse models in order to reduce uncertainties in the CH 4 budget.