P. Bergamaschi et al., IMPLICATIONS OF THE LARGE CARBON KINETIC ISOTOPE EFFECT IN THE REACTION CH4-13(CL FOR THE C)C-12 RATIO OF STRATOSPHERIC CH4/, Geophysical research letters, 23(17), 1996, pp. 2227-2230
Recent investigations of the carbon kinetic isotope effect (KIE) of th
e reaction CH4 + Cl yielded KIE(Cl) = 1.066 +/- 0.002 at 297 K (increa
sing to 1.075 +/- 0.005 at 223 K) [Saueressig el al., 1995]. In order
to assess the effect of the exceptionally large KIE(Cl) on delta(13)C
of stratospheric CH4 we applied a two-dimensional, time dependent chem
ical transport model. The model results demonstrate the strong influen
ce of the CH4 + Cl reaction on delta(13)CH(4) in particular in the mid
dle and upper stratosphere, where this reaction contributes several te
ns of percent to the total CH4 sink. The Cl sink helps to explain the
relatively large overall isotope fractionation of 1.010-1.012 observed
in the lower stratosphere [Brenninkmeijer el al., 1995; Brenninkmeije
r el al., 1996], even though the model results predict a smaller effec
t than observed.