S. Sugawara et al., VERTICAL PROFILE OF THE CARBON ISOTOPIC RATIO OF STRATOSPHERIC METHANE OVER JAPAN, Geophysical research letters, 24(23), 1997, pp. 2989-2992
Stratospheric air samples were collected over Japan on August 31, 1994
using a balloon-borne cryogenic Sampler and then analyzed for the CH4
concentration and delta(13)C in CH4. The delta(13)C value increased f
rom about -47.5 parts per thousand at the tropopause to about -38.9 pa
rts per thousand at 34.7 km, accompanied by a rapid decrease of the CH
4 concentration with height. From the measured values of the CH4 conce
ntration and delta(13)C, th, apparent carbon isotopic fractionation fa
ctor was estimated to be 1.0131+/-0.0006. The contributions of the che
mical CH4 reactions with OH, O(D-1) and Cl were also examined by using
an one-dimensional photochemical-diffusion model. It is suggested fro
m this examination that the reaction of CH4 with Cl is especially impo
rtant for delta(13)C in the stratosphere.