I forward this contribution from Mark Harvey:

Dear Chris,

I am not aware of any reports of 13C fractionation between carbon fuel source and resultant soot.  However, they may exist.   Assuming fractionation during combustion is small, and the fuel source is natural gas methane (13C ~-40 per mil PDB), then your soot 13C should also be ~ -40 per mil PDB. Here are references on methane C13:

Conrad R., 2005. Quantification of methanogenic pathways using stable carbon isotopic signatures: a review and a proposal. Organic Geochemistry, vol. 36, pp. 739-752.

Breas O., Guillou C., Reniero F., and Wada E. 2001. Review: The global methane cycle: Isotopes and mixing ratios, sources and sinks. Isotopes Environ. Health Stud., vol. 37, pp. 257-379.

Quay, P.D., S.L. King, J. Stutsman, D.O. Wilbur, L.P. Steele,I. Fung, R.H. Gammon, T.A. Brown, G.W. Farwell, P.M.Grootes, and F.H. Schmidt, Carbon isotopic composition of atmospheric methane: Fossil and biomass burning sourcestrengths, Global Biogeochem. Cycles, 5, 25-47, 1991

Hope this helps,
Mark

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Arndt Schimmelmann, Ph.D.
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