Hello Dachun and all isotope geochemists,

In his study "Atmospheric nitrogen is a reliable standard for natural 15-N
abundance measurements" (1983, Nature, vol. 303, pp. 685-687), Mariotti
had found that atmospheric nitrogen is isotopically identical all over
France, within the precision of his measurements.  Given the good mixing
of atmospheric air masses, that should be true for all locations.  Is it
possible that you sampled air that was isotpically shifted by the
proximity of a liquid nitrogen storage tank?  Nitrogen that vents from
liquid nitrogen can be expected to isotopically differ from mean
atmospheric nitrogen.

                           Best wishes,        Arndt


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Arndt Schimmelmann
Biogeochemical Laboratories
Indiana University
Department of Geological Sciences
1005 East Tenth Street
Bloomington, IN 47405-1403
U.S.A.
ph 812-855-7645
fax 812-855-7961
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