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Published July 1, 2000 | public
Journal Article

Photo-induced isotopic fractionation of stratospheric N_2O


This paper shows that N_2O isotopic fractionation in the stratosphere may be understood within the limits of the standard photochemical models if mass-dependent photodissociation rates for the various N_2O isotopomers are incorporated. Thus, we conclude that there is no demonstrable reason to invoke a significant chemical source of N_2O in the middle atmosphere. This paper presents a general theory for isotopomer dependent photodissociation rates that accounts for the isotopic fractionation observed in stratospheric N_2O and how photodissociations appear to be both a source and a sink of N_2O in the middle atmosphere. Photo-induced isotopic fractionation effects (PHIFE), explain the distinct fractionation signatures found for ^(15)N/^(14)N and ^(18)O/^(16)O ratios in both laboratory and remote sensing measurements. Furthermore, PHIFE predicts substantially different isotopic fractionations in the stratosphere for the isotopomers ^(15)N^(14)N^(16)O and ^(14)N^(15)N^(16)O, which have identical molecular weights but different isotopic substitution sites. Modeling results based on this theory suggest that there is no demonstrable reason to invoke a significant chemical source of N_2O in the middle atmosphere and that N_2O multi-isotope correlations should prove a useful measure of stratospheric air parcel history.

Additional Information

© 2000 Elsevier Science Ltd. Received 15 June 1999; accepted 28 October 1999. Available online 8 January 2001. The authors wish to thank M. Thiemens, T. Rahn and G.A. Blake for interesting discussions as well as N. Yoshida, T. Röckmann, H. Zhang, and H. Umemoto for sharing their data prior to publication. CEM thanks the N_2O Conference organizers for the invitation to present the PHIFE paper in Tsukuba. YLY was supported in part by NSF ATM-9903790.

Additional details

August 22, 2023
October 17, 2023