Atmos. Chem. Phys. Discuss., 2, 2021-2043, 2002
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
The isotopic fingerprint of the pre-industrial and the anthropogenic N2O source
T. Röckmann1, J. Kaiser1, and C. A. M. Brenninkmeijer2
1Max Planck Institute for Nuclear Physics, Atmospheric Physics Division, Heidelberg, Germany
2Max Planck Institute for Chemistry, Air Chemistry Division, Mainz, Germany

Abstract. We have performed high-precision measurements of the 18O and position dependent 15N isotopic composition of N2O from Antarctic firn air samples. By comparing these data to simulations carried out with a firn air diffusion model, we have reconstructed the temporal evolution of the N2O isotope signatures since pre-industrial times. The heavy isotope content of atmospheric N2O is presently decreasing for all signatures at rates of about -0.038%o yr -1 for 1d15N, -0.044%o yr -1 for 2d15N and  -0.025%o yr -1 for  d18O. The total decrease since pre-industrial times is estimated to be about -2%o  for  d15N at both positions and -1.2%o  for  d18O. Isotope budget calculations using these trends and recent stratospheric measurements allow to isotopically characterize the present and the pre-industrial global average N2O source, as well as the anthropogenic N2O emissions that have caused the global N2O increase since pre-industrial times. The increased fluxes from the depleted surface sources alone are insufficient to explain the inferred temporal isotope changes. In addition, the global average N2O source signature is calculated to be significantly depleted today relative to the pre-industrial value, in agreement with recent indications from soil emission measurements.

Citation: Röckmann, T., Kaiser, J., and Brenninkmeijer, C. A. M.: The isotopic fingerprint of the pre-industrial and the anthropogenic N2O source, Atmos. Chem. Phys. Discuss., 2, 2021-2043, doi:10.5194/acpd-2-2021-2002, 2002.
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