Atmospheric Chemistry and Physics Discussions
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2002
10.5194/acpd-2-2021-2002
http://www.atmos-chem-phys-discuss.net/2/2021/2002/
http://www.atmos-chem-phys-discuss.net/2/2021/2002/acpd-2-2021-2002.html
http://www.atmos-chem-phys-discuss.net/2/2021/2002/acpd-2-2021-2002.pdf
2021
2043
2002-11-13
The isotopic fingerprint of the pre-industrial and the anthropogenic N<sub>2</sub>O source
T. Röckmann
J. Kaiser
C. A. M. Brenninkmeijer
Max Planck Institute for Nuclear Physics, Atmospheric Physics Division, Heidelberg, Germany
Max Planck Institute for Chemistry, Air Chemistry Division, Mainz, Germany
We have performed high-precision measurements of the
<sup>18</sup>O and position dependent <sup>15</sup>N isotopic composition of
N<sub>2</sub>O 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 N<sub>2</sub>O isotope signatures since pre-industrial times. The heavy isotope content
of atmospheric N<sub>2</sub>O is presently decreasing for all signatures at rates of about
-0.038%o
yr <sup>-1</sup> for <sup>1</sup><font face="Symbol" >d</font><sup>15</sup>N,
-0.044%o
yr <sup>-1</sup> for
<sup>2</sup><font face="Symbol" >d</font><sup>15</sup>N
and -0.025%o
yr <sup>-1</sup>
for <sup>
</sup><font face="Symbol" >d</font><sup>18</sup>O. The total decrease since pre-industrial
times is estimated to be about -2%o
for <sup>
</sup><font face="Symbol" >d</font><sup>15</sup>N at both positions and
-1.2%o
for <sup> </sup><font face="Symbol" >d</font><sup>18</sup>O.
Isotope budget calculations using these trends and recent stratospheric measurements allow to
isotopically characterize the present and the pre-industrial global average
N<sub>2</sub>O source, as well as the anthropogenic N<sub>2</sub>O emissions that have caused the global
N<sub>2</sub>O 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
N<sub>2</sub>O source signature is calculated to be significantly depleted today relative to the pre-industrial value, in
agreement with recent indications from soil emission measurements.