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| Titel |
Constraining N2O emissions since 1940 by firn air isotope measurements in both hemispheres |
| VerfasserIn |
Markella Prokopiou, Patricia Martinerie, Célia Sapart, Emmanuel Witrant, Guillaume Monteil, Kentaro Ishijima, Jan Kaiser, Ingeborg Levin, Todd Sowers, Thomas Blunier, David Etheridge, Edward Dlugokencky, Roderik van de Wal, Thomas Röckmann |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250146501
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| Publikation (Nr.) |
 EGU/EGU2017-10529.pdf |
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| Zusammenfassung |
| N2O is currently the 3rd most important anthropogenic greenhouse gas in terms of radiative
forcing and its atmospheric mole fraction is rising steadily. To quantify the growth rate and its
causes, we performed a multi-site reconstruction of the atmospheric N2O mole fraction and
isotopic composition using firn air data collected from Greenland and Antarctica in
combination with a firn diffusion and densification model. The multi-site reconstruction
showed that while the global mean N2O mole fraction increased from (290±1) nmol mol−1
in 1940 to (322±1) nmol mol−1 in 2008 the isotopic δ values of atmospheric N2O decreased
by (- 2.2±0.2) ‰ for δ15Nav, (- 1.0±0.3) ‰ for δ18O, (- 1.3±0.6) ‰ for δ15Nα, and (-
2.8±0.6) ‰ for δ15Nβover the same period. The detailed temporal evolution of the mole
fraction and isotopic composition derived from the firn air model was then used in a two-box
atmospheric model (comprising a stratospheric and a tropospheric box) to infer
changes in the isotopic source signature over time. The precise value of the source
strength depends on the choice of the N2O lifetime, which we choose to be 123 a.
Adopting this lifetime results in total average source isotopic signatures of (- 7.6±0.8)
‰ (vs. Air-N2) for δ15Nav, (32.2±0.2) ‰ (vs. VSMOW) for δ18O, (- 3.0±1.9)
‰ (vs. Air-N2) for δ15Nα, and (- 11.7±2.3) ‰ (vs. Air-N2) for δ15Nβ over the
investigated period. δ15Navand δ15Nβ show some temporal variability while the other
source isotopic signatures remain unchanged. The 15N site-preference (= δ15Nα –
δ15Nβ) can be used to reveal further information on the source emission origins.
Based on the changes in the isotopes we conclude that the main contribution to N2O
changes in the atmosphere since 1940 is from soils, with agricultural soils being
the principal anthropogenic component, which is in line with previous studies. |
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