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Constraining N2O emissions since 1940 using firn air isotope measurements in both hemispheres

Prokopiou, Markella; Martinerie, Patricia; Sapart, Célia J.; Witrant, Emmanuel; Monteil, Guillaume LU ; Ishijima, Kentaro; Bernard, Sophie; Kaiser, Jan; Levin, Ingeborg and Blunier, Thomas, et al. (2017) In Atmospheric Chemistry and Physics 17(7). p.4539-4564
Abstract

N2O is currently the third 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 over the past decades, we performed a multi-site reconstruction of the atmospheric N2O mole fraction and isotopic composition using new and previously published 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)nmolmol-1 in 1940 to (322±1)nmolmol-1 in 2008, the isotopic composition of atmospheric N2O decreased... (More)

N2O is currently the third 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 over the past decades, we performed a multi-site reconstruction of the atmospheric N2O mole fraction and isotopic composition using new and previously published 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)nmolmol-1 in 1940 to (322±1)nmolmol-1 in 2008, the isotopic composition 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 δ15Nβ over 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 box 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 fix at 123 years. The average isotopic composition over the investigated period is δ15Nav Combining double low line (-7.6±0.8)% (vs. air-N2), δ18O Combining double low line (32.2±0.2)% (vs. Vienna Standard Mean Ocean Water-VSMOW) for δ18O, δ15Nα Combining double low line (-3.0±1.9)% and δ15Nβ Combining double low line (-11.7±2.3)%. δ15Nav, and δ15Nβ show some temporal variability, while for the other signatures the error bars of the reconstruction are too large to retrieve reliable temporal changes. Possible processes that may explain trends in 15N are discussed. The 15N site preference (Combining double low line δ15Nα-δ15Nβ) provides evidence of a shift in emissions from denitrification to nitrification, although the uncertainty envelopes are large.

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Atmospheric Chemistry and Physics
volume
17
issue
7
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26 pages
publisher
Copernicus Gesellschaft Mbh
external identifiers
  • scopus:85017181061
  • wos:000408273200001
ISSN
1680-7316
DOI
10.5194/acp-17-4539-2017
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English
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yes
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4a2c30a3-967d-45dc-b546-40201fc04c45
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2017-04-26 15:33:13
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2018-01-07 12:00:58
@article{4a2c30a3-967d-45dc-b546-40201fc04c45,
  abstract     = {<p>N<sub>2</sub>O is currently the third 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 over the past decades, we performed a multi-site reconstruction of the atmospheric N<sub>2</sub>O mole fraction and isotopic composition using new and previously published 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 N<sub>2</sub>O mole fraction increased from (290±1)nmolmol<sup>-1</sup> in 1940 to (322±1)nmolmol<sup>-1</sup> in 2008, the isotopic composition of atmospheric N<sub>2</sub>O decreased by (-2.2±0.2)% for δ<sup>15</sup>Nav, (-1.0±0.3)% for δ<sup>18</sup>O, (-1.3±0.6)% for δ<sup>15</sup>Nα, and (-2.8±0.6)% for δ<sup>15</sup>Nβ over 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 box 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 N<sub>2</sub>O lifetime, which we choose to fix at 123 years. The average isotopic composition over the investigated period is δ<sup>15</sup>Nav Combining double low line (-7.6±0.8)% (vs. air-N2), δ<sup>18</sup>O Combining double low line (32.2±0.2)% (vs. Vienna Standard Mean Ocean Water-VSMOW) for δ<sup>18</sup>O, δ<sup>15</sup>Nα Combining double low line (-3.0±1.9)% and δ<sup>15</sup>Nβ Combining double low line (-11.7±2.3)%. δ<sup>15</sup>Nav, and δ<sup>15</sup>Nβ show some temporal variability, while for the other signatures the error bars of the reconstruction are too large to retrieve reliable temporal changes. Possible processes that may explain trends in 15N are discussed. The <sup>15</sup>N site preference (Combining double low line δ<sup>15</sup>Nα-δ<sup>15</sup>Nβ) provides evidence of a shift in emissions from denitrification to nitrification, although the uncertainty envelopes are large.</p>},
  author       = {Prokopiou, Markella and Martinerie, Patricia and Sapart, Célia J. and Witrant, Emmanuel and Monteil, Guillaume and Ishijima, Kentaro and Bernard, Sophie and Kaiser, Jan and Levin, Ingeborg and Blunier, Thomas and Etheridge, David and Dlugokencky, Ed J. and van de Wal, Roderik S. W. and Röckmann, Thomas},
  issn         = {1680-7316},
  language     = {eng},
  month        = {04},
  number       = {7},
  pages        = {4539--4564},
  publisher    = {Copernicus Gesellschaft Mbh},
  series       = {Atmospheric Chemistry and Physics},
  title        = {Constraining N<sub>2</sub>O emissions since 1940 using firn air isotope measurements in both hemispheres},
  url          = {http://dx.doi.org/10.5194/acp-17-4539-2017},
  volume       = {17},
  year         = {2017},
}