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14C-based separation of fossil and non-fossil CO2 fluxes in cities using relaxed eddy accumulation : Results from tall-tower measurements in Zurich, Paris, and Munich

Kunz, Ann Kristin ; Hammer, Samuel ; Aigner, Patrick ; Bignotti, Laura ; Borchardt, Lars ; Chen, Jia ; Della Coletta, Julian ; Emmenegger, Lukas ; Eritt, Markus and Gutiérrez, Xochilt , et al. (2026) In Atmospheric Chemistry and Physics 26(7). p.4967-5003
Abstract

Relaxed eddy accumulation (REA) measurements for 14CO2 enable the estimation of fossil fuel (ff) CO2 fluxes in urban areas. This work is based on 252 REA ffCO2 flux measurements conducted on tall towers in the cities of Zurich, Paris, and Munich. The ffCO2 fluxes were compared to net eddy covariance CO2 fluxes to quantify the role of non-fossil (nf) CO2 fluxes. While the measurements in Zurich and Paris were limited by small signal-to-noise ratios, improvements in the REA setup, the 14CO2 measurement precision, the sampling strategy, and the source strength increased the significance of the results in Munich. Large nfCO2 fluxes... (More)

Relaxed eddy accumulation (REA) measurements for 14CO2 enable the estimation of fossil fuel (ff) CO2 fluxes in urban areas. This work is based on 252 REA ffCO2 flux measurements conducted on tall towers in the cities of Zurich, Paris, and Munich. The ffCO2 fluxes were compared to net eddy covariance CO2 fluxes to quantify the role of non-fossil (nf) CO2 fluxes. While the measurements in Zurich and Paris were limited by small signal-to-noise ratios, improvements in the REA setup, the 14CO2 measurement precision, the sampling strategy, and the source strength increased the significance of the results in Munich. Large nfCO2 fluxes observed in Munich from the direction of a brewery demonstrate the efficacy of the partitioning approach and illustrate the complexity of urban atmospheric measurement data. Excluding these measurements potentially influenced by large anthropogenic nfCO2 fluxes, the error-weighted average ffCO2 / CO2 flux ratio in Munich was approximately 47 % in summer and 76 % in winter, with the majority of measurements taken between 07:00 and 19:00 local time. Regional excess concentrations had much lower ffCO2 contributions (<63 % in winter and <28 % in summer, in all three cities), demonstrating fundamental differences between local and regional CO2 fluxes. The combination of 14CO2 observations and the REA method is a sophisticated approach that challenges the limits of current analytical capabilities, while providing unique opportunities for quantifying ffCO2 and nfCO2 fluxes.

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organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Atmospheric Chemistry and Physics
volume
26
issue
7
pages
37 pages
publisher
Copernicus GmbH
external identifiers
  • scopus:105037048496
ISSN
1680-7316
DOI
10.5194/acp-26-4967-2026
project
Pilot Application in Urban Landscapes - towards integrated city observatories for greenhouse gases
language
English
LU publication?
yes
additional info
Publisher Copyright: Copyright © 2026 Ann-Kristin Kunz et al.
id
179af5cb-b40a-4870-bbd8-f42e85106f59
date added to LUP
2026-05-06 17:43:14
date last changed
2026-05-07 10:59:19
@article{179af5cb-b40a-4870-bbd8-f42e85106f59,
  abstract     = {{<p>Relaxed eddy accumulation (REA) measurements for <sup>14</sup>CO<sub>2</sub> enable the estimation of fossil fuel (ff) CO<sub>2</sub> fluxes in urban areas. This work is based on 252 REA ffCO<sub>2</sub> flux measurements conducted on tall towers in the cities of Zurich, Paris, and Munich. The ffCO<sub>2</sub> fluxes were compared to net eddy covariance CO<sub>2</sub> fluxes to quantify the role of non-fossil (nf) CO<sub>2</sub> fluxes. While the measurements in Zurich and Paris were limited by small signal-to-noise ratios, improvements in the REA setup, the <sup>14</sup>CO<sub>2</sub> measurement precision, the sampling strategy, and the source strength increased the significance of the results in Munich. Large nfCO<sub>2</sub> fluxes observed in Munich from the direction of a brewery demonstrate the efficacy of the partitioning approach and illustrate the complexity of urban atmospheric measurement data. Excluding these measurements potentially influenced by large anthropogenic nfCO<sub>2</sub> fluxes, the error-weighted average ffCO<sub>2</sub> / CO<sub>2</sub> flux ratio in Munich was approximately 47 % in summer and 76 % in winter, with the majority of measurements taken between 07:00 and 19:00 local time. Regional excess concentrations had much lower ffCO<sub>2</sub> contributions (&lt;63 % in winter and &lt;28 % in summer, in all three cities), demonstrating fundamental differences between local and regional CO<sub>2</sub> fluxes. The combination of <sup>14</sup>CO<sub>2</sub> observations and the REA method is a sophisticated approach that challenges the limits of current analytical capabilities, while providing unique opportunities for quantifying ffCO<sub>2</sub> and nfCO<sub>2</sub> fluxes.</p>}},
  author       = {{Kunz, Ann Kristin and Hammer, Samuel and Aigner, Patrick and Bignotti, Laura and Borchardt, Lars and Chen, Jia and Della Coletta, Julian and Emmenegger, Lukas and Eritt, Markus and Gutiérrez, Xochilt and Hashemi, Josh and Hilland, Rainer and Holst, Christopher and Jordan, Armin and Kljun, Natascha and Kneißl, Richard and Lan, Changxing and Legendre, Virgile and Levin, Ingeborg and Loubet, Benjamin and Mauder, Matthias and Molinier, Betty and Preunkert, Susanne and Ramonet, Michel and Stagakis, Stavros and Christen, Andreas}},
  issn         = {{1680-7316}},
  language     = {{eng}},
  month        = {{04}},
  number       = {{7}},
  pages        = {{4967--5003}},
  publisher    = {{Copernicus GmbH}},
  series       = {{Atmospheric Chemistry and Physics}},
  title        = {{<sup>14</sup>C-based separation of fossil and non-fossil CO<sub>2</sub> fluxes in cities using relaxed eddy accumulation : Results from tall-tower measurements in Zurich, Paris, and Munich}},
  url          = {{http://dx.doi.org/10.5194/acp-26-4967-2026}},
  doi          = {{10.5194/acp-26-4967-2026}},
  volume       = {{26}},
  year         = {{2026}},
}