<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

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. In all three cities, winter CO2 fluxes were predominantly fossil, with mean ffCO2 contributions of about 80 %. Summer fluxes could be most clearly partitioned in Munich, where improvements in the REA setup, the 14CO2 measurement precision, the sampling strategy, and the source strength increased the signal-to-noise ratios compared to Zurich and Paris. In Munich, the observed nfCO2 fluxes were predominantly positive (∼50 % of net summer fluxes), demonstrating the major role of respiration, biofuels, and certain industrial processes. Particularly large nfCO2 fluxes from the direction of a brewery suggest non-respiratory anthropogenic contributions and highlight the complexity of urban environments. Additionally, the absolute CO2 and 14CO2 concentrations of the REA samples were compared to clean background concentrations to estimate ffCO2 excess concentrations. Across all cities, ffCO2 contributions to regional excess concentrations were much lower (&lt;65 % in winter and &lt;30 % in summer) than to local eddy covariance CO2 fluxes, 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.

Authors

Institutions

Publication Details

Published
2025-10-24
DOI
https://doi.org/10.5194/egusphere-2025-4856
Primary Topic
Wind and Air Flow Studies
Type
article
Field-Weighted Citation Impact
0.00
Controls
|||
ALL TIME
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
article

14 C-based separation of fossil and non-fossil CO 2 fluxes in cities using relaxed eddy accumulation: results from tall-tower measurements in Zurich, Paris, and Munich

Natascha Kljun, Michel Ramonet, Rainer Hilland, Betty Molinier et al.
Wind and Air Flow Studies
article

14 C-based separation of fossil and non-fossil CO 2 fluxes in cities using relaxed eddy accumulation: results from tall-tower measurements in Zurich, Paris, and Munich

Natascha Kljun, Michel Ramonet, Rainer Hilland, Betty Molinier, Andreas Christen, Julian Della Coletta, R. Kneißl, Christopher Holst, Stavros Stagakis, Ingeborg Levin, Susanne Preunkert, Laura Bignotti, Xochilt Gutiérrez, Benjamin Loubet, Matthias Mauder, Markus Eritt, Samuel Hammer, Changxing Lan, Patrick Aigner, Lukas Emmenegger, Jia Chen, Armin Jordan, Ann-Kristin Kunz, Virgile Legendre, Lars Borchardt, Josh Hashemi
article en

Abstract

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. In all three cities, winter CO2 fluxes were predominantly fossil, with mean ffCO2 contributions of about 80 %. Summer fluxes could be most clearly partitioned in Munich, where improvements in the REA setup, the 14CO2 measurement precision, the sampling strategy, and the source strength increased the signal-to-noise ratios compared to Zurich and Paris. In Munich, the observed nfCO2 fluxes were predominantly positive (∼50 % of net summer fluxes), demonstrating the major role of respiration, biofuels, and certain industrial processes. Particularly large nfCO2 fluxes from the direction of a brewery suggest non-respiratory anthropogenic contributions and highlight the complexity of urban environments. Additionally, the absolute CO2 and 14CO2 concentrations of the REA samples were compared to clean background concentrations to estimate ffCO2 excess concentrations. Across all cities, ffCO2 contributions to regional excess concentrations were much lower (&lt;65 % in winter and &lt;30 % in summer) than to local eddy covariance CO2 fluxes, 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.

Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung (DE), Centre National de la Recherche Scientifique (FR), University of Freiburg (DE), University of Basel (CH), Lund University (SE), AgroParisTech (FR), Heidelberg University (DE), Commissariat à l'Énergie Atomique et aux Énergies Alternatives (FR), Université Paris-Saclay (FR), Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement (FR), Écologie Fonctionnelle et Écotoxicologie des Agroécosystèmes (FR), Laboratoire des Sciences du Climat et de l'Environnement (FR), CEA Paris-Saclay (FR), National Institute of Meteorology (TN), Max Planck Institute for Biogeochemistry (DE), Garmisch-Partenkirchen Medical Center (DE), Technical University of Munich (DE), Swiss Federal Laboratories for Materials Science and Technology (CH)
Openalex Percentile: Top 72%
Wind and Air Flow Studies
DOIOpen Access PDFOpenAlex
AI Navigator

Ask Laika to Summarize, Analyze, and Connect papers live on the map.

Summarize Papers & Methodologies

Extract key findings, datasets, and comparative methods across publications.

Benchmark Rankings & Visual Analytics

Rank top research institutions, authors, funders, topics, and journals by Field-Weighted Citation Impact (FWCI) and paper volume with instant charts.

Connect Distant Disciplines

Bridge topological clusters on the map to find hidden collaborative intersections.