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Estimation of the fossil fuel component in atmospheric CO2 based on radiocarbon measurements at the Beromünster tall tower, Switzerland

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Berhanu Tesfaye A., Szidat Sönke, Brunner Dominik, Satar Ece, Schanda Rüdiger, Nyfeler Peter, Battaglia Michael, Steinbacher Martin, Hammer Samuel, Leuenberger Markus,
Project ICOS-CH Phase 2
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Original article (peer-reviewed)

Journal Atmospheric Chemistry and Physics
Volume (Issue) 17(17)
Page(s) 10753 - 10766
Title of proceedings Atmospheric Chemistry and Physics
DOI 10.5194/acp-17-10753-2017

Open Access

Type of Open Access Publisher (Gold Open Access)


Abstract. Fossil fuel CO 2 (CO 2ff ) is the major contributor of anthropogenic CO 2 in the atmosphere, and accurate quantification is essential to better understand the carbon cycle. Since October 2012, we have been continuously measuring the mixing ratios of CO, CO 2 , CH 4 , and H 2 O at five different heights at the Beromünster tall tower, Switzerland. Air samples for radiocarbon (Δ 14 CO 2 ) analysis have also been collected from the highest sampling inlet (212.5 m) of the tower on a biweekly basis. A correction was applied for 14 CO 2 emissions from nearby nuclear power plants (NPPs), which have been simulated with the Lagrangian transport model FLEXPART-COSMO. The 14 CO 2 emissions from NPPs offset the depletion in 14 C by fossil fuel emissions, resulting in an underestimation of the fossil fuel component in atmospheric CO 2 by about 16 %. An average observed ratio ( R CO ) of 13.4 ± 1.3 mmol mol −1 was calculated from the enhancements in CO mixing ratios relative to the clean-air reference site Jungfraujoch (ΔCO) and the radiocarbon-based fossil fuel CO 2 mole fractions. The wintertime R CO estimate of 12.5 ± 3.3 is about 30 % higher than the wintertime ratio between in situ measured CO and CO 2 enhancements at Beromünster over the Jungfraujoch background (8.7 mmol mol −1 ) corrected for non-fossil contributions due to strong biospheric contribution despite the strong correlation between ΔCO and ΔCO 2 in winter. By combining the ratio derived using the radiocarbon measurements and the in situ measured CO mixing ratios, a high-resolution time series of CO 2ff was calculated exhibiting a clear seasonality driven by seasonal variability in emissions and vertical mixing. By subtracting the fossil fuel component and the large-scale background, we have determined the regional biospheric CO 2 component that is characterized by seasonal variations ranging between −15 and +30 ppm. A pronounced diurnal variation was observed during summer modulated by biospheric exchange and vertical mixing, while no consistent pattern was found during winter.