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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 CarboCount CH: Quantifying greenhouse gas fluxes and their sensitivity to climate variations: A case study in Central Europe and Switzerland
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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

URL http://doi.org/10.5194/acp-17-10753-2017
Type of Open Access Publisher (Gold Open Access)

Abstract

Fossil fuel CO2 (CO2ff ) is the major contributor of anthropogenic CO2 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, CO2 , CH4 , and H2O at five different heights at the Beromünster tall tower, Switzerland. Air samples for radiocarbon (Δ14CO2 ) 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 CO2 emissions from nearby nuclear power plants (NPPs), which have been simulated with the Lagrangian transport model FLEXPART-COSMO. The 14 CO2 emissions from NPPs offset the depletion in 14C by fossil fuel emissions, resulting in an underestimation of the fossil fuel component in atmospheric CO2 by about 16 %. An average observed ratio (RCO ) 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 CO2 mole fractions. The wintertime RCO estimate of 12.5 ± 3.3 is about 30 % higher than the wintertime ratio between in situ measured CO and CO2 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 ΔCO2 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 CO2 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.
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