Implication of weekly and diurnal 14C calibration on hourly estimates of 
CO-based fossil fuel CO2 at a moderately polluted site in southwestern Germany

Vogel, F. R.; Hammer, S.; Steinhof, A.; Kromer, B.; Levin, I.

doi:10.1111/j.1600-0889.2010.00477.x

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Implication of weekly and diurnal ¹⁴C calibration on hourly estimates of CO-based fossil fuel CO₂ at a moderately polluted site in southwestern Germany

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Steinhof, A.
Service Facility 14C Lab, Dr. A. Steinhof, Max Planck Institute for Biogeochemistry, Max Planck Society;

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http://dx.doi.org/10.1111/j.1600-0889.2010.00477.x
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Citation

Vogel, F. R., Hammer, S., Steinhof, A., Kromer, B., & Levin, I. (2010). Implication of weekly and diurnal ¹⁴C calibration on hourly estimates of CO-based fossil fuel CO₂ at a moderately polluted site in southwestern Germany. Tellus, Series B - Chemical and Physical Meteorology, 62(5), 512-520. doi:10.1111/j.1600-0889.2010.00477.x.

Cite as: https://hdl.handle.net/11858/00-001M-0000-000E-DB21-D

Abstract

A 7-year-long data set of integrated high-precision ¹⁴CO(2) observations combined with occasional hourly ¹⁴CO(2) flask data from the Heidelberg sampling site is presented. Heidelberg is located in the highly populated and industrialized upper Rhine valley in southwestern Germany. The ¹⁴CO(2) data are used in combination with hourly carbon monoxide (CO) observations to estimate regional hourly fossil fuel CO₂ (delta FFCO₂) mixing ratios. We investigate three different ¹⁴C calibration schemes to calculate delta FFCO₂: (1) the long-term median delta CO/delta FFCO₂ ratio of 14.6 ppb ppm-1 (mean: 15.5 +/- 5.6 ppb ppm-1), (2) individual (2-)week-long integrated delta CO/delta FFCO₂ ratios, which take into account the large week-to-week variability of +/- 5.6 ppb ppm-1 (1 Sigma; interquartile range: 5.5 ppb ppm-1), and (3) a calibration which also includes diurnal changes of the delta CO/delta FFCO₂ ratio. We show that in winter a diurnally changing delta CO/delta FFCO₂ ratio provides a much better agreement with the direct ¹⁴C-based hourly delta FFCO₂ estimates whereas summer values are not significantly improved with a diurnal calibration. Using integrated ¹⁴CO(2) samples to determine weekly mean delta CO/delta FFCO₂ ratios introduces a bias in the CO-based delta FFCO₂ estimates which can be corrected for with diurnal grab sample data. Altogether our ¹⁴C-calibrated CO-based method allows determining delta FFCO₂ at a semi-polluted site with a precision of approximately +/- 25%.