Abstract
Continuous analysis of the 13C/12C ratio of atmospheric CO2 (δ13C–CO2) is a powerful tool to quantify CO2 flux strengths of the two major ecosystem processes assimilation and respiration. Traditional laboratory techniques such as isotope ratio mass spectrometry (IRMS) in combination with flask sampling are subject to technical limitations that do not allow to fully characterising variations of atmospheric δ13C–CO2 at all relevant timescales. In our study, we demonstrate the strength of Fourier transform infrared (FTIR) spectroscopy in combination with a PLS-based calibration strategy for online analysis of δ13C–CO2 in ambient air. The ability of the instrument to measure δ13C–CO2 was tested on a grassland field-site and compared with standard laboratory-based IRMS measurements made on field-collected flask samples. Both methods were in excellent agreement, with an average difference of 0.4‰ (n=81). Simultaneously, other important trace gases such as CO, N2O and CH4 were analysed by FTIR spectroscopy.
Acknowledgements
Kerstin Zeyer and Christoph Zellweger are acknowledged for CO2, N2O, CO and CH4 analysis of the multi-component standard gases. We thank Bela Tuzson for helpful discussion. The authors are grateful to Willi Brand and Michael Rothe from the Max Planck Institute for Biochemistry for δ13C–CO2 and analysis of the IRMS laboratory standards. We acknowledge E. Pieper from the Section Mechanical Engineering/Workshop and W. Knecht and R. Gross from the Section Electronics/Metrology for technical assistance. M.J. Zeeman, R.A. Werner and W. Eugster were supported by the Swiss National Science Foundation, grant 200021-105949.