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Volume 16, issue 15 | Copyright
Atmos. Chem. Phys., 16, 9935-9949, 2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 08 Aug 2016

Research article | 08 Aug 2016

Intercomparison of in situ NDIR and column FTIR measurements of CO2 at Jungfraujoch

Michael F. Schibig1,a, Emmanuel Mahieu2, Stephan Henne3, Bernard Lejeune2, and Markus C. Leuenberger1 Michael F. Schibig et al.
  • 1Climate and Environmental Physics, Physics Institute and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
  • 2Institut d'Astrophysique et de Géophysique, Université de Liège, Liège, Belgium
  • 3Empa, Swiss Federal Laboratories for Materials Testing and Research, Dübendorf, Switzerland
  • anow at: National Oceanic and Atmospheric Administration, Earth System Research Laboratory, Boulder, CO 80305, USA

Abstract. We compare two CO2 time series measured at the High Alpine Research Station Jungfraujoch, Switzerland (3580ma.s.l.), in the period from 2005 to 2013 with an in situ surface measurement system using a nondispersive infrared analyzer (NDIR) and a ground-based remote sensing system using solar absorption Fourier transform infrared (FTIR) spectrometry. Although the two data sets show an absolute shift of about 13ppm, the slopes of the annual CO2 increase are in good agreement within their uncertainties. They are 2.04±0.07 and 1.97±0.05ppmyr−1 for the FTIR and the NDIR systems, respectively. The seasonality of the FTIR and the NDIR systems is 4.46±1.11 and 10.10±0.73ppm, respectively. The difference is caused by a dampening of the CO2 signal with increasing altitude due to mixing processes. Whereas the minima of both data series occur in the middle of August, the maxima of the two data sets differ by about 10 weeks; the maximum of the FTIR measurements is in the middle of January, and the maximum of the NDIR measurements is found at the end of March. Sensitivity analyses revealed that the air masses measured by the NDIR system at the surface of Jungfraujoch are mainly influenced by central Europe, whereas the air masses measured by the FTIR system in the column above Jungfraujoch are influenced by regions as far west as the Caribbean and the USA.

The correlation between the hourly averaged CO2 values of the NDIR system and the individual FTIR CO2 measurements is 0.820, which is very encouraging given the largely different sampling volumes. Further correlation analyses showed, that the correlation is mainly driven by the annual CO2 increase and to a lesser degree by the seasonality. Both systems are suitable to monitor the long-term CO2 increase, because this signal is represented in the whole atmosphere due to mixing.

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Two CO2 time series measured at the High Alpine Research Station Jungfraujoch, Switzerland (3580 m a.s.l.), in the period from 2005 to 2013 were compared. One data set was measured in situ whereas the other data set was measured in the column above Jungfraujoch. The trends of the column integrated and the in situ data set are in good agreement, the amplitude of the in situ data set is ca. two times the amplitude of the column integrated data set, because it is closer to the sources and sinks.
Two CO2 time series measured at the High Alpine Research Station Jungfraujoch, Switzerland...