Intercomparison of in situ NDIR and column FTIR measurements of CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; at Jungfraujoch

Michael F Schibig,Emmanuel Mahieu,Stephan Henne,Markus C Leuenberger,Bernard Lejeune

doi:10.5194/acp-16-9935-2016

Abstract

Abstract. We compare 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 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 13 ppm, the slopes of the annual CO2 increase are in good agreement within their uncertainties. They are 2.04 ± 0.07 and 1.97 ± 0.05 ppm yr−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 ± 0.73 ppm, 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.

Highlights

CO2 is the most important anthropogenic greenhouse gas, with a large contribution to the greenhouse effect (Arrhenius, 1896) and an additional radiative forcing of the atmosphere currently evaluated at 1.68 W m−2 (IPCC, 2013)
The strength of the forcing depends on its atmospheric mole fraction, which is ruled by the processes of the carbon cycle as well as by anthropogenic CO2 emissions from fossil fuel combustion and land use change
The Fourier transform infrared (FTIR) slope is 2.04 ± 0.07 ppm yr−1 and the nondispersive infrared analyzer (NDIR) data set shows a slope of 1.97 ± 0.05 ppm yr−1, so they are equal within their uncertainties (Fig. 4)

Summary

Introduction

CO2 is the most important anthropogenic greenhouse gas, with a large contribution to the greenhouse effect (Arrhenius, 1896) and an additional radiative forcing of the atmosphere currently evaluated at 1.68 W m−2 (IPCC, 2013). The strength of the forcing depends on its atmospheric mole fraction, which is ruled by the processes of the carbon cycle as well as by anthropogenic CO2 emissions from fossil fuel combustion and land use change. The major reservoirs of the carbon cycle besides the lithosphere are the soils, the ocean, the biosphere and the atmosphere, where the latter is acting as the main link between the biosphere and the ocean. The processes coupling the biosphere with the atmosphere are photosynthesis, where CO2 is taken up by plants, and respiration, where CO2 is released back to the atmosphere. Photosynthesis and respiration are mainly driven by climatic conditions of the envi-

Methods

Results

Conclusion