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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 9, issue 11
Atmos. Meas. Tech., 9, 5293-5314, 2016
https://doi.org/10.5194/amt-9-5293-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Meas. Tech., 9, 5293-5314, 2016
https://doi.org/10.5194/amt-9-5293-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 01 Nov 2016

Research article | 01 Nov 2016

Continuous and high-precision atmospheric concentration measurements of COS, CO2, CO and H2O using a quantum cascade laser spectrometer (QCLS)

Linda M. J. Kooijmans1, Nelly A. M. Uitslag1, Mark S. Zahniser2, David D. Nelson2, Stephen A. Montzka3, and Huilin Chen1,4 Linda M. J. Kooijmans et al.
  • 1Centre for Isotope Research (CIO), University of Groningen, Groningen, the Netherlands
  • 2Aerodyne Research Inc., MA, USA
  • 3NOAA Earth System Research Laboratory, Boulder, CO, USA
  • 4Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, CO, USA

Abstract. Carbonyl sulfide (COS) has been suggested as a useful tracer for gross primary production as it is taken up by plants in a similar way as CO2. To explore and verify the application of this novel tracer, it is highly desired to develop the ability to perform continuous and high-precision in situ atmospheric measurements of COS and CO2. In this study we have tested a quantum cascade laser spectrometer (QCLS) for its suitability to obtain accurate and high-precision measurements of COS and CO2. The instrument is capable of simultaneously measuring COS, CO2, CO and H2O after including a weak CO absorption line in the extended wavelength range. An optimal background and calibration strategy was developed based on laboratory tests to ensure accurate field measurements. We have derived water vapor correction factors based on a set of laboratory experiments and found that for COS the interference associated with a water absorption line can dominate over the effect of dilution. This interference can be solved mathematically by fitting the COS spectral line separately from the H2O spectral line. Furthermore, we improved the temperature stability of the QCLS by isolating it in an enclosed box and actively cooling its electronics with the same thermoelectric chiller used to cool the laser. The QCLS was deployed at the Lutjewad atmospheric monitoring station (60m; 6°21′E, 53°24′N; 1ma.s.l.) in the Netherlands from July 2014 to April 2015. The QCLS measurements of independent working standards while deployed in the field showed a mean difference with the assigned cylinder value within 3.3ppt COS, 0.05ppm for CO2 and 1.7ppb for CO over a period of 35 days. The different contributions to uncertainty in measurements of COS, CO2 and CO were summarized and the overall uncertainty was determined to be 7.5ppt for COS, 0.23ppm for CO2 and 3.3ppb for CO for 1-minute data. A comparison of in situ QCLS measurements with those from concurrently filled flasks that were subsequently measured by the QCLS showed a difference of −9.7±4.6ppt for COS. Comparison of the QCLS with a cavity ring-down spectrometer showed a difference of 0.12±0.77ppm for CO2 and −0.9±3.8ppb for CO.

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The accuracy of carbon models, used for the prediction of global climate change, is limited by the knowledge of the uptake of carbon by plants through photosynthesis. Carbonyl sulfide (COS) has been suggested as a tracer for this process. To be able to further explore and verify the application of this novel tracer we have tested a laser spectrometer for its suitability to obtain accurate and high precision measurements of COS and CO2 with both laboratory experiments and field measurements.
The accuracy of carbon models, used for the prediction of global climate change, is limited by...
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