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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 | Copyright
Atmos. Meas. Tech., 9, 5265-5279, 2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 31 Oct 2016

Research article | 31 Oct 2016

A versatile, refrigerant- and cryogen-free cryofocusing–thermodesorption unit for preconcentration of traces gases in air

Florian Obersteiner1, Harald Bönisch2, Timo Keber1, Simon O'Doherty3, and Andreas Engel1 Florian Obersteiner et al.
  • 1Institute for Atmospheric and Environmental Science, Goethe University Frankfurt, Frankfurt, Germany
  • 2Institute of Meteorology and Climate Research, KIT, Karlsruhe, Germany
  • 3School of Chemistry, University of Bristol, Bristol, UK

Abstract. We present a compact and versatile cryofocusing–thermodesorption unit, which we developed for quantitative analysis of halogenated trace gases in ambient air. Possible applications include aircraft-based in situ measurements, in situ monitoring and laboratory operation for the analysis of flask samples. Analytes are trapped on adsorptive material cooled by a Stirling cooler to low temperatures (e.g. −80°C) and subsequently desorbed by rapid heating of the adsorptive material (e.g. +200°C). The set-up involves neither the exchange of adsorption tubes nor any further condensation or refocusing steps. No moving parts are used that would require vacuum insulation. This allows for a simple and robust design. Reliable operation is ensured by the Stirling cooler, which neither contains a liquid refrigerant nor requires refilling a cryogen. At the same time, it allows for significantly lower adsorption temperatures compared to commonly used Peltier elements. We use gas chromatography – mass spectrometry (GC–MS) for separation and detection of the preconcentrated analytes after splitless injection. A substance boiling point range of approximately −80 to +150°C and a substance mixing ratio range of less than 1ppt (pmolmol−1) to more than 500ppt in preconcentrated sample volumes of 0.1 to 10L of ambient air is covered, depending on the application and its analytical demands. We present the instrumental design of the preconcentration unit and demonstrate capabilities and performance through the examination of analyte breakthrough during adsorption, repeatability of desorption and analyte residues in blank tests. Examples of application are taken from the analysis of flask samples collected at Mace Head Atmospheric Research Station in Ireland using our laboratory GC–MS instruments and by data obtained during a research flight with our in situ aircraft instrument GhOST-MS (Gas chromatograph for the Observation of Tracers – coupled with a Mass Spectrometer).

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Short summary
The analysis of trace gases in ambient air requires a preconcentration technique, in many cases to make the species of interest detectable and quantifiable. In this paper, such a preconcentration set-up is presented. Target species are trapped on adsorptive material cooled by a Stirling cooler which allows for a very low adsorption temperature but only requires electrical power. A simple and lightweight mechanical design guarantees very good suitability for remote-site field operation.
The analysis of trace gases in ambient air requires a preconcentration technique, in many cases...