02 Sep 2020
02 Sep 2020
Technical note: CO2 is not like CH4 – limits of and corrections to the headspace method to analyse pCO2 in water
- 1Department Lake Research, Helmholtz Centre for Environmental Research -- UFZ, Brückstrasse 3a, 39114 Magdeburg, Germany
- 2Département des Sciences Biologiques, Université du Québec à Montréal, Montréal, Québec, Canada
- 3Catalan Institute for Water Research (ICRA), Emili Grahit 101, 17003 Girona, Spain
- 4University of Girona, Girona, Spain
- 1Department Lake Research, Helmholtz Centre for Environmental Research -- UFZ, Brückstrasse 3a, 39114 Magdeburg, Germany
- 2Département des Sciences Biologiques, Université du Québec à Montréal, Montréal, Québec, Canada
- 3Catalan Institute for Water Research (ICRA), Emili Grahit 101, 17003 Girona, Spain
- 4University of Girona, Girona, Spain
Abstract. Headspace analysis of CO2 frequently has been used to quantify the concentration of CO2 in freshwater. According to basic chemical theory, not considering chemical equilibration of the carbonate system in the sample vials will result in a systematic error. In this paper we provide a method to quantify the potential error resulting from simple application of Henry's law to headspace CO2 samples. By analysing the potential error for different types of water and experimental conditions we conclude that the error incurred by headspace analysis of CO2 is less than 5 % for samples with pH < 7.5. However, the simple headspace calculations can lead to high error (up to −800 %) or even impossible negative values in highly undersaturated samples equilibrated with ambient air, unless the shift in carbonate equilibrium is explicitly considered. The precision of the method can be improved by lowering the headspace ratio and/or the equilibration temperature and use of a CO2 free gas for headspace creation. We provide a direct method to correct CO2 headspace results using separately measured alkalinity.
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Matthias Koschorreck et al.


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RC1: 'review', Anonymous Referee #1, 03 Sep 2020
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AC1: 'response to reviwer 1', Matthias Koschorreck, 04 Sep 2020
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AC1: 'response to reviwer 1', Matthias Koschorreck, 04 Sep 2020
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RC2: 'Review of „Technical note: CO2 is not like CH4 – limits of and corrections to the headspace method to analyse pCO2 in water” by Koschorreck et al.', Anonymous Referee #2, 18 Sep 2020
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AC2: 'fast reply to reviewr 2', Matthias Koschorreck, 13 Oct 2020
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AC2: 'fast reply to reviewr 2', Matthias Koschorreck, 13 Oct 2020
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SC1: 'Comment', Andreas Lorke, 11 Oct 2020
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SC2: 'Comment', Matt Trentman, 15 Oct 2020
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AC3: 'Short reply to the comment by Trentman et al.', Matthias Koschorreck, 06 Nov 2020
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AC3: 'Short reply to the comment by Trentman et al.', Matthias Koschorreck, 06 Nov 2020


-
RC1: 'review', Anonymous Referee #1, 03 Sep 2020
-
AC1: 'response to reviwer 1', Matthias Koschorreck, 04 Sep 2020
-
AC1: 'response to reviwer 1', Matthias Koschorreck, 04 Sep 2020
-
RC2: 'Review of „Technical note: CO2 is not like CH4 – limits of and corrections to the headspace method to analyse pCO2 in water” by Koschorreck et al.', Anonymous Referee #2, 18 Sep 2020
-
AC2: 'fast reply to reviewr 2', Matthias Koschorreck, 13 Oct 2020
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AC2: 'fast reply to reviewr 2', Matthias Koschorreck, 13 Oct 2020
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SC1: 'Comment', Andreas Lorke, 11 Oct 2020
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SC2: 'Comment', Matt Trentman, 15 Oct 2020
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AC3: 'Short reply to the comment by Trentman et al.', Matthias Koschorreck, 06 Nov 2020
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AC3: 'Short reply to the comment by Trentman et al.', Matthias Koschorreck, 06 Nov 2020
Matthias Koschorreck et al.
Matthias Koschorreck et al.
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