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Application and assessment of a membrane-based pCO2 sensor under field and laboratory conditions

Application and assessment of a membrane-based pCO2 sensor under field and laboratory conditions
Application and assessment of a membrane-based pCO2 sensor under field and laboratory conditions
The principle, application, and assessment of the membrane-based ProOceanus CO2-Pro sensor for partial pressure of CO2 (pCO2) are presented. The performance of the sensor is evaluated extensively under field and laboratory conditions by comparing the sensor outputs with direct measurements from calibrated pCO2 measuring systems and the thermodynamic carbonate calculation of pCO2 from discrete samples. Under stable laboratory condition, the sensor agreed with a calibrated water-air equilibrator system at –3.0 ± 4.4 ?atm during a 2-month intercomparison experiment. When applied in field deployments, the larger differences between measurements and the calculated pCO2 references (6.4 ± 12.3 ?atm on a ship of opportunity and 8.7 ± 14.1 ?atm on a mooring) are related not only to sensor error, but also to the uncertainties of the references and the comparison process, as well as changes in the working environments of the sensor. When corrected against references, the overall uncertainties of the sensor results are largely determined by those of the pCO2 references (± 2 and ± 8 ?atm for direct measurements and calculated pCO2, respectively). Our study suggests accuracy of the sensor can be affected by temperature fluctuations of the detector optical cell and calibration error. These problems have been addressed in more recent models of the instrument through improving detector temperature control and through using more accurate standard gases. Another interesting result in our laboratory test is the unexpected change in alkalinity which results in significant underestimation in the pCO2 calculation as compared to the direct measurement (up to 90 ?atm).
1541-5856
264-280
Jiang, Zong-Pei
801435b8-c2e5-476e-84c0-b49ef65ad382
Hydes, David J.
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Hartman, Sue E.
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Hartman, Mark C.
cdd63b60-f89a-4ef8-842d-7803f8213c18
Campbell, Jon M.
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Johnson, Bruce D.
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Schofield, Brian
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Turk, Daniela
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Wallace, Douglas
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Burt, William
d46bccf1-7e64-44e2-9570-82f8568cf344
Thomas, Helmuth
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Cosca, Cathy
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Feely, Richard
4e22724d-a6d0-498f-a43a-1188a6bead1a
Jiang, Zong-Pei
801435b8-c2e5-476e-84c0-b49ef65ad382
Hydes, David J.
ac7371d4-c2b9-4926-bb77-ce58480ecff7
Hartman, Sue E.
2f74a439-395a-4ee7-89a2-eff4cc8d9481
Hartman, Mark C.
cdd63b60-f89a-4ef8-842d-7803f8213c18
Campbell, Jon M.
ccdf3dec-f651-4d59-96d7-41859f78abe5
Johnson, Bruce D.
e2764c7d-0f44-42c6-83e5-9ada6325b3bb
Schofield, Brian
0991f10e-39b5-4b95-b45a-26ea2eca0ab2
Turk, Daniela
1611abe6-3f95-4652-91a1-6b826474c9f5
Wallace, Douglas
5e1d77e4-e9ef-4458-a76c-da9fa38f9b26
Burt, William
d46bccf1-7e64-44e2-9570-82f8568cf344
Thomas, Helmuth
8a133354-0648-4699-98a1-982a1c8264a2
Cosca, Cathy
26ca2413-397c-4f5e-b703-a795b20a6b19
Feely, Richard
4e22724d-a6d0-498f-a43a-1188a6bead1a

Jiang, Zong-Pei, Hydes, David J., Hartman, Sue E., Hartman, Mark C., Campbell, Jon M., Johnson, Bruce D., Schofield, Brian, Turk, Daniela, Wallace, Douglas, Burt, William, Thomas, Helmuth, Cosca, Cathy and Feely, Richard (2014) Application and assessment of a membrane-based pCO2 sensor under field and laboratory conditions. Limnology and Oceanography: Methods, 12, 264-280. (doi:10.4319/lom.2014.12.264).

Record type: Article

Abstract

The principle, application, and assessment of the membrane-based ProOceanus CO2-Pro sensor for partial pressure of CO2 (pCO2) are presented. The performance of the sensor is evaluated extensively under field and laboratory conditions by comparing the sensor outputs with direct measurements from calibrated pCO2 measuring systems and the thermodynamic carbonate calculation of pCO2 from discrete samples. Under stable laboratory condition, the sensor agreed with a calibrated water-air equilibrator system at –3.0 ± 4.4 ?atm during a 2-month intercomparison experiment. When applied in field deployments, the larger differences between measurements and the calculated pCO2 references (6.4 ± 12.3 ?atm on a ship of opportunity and 8.7 ± 14.1 ?atm on a mooring) are related not only to sensor error, but also to the uncertainties of the references and the comparison process, as well as changes in the working environments of the sensor. When corrected against references, the overall uncertainties of the sensor results are largely determined by those of the pCO2 references (± 2 and ± 8 ?atm for direct measurements and calculated pCO2, respectively). Our study suggests accuracy of the sensor can be affected by temperature fluctuations of the detector optical cell and calibration error. These problems have been addressed in more recent models of the instrument through improving detector temperature control and through using more accurate standard gases. Another interesting result in our laboratory test is the unexpected change in alkalinity which results in significant underestimation in the pCO2 calculation as compared to the direct measurement (up to 90 ?atm).

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LOM-13-10-0094_ZPJiang.pdf - Accepted Manuscript
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Accepted/In Press date: March 2014
Published date: April 2014
Organisations: Marine Biogeochemistry

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Local EPrints ID: 363267
URI: http://eprints.soton.ac.uk/id/eprint/363267
ISSN: 1541-5856
PURE UUID: 6e215a22-89c7-44ec-8e9c-c374870e0c98

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Date deposited: 19 Mar 2014 16:37
Last modified: 14 Mar 2024 16:21

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Contributors

Author: Zong-Pei Jiang
Author: David J. Hydes
Author: Sue E. Hartman
Author: Mark C. Hartman
Author: Jon M. Campbell
Author: Bruce D. Johnson
Author: Brian Schofield
Author: Daniela Turk
Author: Douglas Wallace
Author: William Burt
Author: Helmuth Thomas
Author: Cathy Cosca
Author: Richard Feely

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