A Portable Tunable Diode Laser Absorption Spectroscopy System for Dissolved CO2 Detection Using a High-Efficiency Headspace Equilibrator

Continuous observation of aquatic pCO2  at the ocean surface, with a sensitive response time and high spatiotemporal resolution, is essential for research into the carbon biogeochemical cycle. In this work, a portable tunable diode laser absorption spectroscopy (TDLAS) system for dissolved CO2 detec...

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Published inSensors (Basel, Switzerland) Vol. 21; no. 5; p. 1723
Main Authors Zhang, Zhihao, Li, Meng, Guo, Jinjia, Du, Baolu, Zheng, Ronger
Format Journal Article
LanguageEnglish
Published Basel MDPI AG 02.03.2021
MDPI
Subjects
Absorption spectroscopy
Atmosphere
Biogeochemistry
Carbon cycle
Carbon dioxide
Design
dissolved CO2
Empirical equations
Gases
headspace equilibrator
Lasers
Ocean surface
portable system
Response time
Seawater
Semiconductor lasers
Surface chemistry
TDLAS
Time measurement
Tunable lasers
underway measurement
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Summary:Continuous observation of aquatic pCO2  at the ocean surface, with a sensitive response time and high spatiotemporal resolution, is essential for research into the carbon biogeochemical cycle. In this work, a portable tunable diode laser absorption spectroscopy (TDLAS) system for dissolved CO2 detection in surface seawater, coupled with a home-made headspace equilibrator, allowing real time underway measurements, is described. Both the optical detection part and sample extraction part were integrated together into a compact chamber. An empirical equation suitable for this system was acquired, which can convert the concentration from the gas-phase to the aqueous-phase. A monitoring precision of 0.5% was obtained with time-series measurement, and the detection limits of 2.3 ppmv and 0.1 ppmv were determined with 1 s and 128 s averaging time, respectively. Sampling device used in this work was ameliorated so that the response time of system reduced by about 50% compared to the traditional ‘shower head’ system. The fast response time reached the order of 41 s when the final concentration span was 3079 ppmv. For1902 ppmv, this figure was as short as 20 s. Finally, a field underway measurement campaign was carried out and the results were briefly analyzed. Our work proved the feasibility of the TDLAS system for dissolved CO2 rapid detection.
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ISSN:1424-8220
1424-8220
DOI:10.3390/s21051723