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Proceedings Paper

Development of a prototype for dissolved CO2 rapid measurement and preliminary tests
Author(s): Meng Li; Jinjia Guo; Zhihao Zhang; Zhao Luo; Chuan Qin; Ronger Zheng
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Paper Abstract

The measurements of dissolved CO2 in seawater is of great significance for the study of global carbon cycle. At present, the commercial sensors used for dissolved CO2 measurements are mostly equipped with permeable membranes for the purpose of gas-liquid separation, with the advantages of easy operation, low cost, etc.. However, most of these devices measure CO2 after reaching gas equilibrium, so it takes a few minutes to respond, which limited its applications in rapid measurements. In this paper, a set of prototype was developed for the rapid measurements of dissolved CO2. The system was built basing the direct absorption TDLAS. To detect the CO2 absorption line located at 4991.26 cm-1 , a fiber-coupled DFB laser operating at 2004 nm was selected as the light source. A Herriott type multi-pass cavity with an effective optical path length of 10 m and an inner volume of 90 mL was used for absorption measurements. A detection limit of 26 μatm can be obtained with this compact cavity. To realize the rapid measurements of dissolved CO2, a degasser with high degassing rate was necessary. A hollow fiber membrane with a large permeable area used in this paper can achieve degassing rate up to 2.88 kPa/min. Benefitted from the high degassing rate of the degasser and high sensitivity of the compact TDLAS system, a rapid measurement of dissolved CO2 in water can be achieved within 1s time, and the response time of the prototype when the dissolved CO2 concentration changed abruptly in actual measurement was 15 s. To evaluate the performance of the prototype, comparison measurements were carried out with a commercial mass spectrometer. The dissolved CO2 in both seawater and tap-water was measured, and the experimental results showed good consistent trends with R2 of 0.973 and 0.931. The experimental results proved the feasibility of dissolved CO2 rapid measurement. In the near future, more system evaluation experiments will be carried out and the system will be further optimized focusing on the underwater in-situ detection system.

Paper Details

Date Published: 24 October 2017
PDF: 6 pages
Proc. SPIE 10461, AOPC 2017: Optical Spectroscopy and Imaging, 104611D (24 October 2017);
Show Author Affiliations
Meng Li, Ocean Univ. of China (China)
Jinjia Guo, Ocean Univ. of China (China)
Zhihao Zhang, Ocean Univ. of China (China)
Zhao Luo, Ocean Univ. of China (China)
Chuan Qin, Ocean Univ. of China (China)
Ronger Zheng, Ocean Univ. of China (China)

Published in SPIE Proceedings Vol. 10461:
AOPC 2017: Optical Spectroscopy and Imaging
Jin Yu; Zhe Wang; Wei Hang; Bing Zhao; Xiandeng Hou; Mengxia Xie; Tsutomu Shimura, Editor(s)

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