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

Abstract

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.

Volatile Organic Compounds (VOCs) in Soil: Transport Mechanisms, Monitoring, and Removal by Biochar-Modified Capping Layer

“…In addition, the detection and control of malodorous gases remain a huge challenge due to the complexity and low concentration of the pollutant gases and their susceptibility to weather conditions in open-air environments. Laser spectroscopy techniques currently include tunable diode laser absorption spectroscopy (TDLAS) and photoacoustic spectroscopy (PAS), which have been widely employed in atmospheric environmental monitoring, industrial pollution monitoring, medical diagnostics, scientific research, and other fields [63][64][65]. Among them, TDLAS combines with wavelength modulation, frequency modulation, and other techniques to greatly improve the signal-to-noise ratio, and the system sensitivity can reach the order of ppmv or even ppbv.…”

Portable TDLAS Sensor for Online Monitoring of CO2 and H2O Using a Miniaturized Multi-Pass Cell

“…Cavity-ring down spectroscopy (CRDS) and off-axis integrated cavity output spectroscopy (OA-ICOS) have also been increasingly applied for the continuous monitoring of atmospheric CO 2 , CH 4 , and H 2 O [ 8 , 9 , 10 , 11 , 12 , 13 ]. Although CRDS and OA-ICOS sensors have high sensitivity, they require relatively complex setups with laser frequency locking to longitudinal cavity resonances [ 14 ]. Tunable diode laser absorption spectroscopy (TDLAS) also has advantages, such as high sensitivity, high selectivity, and fast response [ 15 , 16 , 17 ].…”

“…Luo et al used a laser controller (Arroyo 6305), data acquisition card (NI 9223), and function generator (RIGOL 4102) to measure gas temperature in a LabVIEW-based TDLAS system [ 27 ]. Zhang et al used a commercial laser controller (CLD1015, Thorlabs), lock-in amplifier (LIA-MV-200-H, FEMTO Messtechnik GmbH, Berlin, Germany), and industrial computer (PCM-3365, Advantech Technology, China) to measure CO 2 using a TDLAS system [ 14 ]. Chang et al developed an oxygen detection system using a laptop equipped with a DAQ card (USB-6211;NI) and a LabVIEW software platform [ 28 ].…”

Research on the Seed Respiration CO2 Detection System Based on TDLAS Technology

“…TDLAS has the characteristics of high sensitivity and high resolution and has been widely used in trace gas detection [10][11][12][13][14]. Many scholars at home and abroad have conducted research on TDLAS technology in the CO 2 concentration detection method and detection sensitivity [15][16][17][18][19]. TDLAS detection methods mainly include WMS and direct absorption spectroscopy.…”