• Economic and Environmental Geology
• /
• v.46 no.6
• /
• pp.495-508
• /
• 2013

Recently, stable isotopes (${\delta}^{18}O$ and ${\delta}D$) of water are increasingly analyzed using laser-based technologies. These methods have advantages over Isotope Ratio Mass Spectrometry (IRMS) in that they can be used for in-situ measurements and require much less maintenance and preparation work. Two types of laser-based methods are currently available, which have different analytical principles; OA-ICOS (off-axis integrated cavity output spectroscopy) and WS-CRDS (wavelength-scanned cavity ring-down spectroscopy). In the WS-CRDS instrument, water is vaporized at controlled environment and transferred to an optical cavity by nitrogen carrier gas, and stable isotopic compositions of water vapor are measured using the degree of absorbance of specific wavelengths and the ratios of attenuation time of the laser intensity with the sensitivity of ppb to tens of ppt level. In this study, we introduce the principle of the WS-CRDS technology and the performance results including stability and comparisons with Isotope Ratio Mass Spectrometry (IRMS) and suggest possible applications of various topics in isotope hydrology.

• Atmosphere
• /
• v.33 no.5
• /
• pp.549-560
• /
• 2023

This study evaluates three distinct observation methods, CRDS, OA-ICOS, and OF-CEAS, in greenhouse gas monitoring equipment for atmospheric CO₂ and CH₄ concentrations. The assessment encompasses fundamental performance, high-concentration measurement accuracy, calibration methods, and the impact of atmospheric humidity on measurement accuracy. Results indicate that within a range of approximately 500 ppm, all three devices demonstrate high accuracy and linearity. However, beyond 1000 ppm, CO₂ accuracy sharply declines (84%), emphasizing the need for caution when interpreting high-concentration CO₂ data. An analysis of calibration methods reveals that both CO₂ and CH₄ measurements achieve high accuracy and linearity through 1-point calibration, suggesting that multi-point calibration is not imperative for precision. In dynamic atmospheric conditions with significant CO₂ and CH₄ concentration variations, a 1-point calibration suffices for reliable data (99% accuracy). The evaluation of humidity impact demonstrates that humidity removal devices significantly reduce air moisture levels, yet this has a negligible effect on dry CO₂ concentrations (less than 0.5% relative error). All three observation method instruments, which have integrated humidity correction to calculate dry CO₂ concentrations, exhibit minor sensitivity to humidity removal devices, implying that additional removal devices may not be essential. Consequently, this study offers valuable insights for comparing data from different measurement devices and provides crucial information to consider in the operation of monitoring sites.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.23 no.1
• /
• pp.32-48
• /
• 2018

The mechanisms of $CH_4$ uptake into and release from the ocean are not well understood due mainly to complexity of the biogeochemical cycle and to lack of regional-scale and/or process-scale observations in the marine boundary layers. Without complete understanding of oceanic mechanisms to control the carbon balance and cycles on a various spatial and temporal scales, however, it is difficult to predict future perturbation of oceanic carbon levels and its influence on the global and regional climates. High frequency, high precision continuous measurements for carbon isotopic compositions from dissolved $CH_4$ in the surface ocean and marine atmosphere can provide additional information about the flux pathways and production/consumption processes occurring in the boundary of two large reservoirs. This paper introduces recent advances on optical instruments for real time $CH_4$ isotope analysis to diagnose potential applications for in situ, continuous measurements of carbon isotopic composition of dissolved $CH_4$. Commercially available, three laser absorption spectrometers - quantum cascade laser spectroscopy (QCLAS), off-axis integrated cavity output spectrometer (OA-ICOS), and cavity ring-down spectrometer (CRDS) are discussed in comparison with the conventional isotope ratio mass spectrometry (IRMS). Details of functioning and performance of a CRDS isotope instrument for atmospheric ${\delta}^{13}C-CH_4$ are also given, showing its capability to detect localized methane emission sources.

• Economic and Environmental Geology
• /
• v.50 no.6
• /
• pp.537-544
• /
• 2017

Stable carbon isotope ratio of carbon dioxide (${\delta}^{13}C_{CO2}$) is used as an important indicator in the researches for global climate change and carbon capture and sequestration technology. The ${\delta}^{13}C$ value has been usually analyzed with Isotope Ratio Mass Spectrometer (IRMS). Recently, the use of Laser Absorption Spectrometry (LAS) is increasing because of the cost efficiency and field applicability. The purpose of this study was to suggest practical procedures to prepare laboratory reference gases for ${\delta}^{13}C_{CO2}$ analysis using LAS. $CO_2$ gas was adjusted to have the concentrations within the analytical range. Then, the concentration of $CO_2$ was assessed in a lab approved by the Korea Laboratory Accreditation Scheme and the ${\delta}^{13}C_{CO2}$ value was measured by IRMS. When the instrument ran over 12 hours, the ${\delta}^{13}C$ values were drifted up to ${\pm}10$‰ if the concentration of $CO_2$ was shifted up to 1.0% of relative standard deviation. Therefore, periodical investigation of analytical suitability and correction should be conducted. Because ${\delta}^{13}C_{CO2}$ showed the dependency on $CO_2$ concentration, we suggested the equation for calibrating the concentration effect. After calibration, ${\delta}^{13}C_{CO2}$ was well matched with the result of IRMS within ${\pm}0.52$‰.