FDM based OA-ICOS for high accuracy 13C quantification in gaseous CO2

Abstract

The wide-range applications of isotope analysis make isotope measurement approaches under attentive focus. Off-axis integrated cavity output spectroscopy technology (OA-ICOS) is the most advanced isotope analysis method; however, further studies are still needed to avoid signal noise and improve accuracy. Zero-phase low pass filtering multivariate Fourier Decomposition Method (FDM) was applied for data analysis in the present study, which has its unique advantage to fix up rapid but seasonal changes for nonlinear and non-stationary time series data. In the present study, δ13C content in gaseous CO2 sample were measured by OA-ICOS at ambient temperature. The experimental data treated by FDM showed less signal fluctuant and clearer value change tendency than what showed in raw data, whereas the data density kept same with that of raw data. In the meantime, the experimental results suggested that it is flexible to decide the variance explanation rate by simply change the order of an FDM filter. This approach meets up with the requirements of different practical application scenarios of isotope analysis, which enhances the feasibility for OA-ICOS application in real-time environmental monitoring field.

Spectroscopic techniques to analyze stable carbon isotopic compositions of carbon dioxide, methane and volatile organic compounds

“…Fourier transform infrared spectroscopy (FTIR) provides an alternative infrared spectroscopy technique to laser spectroscopy. 26,53 The system consists of light source, interferometer, sample cell, detector, and data processing system, and the most favorable interferometer is a Michelson interferometer. 26,29 FTIR uses broadband infrared radiation from a blackbody light source, which covers the entire infrared spectrum, simultaneously.…”

“…26,53 The system consists of light source, interferometer, sample cell, detector, and data processing system, and the most favorable interferometer is a Michelson interferometer. 26,29 FTIR uses broadband infrared radiation from a blackbody light source, which covers the entire infrared spectrum, simultaneously. 26 The light emitted by this light source is modulated using an interferometer to produce an interferometer beam.…”

“…26,29 FTIR uses broadband infrared radiation from a blackbody light source, which covers the entire infrared spectrum, simultaneously. 26 The light emitted by this light source is modulated using an interferometer to produce an interferometer beam. When the beam passes through the sample, it is absorbed or scattered (i.e.…”

“…3). 26,29,53,54 Aer that, the interference signal containing spectral information reaches the detector, which converts the interference signal into an electrical signal, electrical signals are converted into spectral signals through Fourier transform. 26 Compared with the laser light source, even though the brightness of the blackbody light source is lower, it is still advantageous to measure the entire spectrum at one time and to operate in mid-infrared region where absorption bands are stronger than near-infrared region.…”

“…26,29,53,54 Aer that, the interference signal containing spectral information reaches the detector, which converts the interference signal into an electrical signal, electrical signals are converted into spectral signals through Fourier transform. 26 Compared with the laser light source, even though the brightness of the blackbody light source is lower, it is still advantageous to measure the entire spectrum at one time and to operate in mid-infrared region where absorption bands are stronger than near-infrared region. 53 An in situ tracking gas analyzer based on FTIR spectroscopy that is capable of simultaneous and continuous measurements of carbon dioxide (CO 2 ), methane (CH 4 ), carbon monoxide (CO), and nitrous oxide (N 2 O) in air as well as carbon CSIA with high precision and accuracy, was described in detail in the previous study.…”