Gas concentration measurement by optical similitude absorption spectroscopy: methodology and experimental...

Area of Science:

• Spectroscopy
• Analytical Chemistry
• Environmental Science

Background:

• Traditional gas concentration measurements often require calibration cells.
• Light-absorption spectroscopy is sensitive to molecular absorption lines.
• Broad light source spectra can complicate spectral analysis.

Purpose of the Study:

• To introduce a new gas concentration measurement technique: Optical Similitude Absorption Spectroscopy (OSAS).
• To develop a robust inversion methodology for spectrally-integrated differential absorption measurements.
• To demonstrate the application and effectiveness of OSAS in laboratory settings.

Main Methods:

• Developed OSAS, a method utilizing spectral similitude between light source and gas absorption.
• Implemented a Newton-Raphson algorithm for robust spectral data inversion.
• Validated OSAS using methane absorption bands and compared with existing spectroscopic arrangements.

Main Results:

• OSAS successfully retrieves gas concentration from spectrally-integrated differential absorption.
• Demonstrated laboratory application on methane (2ν₃ band, 1.66 µm) with Allan variance analysis.
• OSAS proved effective in non-dispersive infra-red and optical correlation spectroscopy setups.

Conclusions:

• OSAS offers a calibration-cell-free method for gas concentration retrieval.
• The technique shows promise for atmospheric gas pollution and greenhouse gas monitoring.
• OSAS provides a novel approach for analyzing broad spectral absorption features.