Development of a cavity ring-down spectrometer toward multi-species composition

Area of Science:

• Spectroscopy
• Environmental Science
• Analytical Chemistry

Background:

• Air pollution monitoring requires sensitive detection of key molecules.
• Cavity Ring-Down Spectroscopy (CRDS) offers high sensitivity for gas analysis.
• Existing CRDS systems may have limitations in wavelength coverage or calibration.

Purpose of the Study:

• To develop and demonstrate a versatile CRDS for detecting air pollutants.
• To validate a calibration-free, SI-traceable post-processing method for gas analysis.
• To explore future applications in heterogeneous catalysis research.

Main Methods:

• Development of a CRDS system utilizing custom mirrors (99.99% reflectivity) for broad wavelength coverage (1.52–1.80 µm).
• Detection of ro-vibrational transitions of nitrogen oxide (NO) at 1.79 µm and carbon monoxide (CO) at 1.58 µm.
• Application of a post-processing procedure for determining molar fractions in multi-species gas mixtures.

Main Results:

• Achieved a minimum detectable absorbance of 1.1 × 10-10 cm-1 with a 1.2 s integration time.
• Successfully detected NO transitions at 1.79 µm and CO2/water vapor in ambient air at 1.58 µm.
• Demonstrated the calibration-free and SI-traceable nature of the post-processing method for gas mixture analysis.

Conclusions:

• The developed CRDS is highly sensitive and versatile for air pollution monitoring.
• The calibration-free post-processing method is effective for multi-species gas analysis.
• The CRDS system holds promise for future studies in heterogeneous catalysis and reaction monitoring.