Pressure-Dependent Detection of Carbon Monoxide Employing Wavelength Modulation Spectroscopy Using a Herriott-Type Cell.
Wavelength modulation spectroscopy (WMS) combined with a multipass absorption cell has been used to measure a weak absorption line of carbon monoxide (CO) at 1.578 µm. A 0.95m Herriott-type cell provides an effective absorption path length of 55.1 m. The WMS signals from the first and second harmonic output of a lock-in amplifier (WMS-1 f and 2 f, respectively) agree with the Beer-Lambert law, especially at low concentrations. After boxcar averaging, the minimum detection limit achieved is 4.3 ppm for a measurement time of 0.125 s. The corresponding normalized detection limit is 84 ppm m Hz-1/2. If the integrated time is increased to 88 s, the minimum detectable limit of CO can reach to 0.29 ppm based on an Allan variation analysis. The pressure-dependent relationship is validated after accounting for the pressure factor in data processing. Finally, a linear correlation between the WMS-2 f amplitudes and gas concentrations is obtained at concentration ratios less than 15.5%, and the accuracy is better than 92% at total pressure less than 62.7 Torr.
1 Department of Physics, School of Applied Science, Taiyuan University of Science and Technology, Taiyuan, China.
Chuanliang
C
Li
1 Department of Physics, School of Applied Science, Taiyuan University of Science and Technology, Taiyuan, China.
Yingfa
Y
Wu
1 Department of Physics, School of Applied Science, Taiyuan University of Science and Technology, Taiyuan, China.
Xuanbing
X
Qiu
1 Department of Physics, School of Applied Science, Taiyuan University of Science and Technology, Taiyuan, China.
Jilin
J
Wei
2 State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, China.
Lunhua
L
Deng
D000393:Air Pollutants / Q000032:analysis*; D002248:Carbon Monoxide / Q000032:analysis*; D004867:Equipment Design; D057230:Limit of Detection; D016014:Linear Models; D011312:Pressure; D015203:Reproducibility of Results; D019265:Spectroscopy, Near-Infrared / Q000379:methods*
D000393:Air Pollutants; D002248:Carbon Monoxide
CO; Carbon monoxide; Herriot cell; WMS; near-infrared spectroscopy; pressure-dependent; wavelength modulation spectroscopy