An open-path sensor for simultaneous atmospheric pressure detection of CO and CH4 around 2.33 μm

A compact open-path sensor for simultaneous atmospheric pressure detection of trace gases carbon monoxide (CO) and methane (CH4) has been developed by using a single-mode, distribution feedback (DFB) laser operating at similar to 2.33 mu m. A novel spectral interference eliminating approach based on second harmonic wavelength modulation spectroscopy (WMS) detection technique and an approximation method was adopted to solve the problem of interference between adjacent spectral absorption lines at atmospheric pressure and to increase the detection sensitivity and resolution. The relative concentration error of CO was calculated to be less than +/-3.17%, and the detection limit of 0.58 parts per million by volume (ppmv) for CO and 0.4 ppmv for CH4 was achieved at 1-s averaging time, which proves the effectiveness of the proposed approach. A one-week field continuous measurement was performed to demonstrate the stability of the reported sensor system.