Impact of H2O on atmospheric CH4 measurement in near -infrared absorption spectroscopy

A distributed-feedback (DFB) diode laser based near-infrared absorption spectrometer was used to study H2O broadening coefficients for methane (CH4) transitions at 1.653 mu m, which contains well-characterized and relatively isolated transitions of appropriate line strengths for sensitive atmospheric CH4 detection. The influence of H2O broadening on R-3 transitions of CH4 at 6046.9 cm(-1) was experimentally investigated in detail. The results indicate that H2O broadening coefficients are approximately 1.3 times higher than the corresponding air-broadening parameters. Based on the measured H2O induced broadening coefficients, the influence of H2O onactual measurement of atmospheric CH4 in tunable diode laser absorption spectroscopy was theoretically and experimentally discussed and compared, and a good agreement was obtained. The experimental results proved that the difference between air- and H2O-broadenings cannot be neglected for high precision gas concentration measurement, especially in a highly humid environment. (C) 2020 Elsevier B.V. All rights reserved.