Impact of H2O broadening effect on atmospheric CO and N2O detection near 4.57 μm

Abstract

A tunable quantum cascade laser spectrometer (QCLS) was used to study H2O broadening coefficients for CO and N2O transitions at 4.57μm region, which contains well-characterized and relatively isolated transitions of appropriate line strengths for sensitive gas detection. The influence of H2O broadening effect on CO R(11) and N2O P(38e) transitions at 2186.639cm−1 and 2187.099cm−1, respectively, was detailed investigated. Our measurements indicate that H2O broadening coefficients are 1.8 and 1.9 times higher than the corresponding air-broadening parameters, respectively. Based on the experimental data, our simulation confirmed that the WMS-2f shapes of CO and N2O lines will be significantly affected by variations of the water vapor mixing ratio, while no significant dependence on target concentration, and prove that the difference between air- and H2O-broadenings thus cannot be neglected if one wants to measure gas concentrations in a high humid environment with a sub-percent precision.