Methane-in-air standards measured using a 1.65 μm frequency-stabilized cavity ring-down spectrometer

Frequency-stabilized cavity ring-down absorption spectrometry (FS-CRDS) with single-mode excitation using a tunable continuous-wave diode laser is being developed to help support the delivery of reference gas concentration standards. This paper describes initial efforts to compare FS-CRDS measurements with National Institute of Standards and Technology (NIST) methane-in-air standard reference materials to demonstrate the potential of this method to deliver standards-grade measurements with uncertainties of 1 % or lower. The current work demonstrates measurements with residual standard deviations of approximately 1 % for methane sample mole fractions of 50 mu mol mol(-1) and above. The results for lower mole fraction samples are poorer due to the poor signal-to-noise ratios and the higher pressures required for the measurements. The current results are potentially limited by the Voigt line shape which was used to model the data.