Validation of spectroscopic gas analyzer accuracy using gravimetric standard gas mixtures: Impact of background gas composition on CO2 quantitation by cavity ring-down spectroscopy

Abstract

The effect of background gas composition on the measurement of CO2 levels was investigated by wavelengthscanned cavity ring-down spectrometry (WS-CRDS) employing a spectral line centered at the R.1/of the (3 00 1)III ←(0 0 0) band. For this purpose, eight cylinders with various gas compositions were gravimetrically and volumetrically prepared within 2o=0.1 %, and these gas mixtures were introduced into the WS-CRDS analyzer calibrated against standards of ambient air composition. Depending on the gas composition, deviations between CRDSdetermined and gravimetrically (or volumetrically) assigned CO2 concentrations ranged from-9.77 to 5.36 μmol mol-1, e.g., excess N2 exhibited a negative deviation, whereas excess Ar showed a positive one. The total pressure broadening coefficients (TPBCs) obtained from the composition of N2, O2, and Ar thoroughly corrected the deviations up to-0.5 to 0.6 μ mol mol-1, while these values were-0.43 to 1.43 μ mol mol-1considering PBCs induced by only N2. The use of TPBC enhanced deviations to be corrected to ∼0.15 %. Furthermore, the above correction linearly shifted CRDS responses for a large extent of TPBCs ranging from 0.065 to 0.081 cm-1 atm-1. Thus, accurate measurements using optical intensity-based techniques such as WS-CRDS require TPBC-based instrument calibration or use standards prepared in the same background composition of ambient air.