Articles | Volume 10, issue 12
Research article
01 Dec 2017
Research article |  | 01 Dec 2017

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

Jeong Sik Lim, Miyeon Park, Jinbok Lee, and Jeongsoon Lee

Abstract. The effect of background gas composition on the measurement of CO2 levels was investigated by wavelength-scanned 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 2σ = 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 CRDS-determined 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 µmol mol−1, while these values were −0.43 to 1.43 µmol mol−1 considering 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.

Short summary
Effect of background gas composition on the spectroscopic measurement of CO2 concentration at ambient levels has been investigated. The wavelength-scanned cavity ring-down spectroscopy was employed to explore the spectral line shape of CO2 at 1603 nm. It is revealed that the instrument response should be corrected with respect to a total pressure broadening coefficient given by a matrix composition. The correction method is validated by high accurate gravimetric standard gas mixture.