Abstract
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.
Highlights
Emission of carbon dioxide (CO2), the most important greenhouse gas, has been reported to increase, resulting in global climate change (Messerschmidt et al, 2011; Solomon et al, 2007)
Deviations of CO2 concentrations determined by CRDS from those assigned by gravimetry ranged from −2.44 to 1.39 %
CRDS responses of EB0006391 and ME0434 were in good agreement with the assigned CO2 concentrations, showing deviations of less than 0.1 μmol mol−1, whereas extreme deviations of greater than 1 % were observed for cylinders DF4560 and ME5537
Summary
Emission of carbon dioxide (CO2), the most important greenhouse gas, has been reported to increase, resulting in global climate change (Messerschmidt et al, 2011; Solomon et al, 2007). Gas chromatography coupled with flame ionization detection (GC-FID) (van der Laan et al, 2009), nondispersive infrared spectroscopy (NDIR) at 4.26 μm (Lee et al, 2006; Min et al, 2009; Crawley, 2008; Tohjima et al, 2009), Fourier transform infrared (FTIR) spectroscopy (Griffith et al, 2012), tunable diode laser absorption spectroscopy (TDLAS) (Durry et al, 2010), wavelength-scanned cavity ring-down spectroscopy (WS-CRDS) (Crosson, 2008), and other cavity-enhanced absorption spectroscopies (O’Shea et al, 2013) are well-known techniques for quantifying atmospheric CO2.
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