Validation of spectroscopic gas analyzer accuracy using gravimetric standard gas mixtures: impact of background gas composition on CO<sub>2</sub> quantitation by cavity ring-down spectroscopy
The effect of background gas composition on the measurement of CO<sub>2</sub> levels was investigated by wavelength-scanned cavity ring-down spectrometry (WS-CRDS) employing a spectral line centered at the <i>R</i>(1) of the (3 0<sup>0</sup> 1)<sub>III<...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-12-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/10/4613/2017/amt-10-4613-2017.pdf |
| Summary: | The effect of background gas composition on the measurement
of CO<sub>2</sub> levels was investigated by wavelength-scanned cavity ring-down
spectrometry (WS-CRDS) employing a spectral line centered at the <i>R</i>(1) of the
(3 0<sup>0</sup> 1)<sub>III</sub> ← (0 0 0) band. For this purpose, eight
cylinders with various gas compositions were gravimetrically and
volumetrically prepared within 2<i>σ</i> = 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 CO<sub>2</sub> concentrations ranged from −9.77 to 5.36 µmol mol<sup>−1</sup>,
e.g., excess N<sub>2</sub> exhibited a negative deviation, whereas excess Ar
showed a positive one. The total pressure broadening coefficients (TPBCs)
obtained from the composition of N<sub>2</sub>, O<sub>2</sub>, and Ar thoroughly
corrected the deviations up to −0.5 to 0.6 µmol mol<sup>−1</sup>, while these values
were −0.43 to 1.43 µmol mol<sup>−1</sup> considering PBCs induced by only N<sub>2</sub>. The
use of TPBC enhanced deviations to be corrected to ∼ 0.15 %.<br><br>
Furthermore, the above correction linearly shifted CRDS responses for a large
extent of TPBCs ranging from 0.065 to 0.081 cm<sup>−1</sup> atm<sup>−1</sup>. 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. |
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| ISSN: | 1867-1381 1867-8548 |