Impact of Residual Water Vapor on the Simultaneous Measurements of Trace CH<sub>4</sub> and N<sub>2</sub>O in Air with Cavity Ring-Down Spectroscopy
Methane (CH<sub>4</sub>) and nitrous oxide (N<sub>2</sub>O) are among the most important atmospheric greenhouse gases. A gas sensor based on a tunable 7.6 μm continuous-wave external-cavity mode-hop-free (EC-MHF) quantum cascade laser (from 1290 to 1350 cm<sup>−1</su...
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MDPI AG
2021-02-01
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| Series: | Atmosphere |
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| Online Access: | https://www.mdpi.com/2073-4433/12/2/221 |
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| author | Qianhe Wei Bincheng Li Jing Wang Binxing Zhao Ping Yang |
| author_facet | Qianhe Wei Bincheng Li Jing Wang Binxing Zhao Ping Yang |
| author_sort | Qianhe Wei |
| collection | DOAJ |
| description | Methane (CH<sub>4</sub>) and nitrous oxide (N<sub>2</sub>O) are among the most important atmospheric greenhouse gases. A gas sensor based on a tunable 7.6 μm continuous-wave external-cavity mode-hop-free (EC-MHF) quantum cascade laser (from 1290 to 1350 cm<sup>−1</sup>) cavity ring-down spectroscopy (CRDS) technique was developed for the simultaneous detection of CH<sub>4</sub> and N<sub>2</sub>O in ambient air with water vapor (H<sub>2</sub>O) mostly removed via molecular sieve drying to minimize the impact of H<sub>2</sub>O on the simultaneous measurements. Still, due to the broad and strong absorption spectrum of H<sub>2</sub>O in the entire mid-infrared (mid-IR) spectral range, residual H<sub>2</sub>O in the dried ambient air due to incomplete drying and leakage, if not properly accounted for, could cause a significant influence on the measurement accuracy of the simultaneous CH<sub>4</sub> and N<sub>2</sub>O detection. In this paper, the impact of residual H<sub>2</sub>O on the simultaneous CH<sub>4</sub> and N<sub>2</sub>O measurements were analyzed by comparing the CH<sub>4</sub> and N<sub>2</sub>O concentrations determined from the measured spectrum in the spectral range from 1311 to 1312.1 cm<sup>−1</sup> via simultaneous CH<sub>4</sub> and N<sub>2</sub>O measurements and that determined from the measured spectrum in the spectral range from 1311 to 1313 cm<sup>−1</sup> via simultaneous CH<sub>4</sub>, N<sub>2</sub>O, and H<sub>2</sub>O measurements. The measured dependence of CH<sub>4</sub> and N<sub>2</sub>O concentration errors on the simultaneously determined H<sub>2</sub>O concentration indicated that the residual H<sub>2</sub>O caused an under-estimation of CH<sub>4</sub> concentration and over-estimation of N<sub>2</sub>O concentration. The H<sub>2</sub>O induced CH<sub>4</sub> and N<sub>2</sub>O concentration errors were approximately linearly proportional to the residual H<sub>2</sub>O concentration. For the measurement of air flowing at 3 L per min, the residual H<sub>2</sub>O concentration was stabilized to approximately 14 ppmv, and the corresponding H<sub>2</sub>O induced errors were −1.3 ppbv for CH<sub>4</sub> and 3.7 ppbv for N<sub>2</sub>O, respectively. |
| first_indexed | 2024-03-09T05:26:16Z |
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| last_indexed | 2024-03-09T05:26:16Z |
| publishDate | 2021-02-01 |
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| spelling | doaj.art-69c3fede37d443eabcdf9f5e44d715ae2023-12-03T12:36:51ZengMDPI AGAtmosphere2073-44332021-02-0112222110.3390/atmos12020221Impact of Residual Water Vapor on the Simultaneous Measurements of Trace CH<sub>4</sub> and N<sub>2</sub>O in Air with Cavity Ring-Down SpectroscopyQianhe Wei0Bincheng Li1Jing Wang2Binxing Zhao3Ping Yang4School of Optoelectronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu 610054, ChinaSchool of Optoelectronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu 610054, ChinaSchool of Optoelectronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu 610054, ChinaSchool of Optoelectronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu 610054, ChinaInstitute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209, ChinaMethane (CH<sub>4</sub>) and nitrous oxide (N<sub>2</sub>O) are among the most important atmospheric greenhouse gases. A gas sensor based on a tunable 7.6 μm continuous-wave external-cavity mode-hop-free (EC-MHF) quantum cascade laser (from 1290 to 1350 cm<sup>−1</sup>) cavity ring-down spectroscopy (CRDS) technique was developed for the simultaneous detection of CH<sub>4</sub> and N<sub>2</sub>O in ambient air with water vapor (H<sub>2</sub>O) mostly removed via molecular sieve drying to minimize the impact of H<sub>2</sub>O on the simultaneous measurements. Still, due to the broad and strong absorption spectrum of H<sub>2</sub>O in the entire mid-infrared (mid-IR) spectral range, residual H<sub>2</sub>O in the dried ambient air due to incomplete drying and leakage, if not properly accounted for, could cause a significant influence on the measurement accuracy of the simultaneous CH<sub>4</sub> and N<sub>2</sub>O detection. In this paper, the impact of residual H<sub>2</sub>O on the simultaneous CH<sub>4</sub> and N<sub>2</sub>O measurements were analyzed by comparing the CH<sub>4</sub> and N<sub>2</sub>O concentrations determined from the measured spectrum in the spectral range from 1311 to 1312.1 cm<sup>−1</sup> via simultaneous CH<sub>4</sub> and N<sub>2</sub>O measurements and that determined from the measured spectrum in the spectral range from 1311 to 1313 cm<sup>−1</sup> via simultaneous CH<sub>4</sub>, N<sub>2</sub>O, and H<sub>2</sub>O measurements. The measured dependence of CH<sub>4</sub> and N<sub>2</sub>O concentration errors on the simultaneously determined H<sub>2</sub>O concentration indicated that the residual H<sub>2</sub>O caused an under-estimation of CH<sub>4</sub> concentration and over-estimation of N<sub>2</sub>O concentration. The H<sub>2</sub>O induced CH<sub>4</sub> and N<sub>2</sub>O concentration errors were approximately linearly proportional to the residual H<sub>2</sub>O concentration. For the measurement of air flowing at 3 L per min, the residual H<sub>2</sub>O concentration was stabilized to approximately 14 ppmv, and the corresponding H<sub>2</sub>O induced errors were −1.3 ppbv for CH<sub>4</sub> and 3.7 ppbv for N<sub>2</sub>O, respectively.https://www.mdpi.com/2073-4433/12/2/221cavity ring-down spectroscopytrace gas detectionresidual water vapordrying |
| spellingShingle | Qianhe Wei Bincheng Li Jing Wang Binxing Zhao Ping Yang Impact of Residual Water Vapor on the Simultaneous Measurements of Trace CH<sub>4</sub> and N<sub>2</sub>O in Air with Cavity Ring-Down Spectroscopy Atmosphere cavity ring-down spectroscopy trace gas detection residual water vapor drying |
| title | Impact of Residual Water Vapor on the Simultaneous Measurements of Trace CH<sub>4</sub> and N<sub>2</sub>O in Air with Cavity Ring-Down Spectroscopy |
| title_full | Impact of Residual Water Vapor on the Simultaneous Measurements of Trace CH<sub>4</sub> and N<sub>2</sub>O in Air with Cavity Ring-Down Spectroscopy |
| title_fullStr | Impact of Residual Water Vapor on the Simultaneous Measurements of Trace CH<sub>4</sub> and N<sub>2</sub>O in Air with Cavity Ring-Down Spectroscopy |
| title_full_unstemmed | Impact of Residual Water Vapor on the Simultaneous Measurements of Trace CH<sub>4</sub> and N<sub>2</sub>O in Air with Cavity Ring-Down Spectroscopy |
| title_short | Impact of Residual Water Vapor on the Simultaneous Measurements of Trace CH<sub>4</sub> and N<sub>2</sub>O in Air with Cavity Ring-Down Spectroscopy |
| title_sort | impact of residual water vapor on the simultaneous measurements of trace ch sub 4 sub and n sub 2 sub o in air with cavity ring down spectroscopy |
| topic | cavity ring-down spectroscopy trace gas detection residual water vapor drying |
| url | https://www.mdpi.com/2073-4433/12/2/221 |
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