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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/amt-2018-385
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2018-385
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 15 Nov 2018

Research article | 15 Nov 2018

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

High-precision measurements of nitrous oxide and methane in air with cavity ring-down spectroscopy at 7.6 μm

Jing Tang, Bincheng Li, and Jing Wang Jing Tang et al.
  • School of Optoelectronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu 610054, China

Abstract. A high-sensitivity methane (CH4) and nitrous oxide (N2O) sensor based on mid-infrared continuous-wave (cw) cavity ring-down spectroscopy (CRDS) technique was developed for environmental and biomedical trace gas measurements. A tunable external-cavity mode-hop-free (EC-MHF) quantum cascade laser (QCL) operating at 7.4 to 7.8µm was used as the light source. The effect of temperature fluctuation on the measurement sensitivity of the CRDS experimental setup was analyzed and corrected, and a sensitivity limit of absorption coefficient measurement of 7.38×1010cm−1 was achieved at 1330.50cm−1 with an average of 176 measurements, or 26.4-seconds averaging time, and further improved to 1.70×10–10cm−1 with average of 3266 measurements, or 490-seconds averaging time. For the targeted CH4 and N2O absorption lines located at 1298.60cm−1 and 1327.07cm−1, with temperature effect correction detection limits of 18.2pptv and 14.9pptv were experimentally achieved with 24.9-seconds and 20.5-seconds averaging time, and could be further improved to 3.62pptv and 4.67pptv with 513-seconds and 461-seconds averaging time, respectively. Four spectral bands (1298.4cm−1 to 1298.9cm−1, 1310.1cm−1 to 1312.3cm−1, 1326.5cm−1 to 1328cm−1, and 1331.5cm−1 to 1333cm−1) in the spectral range from 1295cm−1 to 1335cm−1 were selected for the separate and simultaneous measurements of CH4 and N2O under normal atmospheric pressure, and all were in good agreements. The concentrations of CH4 and N2O of atmospheric air collected at different locations and of exhaled breath were measured and analyzed. It was found that raining might have effect on the N2O concentration in out-door open-field air and anaerobic bacteria in water and soil of wetland might significantly increase the CH4 concentration in air. The measured N2O concentration in the central city area was somewhat lower than the reported normal level in open air. Our results demonstrated the temporal and spatial variations of CH4 and N2O in air.

Jing Tang et al.
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A high-sensitivity CH4 and N2O sensor based on mid-IR (7.6 µm) cavity ring-down spectroscopy was developed. The effect of temperature fluctuation on measurement sensitivity was analyzed and corrected, and detection limits of 3.62 pptv for CH4 and 4.67 pptv for N2O were experimentally achieved. Separate and continuous measurements of CH4 and N2O concentrations of in-/out-door air at different locations showed the spatial and temporal concentration variations of CH4 and N2O in air.
A high-sensitivity CH4 and N2O sensor based on mid-IR (7.6 µm) cavity ring-down spectroscopy...
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