the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
High precision δ18O measurements of atmospheric dioxygen using optical-feedback cavity-enhanced absorption spectroscopy (OF-CEAS)
Abstract. Atmospheric dioxygen concentration and isotopic composition are closely linked to the carbon cycle through anthropic CO2 emissions and biological processes such as photosynthesis and respiration. Measurement of isotopic ratio of atmospheric dioxygen, trapped in ice core bubbles, bring information about past variation in the hydrological cycle at low latitudes, as well as past productivity. Currently, the interpretation of those variations could be drastically improved with a better (i.e. quantitative) knowledge of the oxygen fractionation that occur during photosynthesis and respiration processes. This could be achieved, for example, during experiment using closed- biological chambers. In order to estimate the fractionation coefficient with a good precision, one of the principal limitations is the need of high frequency on-line measurements of δ18O of O2 and O2 concentration. To address this issue, we developed a new instrument, based on the OF-CEAS (Optical-Feedback Cavity-Enhanced Absorption Spectroscopy) technique, enabling high temporal resolution and continuous measurements of dioxygen concentration as well as δ18O of O2, both simultaneously. Minimum of Allan deviation occurred between 10 and 20 minutes while precision reached 0.002 % for O2 concentration and 0.06 ‰ for δ18O of O2, which correspond to the optimal integration time and analytical precision before drift start degrading the measurements. While humidity did not affect much the measured values, O2 concentration had an influence on δ18O of O2, which should hence be quantified. To ensure good quality of O2 concentration and δ18O of O2 measurements we eventually proposed to measure calibration standard every 20 minutes.
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RC1: 'Comment on amt-2024-14', Anonymous Referee #1, 29 Mar 2024
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2024-14/amt-2024-14-RC1-supplement.pdf
- AC2: 'Reply on RC1', Clément Piel, 26 Jun 2024
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RC2: 'Comment on amt-2024-14', Anonymous Referee #2, 23 Apr 2024
The article is devoted to measurements of d18O and O2 concentrations in the atmosphere by absorption of DFB laser emission at 760 nm. The excellent sensitivity is presented in short (20minutes) and long (several hours) times. The results of measurements are in nice agreement with that of IRMS. The methods of calibration of the device are suggested for continuous monitoring of O2 concentration and d18O.
At the same time many details of the experiments are missing.
- Experimental setup is very useful for understanding further.
- It seems the device long time stability obtained owing to high stability of cuvette (temperature of ~mK fluctuation). Nevertheless, no info in the text about the actual reasons for the stability was provided (precision of measurement, response time of feedback).
- Far wings of absorption line contour are determined by Lorentz (apart from pure Doppler) in all models (Voigt, Rautian etc.). The difference in the applied model in the “main body” of line contour (O16O18) should be shown. One can estimate using cavity parameters the number of points (cavity modes) on that are not more than 10. (It is possible to see also the fluctuations around O16O18 line contour in fig.1.) The question is – is this enough to get the difference in calculation? In text lines 187-203 it is very difficult to understand how it was done. Apart from temperature influence on cavity length mechanical instabilities (for instance by outer pressure fluctuations) should be mentioned.
- Lines 206-215. Why the reflectivity of the second configuration is absent? “Less parasitic fringes” at lower finesse configuration means better spline/averaging of the signal (FSR cavity modes did not change). If it is so, single scan time of the laser frequency and time constant of the detector provided.
- Line 304. “An influence of O2 concentration on d18O of O2 was expected.” Sound like a general rule, but is only valuable for the method applied.
Citation: https://doi.org/10.5194/amt-2024-14-RC2 - AC3: 'Reply on RC2', Clément Piel, 26 Jun 2024
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RC3: 'Comment on amt-2024-14', Anonymous Referee #3, 02 May 2024
This paper reports the development of an optical gas analyzer for high temporal resolution and high precision measurement of δ18O and atmospheric O2 concentration based on the optical-feedback cavity-enhanced absorption spectroscopy (OF-CEAS). The results were compared with the isotope-ratio mass spectrometry (IRMS) and showed good agreement.
General comments:
1, Although this work was based on a commercial device (AP2E) and similar experiments have been performed elsewhere, the experimental details still require detailed explanation.
2, The conclusions of this paper need to be supported by solid experimental data, rather than just stating the conclusions.
3, A detailed review and comparison with other methods, especially spectroscopic methods, should be made.
Specifical comments:
1, Page 2, line 32, the argument should contain high accuracy.
2, Page 3, for O2 concentration measurement, some other spectroscopy can also achieve ppmv level detection limit, such as Opt. Express 20, 2927, 2012. More discussion and comparison of other high sensitivity laser spectroscopy method is needed.
3, line 80, the difference between two models and parallel measurements is unclear.
4, line 99, first OF-CEAS in the visible range, incorrect. Salter et al. (Aanlyst, 137, 4669, 2012) performed optical feedback measurement with 635 nm diode laser.
5, Page 4, a detailed description of the experimental setup is required.
6, line 136, more discussion about the tuning coefficient and the intensity noise is needed.
7, Page 7, page 8, a detailed description of data processing methods is required. The corresponding experimental data need to be presented.
8, line 258, is a data acquisition time of 10 to 20 minutes fast enough for concentration and isotopic measurements?
9, the influence of water vapor requires experimental data.
Citation: https://doi.org/10.5194/amt-2024-14-RC3 - AC1: 'Reply on RC3', Clément Piel, 26 Jun 2024
Status: closed
-
RC1: 'Comment on amt-2024-14', Anonymous Referee #1, 29 Mar 2024
The comment was uploaded in the form of a supplement: https://amt.copernicus.org/preprints/amt-2024-14/amt-2024-14-RC1-supplement.pdf
- AC2: 'Reply on RC1', Clément Piel, 26 Jun 2024
-
RC2: 'Comment on amt-2024-14', Anonymous Referee #2, 23 Apr 2024
The article is devoted to measurements of d18O and O2 concentrations in the atmosphere by absorption of DFB laser emission at 760 nm. The excellent sensitivity is presented in short (20minutes) and long (several hours) times. The results of measurements are in nice agreement with that of IRMS. The methods of calibration of the device are suggested for continuous monitoring of O2 concentration and d18O.
At the same time many details of the experiments are missing.
- Experimental setup is very useful for understanding further.
- It seems the device long time stability obtained owing to high stability of cuvette (temperature of ~mK fluctuation). Nevertheless, no info in the text about the actual reasons for the stability was provided (precision of measurement, response time of feedback).
- Far wings of absorption line contour are determined by Lorentz (apart from pure Doppler) in all models (Voigt, Rautian etc.). The difference in the applied model in the “main body” of line contour (O16O18) should be shown. One can estimate using cavity parameters the number of points (cavity modes) on that are not more than 10. (It is possible to see also the fluctuations around O16O18 line contour in fig.1.) The question is – is this enough to get the difference in calculation? In text lines 187-203 it is very difficult to understand how it was done. Apart from temperature influence on cavity length mechanical instabilities (for instance by outer pressure fluctuations) should be mentioned.
- Lines 206-215. Why the reflectivity of the second configuration is absent? “Less parasitic fringes” at lower finesse configuration means better spline/averaging of the signal (FSR cavity modes did not change). If it is so, single scan time of the laser frequency and time constant of the detector provided.
- Line 304. “An influence of O2 concentration on d18O of O2 was expected.” Sound like a general rule, but is only valuable for the method applied.
Citation: https://doi.org/10.5194/amt-2024-14-RC2 - AC3: 'Reply on RC2', Clément Piel, 26 Jun 2024
-
RC3: 'Comment on amt-2024-14', Anonymous Referee #3, 02 May 2024
This paper reports the development of an optical gas analyzer for high temporal resolution and high precision measurement of δ18O and atmospheric O2 concentration based on the optical-feedback cavity-enhanced absorption spectroscopy (OF-CEAS). The results were compared with the isotope-ratio mass spectrometry (IRMS) and showed good agreement.
General comments:
1, Although this work was based on a commercial device (AP2E) and similar experiments have been performed elsewhere, the experimental details still require detailed explanation.
2, The conclusions of this paper need to be supported by solid experimental data, rather than just stating the conclusions.
3, A detailed review and comparison with other methods, especially spectroscopic methods, should be made.
Specifical comments:
1, Page 2, line 32, the argument should contain high accuracy.
2, Page 3, for O2 concentration measurement, some other spectroscopy can also achieve ppmv level detection limit, such as Opt. Express 20, 2927, 2012. More discussion and comparison of other high sensitivity laser spectroscopy method is needed.
3, line 80, the difference between two models and parallel measurements is unclear.
4, line 99, first OF-CEAS in the visible range, incorrect. Salter et al. (Aanlyst, 137, 4669, 2012) performed optical feedback measurement with 635 nm diode laser.
5, Page 4, a detailed description of the experimental setup is required.
6, line 136, more discussion about the tuning coefficient and the intensity noise is needed.
7, Page 7, page 8, a detailed description of data processing methods is required. The corresponding experimental data need to be presented.
8, line 258, is a data acquisition time of 10 to 20 minutes fast enough for concentration and isotopic measurements?
9, the influence of water vapor requires experimental data.
Citation: https://doi.org/10.5194/amt-2024-14-RC3 - AC1: 'Reply on RC3', Clément Piel, 26 Jun 2024
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