the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 24 Jun 2025
CO2 deviation in a cylinder due to consumption of a standard gas mixture
Abstract. The CO2 molar fraction in standard gas mixtures is known to deviate as a result of adsorption/desorption to/from the inner surface of a high-pressure cylinder and thermal diffusion fractionation caused by the temperature distribution in the cylinder. This deviation reduces the consistency of atmospheric CO2 observations, because the standard gas mixtures are used to calibrate all measurement systems for precise CO2 observations. To maintain the consistency of CO2 values over the long term, a quantitative understanding of the deviations in the CO2 molar fraction in a standard gas mixture is needed. Thus far, this understanding has not been achieved sufficiently well, because the contribution of thermal diffusion fractionation is less well understood than that of adsorption/desorption. In this study, offsets of 0.013 ± 0.015 μmol mol−1 and −0.014 ± 0.011 μmol mol−1 were observed in the outflowing gas from horizontally and vertically positioned cylinders, respectively, at a flow rate of 0.080 L min−1. These offsets are attributed to thermal diffusion effects, which diluted and enriched the CO2 mole fraction by −0.045 μmol mol−1 (horizontal cylinder) and 0.048 μmol mol−1 (vertical cylinder) as the relative pressure dropped to 0.03. In the experiments at same flow rate, the adsorption/desorption effect enriched the CO2 mole fraction by 0.06 μmol mol−1 (horizontal cylinder) and 0.10 μmol mol−1 (vertical cylinder). Therefore, attention should be paid to both thermal diffusion fractionation and adsorption/desorption effects for precise calibration of long-term observations of CO2 molar fractions, although past studies have ignored the contribution of thermal diffusion fractionation at the low flow rates (<0.3 L min−1) examined in this study. Furthermore, the deviation of the CO2 molar fraction depends only on the pressure relative to the initial pressure of the cylinder. This result suggests that the recommendation by the World Meteorological Organization (WMO) to replace the standard gas mixture once the cylinder pressure drops to 2 MPa needs to be revised.
-
Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
-
Preprint
(1985 KB)
-
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1985 KB) - Metadata XML
- BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2025-2618', Anonymous Referee #1, 15 Jul 2025
-
AC1: 'Reply on RC1', Nobuyuki Aoki, 27 Aug 2025
We appreciate your review and feedback on our manuscript. We acknowledge that their contributions will improve the quality of this study.
Our responses to the reviewers' comments are as follows:
While IRMS analyses described within this work are sounds measurements the connection to thermal diffusion is unclear. Exclusion of this section still provides a quantifiable difference in amount fraction based on position of the cylinder and the flow rate.
Response: We appreciate your comment regarding the connection between the IRMS analyses and thermal diffusion. The decanting experiment allowed us to quantify deviations from CO₂ amount fraction at low flow rates for vertically positioned cylinders; however, it was insufficient to conclusively determine the presence or absence of an offset at low flow rates. To address this limitation, we conducted IRMS analyses, which confirmed a positive offset at low flow rates in vertically oriented cylinders, as detailed in Section 3.2.3. As you correctly noted, the relationship between these IRMS results and thermal diffusion was not clearly described. In response, we have added a clarifying statement regarding this connection in the revised manuscript (page7, line 3–5, page17, line 17–18, page 20, line 5–6 and lines 10–22).
If isotopic composition is to be explored, inclusion of delta 13C-CO2 and delta 18O-CO2 would be more constructive as it is directly applicable to measurements at hand. Additionally, these analyses were performed using an optical analyzer only quantifying 12C-CO2, it is possible that some of the difference seen could be based on release of one isotopologue over the other.
Response: Thank you for highlighting the potential influence of isotopic composition on the results. We acknowledge that the use of an optical analyzer that primarily detects ¹²C¹⁶O₂ could, in principle, lead to bias if significant isotopic fractionation due to the adsorption and thermal diffusion fractionation effects were present. However, the adsorption effect is governed by van der Waals forces. The intermolecular van der Waals forces are determined by the electronic structure of molecules—such as their polarity and polarizability. Their electronic structures between isotopologues are essentially identical. As a result, isotopic fractionation due to the adsorption is negligible. Furthermore, Thermal diffusion fractionation effect was roughly estimated based on δ(²⁹N₂/²⁸N₂) value because deviation of δ(13CO₂) can be approximated from that of δ(²⁹N₂/²⁸N₂). A sentence addressing this point has been included in the revised manuscript (page 23, line 23 – page 24, line 18).
The blending process described on page 5, lines 7 - 12, sounds like the CO2 and air were housed in separate containers and not mixed together. A gentle change in wording could make this clear for a broader audience.
Response: We revised the text to make the blending process clear (page 5, lines 11 – page 6, line 3)
Mole and molar fraction are both used within the text.
Response: We unified mole and molar fraction used within the text into molar fraction.
Page 6, line 9, the spelling for the instrument needs corrected from "Picaro" to "Picarro"
Response: The spelling of "Picaro" on page 6, lines 16 and 20 has been corrected to "Picarro."
Equations included after page 7 no longer include commas
Response: We added commas to the equations included after page 7.
Page 14, line 9, includes "quantitively", I recommend changes this to "quantitatively".
Response: We revised from “quantitively” to “quantitatively” according to your comment (page 13, line 16).
Figures 6 and 8 have different formatting from others.
Response: The formatting of figure 6 and 8 were revised.
Citation: https://doi.org/10.5194/egusphere-2025-2618-AC1
-
AC1: 'Reply on RC1', Nobuyuki Aoki, 27 Aug 2025
-
RC2: 'Comment on egusphere-2025-2618', Anonymous Referee #2, 25 Jul 2025
The manuscript "CO2 deviation in a cylinder due to consumption of a standard gas mixture" by Nobuyuki Aoki and Shigeyuki Ishidoya quantifies CO₂ deviations in standard gas cylinders due to adsorption/desorption and thermal diffusion effects. The paper is well written and structured. Overall, it is sufficiently original and contains relevant, novel information to merit publication in AMT, provided some minor issues are addressed.
General comments
The measurement technique used only detects the main isotopes of CO₂, which, as the other referee pointed out, influences the results presented in this work. However, this influence is probably small when considering amount fraction measurements of CO₂. Nevertheless, I encourage the authors to mention this and, if possible, provide an estimate of the degree to which the results could be biased as a result.
At the end of the paper (Page 27, lines 8-13), recommendations regarding the positioning, flow rates and the cylinder pressure are made. These recommendations are sound; however, I would exercise caution regarding the recommendation to use the lowest possible flow rates, as other effects, such as absorption/desorption in pressure regulators, may play an important role in practice. As these cannot be ruled out, they should be mentioned in the paper.
Specific comments
Page 5, lines 4-7: The calibration procedure is unclear.
Page 11, lines 12-14: Cylinder orientation should be mentioned.
It is not clear to me whether the top, middle or bottom positions for temperature measurements were the same for horizontally and vertically positioned cylinders. It would be helpful to include a small illustration.
Figure 5: The quality of the figure is poor and needs to be improved.
Citation: https://doi.org/10.5194/egusphere-2025-2618-RC2 -
AC2: 'Reply on RC2', Nobuyuki Aoki, 27 Aug 2025
We appreciate your review and feedback on our manuscript. We acknowledge that their contributions will improve the quality of this study.
Our responses to the reviewers' comments are as follows:
The manuscript "CO2 deviation in a cylinder due to consumption of a standard gas mixture" by Nobuyuki Aoki and Shigeyuki Ishidoya quantifies CO₂ deviations in standard gas cylinders due to adsorption/desorption and thermal diffusion effects. The paper is well written and structured. Overall, it is sufficiently original and contains relevant, novel information to merit publication in AMT, provided some minor issues are addressed.
General comments
The measurement technique used only detects the main isotopes of CO₂, which, as the other referee pointed out, influences the results presented in this work. However, this influence is probably small when considering amount fraction measurements of CO₂. Nevertheless, I encourage the authors to mention this and, if possible, provide an estimate of the degree to which the results could be biased as a result.
Response: Thank you for highlighting the potential influence of isotopic composition on the results. We acknowledge that the use of an optical analyzer that primarily detects ¹²C¹⁶O₂ could, in principle, lead to bias if significant isotopic fractionation due to the adsorption and thermal diffusion fractionation effects were present. However, the adsorption effect is governed by van der Waals forces. The intermolecular van der Waals forces are determined by the electronic structure of molecules—such as their polarity and polarizability. Their electronic structures between isotopologues are essentially identical. As a result, isotopic fractionation due to the adsorption is negligible. Furthermore, thermal diffusion fractionation effect was roughly estimated based on δ(²⁹N₂/²⁸N₂) value because deviation of δ(13CO₂) can be approximated from that of δ(²⁹N₂/²⁸N₂). A sentence addressing this point has been included in the revised manuscript (page 23, line 23 – page 24, line 18).
At the end of the paper (Page 27, lines 8-13), recommendations regarding the positioning, flow rates and the cylinder pressure are made. These recommendations are sound; however, I would exercise caution regarding the recommendation to use the lowest possible flow rates, as other effects, such as absorption/desorption in pressure regulators, may play an important role in practice. As these cannot be ruled out, they should be mentioned in the paper.
Response: We revised the sentence to “The flow rate of outflowing gas from the cylinders should be as low as possible to reduce the contribution of thermal diffusion fractionation, although other effects, such as absorption/desorption in pressure regulators, should be also considered” (page 28, line 21-22)
Specific comments
Page 5, lines 4-7: The calibration procedure is unclear.
Response: We revised the calibration procedure (Page 5, lines 5-11)
Page 11, lines 12-14: Cylinder orientation should be mentioned.
It is not clear to me whether the top, middle or bottom positions for temperature measurements were the same for horizontally and vertically positioned cylinders. It would be helpful to include a small illustration.
Response: Positions for temperature measurements were added in the Figure 1.
Figure 5: The quality of the figure is poor and needs to be improved.
Response: The quality of figure 5 was improved.
Citation: https://doi.org/10.5194/egusphere-2025-2618-AC2
-
AC2: 'Reply on RC2', Nobuyuki Aoki, 27 Aug 2025
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2025-2618', Anonymous Referee #1, 15 Jul 2025
While IRMS analyses described within this work are sounds measurements the connection to thermal diffusion is unclear. Exclusion of this section still provides a quantifiable difference in amount fraction based on position of the cylinder and the flow rate. If isotopic composition is to be explored, inclusion of delta 13C-CO2 and delta 18O-CO2 would be more constructive as it is directly applicable to measurements at hand. Additionally, these analyses were performed using an optical analyzer only quantifying 12C-CO2, it is possible that some of the difference seen could be based on release of one isotopologue over the other.
The blending process described on page 5, lines 7 - 12, sounds like the CO2 and air were housed in separate containers and not mixed together. A gentle change in wording could make this clear for a broader audience.
Mole and molar fraction are both used within the text.
Page 6, line 9, the spelling for the instrument needs corrected from "Picaro" to "Picarro"
Equations included after page 7 no longer include commas
Page 14, line 9, includes "quantitively", I recommend changes this to "quantitatively".
Figures 6 and 8 have different formatting from others .
Citation: https://doi.org/10.5194/egusphere-2025-2618-RC1 -
AC1: 'Reply on RC1', Nobuyuki Aoki, 27 Aug 2025
We appreciate your review and feedback on our manuscript. We acknowledge that their contributions will improve the quality of this study.
Our responses to the reviewers' comments are as follows:
While IRMS analyses described within this work are sounds measurements the connection to thermal diffusion is unclear. Exclusion of this section still provides a quantifiable difference in amount fraction based on position of the cylinder and the flow rate.
Response: We appreciate your comment regarding the connection between the IRMS analyses and thermal diffusion. The decanting experiment allowed us to quantify deviations from CO₂ amount fraction at low flow rates for vertically positioned cylinders; however, it was insufficient to conclusively determine the presence or absence of an offset at low flow rates. To address this limitation, we conducted IRMS analyses, which confirmed a positive offset at low flow rates in vertically oriented cylinders, as detailed in Section 3.2.3. As you correctly noted, the relationship between these IRMS results and thermal diffusion was not clearly described. In response, we have added a clarifying statement regarding this connection in the revised manuscript (page7, line 3–5, page17, line 17–18, page 20, line 5–6 and lines 10–22).
If isotopic composition is to be explored, inclusion of delta 13C-CO2 and delta 18O-CO2 would be more constructive as it is directly applicable to measurements at hand. Additionally, these analyses were performed using an optical analyzer only quantifying 12C-CO2, it is possible that some of the difference seen could be based on release of one isotopologue over the other.
Response: Thank you for highlighting the potential influence of isotopic composition on the results. We acknowledge that the use of an optical analyzer that primarily detects ¹²C¹⁶O₂ could, in principle, lead to bias if significant isotopic fractionation due to the adsorption and thermal diffusion fractionation effects were present. However, the adsorption effect is governed by van der Waals forces. The intermolecular van der Waals forces are determined by the electronic structure of molecules—such as their polarity and polarizability. Their electronic structures between isotopologues are essentially identical. As a result, isotopic fractionation due to the adsorption is negligible. Furthermore, Thermal diffusion fractionation effect was roughly estimated based on δ(²⁹N₂/²⁸N₂) value because deviation of δ(13CO₂) can be approximated from that of δ(²⁹N₂/²⁸N₂). A sentence addressing this point has been included in the revised manuscript (page 23, line 23 – page 24, line 18).
The blending process described on page 5, lines 7 - 12, sounds like the CO2 and air were housed in separate containers and not mixed together. A gentle change in wording could make this clear for a broader audience.
Response: We revised the text to make the blending process clear (page 5, lines 11 – page 6, line 3)
Mole and molar fraction are both used within the text.
Response: We unified mole and molar fraction used within the text into molar fraction.
Page 6, line 9, the spelling for the instrument needs corrected from "Picaro" to "Picarro"
Response: The spelling of "Picaro" on page 6, lines 16 and 20 has been corrected to "Picarro."
Equations included after page 7 no longer include commas
Response: We added commas to the equations included after page 7.
Page 14, line 9, includes "quantitively", I recommend changes this to "quantitatively".
Response: We revised from “quantitively” to “quantitatively” according to your comment (page 13, line 16).
Figures 6 and 8 have different formatting from others.
Response: The formatting of figure 6 and 8 were revised.
Citation: https://doi.org/10.5194/egusphere-2025-2618-AC1
-
AC1: 'Reply on RC1', Nobuyuki Aoki, 27 Aug 2025
-
RC2: 'Comment on egusphere-2025-2618', Anonymous Referee #2, 25 Jul 2025
The manuscript "CO2 deviation in a cylinder due to consumption of a standard gas mixture" by Nobuyuki Aoki and Shigeyuki Ishidoya quantifies CO₂ deviations in standard gas cylinders due to adsorption/desorption and thermal diffusion effects. The paper is well written and structured. Overall, it is sufficiently original and contains relevant, novel information to merit publication in AMT, provided some minor issues are addressed.
General comments
The measurement technique used only detects the main isotopes of CO₂, which, as the other referee pointed out, influences the results presented in this work. However, this influence is probably small when considering amount fraction measurements of CO₂. Nevertheless, I encourage the authors to mention this and, if possible, provide an estimate of the degree to which the results could be biased as a result.
At the end of the paper (Page 27, lines 8-13), recommendations regarding the positioning, flow rates and the cylinder pressure are made. These recommendations are sound; however, I would exercise caution regarding the recommendation to use the lowest possible flow rates, as other effects, such as absorption/desorption in pressure regulators, may play an important role in practice. As these cannot be ruled out, they should be mentioned in the paper.
Specific comments
Page 5, lines 4-7: The calibration procedure is unclear.
Page 11, lines 12-14: Cylinder orientation should be mentioned.
It is not clear to me whether the top, middle or bottom positions for temperature measurements were the same for horizontally and vertically positioned cylinders. It would be helpful to include a small illustration.
Figure 5: The quality of the figure is poor and needs to be improved.
Citation: https://doi.org/10.5194/egusphere-2025-2618-RC2 -
AC2: 'Reply on RC2', Nobuyuki Aoki, 27 Aug 2025
We appreciate your review and feedback on our manuscript. We acknowledge that their contributions will improve the quality of this study.
Our responses to the reviewers' comments are as follows:
The manuscript "CO2 deviation in a cylinder due to consumption of a standard gas mixture" by Nobuyuki Aoki and Shigeyuki Ishidoya quantifies CO₂ deviations in standard gas cylinders due to adsorption/desorption and thermal diffusion effects. The paper is well written and structured. Overall, it is sufficiently original and contains relevant, novel information to merit publication in AMT, provided some minor issues are addressed.
General comments
The measurement technique used only detects the main isotopes of CO₂, which, as the other referee pointed out, influences the results presented in this work. However, this influence is probably small when considering amount fraction measurements of CO₂. Nevertheless, I encourage the authors to mention this and, if possible, provide an estimate of the degree to which the results could be biased as a result.
Response: Thank you for highlighting the potential influence of isotopic composition on the results. We acknowledge that the use of an optical analyzer that primarily detects ¹²C¹⁶O₂ could, in principle, lead to bias if significant isotopic fractionation due to the adsorption and thermal diffusion fractionation effects were present. However, the adsorption effect is governed by van der Waals forces. The intermolecular van der Waals forces are determined by the electronic structure of molecules—such as their polarity and polarizability. Their electronic structures between isotopologues are essentially identical. As a result, isotopic fractionation due to the adsorption is negligible. Furthermore, thermal diffusion fractionation effect was roughly estimated based on δ(²⁹N₂/²⁸N₂) value because deviation of δ(13CO₂) can be approximated from that of δ(²⁹N₂/²⁸N₂). A sentence addressing this point has been included in the revised manuscript (page 23, line 23 – page 24, line 18).
At the end of the paper (Page 27, lines 8-13), recommendations regarding the positioning, flow rates and the cylinder pressure are made. These recommendations are sound; however, I would exercise caution regarding the recommendation to use the lowest possible flow rates, as other effects, such as absorption/desorption in pressure regulators, may play an important role in practice. As these cannot be ruled out, they should be mentioned in the paper.
Response: We revised the sentence to “The flow rate of outflowing gas from the cylinders should be as low as possible to reduce the contribution of thermal diffusion fractionation, although other effects, such as absorption/desorption in pressure regulators, should be also considered” (page 28, line 21-22)
Specific comments
Page 5, lines 4-7: The calibration procedure is unclear.
Response: We revised the calibration procedure (Page 5, lines 5-11)
Page 11, lines 12-14: Cylinder orientation should be mentioned.
It is not clear to me whether the top, middle or bottom positions for temperature measurements were the same for horizontally and vertically positioned cylinders. It would be helpful to include a small illustration.
Response: Positions for temperature measurements were added in the Figure 1.
Figure 5: The quality of the figure is poor and needs to be improved.
Response: The quality of figure 5 was improved.
Citation: https://doi.org/10.5194/egusphere-2025-2618-AC2
-
AC2: 'Reply on RC2', Nobuyuki Aoki, 27 Aug 2025
Peer review completion
Journal article(s) based on this preprint
Viewed
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 749 | 52 | 25 | 826 | 21 | 42 |
- HTML: 749
- PDF: 52
- XML: 25
- Total: 826
- BibTeX: 21
- EndNote: 42
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
Shigeyuki Ishidoya
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1985 KB) - Metadata XML
While IRMS analyses described within this work are sounds measurements the connection to thermal diffusion is unclear. Exclusion of this section still provides a quantifiable difference in amount fraction based on position of the cylinder and the flow rate. If isotopic composition is to be explored, inclusion of delta 13C-CO2 and delta 18O-CO2 would be more constructive as it is directly applicable to measurements at hand. Additionally, these analyses were performed using an optical analyzer only quantifying 12C-CO2, it is possible that some of the difference seen could be based on release of one isotopologue over the other.
The blending process described on page 5, lines 7 - 12, sounds like the CO2 and air were housed in separate containers and not mixed together. A gentle change in wording could make this clear for a broader audience.
Mole and molar fraction are both used within the text.
Page 6, line 9, the spelling for the instrument needs corrected from "Picaro" to "Picarro"
Equations included after page 7 no longer include commas
Page 14, line 9, includes "quantitively", I recommend changes this to "quantitatively".
Figures 6 and 8 have different formatting from others .