the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 14 Jun 2023
Atmospheric oxygen as a tracer for fossil fuel carbon dioxide: a sensitivity study in the UK
Abstract. We investigate the use of oxygen (O2) and carbon dioxide (CO2) measurements for the estimation of the fossil fuel component of atmospheric CO2 in the UK. Atmospheric potential oxygen (APO) – a tracer that combines O2 and CO2, minimising the influence of terrestrial biosphere fluxes – is simulated at three sites in the UK, two of which make atmospheric APO measurements. We present a set of model experiments that estimate the sensitivity of APO simulations to key inputs: fluxes from the ocean, fossil fuel flux magnitude and distribution, the APO baseline, and the ratio of O2 to CO2 fluxes from fossil fuel combustion and the terrestrial biosphere. To estimate the influence of uncertainties in ocean fluxes, we compared three ocean O2 flux estimates, from the NEMO – ERSEM and ECCO-Darwin ocean models, and the Jena CarboScope APO inversion. The sensitivity of APO to fossil fuel emission magnitudes and to terrestrial biosphere and fossil fuel exchange ratios was investigated through Monte Carlo sampling within literature uncertainty ranges, and by comparing different inventory estimates. Of the factors that could potentially compromise APO-derived fossil fuel CO2 estimates, we find that the ocean O2 flux estimate has the largest overall influence at the three sites in the UK. At times, this influence is comparable to the contribution to APO of simulated fossil fuel CO2. We find that simulations using different ocean fluxes differ from each other substantially, with no single model estimate, or a simulation with zero ocean flux, providing a significantly closer fit to the observations. Furthermore, the uncertainty in the ocean contribution to APO could lead to uncertainty in defining an appropriate regional background from the data. Our findings suggest that the contribution of non-terrestrial sources need to be well accounted for, in order to reduce their potential influence on inferred fossil fuel CO2.
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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.
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Preprint
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Supplement
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(6618 KB) - Metadata XML
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Supplement
(10202 KB) - BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-385', Anonymous Referee #2, 06 Jul 2023
Please see my comments in the attached file.
- AC1: 'Reply on RC1', Matthew Rigby, 14 Dec 2023
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RC2: 'Comment on egusphere-2023-385', Anonymous Referee #4, 15 Oct 2023
The authors investigated the sensitivity of Atmospheric Potential Oxygen (APO) simulations to different input variables such as ocean fluxes, fossil fuel fluxes, and the ratio of O2 to CO2 fluxes. Their results have revealed a substantial uncertainty in the ocean contribution to APO, which suggests that accounting for non-terrestrial fluxes accurately and defining an appropriate regional background is very important for the APO-derived fossil fuel CO2 emission estimation. Overall, this manuscript presents useful analysis results and can guide the APO-based emission inversion method. I suggest that the paper be published after my following comments are well addressed.
General comments:
- The structure of the results is challenging to follow. Sections 3.1 to 3.5 discuss sensitivity results related to APO simulation, while Section 3.6 presents estimated CO2. It's unclear whether the main focus of this work is on the robustness of the methodology or the CO2 emission results. If the goal is to infer CO2 emissions, why not directly use CO2 emission results for sensitivity testing?
- Given the complexity of the study's methodology, it would be helpful to provide an overall workflow figure at the beginning to help readers better understand the process. Similarly, creating a table listing all sensitivity test settings could improve the readability of the sensitivity tests.
- In my opinion, the usage of the term ‘the regional contribution’ may not be suitable for this study. Generally, ‘regional contribution’ refers to the portion or influence of a specific region on a particular phenomenon or variable. In this study, ‘the regional contribution’ is used to indicate contributions from ocean and fossil fuel components, which could lead to misunderstanding.
- The selection of August and December as the study period should be explained and justified, especially when the other months, like June (with the lowest R2) and November (with the highest R2) as shown in Figure 6, might be more prominent.
- The presentation of data in figures is quite simplistic, and there is a lack of standardization in the formatting of words inside the figures. For example, 'co2' should be written as 'CO2.' It's necessary to review all figures and consider diversifying the ways data is presented.
Specific comments:
Caption in Figure 1. What is fullname of UKGHG?
Figure 4. Combine Figure 4, there is no need to split it across two pages.
Figure 6. When using gray lines as major grid lines, I recommend that the author refrain from using gray lines for plotting the "no ocean" results. Please review all your figures to correct them.
Table 1. The table caption should be positioned above the table.
Citation: https://doi.org/10.5194/egusphere-2023-385-RC2 - AC2: 'Reply on RC2', Matthew Rigby, 14 Dec 2023
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-385', Anonymous Referee #2, 06 Jul 2023
Please see my comments in the attached file.
- AC1: 'Reply on RC1', Matthew Rigby, 14 Dec 2023
-
RC2: 'Comment on egusphere-2023-385', Anonymous Referee #4, 15 Oct 2023
The authors investigated the sensitivity of Atmospheric Potential Oxygen (APO) simulations to different input variables such as ocean fluxes, fossil fuel fluxes, and the ratio of O2 to CO2 fluxes. Their results have revealed a substantial uncertainty in the ocean contribution to APO, which suggests that accounting for non-terrestrial fluxes accurately and defining an appropriate regional background is very important for the APO-derived fossil fuel CO2 emission estimation. Overall, this manuscript presents useful analysis results and can guide the APO-based emission inversion method. I suggest that the paper be published after my following comments are well addressed.
General comments:
- The structure of the results is challenging to follow. Sections 3.1 to 3.5 discuss sensitivity results related to APO simulation, while Section 3.6 presents estimated CO2. It's unclear whether the main focus of this work is on the robustness of the methodology or the CO2 emission results. If the goal is to infer CO2 emissions, why not directly use CO2 emission results for sensitivity testing?
- Given the complexity of the study's methodology, it would be helpful to provide an overall workflow figure at the beginning to help readers better understand the process. Similarly, creating a table listing all sensitivity test settings could improve the readability of the sensitivity tests.
- In my opinion, the usage of the term ‘the regional contribution’ may not be suitable for this study. Generally, ‘regional contribution’ refers to the portion or influence of a specific region on a particular phenomenon or variable. In this study, ‘the regional contribution’ is used to indicate contributions from ocean and fossil fuel components, which could lead to misunderstanding.
- The selection of August and December as the study period should be explained and justified, especially when the other months, like June (with the lowest R2) and November (with the highest R2) as shown in Figure 6, might be more prominent.
- The presentation of data in figures is quite simplistic, and there is a lack of standardization in the formatting of words inside the figures. For example, 'co2' should be written as 'CO2.' It's necessary to review all figures and consider diversifying the ways data is presented.
Specific comments:
Caption in Figure 1. What is fullname of UKGHG?
Figure 4. Combine Figure 4, there is no need to split it across two pages.
Figure 6. When using gray lines as major grid lines, I recommend that the author refrain from using gray lines for plotting the "no ocean" results. Please review all your figures to correct them.
Table 1. The table caption should be positioned above the table.
Citation: https://doi.org/10.5194/egusphere-2023-385-RC2 - AC2: 'Reply on RC2', Matthew Rigby, 14 Dec 2023
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(6618 KB) - Metadata XML
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Supplement
(10202 KB) - BibTeX
- EndNote
- Final revised paper