the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 Mar 2023
Technical Note: The impact of industrial activity on the amount of atmospheric O2
Abstract. Concurrent measurements of atmospheric O2 and CO2 amount fractions have been used for decades now to estimate fluxes of carbon to and from the oceans and the land biosphere. The equations used in these estimates explicitly include fossil fuel combustion but largely ignore fluxes of O2 associated with the refining of metals and other industrially important elements. Here, we quantify the O2 fluxes associated with the processing of iron, aluminum and copper. We also consider the potential impact of sulfur. We find that inclusion of the fluxes due to metals leads to an increased estimate of ocean carbon uptake in the years 2000–2010 of 
Pg a-1 with a corresponding decrease in estimated land uptake. A rough estimate of sulfur chemistry during fossil fuel combustion also increases ocean uptake but by a much smaller amount. These corrections are small compared to existing estimates of the fluxes and their uncertainties ((2.27 ± 0.60) and (1.05 ± 0.84) Pg a-1 for ocean and land respectively (Keeling and Manning, 2014)) but should be employed in future analyses.
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Interactive discussion
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RC1: 'Review of “Technical Note: The impact of industrial activity on the amount of atmospheric O2” by M. Battle and colleagues', Anonymous Referee #1, 27 Mar 2023
This manuscript presents an assessment of the impact of iron, aluminium and copper processing on global-scale atmospheric O2 budgets that are commonly used for land-ocean carbon sink partitioning. Although the correction reported by the authors is small in comparison to the uncertainties of the ocean and land carbon sinks, since it is a bias it is nevertheless important and perhaps appears more significant when considering the magnitude of carbon budget system discrepancies, such as the ‘Budget Imbalance’ term of the Global Carbon Budget, for example.
I find this manuscript to be well-written, well-structured, succinct and informative; the subject matter is a good fit to this journal. I think the handling of uncertainties and acknowledgements of any omissions or simplifications where they occur is especially well-handled, despite the difficulty in assessing some of these. In particular, I am glad to see that the three significant figures of the USGS values have not been taken at face value, with more realistic estimates of uncertainty used instead.
I only have a few technical comments:
- The authors may wish to consider defining a few of the more common chemical formulae where they are first used, such as SO2, for the benefit of the interested reader who does not have a background in chemistry.
- Page 7, line 13. I believe the citation here should be Keeling et al. (1988), not Keeling et al. (1998).
- Although I don’t think it is a requirement, the authors may want to consider changing the spelling of aluminum to aluminium as per the journal in-house standards (and in accordance with IUPAC), for the benefit of international readers.
Citation: https://doi.org/10.5194/acp-2022-765-RC1 -
RC2: 'Comment on acp-2022-765', Anonymous Referee #2, 29 Mar 2023
This is study provides an interesting discussion on adjustments that should be made for the method where atmospheric O2 and CO2 are used to estimate the ocean and terrestrial biosphere sink. Using this method requires to know the link between O2 and CO2 for different processes in the carbon cycle, including fossil fuel combustion. This study shows that during metal production no such link between atmospheric O2 and CO2 is present, because when oxidized metals are refined only CO2 is added to the atmosphere and no atmospheric O2 is lost. The authors describe a new method to correct for this by adding a metal flux to the O2 budget. The metal flux is based on iron, aluminium and coper. From inventories of these metals the O2 flux is determined. It is concluded that the O2 correction is relatively small but has some effect on the ocean and terrestrial biosphere sink calculations and should therefore be taken into account.
Overall, the study shows a well explained and clear overview of how adjustments should be made for metal production in the atmospheric O2 signal. The figure captures directly what the authors did and shows a clear distinction between the different metals. By thoroughly analysing the effect of different metals, the authors give a complete description of what would happen with the ocean and terrestrial biosphere budget based on the O2 and CO2 method after the metal correction. It is very relevant to make the O2 and CO2 method more detailed, as this field is progressing to a more local scale (Liu et al., 2022; Pickers et al., 2022). By moving to local scales we have to include more detailed information on how O2 and CO2 are, or are not linked. This study therefore contributes further to our knowledge about the O2 budget and I therefore recommend this paper for publication.
Below, I list some minor recommendations that should be addressed or made clearer. I would like to point out that I am not specialised in chemistry and therefore could not in full detail determine if every assumption and claim the authors make is correct.
Comments:
One of the bigger things that is not clear is how metals can be refined without using any atmospheric O2. The assumption that for refining of metals no atmospheric O2 is needed seems circular. I will give here an example with Fe2O3. In the study it is shown that Fe2O3 can react on its own to Fe and O2 and that this O2 is then used to react with C to form CO, which then can be used to react with Fe2O3. This reasoning makes it unclear why CO is even needed to get Fe out of Fe2O3 or when CO is needed, how Fe2O3 can produce somehow enough O2 on its own to sustain the reaction with CO. It seems that in some way atmospheric O2 is needed for this reaction and take this into account when calculating Zmetals. Could the authors elaborate on this, and write more clearly down why atmospheric O2 is not involved? This is a vital assumption of the study and should therefore be explained in more detail. A better explanation would strengthen the argument that the reduction of metals needs to be taken into account in the atmospheric O2 budget.
Another point that needs some more clarification is why the O2 budget has to be corrected by using Zmetals and not for example add a separate term to the CO2 budget (Fmetals) or even adjust the αff? If refining of metals only produces an atmospheric CO2 flux, why not remove the metal contribution entirely from Fff and add an extra term called Fmetals to the CO2 budget? αff could also be adjusted by removing the OR originated from the metal production. By adjusting Fff and αff and adding a Fmetals term it represents more closely what is happening in reality. Could the authors elaborate why the choice was made to use Zmetals? And if the metal correction always has to be applied by using Zmetals?
Minor comments:
- pg 1, line 20 – pg 2, line 2: From the introduction it does not become clear right away that O2 is not linked with CO2 in the production of metals and that the O2 flux that is associate with metal production should therefore be neglected. Could the authors explain this in more detail in the introduction? By elaborating on this already in the introduction, the point of the study is made clear earlier and therefore the aim of the paper becomes more clear for the reader.
- Pg 2, line 25: When looking at the reaction of hematite, is the OR for this reaction then 0.5 and used in the αff? Could the authors specify this?
- Pg 3, line 21: please write C, S, Si, P and Mn first in full. By doing so, this specific paragraph is made easier to follow for the reader.
- Pg 4, line 21: could the authors also add the full net equation for aluminium, similar to Iron? This makes it clearer what the connection was with αff and what OR was used. It makes it also more understandable for what specific link between O2 and CO2 we should adjust.
- Pg 5, line 22: The same point as above; could the authors also add a net equation for Copper? I understand that the copper production is more complicated. However, I was wondering if some kind of equation is possible to make the link between O2, Cu and CO2 more clear and make the text more consistent compared with aluminium and iron.
- Pg 7, line 14: It is not clear from the text how the number of 2.4 Tmol is reached. This number seems to appear out of nowhere, which makes it for the reader quite confusing. Could the authors further elaborate on this?
- Pg 8, line 25: could the authors add the full number of the estimated carbon fluxes for the ocean and the terrestrial biosphere together with their uncertainties from the study of Keeling & Manning. (2014). This addition will put the change in these sinks caused by the correction of the Zmetals contribution more in perspective.
- Pg 8, line 35: please specify the unit of the oceanic carbon sink better. It is more common to write the units Pg a-1 as PgC yr-1, as this makes it directly clear that it is about a carbon sink and not a CO2
- For the tables 1, 2, 3: please be more clear about the units. Tm should be written as Tmol. The numbers in these tables are directly used as the flux in figure 1. Therefore another option is to already mention that the units in these tables are: Tmol a-1 or even Tmol yr-1 (see point above).
- For the captions of the tables and the figures: It is written here that this is the: ‘associated flux of O2 to the atmosphere.’ However, shouldn’t it be more correct to call it a correction? As this is not really a flux , but rather a correction that needs to be made because the O2 sink of fossil fuels is overestimated by assuming O2 is linked to CO2 in the process of metal refining.
References:
Keeling, R. F., & Manning, A. C. (2014). Studies of Recent Changes in Atmospheric O2 Content. In Treatise on Geochemistry: Second Edition (2nd ed., Vol. 5). Elsevier Ltd. https://doi.org/10.1016/B978-0-08-095975-7.00420-4
Liu, X., Huang, J., Wang, L., Lian, X., Li, C., Ding, L., Wei, Y., Chen, S., Wang, Y., Li, S., & Shi, J. (2022). “Urban Respiration” Revealed by Atmospheric O2 Measurements in an Industrial Metropolis. Environmental Science and Technology. https://doi.org/10.1021/acs.est.2c07583
Pickers, P. A., Manning, A. C., Le Quéré, C., Forster, G. L., Luijkx, I. T., Gerbig, C., Fleming, L. S., & Sturges, W. T. (2022). Novel quantification of regional fossil fuel CO 2 reductions during COVID-19 lockdowns using atmospheric oxygen measurements. In Sci. Adv (Vol. 8). https://icos-cp.
Citation: https://doi.org/10.5194/acp-2022-765-RC2 -
RC3: 'Comment on acp-2022-765', Anonymous Referee #3, 30 Mar 2023
Review of “Technical Note: The impact of industrial activity on the amount of atmospheric O2” by Battle et al.
In this paper, the authors evaluate the contribution of O2 flux associated with the processing of iron, aluminum, copper and sulfur to the budgets for atmospheric O2 and CO2. This contribution, Zmetal in this paper, has been overlooked in the past budgets analysis. The authors estimated Z_metal by analyzing statistical data carefully, and they reported needed corrections for land and ocean carbon uptakes associated with inclusion of the Z_metal. The paper is well written and clear. I recommend this paper for publication in ACP with a few additional minor revisions below.
- P1, Line 8-10 and P8, Line 25-33: The authors stated Z_metal should be included in future analyses for O2 and CO2 budgets. However, Z_metal is much smaller than F_ff, F_land F_ocean, and its impact on land and ocean carbon uptakes is within uncertainties. They also mentioned Z_metal become more significant when APO is the focus. However, if we focus on seasonal APO cycle, then seasonal changes in air-sea O2 flux are much larger than that in Z_metal. I think inclusion of Z_metal will be important for the estimation of APO_climate (Resplandy et al., 2019), of which long-term change is much smaller than APO_ff and probably comparable to the contribution of Z_metal. I would like to hear the authors’ thoughts on this.
- P9, line 17 and Table 4: In this sentence and Table, Z_metal is treated as net oxygen “sink”. However, I think Z_metal is net oxygen “source” (annual flux of O2 to the atmosphere), from Fig. 1, Table 1 and 2. Please make the definition of source/sink clearer.
- The words with or without space before unit are mixed throughout the paper (e.g. “12Tmol a-1” and “2.4 Tmol a-1”). Please consolidate.
Citation: https://doi.org/10.5194/acp-2022-765-RC3 - AC1: 'Comment on acp-2022-765', Mark Battle, 04 May 2023
Interactive discussion
Status: closed
-
RC1: 'Review of “Technical Note: The impact of industrial activity on the amount of atmospheric O2” by M. Battle and colleagues', Anonymous Referee #1, 27 Mar 2023
This manuscript presents an assessment of the impact of iron, aluminium and copper processing on global-scale atmospheric O2 budgets that are commonly used for land-ocean carbon sink partitioning. Although the correction reported by the authors is small in comparison to the uncertainties of the ocean and land carbon sinks, since it is a bias it is nevertheless important and perhaps appears more significant when considering the magnitude of carbon budget system discrepancies, such as the ‘Budget Imbalance’ term of the Global Carbon Budget, for example.
I find this manuscript to be well-written, well-structured, succinct and informative; the subject matter is a good fit to this journal. I think the handling of uncertainties and acknowledgements of any omissions or simplifications where they occur is especially well-handled, despite the difficulty in assessing some of these. In particular, I am glad to see that the three significant figures of the USGS values have not been taken at face value, with more realistic estimates of uncertainty used instead.
I only have a few technical comments:
- The authors may wish to consider defining a few of the more common chemical formulae where they are first used, such as SO2, for the benefit of the interested reader who does not have a background in chemistry.
- Page 7, line 13. I believe the citation here should be Keeling et al. (1988), not Keeling et al. (1998).
- Although I don’t think it is a requirement, the authors may want to consider changing the spelling of aluminum to aluminium as per the journal in-house standards (and in accordance with IUPAC), for the benefit of international readers.
Citation: https://doi.org/10.5194/acp-2022-765-RC1 -
RC2: 'Comment on acp-2022-765', Anonymous Referee #2, 29 Mar 2023
This is study provides an interesting discussion on adjustments that should be made for the method where atmospheric O2 and CO2 are used to estimate the ocean and terrestrial biosphere sink. Using this method requires to know the link between O2 and CO2 for different processes in the carbon cycle, including fossil fuel combustion. This study shows that during metal production no such link between atmospheric O2 and CO2 is present, because when oxidized metals are refined only CO2 is added to the atmosphere and no atmospheric O2 is lost. The authors describe a new method to correct for this by adding a metal flux to the O2 budget. The metal flux is based on iron, aluminium and coper. From inventories of these metals the O2 flux is determined. It is concluded that the O2 correction is relatively small but has some effect on the ocean and terrestrial biosphere sink calculations and should therefore be taken into account.
Overall, the study shows a well explained and clear overview of how adjustments should be made for metal production in the atmospheric O2 signal. The figure captures directly what the authors did and shows a clear distinction between the different metals. By thoroughly analysing the effect of different metals, the authors give a complete description of what would happen with the ocean and terrestrial biosphere budget based on the O2 and CO2 method after the metal correction. It is very relevant to make the O2 and CO2 method more detailed, as this field is progressing to a more local scale (Liu et al., 2022; Pickers et al., 2022). By moving to local scales we have to include more detailed information on how O2 and CO2 are, or are not linked. This study therefore contributes further to our knowledge about the O2 budget and I therefore recommend this paper for publication.
Below, I list some minor recommendations that should be addressed or made clearer. I would like to point out that I am not specialised in chemistry and therefore could not in full detail determine if every assumption and claim the authors make is correct.
Comments:
One of the bigger things that is not clear is how metals can be refined without using any atmospheric O2. The assumption that for refining of metals no atmospheric O2 is needed seems circular. I will give here an example with Fe2O3. In the study it is shown that Fe2O3 can react on its own to Fe and O2 and that this O2 is then used to react with C to form CO, which then can be used to react with Fe2O3. This reasoning makes it unclear why CO is even needed to get Fe out of Fe2O3 or when CO is needed, how Fe2O3 can produce somehow enough O2 on its own to sustain the reaction with CO. It seems that in some way atmospheric O2 is needed for this reaction and take this into account when calculating Zmetals. Could the authors elaborate on this, and write more clearly down why atmospheric O2 is not involved? This is a vital assumption of the study and should therefore be explained in more detail. A better explanation would strengthen the argument that the reduction of metals needs to be taken into account in the atmospheric O2 budget.
Another point that needs some more clarification is why the O2 budget has to be corrected by using Zmetals and not for example add a separate term to the CO2 budget (Fmetals) or even adjust the αff? If refining of metals only produces an atmospheric CO2 flux, why not remove the metal contribution entirely from Fff and add an extra term called Fmetals to the CO2 budget? αff could also be adjusted by removing the OR originated from the metal production. By adjusting Fff and αff and adding a Fmetals term it represents more closely what is happening in reality. Could the authors elaborate why the choice was made to use Zmetals? And if the metal correction always has to be applied by using Zmetals?
Minor comments:
- pg 1, line 20 – pg 2, line 2: From the introduction it does not become clear right away that O2 is not linked with CO2 in the production of metals and that the O2 flux that is associate with metal production should therefore be neglected. Could the authors explain this in more detail in the introduction? By elaborating on this already in the introduction, the point of the study is made clear earlier and therefore the aim of the paper becomes more clear for the reader.
- Pg 2, line 25: When looking at the reaction of hematite, is the OR for this reaction then 0.5 and used in the αff? Could the authors specify this?
- Pg 3, line 21: please write C, S, Si, P and Mn first in full. By doing so, this specific paragraph is made easier to follow for the reader.
- Pg 4, line 21: could the authors also add the full net equation for aluminium, similar to Iron? This makes it clearer what the connection was with αff and what OR was used. It makes it also more understandable for what specific link between O2 and CO2 we should adjust.
- Pg 5, line 22: The same point as above; could the authors also add a net equation for Copper? I understand that the copper production is more complicated. However, I was wondering if some kind of equation is possible to make the link between O2, Cu and CO2 more clear and make the text more consistent compared with aluminium and iron.
- Pg 7, line 14: It is not clear from the text how the number of 2.4 Tmol is reached. This number seems to appear out of nowhere, which makes it for the reader quite confusing. Could the authors further elaborate on this?
- Pg 8, line 25: could the authors add the full number of the estimated carbon fluxes for the ocean and the terrestrial biosphere together with their uncertainties from the study of Keeling & Manning. (2014). This addition will put the change in these sinks caused by the correction of the Zmetals contribution more in perspective.
- Pg 8, line 35: please specify the unit of the oceanic carbon sink better. It is more common to write the units Pg a-1 as PgC yr-1, as this makes it directly clear that it is about a carbon sink and not a CO2
- For the tables 1, 2, 3: please be more clear about the units. Tm should be written as Tmol. The numbers in these tables are directly used as the flux in figure 1. Therefore another option is to already mention that the units in these tables are: Tmol a-1 or even Tmol yr-1 (see point above).
- For the captions of the tables and the figures: It is written here that this is the: ‘associated flux of O2 to the atmosphere.’ However, shouldn’t it be more correct to call it a correction? As this is not really a flux , but rather a correction that needs to be made because the O2 sink of fossil fuels is overestimated by assuming O2 is linked to CO2 in the process of metal refining.
References:
Keeling, R. F., & Manning, A. C. (2014). Studies of Recent Changes in Atmospheric O2 Content. In Treatise on Geochemistry: Second Edition (2nd ed., Vol. 5). Elsevier Ltd. https://doi.org/10.1016/B978-0-08-095975-7.00420-4
Liu, X., Huang, J., Wang, L., Lian, X., Li, C., Ding, L., Wei, Y., Chen, S., Wang, Y., Li, S., & Shi, J. (2022). “Urban Respiration” Revealed by Atmospheric O2 Measurements in an Industrial Metropolis. Environmental Science and Technology. https://doi.org/10.1021/acs.est.2c07583
Pickers, P. A., Manning, A. C., Le Quéré, C., Forster, G. L., Luijkx, I. T., Gerbig, C., Fleming, L. S., & Sturges, W. T. (2022). Novel quantification of regional fossil fuel CO 2 reductions during COVID-19 lockdowns using atmospheric oxygen measurements. In Sci. Adv (Vol. 8). https://icos-cp.
Citation: https://doi.org/10.5194/acp-2022-765-RC2 -
RC3: 'Comment on acp-2022-765', Anonymous Referee #3, 30 Mar 2023
Review of “Technical Note: The impact of industrial activity on the amount of atmospheric O2” by Battle et al.
In this paper, the authors evaluate the contribution of O2 flux associated with the processing of iron, aluminum, copper and sulfur to the budgets for atmospheric O2 and CO2. This contribution, Zmetal in this paper, has been overlooked in the past budgets analysis. The authors estimated Z_metal by analyzing statistical data carefully, and they reported needed corrections for land and ocean carbon uptakes associated with inclusion of the Z_metal. The paper is well written and clear. I recommend this paper for publication in ACP with a few additional minor revisions below.
- P1, Line 8-10 and P8, Line 25-33: The authors stated Z_metal should be included in future analyses for O2 and CO2 budgets. However, Z_metal is much smaller than F_ff, F_land F_ocean, and its impact on land and ocean carbon uptakes is within uncertainties. They also mentioned Z_metal become more significant when APO is the focus. However, if we focus on seasonal APO cycle, then seasonal changes in air-sea O2 flux are much larger than that in Z_metal. I think inclusion of Z_metal will be important for the estimation of APO_climate (Resplandy et al., 2019), of which long-term change is much smaller than APO_ff and probably comparable to the contribution of Z_metal. I would like to hear the authors’ thoughts on this.
- P9, line 17 and Table 4: In this sentence and Table, Z_metal is treated as net oxygen “sink”. However, I think Z_metal is net oxygen “source” (annual flux of O2 to the atmosphere), from Fig. 1, Table 1 and 2. Please make the definition of source/sink clearer.
- The words with or without space before unit are mixed throughout the paper (e.g. “12Tmol a-1” and “2.4 Tmol a-1”). Please consolidate.
Citation: https://doi.org/10.5194/acp-2022-765-RC3 - AC1: 'Comment on acp-2022-765', Mark Battle, 04 May 2023
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