From the journal Environmental Science: Atmospheres Peer review history

18-Jun-2021

Dear Professor Simmonds:

Manuscript ID: EA-ART-05-2021-000040
TITLE: Natural Greenhouse Gas and Ozone-depleting Substance Sources and Sinks from the Peat Bogs of Connermara, Ireland from 1994-2020.

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Dr Lin Wang
Associate Editor, Environmental Science: Atmospheres

Environmental Science: Atmospheres is accompanied by sister journals Environmental Science: Nano, Environmental Science: Processes and Impacts, and Environmental Science: Water Research; publishing high-impact work across all aspects of environmental science and engineering. Find out more at: http://rsc.li/envsci

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Reviewer 1

This is an important paper in that it provides trends of methane, chloroform, hydrogen and ozone concentrations, plus deposition velocities for hydrogen and emission rates of methane and chloroform during nocturnal inversion events over a 27-year study period from a northern peat bog in a maritime climate. Their data analysis will be highly relevant to atmospheric chemistry models.
Generally, the paper is well written, but in places more detailed information would help the reader (see list comments below). But the structure of this paper does not follow the standard format ‘Abstract - Intro - Results- Discussion- Conclusion’. I assume section 3 is the result section? Section 4 supposed to be a combined Discussion and Conclusion, but in reality this section does not include any concluding remarks. I was hoping for a summary of the various concentration trends and impact on policy. Figure 2 & 3 would benefit from trend lines and it would nice to include annual average temperatures to Fig 3 a.

Detailed comments:
Page 2: last paragraph, 2nd line: change the font to black
Page 3: It would be helpful to provide a map showing the Mace Head location and size of the peatland surrounding this station. References 16,17 are good to quote, but do not substitute the map.
Page 4: change CH4 to ‘CH4’ in row 1, and to ‘ Methane’ in row 2
Page 4: 2nd paragraph: add a reference to the ‘working standards’
Page 5: 3rd paragraph: Fig1a shows CH4 and NOT H2 data. H2 data are in Fig 1c. Check your document for the correct figure numbers for CH4, CHCL3 and H2.
Page 5: 3rd paragraph last sentence: For clarification add: ‘Four events of calm conditions are marked….’
Fig 1 legend requires description of the horizontal black bars
Page 5: 4th paragraph: CH4 data are in Fig 1a and NOT in Fig 1b. The maximum peak of CH4 is less than 2080 ppb.
Page 7: Is section 3 the start of the Result and Discussion section?
Provide an explanation for not including data beyond 21:00 hrs?
Change ‘2100 hrs’ to ‘21:00 hrs’
Page 9: 2nd & 3rd paragraphs: Figure 2 is a rather noisy graph. Trend lines for the 3 gases would support the text a bit better and are easier to interpret.
Page 9:3rd paragraph: What is the reason for the anomalous CH4 fluxes in 2014 – 2016?
Page 10: 1st paragraph discussion section: It would be helpful to elaborate on these two studies (Finland, California): 1) are these long-term or short-term studies, and what was their temperature increase over their study periods compared to your study? 2) Are there other studies that should be included. 3) Why are the H2 deposition rates at these two sites very similar? Was the urban site also vegetated? 4) A graph showing the temperature increase during your study period may be helpful (either add to Fig 3 or Fig 4).
Page 10: 2nd paragraph CHCL3: you only provide a reference for the Irish peatlands (ref.8). I don’t think this qualifies your phrase ‘several temperate ecosystems’ .
Please provide a reference to : ‘in our previous study of the Connemara peat bogs for the overlapping period 1995 – 2008.’ Is it reference 10 you need to add?
Please stick to the unit ng m-2 s-1 for CHCl3 : ¬‘Previously we found emission rates in the range 0.44 – 12.94 μg m-2 hour-1’ also in the next 2 lines.
Page 10: 4th paragraph: to be more precise change ‘for natural pristine peatland bog sites’ to ‘for natural pristine bogs from northern peatlands’

Reviewer 2

Comments

This work explores the long-term (from April 1987 to March 2003) atmospheric CHCl3, H2 and O3 flux rates in the Connemara peat bogs. Please address the following questions before its possible publication.


1. On page 5. Please make an explanation to why reducing the oxidation capacity of the atmosphere can exacerbate ozone. Is it because the titration effect of O3-NO or other reasons?

2. On page 9, is it better to use “21:00” instead of “2100”.

3. On page 10, why are CHCl3 emission estimates in this work much higher than that in the previous ones. Any specific reason for this discrepancy? Stating “the differences are unlikely to be statistically significant” is not enough, please give more explanations.

4. On page 11, authors show that the observed increase in rainfall was ascribed to the increase in CH4 emissions. Could authors please explain more on this and is it possible to quantify this effect?

5. On page 3, authors state that H2 can lower the oxidation capacity of the atmosphere, thus exacerbating the global warming from ozone (O3). On the contrary, as the oxidation capacity of the atmosphere gets reduced, less O3 is generated from the titration effect of O3 and NO.

6. More in-depth analysis may be needed in the discussion and conclusion. I recommend to build a table to compare your results with that from preceding studies and then talk more incisively about the differences and similarities, e.g. what characteristics of the investigated bog made your observation special or unique from others.

7. The authors are better to more elaborately discuss about the relationships among H2, CH4 and chloroform in your works.

The authors are grateful to the referees for the time and thought that they have put into their reviews and comments regarding this paper. We have incorporated all of the comments into the revised manuscript, which has led to substantial improvements. Responses to all comments follow. The original comments from the referees are in plain text and our responses are in blue italics.
Referee: 1

Comments to the Author
This is an important paper in that it provides trends of methane, chloroform, hydrogen and ozone concentrations, plus deposition velocities for hydrogen and emission rates of methane and chloroform during nocturnal inversion events over a 27-year study period from a northern peat bog in a maritime climate. Their data analysis will be highly relevant to atmospheric chemistry models.

Thank you for these comments.

Generally, the paper is well written, but in places more detailed information would help the reader (see list comments below). But the structure of this paper does not follow the standard format ‘Abstract - Intro – Results – Discussion – Conclusion’. I assume section 3 is the result section? Section 4 supposed to be a combined Discussion and Conclusion, but in reality, this section does not include any concluding remarks.

Thank you for these comments. The structure has been changed as requested.

I was hoping for a summary of the various concentration trends and impact on policy.

A concluding paragraph has been added drawing attention to the global biogeochemical significance of our study.

Figure 2 & 3 would benefit from trend lines and it would nice to include annual average temperatures to Fig 3 a.

Thank you, these are good suggestions. Trend lines have been added to Figure 2 and temperatures have been added to Figure3.

Detailed comments:

Page 2: last paragraph, 2nd line: change the font to black

Thank you, the type colour has been changed.

Page 3: It would be helpful to provide a map showing the Mace Head location and size of the peatland surrounding this station. References 16,17 are good to quote, but do not substitute the map.

Page 4: change CH4 to ‘CH4’ in row 1, and to ‘ Methane’ in row 2

Thank you, these changes have been made.

Page 4: 2nd paragraph: add a reference to the ‘working standards’

Page 5: 3rd paragraph: Fig1a shows CH4 and NOT H2 data. H2 data are in Fig 1c. Check your document for the correct figure numbers for CH4, CHCl3 and H2.

Thank you these have been checked.

Page 5: 3rd paragraph last sentence: For clarification add: ‘Four events of calm conditions are marked….’

Thank you, the text has been clarified.

Fig 1 legend requires description of the horizontal black bars

Thank you, the legend has been amended.

Page 5: 4th paragraph: CH4 data are in Fig 1a and NOT in Fig 1b. The maximum peak of CH4 is less than 2080 ppb.

Thank you, these changes have been made.

Page 7: Is section 3 the start of the Result and Discussion section?

The Discussion and Conclusions section starts on page 10.

Provide an explanation for not including data beyond 21:00 hrs?

Thank you, an explanation has been included in the text.

Change ‘2100 hrs’ to ‘21:00 hrs’

Thank you, this has been changed.

Page 9: 2nd & 3rd paragraphs: Figure 2 is a rather noisy graph. Trend lines for the 3 gases would support the text a bit better and are easier to interpret.

Thank you for the suggestion. Trend lines have been added to Figure 2.

Page 9:3rd paragraph: What is the reason for the anomalous CH4 fluxes in 2014 – 2016?

We have no explanation as to why these fluxes were anomalously low during 2014 -2 1016 except inherent variability in the peat bog ecosystems. The text has been amended to say this.

Page 10: 1st paragraph discussion section: It would be helpful to elaborate on these two studies (Finland, California):

Thank you, some details have been added.

1) are these long-term or short-term studies, and what was their temperature increase over their study periods compared to your study?

The temperature increase in the Finland urban park study was from -5 to 20oC, which is larger than the increase in annual mean temperatures seen in Ireland.

2) Are there other studies that should be included.

To our knowledge there are no other studies that should be included.

3) Why are the H2 deposition rates at these two sites very similar? Was the urban site also vegetated?

The Finland urban park study was carried out in an area dominated by low cut grass and broad-leaved trees. The environment was therefore very different from our Connemara bog study. Our deposition velocity has wide error bars so the agreement with the Finland study is fortuitous.

A graph showing the temperature increase during your study period may be helpful (either add to Fig 3 or Fig 4).

Thank you, temperature has been added to Figure 3.

Page 10: 2nd paragraph CHCl3: you only provide a reference for the Irish peatlands (ref.8). I don’t think this qualifies your phrase ‘several temperate ecosystems’ .

Reference 8 includes a review of CHCl3 emissions from a number of ‘temperate ecosystems’ in addition to the coastal peatlands of Ireland.

Please provide a reference to : ‘in our previous study of the Connemara peat bogs for the overlapping period 1995 – 2008.’ Is it reference 10 you need to add?

Thank you, reference 10 has been added.

Please stick to the unit ng m-2 s-1 for CHCl3 : ¬‘Previously we found emission rates in the range 0.44 – 12.94 μg m-2 hour-1’ also in the next 2 lines.

Thank you, both sets of units are now provided.

Page 10: 4th paragraph: to be more precise change ‘for natural pristine peatland bog sites’ to ‘for natural pristine bogs from northern peatlands’

Thank you, this change has been made.


Referee: 2

Comments to the Author

Comments

1. On page 5. Please make an explanation to why reducing the oxidation capacity of the atmosphere can exacerbate ozone. Is it because the titration effect of O3-NO or other reasons?

Good point. Reducing the oxidation capacity leads to increased methane levels and methane oxidation is a major source of tropospheric ozone. This explanation has been added to the text.

2. On page 9, is it better to use “21:00” instead of “2100”.

Thank you, this has been changed.

3. On page 10, why are CHCl3 emission estimates in this work much higher than that in the previous ones. Any specific reason for this discrepancy? Stating “the differences are unlikely to be statistically significant” is not enough, please give more explanations.

Thank you. CHCl3 mixing ratios are highly variable in the Connemara bogs as previous studies have shown, see references 8 and 10. The reasons for this inherent variability are not understood. However, because of this variability, the two estimates are not statistically significantly different.

4. On page 11, authors show that the observed increase in rainfall was ascribed to the increase in CH4 emissions. Could authors please explain more on this and is it possible to quantify this effect?

The text explains how an observed increase in rainfall could lead to an increase in methane emissions through change in water table depth. However, we lack any specific data on the ecosystem water table depth or temperatures so we cannot provide the quantification that you require. The text has been amended to refer to our lack of basic understanding of the peatland ecosystem.

5. On page 3, authors state that H2 can lower the oxidation capacity of the atmosphere, thus exacerbating the global warming from ozone (O3). On the contrary, as the oxidation capacity of the atmosphere gets reduced, less O3 is generated from the titration effect of O3 and NO.

Reducing the oxidation capacity leads to increased methane levels and methane oxidation is a major source of tropospheric ozone. This is nothing to do with the NO – O3 – NO2 relationships seen in polluted atmospheres in winter.


6. More in-depth analysis may be needed in the discussion and conclusion. I recommend to build a table to compare your results with that from preceding studies and then talk more incisively about the differences and similarities, e.g. what characteristics of the investigated bog made your observation special or unique from others.

Thank you for raising this good point. Unfortunately, there are few studies with which to compare our results and we have discussed them all in the text already. There is nothing else to add in a Table that is not already in the text.

7. The authors are better to more elaborately discuss about the relationships among H2, CH4 and chloroform in your works.

A concluding paragraph has been added drawing attention to the global biogeochemical significance of our findings.

20-Jul-2021

Dear Professor Simmonds:

Manuscript ID: EA-ART-05-2021-000040.R1
TITLE: Natural Greenhouse Gas and Ozone-depleting Substance Sources and Sinks from the Peat Bogs of Connermara, Ireland from 1994-2020.

Thank you for submitting your revised manuscript to Environmental Science: Atmospheres. After considering the changes you have made, I am pleased to accept your manuscript for publication in its current form. I have copied any final comments from the reviewer(s) below.

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With best wishes,

Dr Lin Wang
Associate Editor, Environmental Science: Atmospheres

Environmental Science: Atmospheres is accompanied by sister journals Environmental Science: Nano, Environmental Science: Processes and Impacts, and Environmental Science: Water Research; publishing high-impact work across all aspects of environmental science and engineering. Find out more at: http://rsc.li/envsci

Reviewer 1

Please check Fig 3, all data points are displayed on the far right of x axis