From the journal Environmental Science: Atmospheres Peer review history

22-Jun-2023

Dear Dr Passig:

Manuscript ID: EA-ART-04-2023-000056
TITLE: Detection of Ship Emissions from Distillate Fuel Operation via Single-Particle Profiling of Polycyclic Aromatic Hydrocarbons

Thank you for your submission to Environmental Science: Atmospheres, published by the Royal Society of Chemistry. I sent your manuscript to reviewers and I have now received their reports which are copied below.

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Prof. Nønne Prisle
Associate Editor, Environmental Sciences: Atmospheres

************

Reviewer 1

This paper presents a new approach for detecting atmospheric particles produced by ships operating on distillate fuel. The method uses single particle mass spectrometry to identify a specific PAH pattern in the ship emissions. The PAH pattern was identified in a series of ship engine tests and used to assign particles emitted from a passing ship at a coastal measurement site.

Scope: This work is clearly within the scope of the journal.

Originality: This is the first application of single particle mass spectrometry to investigate the PAH patterns produced by ships operating on distillate fuel.

Importance: Distillate fuel is increasingly being used by ships, particularly in emission control areas around coastlines. However, it does not contain the traditional chemical markers (V, Ni, and Fe) and identification of the emissions in ambient air is therefore challenging. This method overcomes the lack of metal markers, by utilising a reproducible PAH pattern which is produced by ships using the distillate fuel.

Impact: This study presents an approach that could be used to identify ship plumes in studies of PM2.5 source apportionment.

Reliability: The work is very well described and clearly of high quality. The authors have used a robust approach involving both engine tests and field measurements to produce reliable data.

The paper is very well written and presented. It can be accepted for publication after the following very minor issues are addressed.

1. At the end of section titled "SPMS Interpretation", the authors state that the method does not distinguish between PAH isomers, such as phenanthrene and anthracene. However, in a later section on Page 6 (first column) where the observed PAH patterns (Figure 1) are discussed, they are immediately assigned to phenanthrene and its alkylated relatives. The reasons for this are subsequently outlined, but I think this part could read better if it is first stated that the parent PAH could be due to phenanthrene or anthracene and then point towards the other research that supports assignment to phenanthrene and alkylated phenanthrenes, as opposed to anthracene.

2. Figures 1, 3, 4, S1, S3 and S5 do not have a y-axis label.

3. On page 8, column 2; Use originate instead of origin

4. On page 9, column 1; define OC

5. On page 9, column 2; should be "....points to ship traffic...."

6. Figure 6 caption; Use circled instead of circulated

7. On page 10, column 1; Use circled instead of circulated

8. On page 10, column 2; Do not understand use of the word "aggregates". Suggest "...from old cars and off-road vehicles..."

9. On page 11, column 1; clean up of diesel exhaust is not just for gas. Suggest "...equipped with exhaust treatment."

10. On page 21, Figure S1 caption; Should refer to Figure 3(a) not Figure 2(a)

11. On page 22, Figure S2 caption; For clarity and to be consistent with the text in the main manuscript, suggest "....drops rapidly below 200 nm and reaches..."

11. On page 23, Figure S4 caption; Suggest "The majority (88%) belongs....."

12. On page 23, Figure S5 caption; Suggest "...and the C2H3O+ fragment at m/z = +43."

13. On page 23, Figure S5 caption; Use circled instead of circulated

14. On page 23, Figure S5 caption; Suggest "...and the C2H3O+ fragment at m/z = +43."

Reviewer 2

A developed analytical method based on single-particle mass spectrometry was successfully applied to ship engine's exhaust aerosol in the laboratory and in the field. Typical PAH patterns of phenanthrene + alkylated phenanthrenes result from unburnt fuel and could be assigned to ship emissions in the field. Land-based Diesel emissions produce similar patterns but mostly do not interfere with the application for ships. The method has a lot of potential to be used for ship emission monitoring.

- The figures of the mass spectra are too small and can hardly be read.
- Correct nomenclature of PAH should be used: (methods) benzo(a)pyrene -> [] bracket and a in italic
- west, south, etc -> West, South etc.
- Figure 1: add information, where soot is visible (the C- columns?) and add in the figure caption after "...PAH pattern (red)....". And what exactly is meant by "Cabon clusters" and "important fragments"? Please explain in the caption
- page 7: ...and the larger particles show stronger organic carbon peaks....it is not clear to me what is meant here in Figure 3 (more red peaks in Figure 3b than 3a?), please make it more clear
- page 7: compared to Toner et al....
- Figure 4: I can hardly see any differences in the four figures, please make it more clear
- page 9: Figure S4 in the Supporting Information shows one of the resulting clusters...I cannot see this directly in Figure S4, please label in Fig S4 what you want to show

EA-ART-04-2023-000056
Response to Reviewers


Referee: 1

Comments to the Author
This paper presents a new approach for detecting atmospheric particles produced by ships operating on distillate fuel. The method uses single particle mass spectrometry to identify a specific PAH pattern in the ship emissions. The PAH pattern was identified in a series of ship engine tests and used to assign particles emitted from a passing ship at a coastal measurement site.

Scope: This work is clearly within the scope of the journal.

Originality: This is the first application of single particle mass spectrometry to investigate the PAH patterns produced by ships operating on distillate fuel.

Importance: Distillate fuel is increasingly being used by ships, particularly in emission control areas around coastlines. However, it does not contain the traditional chemical markers (V, Ni, and Fe) and identification of the emissions in ambient air is therefore challenging. This method overcomes the lack of metal markers, by utilising a reproducible PAH pattern which is produced by ships using the distillate fuel.

Impact: This study presents an approach that could be used to identify ship plumes in studies of PM2.5 source apportionment.

Reliability: The work is very well described and clearly of high quality. The authors have used a robust approach involving both engine tests and field measurements to produce reliable data.

The paper is very well written and presented. It can be accepted for publication after the following very minor issues are addressed.

>> We thank the referee for reviewing the manuscript and for the very positive feedback!

1. At the end of section titled "SPMS Interpretation", the authors state that the method does not distinguish between PAH isomers, such as phenanthrene and anthracene. However, in a later section on Page 6 (first column) where the observed PAH patterns (Figure 1) are discussed, they are immediately assigned to phenanthrene and its alkylated relatives. The reasons for this are subsequently outlined, but I think this part could read better if it is first stated that the parent PAH could be due to phenanthrene or anthracene and then point towards the other research that supports assignment to phenanthrene and alkylated phenanthrenes, as opposed to anthracene.

>> Thank you! We rephrased the paragraph, now starting with the description of the series beginning at m/z=178 and the statements on phenanthrene/anthracene immediately thereafter. “… dominated by a signal series in m/z sequences of 14 Da beginning at m/z=178 […] The peak at m/z=178 can stem from both phenanthrene and anthracene, however, anthracene is nearly exclusively produced in the combustion process and has a lower degree of substitution60…“

2. Figures 1, 3, 4, S1, S3 and S5 do not have a y-axis label.
>> We apologize for this error. We added y-axis labels to all these figures accordingly. Please note that the modifications in the Supporting Information are not tracked/highlighted.

3. On page 8, column 2; Use originate instead of origin
>> Corrected.

4. On page 9, column 1; define OC
>> Thank you. Corrected.

5. On page 9, column 2; should be "....points to ship traffic...."
>> Corrected.

6. Figure 6 caption; Use circled instead of circulated
>> Thank you. Corrected.

7. On page 10, column 1; Use circled instead of circulated
>> Ditto.

8. On page 10, column 2; Do not understand use of the word "aggregates". Suggest "...from old cars and off-road vehicles..."
>> Changed “aggregates” to “stationary engines”.

9. On page 11, column 1; clean up of diesel exhaust is not just for gas. Suggest "...equipped with exhaust treatment."
>> Thank you. Changed accordingly.

10. On page 21, Figure S1 caption; Should refer to Figure 3(a) not Figure 2(a)
>> Corrected.

11. On page 22, Figure S2 caption; For clarity and to be consistent with the text in the main manuscript, suggest "....drops rapidly below 200 nm and reaches..."
>> Changed accordingly.

11. On page 23, Figure S4 caption; Suggest "The majority (88%) belongs....."
>> Changed accordingly.

12. On page 23, Figure S5 caption; Suggest "...and the C2H3O+ fragment at m/z = +43."
>> Changed accordingly.

13. On page 23, Figure S5 caption; Use circled instead of circulated
>> Corrected.

14. On page 23, Figure S5 caption; Suggest "...and the C2H3O+ fragment at m/z = +43."
>> Changed accordingly.

Referee: 2

Comments to the Author
A developed analytical method based on single-particle mass spectrometry was successfully applied to ship engine's exhaust aerosol in the laboratory and in the field. Typical PAH patterns of phenanthrene + alkylated phenanthrenes result from unburnt fuel and could be assigned to ship emissions in the field. Land-based Diesel emissions produce similar patterns but mostly do not interfere with the application for ships. The method has a lot of potential to be used for ship emission monitoring.

>> We thank the referee for reviewing the manuscript and the positive comments. We believe that addressing the reviewer’s helpful comments will improve the clarity of our manuscript.

- The figures of the mass spectra are too small and can hardly be read.
>> Thank you. We increased the size of annotations in the mass spectra. Moreover, we decreased the x-axis limits and changed the aspect ratio of Fig. 1, so that details are larger. In addition, we will provide high-resolution and vector images for production.

- Correct nomenclature of PAH should be used: (methods) benzo(a)pyrene -> [] bracket and a in italic
>> Thank you. Corrected accordingly.

- west, south, etc -> West, South etc.
>> Changed accordingly.

- Figure 1: add information, where soot is visible (the C- columns?) and add in the figure caption after "...PAH pattern (red)....". And what exactly is meant by "Cabon clusters" and "important fragments"? Please explain in the caption
>> Thank you. We changed and extended the figure caption accordingly.

- page 7: ...and the larger particles show stronger organic carbon peaks....it is not clear to me what is meant here in Figure 3 (more red peaks in Figure 3b than 3a?), please make it more clear
>> Thank you. To improve clarity, we rephrased it to “…and the larger particles show stronger phosphate and nitrate signals and more fragment peaks from organic carbon, e.g. in the PAH spectrum.”

- page 7: compared to Toner et al....
>> Corrected.

- Figure 4: I can hardly see any differences in the four figures, please make it more clear
>> Yes. There are only minor differences, which underlines the suitability of the PAH pattern as a marker. We rephrased the caption to better explain the shift in the mass spectra, e.g.: “With increasing engine load, the only noticeable change in the average PAH mass spectra (each n=3,500) is a subtle shift towards lighter PAHs….”

- page 9: Figure S4 in the Supporting Information shows one of the resulting clusters...I cannot see this directly in Figure S4, please label in Fig S4 what you want to show
>> We apologize for the lack of clarity here. We inserted the missing information in Fig. S4 and modified the caption accordingly. Please note that the modifications in the Supporting Information are not tracked/highlighted.

12-Jul-2023

Dear Dr Passig:

Manuscript ID: EA-ART-04-2023-000056.R1
TITLE: Detection of Ship Emissions from Distillate Fuel Operation via Single-Particle Profiling of Polycyclic Aromatic Hydrocarbons

Thank you for submitting your revised manuscript to Environmental Science: Atmospheres. 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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Prof. Nønne Prisle
Associate Editor, Environmental Sciences: Atmospheres

Reviewer 1

The authors have done a good job of addressing comments from both reviewers.