Measurement Report: Polycyclic aromatic hydrocarbons (PAHs) and their alkylated (RPAHs), nitrated (NPAHs) and oxygenated (OPAHs) derivatives in the global marine atmosphere: occurrence, spatial variations, and source apportionment

Li, Rui; Shen, Yubing; Shao, Yumeng; Gao, Yining; Yao, Ziwei; Liu, Qian; Liu, Xing; Shi, Guitao

doi:https://doi.org/10.5194/egusphere-2024-3740

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https://doi.org/10.5194/egusphere-2024-3740

Preprints

03 Feb 2025

| 03 Feb 2025

Measurement Report: Polycyclic aromatic hydrocarbons (PAHs) and their alkylated (RPAHs), nitrated (NPAHs) and oxygenated (OPAHs) derivatives in the global marine atmosphere: occurrence, spatial variations, and source apportionment

Rui Li, Yubing Shen, Yumeng Shao, Yining Gao, Ziwei Yao, Qian Liu, Xing Liu, and Guitao Shi

Abstract. Ambient polycyclic aromatic hydrocarbons (PAHs) and their derivatives have severe adverse impacts on organism health and ecosystem safety. However, their global distributions, sources, and fate in marine aerosols remain poorly understood. To fill the knowledge gap, high-volume air samples were collected along a transect from China to Antarctica and analyzed for particulate PAHs and derivatives. The highest PAH concentrations in marine aerosols were observed in the Western Pacific (WP: 447±228 pg/m³), followed by the East China Sea (ECS: 195 pg/m³), Antarctic Ocean (AO: 111±91 pg/m³), East Australian Sea (EAS: 104±88 pg/m³), and the lowest in the Bismarck Sea (BS: 17±12 pg/m³). Unexpectedly, PAH concentrations in the AO were even higher than those in the EAS and BS. This could be attributed to the relatively low anthropogenic PAH emissions from Australia and Papua New Guinea, whereas AO is often affected by emissions from engine combustion and biomass burning. In contrast to the distribution of PAHs, OPAH levels in the EAS were much higher than those in the AO. It was assumed that OPAHs mainly originated from the secondary formation of parent PAHs through reactions with O₃ and OH radicals, both of which are more prevalent in EAS. Several source apportionment models suggested that PAHs and their derivatives in marine aerosols are dominated by three sources: coal burning and engine combustion emissions (56 %), wood and biomass burning (30 %), and secondary formation (14 %). Specifically, marine aerosols in ECS and WP were significantly affected by coal burning and engine combustion, while those in BS and EAS were mainly influenced by wildfire and coal combustion. AO was primarily dominated by biomass burning and local shipping emissions.

Received: 29 Nov 2024 – Discussion started: 03 Feb 2025

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Rui Li, Yubing Shen, Yumeng Shao, Yining Gao, Ziwei Yao, Qian Liu, Xing Liu, and Guitao Shi

Status: closed

RC1: 'Comment on egusphere-2024-3740', Anonymous Referee #1, 12 Mar 2025

General comments:
This study provides a comprehensive analysis of the global distribution, spatial variation, and source apportionment of polycyclic aromatic hydrocarbons (PAHs) and their derivatives in the marine atmosphere through large-scale sampling and the PMF model. Notably, the findings fill a knowledge gap regarding the occurrence and composition of particle-phase alkylated, nitrated, and oxygenated PAHs in marine aerosols. These results will facilitate the understanding of the impact of PAH derivatives pollution on marine ecosystems. Therefore, I recommend that the manuscript be published in this journal after minor revisions.
However, the quality assurance/quality control (QA/QC) section requires further elaboration. More detailed explanations regarding the background signal subtraction in mass spectrometry data processing, the calculation of the method detection limit (MDL) and the method quantification limit (MQL), and the linear range of the standard curves should be provided. Moreover, the construction of the PMF model and the description of pollution sources need to be further clarified. Specific comments are provided below.

Specific comments:
(1) Line 48: Replace “spatiotemporal characteristics” with “spatial characteristics”, as the introduction and results in this study focus on spatial rather than temporal trends. Temporal aspects (e.g., seasonal influences) could be emphasized in the implication section.
(2) Lines 84–87: Please specify the reference standards used in the mass spectrometric analysis and whether internal standards were added to evaluate the recovery and instrument stability.
(3) Lines 114–116: To avoid bias introduced by missing data, did the authors use the MDL/2 method for statistical analysis when handling concentration data below the detection limit?
(4) Line 129–131: The range of predefined factor numbers, the ratio of Q_Robust to Q_True, and the optimal number of factors should be provided when constructing the PMF model.
(5) Line 138–140: To ensure model reliability, the coefficient of determination (R²) between the predicted and observed concentrations of PAHs and their derivatives, along with the significance P-value, should also be provided.
(6) Lines 182–187: While the absolute concentrations of OPAHs at some high-latitude sites were comparable to or slightly lower than those of PAHs, the total concentrations of OPAHs were significantly higher than those of PAHs (P < 0.01). Could this significant difference be attributed to the higher concentrations of O₃ and OH radicals at lower latitudes, which promote the oxidation of PAHs? The current explanation seems somewhat unclear.
(7) Line 194–197: It is recommended to add a figure illustrating the distribution of sampling points in the five areas to facilitate understanding.
(8) Line 213–215: The claim that Pyr, BeP, and BaP levels in the Antarctic Ocean (AO) exceed those in the East China Sea (ECS) due to shipping emissions could be misleading, as it may imply that the AO has more shipping activity. I recommend removing this statement and instead emphasizing the impact of wildfires on BbF levels.
(9) Line 261–262: Consider removing “Compared with other PAH derivatives, RPAHs showed low correlation coefficient with meteorological parameters”, as it does not support the conclusion of this paragraph. If retained, provide an explanation for this observation.
(10) Line 506–518: In Figure 4, using identical numbers for different compounds is confusing. It would be clearer to use compound names or their abbreviations instead. Moreover, please clarify what “B” represents on the y-axis of Figures 4c–4d in the figure caption.

Citation: https://doi.org/10.5194/egusphere-2024-3740-RC1
RC2:
'Comment on egusphere-2024-3740', Anonymous Referee #2, 09 May 2025

This manuscript reports measurements of aerosol particle phase polycyclic aromatic hydrocarbons (PAH) and their derivatives along a transect from China to Antarctica based on high volume filter samples obtained during a ship cruise. Such measurements are scarce, and they thus provide valuable new data over regions rarely cover so far and contribute to increasing the global coverage of PAHs over the oceans, especially in remote locations. Apart from reporting the measurements, the authors use specific compound ratios as well as a statistical source apportionment method to address the potential sources of PAH in the different regions. This allows to place the measurements in the context of potential source regions as well as oxidation during transport favoring the formation of oxygenated PAHs. The analytical procedures are well described and the data analysis appears sound. The overall conclusions remain somewhat limited due to the limitations also clearly described in the manuscript, e.g., lack of gas phase measurements or of surface water measurements. Therefore, I am supportive of publication as a measurement report.
In general, the manuscript is well written and structured, though the English language could be improved in some places, especially in terms of using articles. The authors should do another round for that, as the quality of language and grammar decreases towards the end of the manuscript, simply meaning that focussing on these aspects again from the beginning to the end would be important. Remaining corrections could be done at the copy-editing stage. The content is nowhere obscured due to this.
A few specific comments are listed below.
Introduction section, and maybe also in the discussion of the results: I was wondering why the study by Zhang et al. (2022) was not cited, as this seems to be related quite a bit to the topic of the present work.
line 51: A growing body of literature...
line 60: better 'oceans' than 'seas' (also everywhere else in the text), and 'with intense anthropogenic activities'
line 65: 'volatilization from soil and snow...'
line 72/73: This sentence is not clear. If these studies simultaneously study different regional oceans, they would also get global coverage. maybe just delete 'simultaneously' if that is then more correct.
line 75: 'It is important...' (or 'urgent')
line 88: if the end of the cruise refers to the continent of Antarctica, it should be called 'Antarctica', not Antarctic. Please amend throughout the manuscript. In the abstract it is already correct.
line 89: '...of the shipping route...'
line 209: what is the basis for assuming that Australia features low PAH emissions? This could also be brought back where the sources with the various indicators and PMF are discussed.
line 212: '...than those in ECS, and the BbF levels were...'
line 215: '...that the marine aerosol in AO was...'. Here you refer to a single aerosol type, so it should be used in singular. Otherwise you should talk about aerosol particles. Please try to be consistent with this throughout the manuscript.
line 217: could oxidation also be the reason for the low PAH content outside Australia?
line 232: PAH do not have oxidation capacity. What do you want to say here? The potential of PAH to get oxidised?
line 235: 'displayed similar...'
line 243: 'It has been well documented...'
line 246: '... in the Southern hemisphere'
line 257: is adsorption kinetics relevant here? I would assume that equilibrium partitioning is the main parameter determining temperature dependent composition.
line 266-268: please clarify which ratio is attributed to which source.
line 269: here it might be relevant to discuss how oxidation would affect this ratio.
line 276: better 'significant' than unignorable?
line 280: around this discussion: recent changes to international regulation of shipping emissions might also affect the PAH profiles. Have these changes occurred prior to or after the measurements reported here? this could also be mentioned in the introduction section.
line 297: here, at the end of the discussion, the case of low PAH levels outside Australia could be discussed again.
line 306: 'can be related to precursor emissions...'
Figures:
All figure captions need to be placed below the figures.
For the paneled figures: please adapt all font sizes to become equal and well readable. For Figure 2, for instance, the two plots on the left could be made more narrow with narrower symbols to allow for more space for the rest.
Reference
Xue Zhang, Zi-Feng Zhang, Xianming Zhang, Fu-Jie Zhu, Yi-Fan Li, Minghong Cai, Roland Kallenborn, Polycyclic Aromatic Hydrocarbons in the Marine Atmosphere from the Western Pacific to the Southern Ocean: Spatial Variability, Gas/Particle Partitioning, and Source Apportionment, Environmental Science & Technology, 10.1021/acs.est.1c08429, 56, 10, (6253-6261), (2022).

Citation: https://doi.org/10.5194/egusphere-2024-3740-RC2
- AC1: 'Comment on egusphere-2024-3740', Rui Li, 06 Jun 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-3740/egusphere-2024-3740-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-3740-AC1
AC1: 'Comment on egusphere-2024-3740', Rui Li, 06 Jun 2025

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-3740/egusphere-2024-3740-AC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2024-3740-AC1

Status: closed

RC1: 'Comment on egusphere-2024-3740', Anonymous Referee #1, 12 Mar 2025

General comments:
This study provides a comprehensive analysis of the global distribution, spatial variation, and source apportionment of polycyclic aromatic hydrocarbons (PAHs) and their derivatives in the marine atmosphere through large-scale sampling and the PMF model. Notably, the findings fill a knowledge gap regarding the occurrence and composition of particle-phase alkylated, nitrated, and oxygenated PAHs in marine aerosols. These results will facilitate the understanding of the impact of PAH derivatives pollution on marine ecosystems. Therefore, I recommend that the manuscript be published in this journal after minor revisions.
However, the quality assurance/quality control (QA/QC) section requires further elaboration. More detailed explanations regarding the background signal subtraction in mass spectrometry data processing, the calculation of the method detection limit (MDL) and the method quantification limit (MQL), and the linear range of the standard curves should be provided. Moreover, the construction of the PMF model and the description of pollution sources need to be further clarified. Specific comments are provided below.

Specific comments:
(1) Line 48: Replace “spatiotemporal characteristics” with “spatial characteristics”, as the introduction and results in this study focus on spatial rather than temporal trends. Temporal aspects (e.g., seasonal influences) could be emphasized in the implication section.
(2) Lines 84–87: Please specify the reference standards used in the mass spectrometric analysis and whether internal standards were added to evaluate the recovery and instrument stability.
(3) Lines 114–116: To avoid bias introduced by missing data, did the authors use the MDL/2 method for statistical analysis when handling concentration data below the detection limit?
(4) Line 129–131: The range of predefined factor numbers, the ratio of Q_Robust to Q_True, and the optimal number of factors should be provided when constructing the PMF model.
(5) Line 138–140: To ensure model reliability, the coefficient of determination (R²) between the predicted and observed concentrations of PAHs and their derivatives, along with the significance P-value, should also be provided.
(6) Lines 182–187: While the absolute concentrations of OPAHs at some high-latitude sites were comparable to or slightly lower than those of PAHs, the total concentrations of OPAHs were significantly higher than those of PAHs (P < 0.01). Could this significant difference be attributed to the higher concentrations of O₃ and OH radicals at lower latitudes, which promote the oxidation of PAHs? The current explanation seems somewhat unclear.
(7) Line 194–197: It is recommended to add a figure illustrating the distribution of sampling points in the five areas to facilitate understanding.
(8) Line 213–215: The claim that Pyr, BeP, and BaP levels in the Antarctic Ocean (AO) exceed those in the East China Sea (ECS) due to shipping emissions could be misleading, as it may imply that the AO has more shipping activity. I recommend removing this statement and instead emphasizing the impact of wildfires on BbF levels.
(9) Line 261–262: Consider removing “Compared with other PAH derivatives, RPAHs showed low correlation coefficient with meteorological parameters”, as it does not support the conclusion of this paragraph. If retained, provide an explanation for this observation.
(10) Line 506–518: In Figure 4, using identical numbers for different compounds is confusing. It would be clearer to use compound names or their abbreviations instead. Moreover, please clarify what “B” represents on the y-axis of Figures 4c–4d in the figure caption.

Citation: https://doi.org/10.5194/egusphere-2024-3740-RC1
RC2:
'Comment on egusphere-2024-3740', Anonymous Referee #2, 09 May 2025

This manuscript reports measurements of aerosol particle phase polycyclic aromatic hydrocarbons (PAH) and their derivatives along a transect from China to Antarctica based on high volume filter samples obtained during a ship cruise. Such measurements are scarce, and they thus provide valuable new data over regions rarely cover so far and contribute to increasing the global coverage of PAHs over the oceans, especially in remote locations. Apart from reporting the measurements, the authors use specific compound ratios as well as a statistical source apportionment method to address the potential sources of PAH in the different regions. This allows to place the measurements in the context of potential source regions as well as oxidation during transport favoring the formation of oxygenated PAHs. The analytical procedures are well described and the data analysis appears sound. The overall conclusions remain somewhat limited due to the limitations also clearly described in the manuscript, e.g., lack of gas phase measurements or of surface water measurements. Therefore, I am supportive of publication as a measurement report.
In general, the manuscript is well written and structured, though the English language could be improved in some places, especially in terms of using articles. The authors should do another round for that, as the quality of language and grammar decreases towards the end of the manuscript, simply meaning that focussing on these aspects again from the beginning to the end would be important. Remaining corrections could be done at the copy-editing stage. The content is nowhere obscured due to this.
A few specific comments are listed below.
Introduction section, and maybe also in the discussion of the results: I was wondering why the study by Zhang et al. (2022) was not cited, as this seems to be related quite a bit to the topic of the present work.
line 51: A growing body of literature...
line 60: better 'oceans' than 'seas' (also everywhere else in the text), and 'with intense anthropogenic activities'
line 65: 'volatilization from soil and snow...'
line 72/73: This sentence is not clear. If these studies simultaneously study different regional oceans, they would also get global coverage. maybe just delete 'simultaneously' if that is then more correct.
line 75: 'It is important...' (or 'urgent')
line 88: if the end of the cruise refers to the continent of Antarctica, it should be called 'Antarctica', not Antarctic. Please amend throughout the manuscript. In the abstract it is already correct.
line 89: '...of the shipping route...'
line 209: what is the basis for assuming that Australia features low PAH emissions? This could also be brought back where the sources with the various indicators and PMF are discussed.
line 212: '...than those in ECS, and the BbF levels were...'
line 215: '...that the marine aerosol in AO was...'. Here you refer to a single aerosol type, so it should be used in singular. Otherwise you should talk about aerosol particles. Please try to be consistent with this throughout the manuscript.
line 217: could oxidation also be the reason for the low PAH content outside Australia?
line 232: PAH do not have oxidation capacity. What do you want to say here? The potential of PAH to get oxidised?
line 235: 'displayed similar...'
line 243: 'It has been well documented...'
line 246: '... in the Southern hemisphere'
line 257: is adsorption kinetics relevant here? I would assume that equilibrium partitioning is the main parameter determining temperature dependent composition.
line 266-268: please clarify which ratio is attributed to which source.
line 269: here it might be relevant to discuss how oxidation would affect this ratio.
line 276: better 'significant' than unignorable?
line 280: around this discussion: recent changes to international regulation of shipping emissions might also affect the PAH profiles. Have these changes occurred prior to or after the measurements reported here? this could also be mentioned in the introduction section.
line 297: here, at the end of the discussion, the case of low PAH levels outside Australia could be discussed again.
line 306: 'can be related to precursor emissions...'
Figures:
All figure captions need to be placed below the figures.
For the paneled figures: please adapt all font sizes to become equal and well readable. For Figure 2, for instance, the two plots on the left could be made more narrow with narrower symbols to allow for more space for the rest.
Reference
Xue Zhang, Zi-Feng Zhang, Xianming Zhang, Fu-Jie Zhu, Yi-Fan Li, Minghong Cai, Roland Kallenborn, Polycyclic Aromatic Hydrocarbons in the Marine Atmosphere from the Western Pacific to the Southern Ocean: Spatial Variability, Gas/Particle Partitioning, and Source Apportionment, Environmental Science & Technology, 10.1021/acs.est.1c08429, 56, 10, (6253-6261), (2022).

Citation: https://doi.org/10.5194/egusphere-2024-3740-RC2
- AC1: 'Comment on egusphere-2024-3740', Rui Li, 06 Jun 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-3740/egusphere-2024-3740-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-3740-AC1
AC1: 'Comment on egusphere-2024-3740', Rui Li, 06 Jun 2025

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-3740/egusphere-2024-3740-AC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2024-3740-AC1

Rui Li, Yubing Shen, Yumeng Shao, Yining Gao, Ziwei Yao, Qian Liu, Xing Liu, and Guitao Shi

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https://doi.org/10.5194/egusphere-2024-3740-supplement

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Measurement Report: Polycyclic aromatic hydrocarbons (PAHs) and their alkylated (RPAHs), nitrated (NPAHs) and oxygenated (OPAHs) derivatives in the global marine atmosphere: occurrence, spatial variations, and source apportionment R. Li https://zenodo.org/records/14291911

Rui Li, Yubing Shen, Yumeng Shao, Yining Gao, Ziwei Yao, Qian Liu, Xing Liu, and Guitao Shi

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Short summary

It is the first time to reveal the global variations of PAHs derivatives in the marine air. We found that marine aerosols in East China Sea (ECS) and Western Pacific (WP) were significantly affected by coal and engine combustion, while those in Bismarck Sea (BS) and East Australian Sea (EAS) were mainly influenced by wildfire and coal combustion. Antarctic Ocean (AO) was dominated by biomass burning and local shipping emissions. This finding help elucidate the mechanism of global PAH cycle.


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