the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 17 Mar 2025
Anthropogenic air pollutants strongly interact with natural aerosols over the eastern China seas: key processes, size distributions, and seasonalities
Abstract. Marine aerosols play important roles in climate, marine biogeochemistry, and coastal air quality. Over the eastern China seas adjacent to densely populated East Asia, aerosols are mutually affected by anthropogenic pollution and natural emissions. However, the impacts of anthropogenic-natural interactions on aerosol composition and properties are not well understood due to limited systematic observations. Here we characterized the composition of size-resolved aerosols over this region across four seasonal cruise campaigns, identifying major aerosol sources and influencing processes. Aerosol mass concentrations typically show trimodal distributions, with fine-mode mass dominating in spring and winter due to strong influences of continental pollution. However, in 40.9 % of samples, continental secondary aerosols are highly aged, lacking a fine-mode NO3– peak. Gaseous HNO3 evaporated from continental secondary aerosols and anthropogenic NOx react with natural dust and sea spray aerosols (SSA), forming coarse-mode NO3–, which contributes 43.2 % and 12.7 % of total NO3–, respectively. This shifts NO3– from fine to coarse mode, altering the spatial pattern of nitrogen deposition and its ecological effects. Additionally, 27.7 % of SSA Cl– is depleted on average, reaching 40.8 % in summer, which is an important source of reactive halogens that affect ozone chemistry. Shipping emissions contribute to ~20 % of SO42– in spring and summer before the International Maritime Organization’s 2020 regulation, but this contribution likely decreases by one order of magnitude thereafter. This analysis highlights the importance of anthropogenic-natural interactions over coastal seas, underscoring the need for further studies to assess their subsequent environmental impacts.
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- RC1: 'Comment on egusphere-2025-678', Anonymous Referee #1, 08 Apr 2025
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RC2: 'Comment on egusphere-2025-678', Anonymous Referee #2, 30 Apr 2025
This study investigates the chemical composition, size distribution, and source contributions of aerosols over the eastern China seas based on four seasonal cruise campaigns. Using size-resolved sampling and PMF analysis, the authors identify key anthropogenic and natural sources. The work highlights important processes such as NO3 redistribution and Cl depletion, and discusses their implications for regional air quality and deposition.
While the study presents a comprehensive dataset and detailed analyses, the connection between the results and discussion sections is somewhat fragmented. A few conclusions are not clearly supported by the data. The four parts of the discussion read more like standalone topics rather than integrated components of one topic.
I recommend addressing the following comments to improve the clarity of the manuscript.
- The autumn cruise sampling was conducted during the COVID pandemic. Have the authors considered the potential influence of COVID-related emission changes? How might this affect the observations in this study?
- Additionally, for the autumn cruise, it appears that samples 9, 10, and 11 were collected at the same location, which is very close to land. How could this affect the results? Do these three samples reflect more emissions from port activities (e.g., shipping emissions, primary anthropogenic sources)? For example, in Figure 3, sample 10 from the autumn cruise shows much higher SO4, NO3, and NH4 concentrations and lower Na and Cl concentrations than other autumn samples. Samples 9–11 also appear to show different levels of C2O4 and trace metals.
- Line 149: Given the large uncertainties in PM mass concentration, the comparison here does not appear convincing.
- Section 3.2: The results for EC measurements are missing.
- Line 202: “cme”?
- Lines 254–255: Please list the sample numbers for the co-transport events. How were these events identified? Have the authors examined wind data during these events? Does the wind information support the interpretation?
- Lines 266–270: The authors discuss coarse-mode NO3 formation via nitrogen-containing gases in the previous paragraph and now discuss a transformation from fine-mode to coarse-mode particles. Do the authors suggest that nitrogen gases typically react with fine particles to form particle-phase NO3 in the absence of dust? The relationship between nitrogen gases, fine-mode NO3, and coarse-mode NO3 needs clarification.
- Lines 281–283: Is there any data comparing the formation of NaNO3 dust-associated NO3?
- Line 285: The meaning of this sentence is unclear. Please revise.
- Is there data in this study that supports the proposed transformation mechanism of NO3 SO4?
- Line 287: Delete “Meanwhile.”
- Line 296: Please specify the precursors of C2O4. Are these precursors different in continental vs. marine environments?
- Lines 305–306: Is the unimodal distribution of NO3 more likely due to the lack of fine-mode NH4NO3 from land sources, rather than transformation to coarse particles?
- The authors frequently refer to aerosol aging. Were there any measurements related to chemical composition (e.g., O:C ratio)? Or is the discussion of aging solely based on PMF results?
- Figure S5: It appears the R² is driven primarily by the highest x-axis data point.
- Are the authors equating the R² value to “70% variance explained”? If so, this may not be statistically accurate.
- Lines 334–335: In the PMF “aged SSA” factor and the related discussion, Cl appears to be zero. Is this how aged SSA is defined in this study or in the literature? Is such a complete depletion realistic in ambient conditions?
- Line 335: The authors use the SO4/Na ratio from seawater to estimate SO4. Does this assume that the ratio remains constant even in aged aerosols?
- Lines 341–342: What data supports this calculation and conclusion?
- Lines 343–345: Does “70.7%” refer to R² and “57.2%” to the slope? Clarify how R² reflects spatiotemporal variance. This discussion needs expansion.
- Lines 351–353: Previously, the authors highlighted that the transformation of NO3 affects its lifetime and deposition. Now, they argue that reactions between SSA and acidic gases occur more readily on smaller particles. Can the authors compare these two mechanisms and identify which is likely more dominant?
- Lines 370–371: A reference is needed here.
- Lines 395–397: Is there any data regarding reductions in V and Ni concentrations in marine fuels? Given the large drop in aerosol-phase V and Ni in this study, could other factors be involved?
- Related to comment #4: Since EC is an important marker for shipping emissions and was measured, the authors should elaborate on EC results and their relevance.
- Line 448: The section number should be corrected to “5.”
Citation: https://doi.org/10.5194/egusphere-2025-678-RC2 - AC1: 'Responses to Reviewers' Comments on egusphere-2025-678', Shengqian Zhou, 19 Jul 2025
Status: closed
-
RC1: 'Comment on egusphere-2025-678', Anonymous Referee #1, 08 Apr 2025
This manuscript investigates the seasonal chemical composition of particulate matter over the eastern China seas, based on shipborne measurements. A Size-resolved PMF analysis was employed to analyze the chemical composition data, and the effects of shipping emissions were discussed. Readers are frequently required to cross-reference multiple figures—often out of sequential order—to understand the presented arguments. For example, the discussion in Lines 299–307 necessitates referencing Figures 3 and 8 simultaneously, which disrupts the flow. A thorough reorganization of the manuscript structure and figure arrangement is strongly recommended to enhance readability.
Moreover, the key scientific conclusions are insufficiently clear. The title highlights the interaction between anthropogenic emissions and natural aerosols, but the main text lacks adequate discussion or supporting evidence on this topic. As currently presented, the work is more akin to a “measurement report” than a comprehensive “research article.” Nevertheless, it may be considered for publication after the following major concerns are fully addressed:
- Line 266-267: Is there any literature or observational evidence supporting the shift of nitrate from fine to coarse particles? I am also curious whether coagulation effects could contribute to the observed increase in coarse-mode nitrate concentrations. Since the coagulation of smaller particles may lead to the formation of larger ones—or smaller particles could be scavenged by larger particles—this process could also result in a shift of chemical species toward larger size fractions.
- Section 3.3: The PMF model analyzed size-resolved chemical composition. However, the PMF factors were characterized by the size-integrated concentration. It is recommended to characterize PMF factors by both their size-integrated contributions and their mass size distributions. Additionally, diagnostic plots such as the Q/Qexp plot should be included in the SI to demonstrate the model’s performance.
- Line 254-255: It is advisable to clearly indicate the co-transport events in Figure 8. Moreover, the specific dates of these events should be provided. Please clarify the method used to identify these events—was it based on abrupt changes in mass concentrations, backward trajectory analysis, or another approach?
- Line 257-258: A discussion of the mass distribution of NO3- and SO42- of each factor would be very helpful.
- Line 258-259: Please consider quantifying and presenting the mass contributions of different PMF factors to NO₃⁻. A bar chart or tabulated data could greatly improve clarity.
- Line 280-283: Can the author provide a rough estimate of the mass contribution of the NaNO₃ formation pathway to coarse-mode nitrate? Since the conclusion is primarily based on size distribution data, it would be more convincing to support it with additional evidence or quantitative estimation.
- Line 294-296: Please specify which figure or table supports this conclusion. It is important to ensure that every claim is clearly linked to the corresponding data presentation.
- Line 301-302: It is difficult to identify the “strong impact” samples in Figure 3. Consider providing a separate figure showing the size distribution of NO₃⁻ during the periods classified as having strong anthropogenic influence. Additionally, please clarify the criteria used to define these periods.
- Line 303-304: Please provide some discussion of air masses, such as wind filed in different seasons or backward trajectory analysis.
- Line 305-306: Please specify which sample(s) in Figure 3 were influenced by sea fog conditions. A note or label in the figure would help readers easily identify these cases.
- Line 308-310: The R² value in Figure S5 represents the fit of the linear regression model for PM₁.₈ mass. However, it does not necessarily imply that CS&B and AC&MS explain 70% of the variance in PM₁.₈. Notably, the regression slope is about 0.5, suggesting that CS&B and AC&MS jointly account for only ~50% of PM₁.₈ mass. Please revise this statement to accurately reflect the regression results.
- Line 310-311: Please clarify what is meant by “explained variance.” If referring to statistical variance explained by regression, it should be supported with appropriate statistical metrics.
- 10: I It is unexpected that the aged sea salt factor contributes notably to NO₃⁻ in the fine size range (0.1–0.32 μm). The manuscript previously suggested negligible fine-mode NO₃⁻ for highly aged aerosols. Please provide further explanation or hypothesis for this observation.
- Line 341-342: How was the “3.4 times” increase calculated? Was this based on empirical data or cited from previous literature? Please clarify the basis and, if calculated, include the equation or data used.
- Line 342-345: Same concern as in Comment 11: The use of R² and the slope should be carefully interpreted. Please rephrase this sentence to ensure the conclusion aligns with the regression outcome
- Line 345-346: Please provide data corresponding to strong dust transport events. Clarify which specific samples were collected during these events and consider highlighting them in relevant figures or tables.
- Line 351-354: Please elaborate on how the faster reaction rate of aged sea salt results in a smaller median particle diameter. Could you also provide a rough estimation or reference regarding the reaction rate differences between aged and fresh sea salt?
- Line 356-357: Clarify how the chloride depletion ratio was determined. Was it calculated from molar ratios of Na⁺ and Cl⁻ in the measurement data, or derived from another method?
- Line 376-378: Please present the seasonal variation in the size distribution of Ca²⁺ in either figure or tabular format to support the corresponding discussion.
- Line 387-394: Although the text discusses the seasonal variation of V and Ni, the corresponding data are not presented. Please include a figure or table showing the concentration and size distribution of V and Ni in different seasons.
- Line 464: Please provide additional evidence to support the claim of fine-mode NH₄NO₃ decomposition, such as thermodynamic analysis, ambient temperature data, or references to previous studies
- Line 474-477: Bromide and halogen radicals are mentioned in the conclusion, yet they are not discussed in the main body of the text. Please either integrate the relevant discussion into the manuscript or remove this sentence from the conclusion to avoid confusion.
Citation: https://doi.org/10.5194/egusphere-2025-678-RC1 -
RC2: 'Comment on egusphere-2025-678', Anonymous Referee #2, 30 Apr 2025
This study investigates the chemical composition, size distribution, and source contributions of aerosols over the eastern China seas based on four seasonal cruise campaigns. Using size-resolved sampling and PMF analysis, the authors identify key anthropogenic and natural sources. The work highlights important processes such as NO3 redistribution and Cl depletion, and discusses their implications for regional air quality and deposition.
While the study presents a comprehensive dataset and detailed analyses, the connection between the results and discussion sections is somewhat fragmented. A few conclusions are not clearly supported by the data. The four parts of the discussion read more like standalone topics rather than integrated components of one topic.
I recommend addressing the following comments to improve the clarity of the manuscript.
- The autumn cruise sampling was conducted during the COVID pandemic. Have the authors considered the potential influence of COVID-related emission changes? How might this affect the observations in this study?
- Additionally, for the autumn cruise, it appears that samples 9, 10, and 11 were collected at the same location, which is very close to land. How could this affect the results? Do these three samples reflect more emissions from port activities (e.g., shipping emissions, primary anthropogenic sources)? For example, in Figure 3, sample 10 from the autumn cruise shows much higher SO4, NO3, and NH4 concentrations and lower Na and Cl concentrations than other autumn samples. Samples 9–11 also appear to show different levels of C2O4 and trace metals.
- Line 149: Given the large uncertainties in PM mass concentration, the comparison here does not appear convincing.
- Section 3.2: The results for EC measurements are missing.
- Line 202: “cme”?
- Lines 254–255: Please list the sample numbers for the co-transport events. How were these events identified? Have the authors examined wind data during these events? Does the wind information support the interpretation?
- Lines 266–270: The authors discuss coarse-mode NO3 formation via nitrogen-containing gases in the previous paragraph and now discuss a transformation from fine-mode to coarse-mode particles. Do the authors suggest that nitrogen gases typically react with fine particles to form particle-phase NO3 in the absence of dust? The relationship between nitrogen gases, fine-mode NO3, and coarse-mode NO3 needs clarification.
- Lines 281–283: Is there any data comparing the formation of NaNO3 dust-associated NO3?
- Line 285: The meaning of this sentence is unclear. Please revise.
- Is there data in this study that supports the proposed transformation mechanism of NO3 SO4?
- Line 287: Delete “Meanwhile.”
- Line 296: Please specify the precursors of C2O4. Are these precursors different in continental vs. marine environments?
- Lines 305–306: Is the unimodal distribution of NO3 more likely due to the lack of fine-mode NH4NO3 from land sources, rather than transformation to coarse particles?
- The authors frequently refer to aerosol aging. Were there any measurements related to chemical composition (e.g., O:C ratio)? Or is the discussion of aging solely based on PMF results?
- Figure S5: It appears the R² is driven primarily by the highest x-axis data point.
- Are the authors equating the R² value to “70% variance explained”? If so, this may not be statistically accurate.
- Lines 334–335: In the PMF “aged SSA” factor and the related discussion, Cl appears to be zero. Is this how aged SSA is defined in this study or in the literature? Is such a complete depletion realistic in ambient conditions?
- Line 335: The authors use the SO4/Na ratio from seawater to estimate SO4. Does this assume that the ratio remains constant even in aged aerosols?
- Lines 341–342: What data supports this calculation and conclusion?
- Lines 343–345: Does “70.7%” refer to R² and “57.2%” to the slope? Clarify how R² reflects spatiotemporal variance. This discussion needs expansion.
- Lines 351–353: Previously, the authors highlighted that the transformation of NO3 affects its lifetime and deposition. Now, they argue that reactions between SSA and acidic gases occur more readily on smaller particles. Can the authors compare these two mechanisms and identify which is likely more dominant?
- Lines 370–371: A reference is needed here.
- Lines 395–397: Is there any data regarding reductions in V and Ni concentrations in marine fuels? Given the large drop in aerosol-phase V and Ni in this study, could other factors be involved?
- Related to comment #4: Since EC is an important marker for shipping emissions and was measured, the authors should elaborate on EC results and their relevance.
- Line 448: The section number should be corrected to “5.”
Citation: https://doi.org/10.5194/egusphere-2025-678-RC2 - AC1: 'Responses to Reviewers' Comments on egusphere-2025-678', Shengqian Zhou, 19 Jul 2025
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This manuscript investigates the seasonal chemical composition of particulate matter over the eastern China seas, based on shipborne measurements. A Size-resolved PMF analysis was employed to analyze the chemical composition data, and the effects of shipping emissions were discussed. Readers are frequently required to cross-reference multiple figures—often out of sequential order—to understand the presented arguments. For example, the discussion in Lines 299–307 necessitates referencing Figures 3 and 8 simultaneously, which disrupts the flow. A thorough reorganization of the manuscript structure and figure arrangement is strongly recommended to enhance readability.
Moreover, the key scientific conclusions are insufficiently clear. The title highlights the interaction between anthropogenic emissions and natural aerosols, but the main text lacks adequate discussion or supporting evidence on this topic. As currently presented, the work is more akin to a “measurement report” than a comprehensive “research article.” Nevertheless, it may be considered for publication after the following major concerns are fully addressed: