Measurement report: Crustal materials play an increasing role in elevating particle pH: Insights from 12-year records in a typical inland city of China

Zhang, Hongyu; Wang, Shenbo; Dong, Zhangsen; Li, Xiao; Zhang, Ruiqin

doi:https://doi.org/10.5194/egusphere-2024-2869

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https://doi.org/10.5194/egusphere-2024-2869

Preprints

05 Nov 2024

| 05 Nov 2024

Measurement report: Crustal materials play an increasing role in elevating particle pH: Insights from 12-year records in a typical inland city of China

Hongyu Zhang, Shenbo Wang, Zhangsen Dong, Xiao Li, and Ruiqin Zhang

Abstract. Particle acidity is a critical parameter that affects atmospheric chemistry. Concerns have been raised about the exacerbating aerosol and rainfall acidity due to China’s ongoing efforts to reduce ammonia emissions. Therefore, it is urgent to clarify the changing trends in particle pH response to air pollution control policies, especially in North China, which is significantly affected by dust aerosol. 12-years observational data in Zhengzhou reveal that the annual average PM_2.5 concentration decreased from 212 ± 102 μg/m³ in 2013 to 60 ± 41 μg/m³ in 2022, with the largest reduction in sulfate (79 %). Correspondingly, the annual particle pH increased by 0.11 units from 2013 to 2019. In addition, the elevated particle pH in 2015 and 2018 was notably influenced by the increase in TNH_x (NH₃ + NH₄⁺). Note that the crustal material concentrations and their proportions increased significantly during 2019–2022, which might be responsible for the resuspension of surrounding soil dust. Even though the TNH_x concentration was decreasing, the annual average growth rate of pH values increased to 0.21 units from 2019 to 2022. This phenomenon is not unique to Zhengzhou, as major cities in the North China Plain have also experienced a pronounced upward trend in coarse particles after 2019. Therefore, the future ammonia reduction policies in North China may not lead to a rapid increase in particle acidity buffering by the crustal materials.

Received: 14 Sep 2024 – Discussion started: 05 Nov 2024

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.

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08 Jul 2025

Measurement report: Crustal materials play an increasing role in elevating particle pH – insights from 12-year records in a typical inland city of China

Hongyu Zhang, Shenbo Wang, Zhangsen Dong, Xiao Li, and Ruiqin Zhang

Atmos. Chem. Phys., 25, 6943–6955, https://doi.org/10.5194/acp-25-6943-2025,https://doi.org/10.5194/acp-25-6943-2025, 2025

Short summary

Hongyu Zhang, Shenbo Wang, Zhangsen Dong, Xiao Li, and Ruiqin Zhang

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-2869', Anonymous Referee #1, 03 Dec 2024

In this article, the authors analyze 12 years of field observation data from Zhengzhou, China, to investigate trends in aerosol composition concentrations and its acidity. This approach is well-aligned with the scope and objectives of the “Measurement Report”, making the study highly relevant. However, there are contentious aspects in the discussion and final conclusions of this article. Specifically, whether crustal materials play a dominant role in driving the changes in aerosol acidity remains uncertain. This issue affects several parts of the article, including its main argument and even the title. I believe the authors are capable of making substantial revisions to the article.
Here are my specific recommendations:
Lines 15-17: Compared to the reduction of ammonia emissions, the reductions in acidic precursors such as SO₂ and NO_x have been more significant, leading to an overall increase in atmospheric acidity (including aerosols, clouds, and precipitation). Studying the trends in aerosol acidity is highly meaningful, but it is essential to consider the combined impact of the reduction in both acidic and basic precursors.
Lines 19-21: The 12-year observation period and the corresponding years for the PM concentration results do not align. While I understand that the authors began observations in 2011, the abstract should be rephrased to ensure clarity and consistency in the presentation of the time frame.
Lines 28-29: According to mainstream forecasts regarding the need for further PM reduction under China’s carbon peaking and carbon neutrality policy, future emission reduction strategies will primarily focus on acidic precursors. The expression here needs to be more precise and cautious.
Lines 63-65: There is a lack of logical flow from the previous discussion of acidity changes to the conclusion/summary in this sentence. Additionally, aerosol acidity is unlikely to be neutral or even approach neutrality by nature in general.
Lines 66-67: This may not be entirely accurate. The relative contribution of sulfate and nitrate does not directly determine aerosol acidity. The authors need to identify the true driving factors behind the pH trend. In my opinion, the main drivers are the NH₃/NH₄⁺ multiphase buffering, ALWC, and non-volatile cations, rather than other components or temperature. This is because, over the long term, the impact of temperature variations on pH is minimal within the same season.
Lines 85-86: Given the limitations, under what circumstances does it go from 4 to 7?
Lines 93-94: After reviewing the research progress, I suggest concluding with a summary that introduces the focus of this article. Specifically, what makes Zhengzhou and other cities different, what issue this study aims to address based on previous research, and what contributions this study makes. This is essential in scientific writing.
Line 123: Provide the version of ISORROPIA and the time resolution of the input components.
Line 160: The spring of 2021 saw multiple rare dust storms in the North China Plain, but why was the CM not high in 2021? Additionally, the resolution of the figures in both the main text and SI needs to be improved to at least 300 dpi, as many figures in the SI are unclear.
Line 170 (Figure S3): It is recommended to use the same y-axis range for consistency. Regarding the drivers of seasonal variations (increase or decrease), I believe the discussion here lacks sufficient rigor, with an incomplete chain of evidence. I suggest that the authors consider separately discussing natural and anthropogenic sources, especially the impact of spring dust storm events on dust levels. In section 3.3, the source-related discussion is also mentioned, and therefore, this part needs to be strengthened.
Lines 239-241: I believe ALWC is an important factor influencing pH, and it should not be solely attributed to sulfate. The authors need to carefully consider this point. Specifically, it should be evaluated whether the continuous decrease in ALWC affects pH, and whether this impact might even outweigh the influence of changes in aerosol composition.
Lines 280-282: Where is the data for this section sourced from?
Lines 283-286: Although many researchers have done significant work on the impact of ammonia reduction on PM levels, I believe that under China’s current policies, future emission reductions will not primarily focus on ammonia. Therefore, the authors need to reconsider whether the focus of this "Measurement Report" should be placed on ammonia. I suggest that the authors revise all statements related to ammonia, including the title.

Citation: https://doi.org/10.5194/egusphere-2024-2869-RC1
- AC1: 'Reply on RC1', Hongyu Zhang, 17 Feb 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2869/egusphere-2024-2869-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-2869-AC1
- AC3: 'Reply on RC1', Hongyu Zhang, 17 Feb 2025
  
  Sorry for the mistake. The image numbering order in the manuscript of the previous file was incorrect. We have made the necessary corrections and re-uploaded the revised file.
  
  Citation: https://doi.org/10.5194/egusphere-2024-2869-AC3
RC2:
'Comment on egusphere-2024-2869', Anonymous Referee #2, 03 Jan 2025
Zhang et al. analyzed the particle pH collected in a Chinese inland city. This analysis is based on 4228 filter samples collected from four seasons in 2011 – 2022. As a measurement report, the study fits into the scope of Atmospheric Chemistry and Physics. The authors claim that the evolving particle pH was driven by the interplay of declines in SO₄^2-, increases in TNH_x, and rises in Ca²⁺concentrations over time. The manuscript can be considered for publication once the comments below are addressed.
Major Comment
Lines 111 -112 and 120 – 121: It is unclear whether Ti was measured or not.

Lines 135 – 136: The linear regression proposed by Wei et al. (2023) is based on the dataset collected in the wintertime but not from 2013 to 2020. This needs clarification. Since the regression was based on wintertime data, it is questionable if the relationship is still valid for data in seasons other than winter.

Section 2.2.3: Why was 1000 m chosen as the height in the HYSPLIT simulations? If 1000 m was already well above the boundary layer height, how do the simulated back trajectory simulations represent the ground-level measurements? In addition, how was the optimum number of clusters chosen by the authors? What clustering technique was used in the analysis? What data was used as the meteorological input?

Sections 3.1 and 3.2: How did the author estimate the decreases in the mass concentrations? Which year was chosen as the reference year? A proper analysis using Mann-Kendall and Sen’s slope should be carried out here and in other places associated with trend analysis.

Please briefly describe the Air Pollution Prevention and Control Action Plan and Three-Year Action Plan in the main text. In general, readers outside China have no idea about these policies.

Please explain why Zhengzhou is representative of a typical inland city in North China in the main text. There is no background information about aerosol research conducted in Zhengzhou and how they compare with those findings in other typical Chinese megacities, such as Beijing or Shanghai.

Minor Comment
Figure S1: Please label the highways, coal-fired power plant, and gas-fired power plant on the map.

Section 2.1: What are the uncertainties in the measured concentrations for individual components?

Lines 114 – 115: Apart from just citing references here, please provide the details about analytical methods and quality control in the supplement.

Section 2.2.2: What was the set activity coefficient of H⁺ in the model?

Line 172: There is no data showing that the WS was higher in spring and summer compared to autumn and winter.

Figure S4: Is there any data for Ca²⁺ in 2015?

Lines 229 – 231: Please provide a discussion about why the pH trend is similar to those in Beijing but different from those in Shanghai and Hong Kong.

Figure 5: How did the authors estimate the contribution of a component to the changes in pH?

Where is the figure or table associated with Lines 256 – 266?

Technical Comment
Line 17: It is unclear what is "particle pH response".

Line 19: It should be “12-year”

Graphical abstract: Please use a different color for the pH. Apparently, the color light blue is too bright for visualization.

Line 57: Please use a word different than “research hotspot”.

Line 64: Please use a different term instead of “fostered a persistent belief”.

Eq 4: It should be “NH₄⁺”

Figures in main text and SI: the labels for x- and y- axis and annotations are too small to read. All figures need to be modified for better visualization.

Lines 173 and 174: more effective than what?

Line 246: NO₃^- can be used to replace nitrate ions.

Line 252: SO₄^2-/NO₃^- can means the ratio between SO₄^2- and NO₃^-. I assume the authors use “/” to represent “or” here. If so, please use the word “or”.

The format of “TNH_x” should be consistent throughout the manuscript.

Some color choices in figures need to be reconsidered. Certain annotations in color are not color-friendly for visualization.
Citation: https://doi.org/10.5194/egusphere-2024-2869-RC2
- AC2: 'Reply on RC2', Hongyu Zhang, 17 Feb 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2869/egusphere-2024-2869-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-2869-AC2
- AC4: 'Reply on RC2', Hongyu Zhang, 17 Feb 2025
  
  Sorry for the mistake. The image numbering order in the manuscript of the previous file was incorrect. We have made the necessary corrections and re-uploaded the revised file.
  
  Citation: https://doi.org/10.5194/egusphere-2024-2869-AC4

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-2869', Anonymous Referee #1, 03 Dec 2024

In this article, the authors analyze 12 years of field observation data from Zhengzhou, China, to investigate trends in aerosol composition concentrations and its acidity. This approach is well-aligned with the scope and objectives of the “Measurement Report”, making the study highly relevant. However, there are contentious aspects in the discussion and final conclusions of this article. Specifically, whether crustal materials play a dominant role in driving the changes in aerosol acidity remains uncertain. This issue affects several parts of the article, including its main argument and even the title. I believe the authors are capable of making substantial revisions to the article.
Here are my specific recommendations:
Lines 15-17: Compared to the reduction of ammonia emissions, the reductions in acidic precursors such as SO₂ and NO_x have been more significant, leading to an overall increase in atmospheric acidity (including aerosols, clouds, and precipitation). Studying the trends in aerosol acidity is highly meaningful, but it is essential to consider the combined impact of the reduction in both acidic and basic precursors.
Lines 19-21: The 12-year observation period and the corresponding years for the PM concentration results do not align. While I understand that the authors began observations in 2011, the abstract should be rephrased to ensure clarity and consistency in the presentation of the time frame.
Lines 28-29: According to mainstream forecasts regarding the need for further PM reduction under China’s carbon peaking and carbon neutrality policy, future emission reduction strategies will primarily focus on acidic precursors. The expression here needs to be more precise and cautious.
Lines 63-65: There is a lack of logical flow from the previous discussion of acidity changes to the conclusion/summary in this sentence. Additionally, aerosol acidity is unlikely to be neutral or even approach neutrality by nature in general.
Lines 66-67: This may not be entirely accurate. The relative contribution of sulfate and nitrate does not directly determine aerosol acidity. The authors need to identify the true driving factors behind the pH trend. In my opinion, the main drivers are the NH₃/NH₄⁺ multiphase buffering, ALWC, and non-volatile cations, rather than other components or temperature. This is because, over the long term, the impact of temperature variations on pH is minimal within the same season.
Lines 85-86: Given the limitations, under what circumstances does it go from 4 to 7?
Lines 93-94: After reviewing the research progress, I suggest concluding with a summary that introduces the focus of this article. Specifically, what makes Zhengzhou and other cities different, what issue this study aims to address based on previous research, and what contributions this study makes. This is essential in scientific writing.
Line 123: Provide the version of ISORROPIA and the time resolution of the input components.
Line 160: The spring of 2021 saw multiple rare dust storms in the North China Plain, but why was the CM not high in 2021? Additionally, the resolution of the figures in both the main text and SI needs to be improved to at least 300 dpi, as many figures in the SI are unclear.
Line 170 (Figure S3): It is recommended to use the same y-axis range for consistency. Regarding the drivers of seasonal variations (increase or decrease), I believe the discussion here lacks sufficient rigor, with an incomplete chain of evidence. I suggest that the authors consider separately discussing natural and anthropogenic sources, especially the impact of spring dust storm events on dust levels. In section 3.3, the source-related discussion is also mentioned, and therefore, this part needs to be strengthened.
Lines 239-241: I believe ALWC is an important factor influencing pH, and it should not be solely attributed to sulfate. The authors need to carefully consider this point. Specifically, it should be evaluated whether the continuous decrease in ALWC affects pH, and whether this impact might even outweigh the influence of changes in aerosol composition.
Lines 280-282: Where is the data for this section sourced from?
Lines 283-286: Although many researchers have done significant work on the impact of ammonia reduction on PM levels, I believe that under China’s current policies, future emission reductions will not primarily focus on ammonia. Therefore, the authors need to reconsider whether the focus of this "Measurement Report" should be placed on ammonia. I suggest that the authors revise all statements related to ammonia, including the title.

Citation: https://doi.org/10.5194/egusphere-2024-2869-RC1
- AC1: 'Reply on RC1', Hongyu Zhang, 17 Feb 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2869/egusphere-2024-2869-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-2869-AC1
- AC3: 'Reply on RC1', Hongyu Zhang, 17 Feb 2025
  
  Sorry for the mistake. The image numbering order in the manuscript of the previous file was incorrect. We have made the necessary corrections and re-uploaded the revised file.
  
  Citation: https://doi.org/10.5194/egusphere-2024-2869-AC3
RC2:
'Comment on egusphere-2024-2869', Anonymous Referee #2, 03 Jan 2025
Zhang et al. analyzed the particle pH collected in a Chinese inland city. This analysis is based on 4228 filter samples collected from four seasons in 2011 – 2022. As a measurement report, the study fits into the scope of Atmospheric Chemistry and Physics. The authors claim that the evolving particle pH was driven by the interplay of declines in SO₄^2-, increases in TNH_x, and rises in Ca²⁺concentrations over time. The manuscript can be considered for publication once the comments below are addressed.
Major Comment
Lines 111 -112 and 120 – 121: It is unclear whether Ti was measured or not.

Lines 135 – 136: The linear regression proposed by Wei et al. (2023) is based on the dataset collected in the wintertime but not from 2013 to 2020. This needs clarification. Since the regression was based on wintertime data, it is questionable if the relationship is still valid for data in seasons other than winter.

Section 2.2.3: Why was 1000 m chosen as the height in the HYSPLIT simulations? If 1000 m was already well above the boundary layer height, how do the simulated back trajectory simulations represent the ground-level measurements? In addition, how was the optimum number of clusters chosen by the authors? What clustering technique was used in the analysis? What data was used as the meteorological input?

Sections 3.1 and 3.2: How did the author estimate the decreases in the mass concentrations? Which year was chosen as the reference year? A proper analysis using Mann-Kendall and Sen’s slope should be carried out here and in other places associated with trend analysis.

Please briefly describe the Air Pollution Prevention and Control Action Plan and Three-Year Action Plan in the main text. In general, readers outside China have no idea about these policies.

Please explain why Zhengzhou is representative of a typical inland city in North China in the main text. There is no background information about aerosol research conducted in Zhengzhou and how they compare with those findings in other typical Chinese megacities, such as Beijing or Shanghai.

Minor Comment
Figure S1: Please label the highways, coal-fired power plant, and gas-fired power plant on the map.

Section 2.1: What are the uncertainties in the measured concentrations for individual components?

Lines 114 – 115: Apart from just citing references here, please provide the details about analytical methods and quality control in the supplement.

Section 2.2.2: What was the set activity coefficient of H⁺ in the model?

Line 172: There is no data showing that the WS was higher in spring and summer compared to autumn and winter.

Figure S4: Is there any data for Ca²⁺ in 2015?

Lines 229 – 231: Please provide a discussion about why the pH trend is similar to those in Beijing but different from those in Shanghai and Hong Kong.

Figure 5: How did the authors estimate the contribution of a component to the changes in pH?

Where is the figure or table associated with Lines 256 – 266?

Technical Comment
Line 17: It is unclear what is "particle pH response".

Line 19: It should be “12-year”

Graphical abstract: Please use a different color for the pH. Apparently, the color light blue is too bright for visualization.

Line 57: Please use a word different than “research hotspot”.

Line 64: Please use a different term instead of “fostered a persistent belief”.

Eq 4: It should be “NH₄⁺”

Figures in main text and SI: the labels for x- and y- axis and annotations are too small to read. All figures need to be modified for better visualization.

Lines 173 and 174: more effective than what?

Line 246: NO₃^- can be used to replace nitrate ions.

Line 252: SO₄^2-/NO₃^- can means the ratio between SO₄^2- and NO₃^-. I assume the authors use “/” to represent “or” here. If so, please use the word “or”.

The format of “TNH_x” should be consistent throughout the manuscript.

Some color choices in figures need to be reconsidered. Certain annotations in color are not color-friendly for visualization.
Citation: https://doi.org/10.5194/egusphere-2024-2869-RC2
- AC2: 'Reply on RC2', Hongyu Zhang, 17 Feb 2025
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-2869/egusphere-2024-2869-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-2869-AC2
- AC4: 'Reply on RC2', Hongyu Zhang, 17 Feb 2025
  
  Sorry for the mistake. The image numbering order in the manuscript of the previous file was incorrect. We have made the necessary corrections and re-uploaded the revised file.
  
  Citation: https://doi.org/10.5194/egusphere-2024-2869-AC4

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Hongyu Zhang on behalf of the Authors (18 Feb 2025) Author's response

EF by Mario Ebel (19 Feb 2025) Manuscript Author's tracked changes

ED: Referee Nomination & Report Request started (25 Feb 2025) by Alex Lee

RR by Anonymous Referee #1 (09 Mar 2025)

RR by Anonymous Referee #2 (17 Mar 2025)

Suggestions for revision or reasons for rejection

The authors have addressed most of my comments. However, there are still a few places that require clarification before the manuscript can be accepted.

Major Comments:
1. Section 2.2.3: The author stated that the choice of 1000 m ASL as the receptor height was based on the elevation of the Taihang Mountains (1000 – 1500 m ASL). I am not convinced that using 100 m ASL as the receptor height in the HYSPLIT model will lead to unrealistic results. In fact, using 100 m ASL does not influence the movement of an air mass; it can still have a trajectory above 1000 m.

To support the selection of 1000 m ASL, the authors must show consistent HYSPLIT results, irrespective of whether a receptor height of 100 meters or 1000 meters ASL is used during a chosen period for a case study. Otherwise, I recommend that the authors redo the analysis using a receptor height of 100 meters, as this height is more representative of conditions within the boundary layer due to its proximity to the surface.

Minor Comments:
1. Figure S2: Could the authors clarify why there are more data points in Fig S2 (b) compared with Fig S2 (a)?
2. Lines 190 – 201: The statement is too descriptive and long to follow. The authors need to include a plot showing the SPVAR and TSV as a function of cluster number in the SI.
3. Line 207: What are the priority areas?
4. Lines 204 – 224: The information is very descriptive and reads like a report. It needs to be properly shortened to improve the readability.
5. The response to “What was the set activity coefficient of H in the model?” needs to be included in the section of the method.
6. Lines 314 – 315: Could the authors include references to support the statement “the comparable chemical composition trends and meteorological conditions”?
7. Lines 318 – 319: More discussion needs to be provided on how higher temperatures and more rainfall drive the distinct pH trends in Shanghai and Hong Kong.

Hide

ED: Reconsider after major revisions (19 Mar 2025) by Alex Lee

AR by Hongyu Zhang on behalf of the Authors (10 Apr 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (11 Apr 2025) by Alex Lee

RR by Anonymous Referee #2 (19 Apr 2025)

ED: Publish as is (21 Apr 2025) by Alex Lee

AR by Hongyu Zhang on behalf of the Authors (23 Apr 2025) Manuscript

Journal article(s) based on this preprint

08 Jul 2025

Measurement report: Crustal materials play an increasing role in elevating particle pH – insights from 12-year records in a typical inland city of China

Hongyu Zhang, Shenbo Wang, Zhangsen Dong, Xiao Li, and Ruiqin Zhang

Atmos. Chem. Phys., 25, 6943–6955, https://doi.org/10.5194/acp-25-6943-2025,https://doi.org/10.5194/acp-25-6943-2025, 2025

Short summary

Hongyu Zhang, Shenbo Wang, Zhangsen Dong, Xiao Li, and Ruiqin Zhang

Supplement

https://doi.org/10.5194/egusphere-2024-2869-supplement

Data sets

Measurement report: Crustal materials play an increasing role in elevating particle pH: Insights from 12-year records in a typical inland city of China-Data H. Zhang https://doi.org/10.5281/zenodo.14032007

Hongyu Zhang, Shenbo Wang, Zhangsen Dong, Xiao Li, and Ruiqin Zhang

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To address this, 12-year observational data in Zhengzhou were investigated and revealed that the resuspension of surrounding soil dust determined the rebound of crustal material concentrations after 2019, further elevating the particle pH. Therefore, the future ammonia reduction policies in North China may not lead to a rapid increase in particle acidity buffering by the crustal materials, but it is necessary to consider synergistic control with dust sources.


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