Measurement Report: Seasonal variation and anthropogenic influence on cloud condensation nuclei (CCN) activity in the South China Sea: Insights from shipborne observations during summer and winter of 2021

Ou, Hengjia; Cai, Mingfu; Zhang, Yongyun; Ni, Xue; Liang, Baoling; Sun, Qibin; Mai, Shixin; Sun, Cuizhi; Zhou, Shengzhen; Wang, Haichao; Sun, Jiaren; Zhao, Jun

doi:https://doi.org/10.5194/egusphere-2024-956

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https://doi.org/10.5194/egusphere-2024-956

Preprints

08 May 2024

| 08 May 2024

Measurement Report: Seasonal variation and anthropogenic influence on cloud condensation nuclei (CCN) activity in the South China Sea: Insights from shipborne observations during summer and winter of 2021

Hengjia Ou, Mingfu Cai, Yongyun Zhang, Xue Ni, Baoling Liang, Qibin Sun, Shixin Mai, Cuizhi Sun, Shengzhen Zhou, Haichao Wang, Jiaren Sun, and Jun Zhao

Abstract. Understanding seasonal variation in cloud condensation nuclei (CCN) activity and the impact of anthropogenic emissions in marine environments is crucial for assessing climate change. In this study, two shipborne observations in the South China Sea (SCS) during the summer and winter of 2021 were conducted. During summer, higher particle number concentrations but lower mass concentrations of non-refractory submicron particles (NR-PM₁) were observed. These differences were attributed to the dominance of particles in the Aitken mode during summer and in the accumulation mode during winter. Moreover, particles during summer were more hygroscopic with higher activation ratios (ARs) at all supersaturation (SS). Based on backward trajectory analysis, the whole campaign was classified into terrestrial and mixed air mass influence periods. Particles measured during the terrestrial period consistently exhibited lower hygroscopicity values. Additionally, minor variations were shown for all NR-PM₁ components under different air mass influences during summer, while the mass fraction of nitrate increased significantly under terrestrial influence during winter. Particle number size distribution (PNSD) exhibited unimodal distribution during terrestrial period and bimodal distribution during mixed air mass influence period, with winter displaying a more pronounced bimodal pattern than summer. The impact of PNSD on AR was greater than on aerosol hygroscopicity in summer, and vice versa in winter. During terrestrial period, significant variations in PNSD were observed with the offshore distance, and the largest variation was seen in Aitken mode during both summer and winter. Meanwhile, aerosol hygroscopicity shows an increasing trend with the offshore distance, which is primarily attributed to the increase of sulfate fraction during summer and the decrease of the black carbon fraction during winter. Using a single parameterized PNSD in the N_CCN prediction can lead to errors exceeding 100 % during both summer and winter, with dominant terrestrial air masses in the SCS atmosphere, while using a constant hygroscopicity parameter would lower the errors in the N_CCN prediction (~15 % during winter and ~10 % during summer). Our study shows significant differences in aerosol properties between winter and summer seasons and highlights the influence of anthropogenic emissions on the CCN activity in the SCS.

Received: 29 Mar 2024 – Discussion started: 08 May 2024

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Journal article(s) based on this preprint

27 Feb 2025

Measurement report: Cloud condensation nuclei (CCN) activity in the South China Sea from shipborne observations during the summer and winter of 2021 – seasonal variation and anthropogenic influence

Hengjia Ou, Mingfu Cai, Yongyun Zhang, Xue Ni, Baoling Liang, Qibin Sun, Shixin Mai, Cuizhi Sun, Shengzhen Zhou, Haichao Wang, Jiaren Sun, and Jun Zhao

Atmos. Chem. Phys., 25, 2495–2513, https://doi.org/10.5194/acp-25-2495-2025,https://doi.org/10.5194/acp-25-2495-2025, 2025

Short summary

Hengjia Ou, Mingfu Cai, Yongyun Zhang, Xue Ni, Baoling Liang, Qibin Sun, Shixin Mai, Cuizhi Sun, Shengzhen Zhou, Haichao Wang, Jiaren Sun, and Jun Zhao

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-956', Anonymous Referee #1, 26 Jun 2024

Please find the reviewer comments below.;

Citation: https://doi.org/10.5194/egusphere-2024-956-RC1
- AC1: 'Reply on RC1', Mingfu Cai, 31 Jul 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-956/egusphere-2024-956-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-956-AC1
RC2:
'Comment on egusphere-2024-956', Anonymous Referee #2, 27 Jun 2024

This manuscript investigates the aerosol and CCN properties over the South China Sea area. The manuscript generally provides some interesting results regarding the seasonal variation and the anthropogenic influences in this area. However, the writing of the manuscript needs a lot of improvements. The focus of the manuscript may also need some changes. Below are some suggestions:
1. I find it very distracting when results from this study are mixed with a lot of results from previous studies in Section 3. It is very difficult to get the point of this study when it is mixed with other studies. For example, lines 227-234, some measurements of particle number concentration are listed. It actually doesn’t mean much if only to compare which one is higher and which one is lower. I would suggest adding a table to summarize these measurements so that it is a lot easier for the readers to see which one is higher and which one is lower. Alternatively, results from previous studies can be organized into the Introduction section so that the readers can have a better background from the beginning. The comparison between the previous results and this study can also be organized into a new Discussion section. Basically I would prefer that Section 3 focuses on the results only from this study. Similarly, lines 236-238, lines 249-251, lines 256-265, lines 298-308, lines 321-323, lines 344-345, lines 362-367, lines 374-377, lines 380-388, and lines 392-396 are all results from previous studies. Please put these previous results in a table, or put them into Introduction or a new Discussion section. This would help the readers to integrate the results from this study.
2. It is very interesting to see that aerosol and CCN properties are quite different in summer and winter. This indicates that the seasonal variations of aerosol and CCN properties should be considered in regional or climate models when studying aerosol-cloud interaction for this area. I especially agree that particle composition and kappa are quite different in summer and winter. However, it is not very clear if particle number concentration is significantly different in summer and winter. The manuscript emphasizes that summer has much higher number concentration when the marine atmosphere is influenced by terrestrial air masses (lines 226-227). I agree. But how about the average number concentration in the whole observed period in summer? Is it still much higher than that in winter? For many days when the atmosphere is influenced by mixed air masses, particle number concentration seems to be similar in summer and winter. So please check if the number concentration in the whole summer period is on average much higher than that in winter. The panel d in Figure 2 cannot provide such information because summer and winter are not plotted with the same scale. It would help if the properties are plotted in the same scale for summer and winter in Figure 2.
In addition, regarding the dominant mode in PNSD, it is said in line 30 that PNSD has a dominance of Aitken mode in summer and a dominance of accumulation mode in winter. But based on Figure 2 and Figure 3, I would say that both Aitken mode and accumulation mode are important in winter. It is not appropriate to conclude that the dominant mode in winter is accumulation mode. So I would see more evidence regarding the dominant mode. Maybe you could calculate the total number concentration in Aitken mode and in accumulation mode and compare to see which one is dominant.
3. I think the size-resolved AR should be shown, especially because D50 is determined by fitting the AR and dry diameter at each supersaturation.
4. The method in 2.2.1 (equation 1) and 2.2.2 (equation 4) seem to be in conflict. In equation 1, I assume that the activation ratio is size-resolved? However, in Equation 4, the activation ratio is the bulk activation ratio? So please clarify whether AR represents the size-resolved or the bulk activation ratio.
5. Regarding the size-dependent kappa value in lines 282-283, please clarify the reasons why kappa value is size-dependent.
6. Regarding the AR ratio in lines 390-391 in Section 3.3, what does “beyond D50” mean? The meaning of this sentence is not clear. Please revise. This is very important for understanding the sensitivity tests afterwards. I think it’s quite interesting that PNSD is the most important factor influencing Nccn in summer, whereas hygroscopicity is the most important factor in winter (lines 416-417). This is based on the sensitivity tests performed in this study. I wonder if the authors can provide any underlying physical reasons for this.
7. Section 3.4 seems to have conflicting results with Section 3.3. It is shown in Section 3.3 that PNSD determines Nccn in summer and hygroscopicity determines Nccn in winter. However, in Section 3.4, it is shown that PNSD is important for Nccn in both summer and winter. I think Section 3.3 and Section 3.4 should be better integrated. The writing should be more concise and focused.
Minor points:
1. Please provide a little discussion on cloud climatology for the studied area. It would be good to see that there is a relatively high cloud fraction, especially warm cloud in the studied area.
2. Lines 431-433 are very similar to lines 448-450. The writing should be improved.
3. The manuscript title and the titles in Section 3 are kind of confusing. A lot of “impact of … on….” Or “influence of … on …” are seen in the titles. For example,
Title of the manuscript: “anthropogenic influence on CCN activation”
Title of 3.2: Impact of chemical composition on hygroscopicity
Title of 3.2.1: impact of inorganic components
Title of 3.2.2: impact of organic components
Title of 3.4: influence of spatial distribution of particle properties on NCCN
In addition, the title of 3.1 is too simple. This title does not provide much information.
There are also some inconsistency in the titles. For example, I can see that seasonal variation is a focus of this study based on the title of the manuscript. However, only the title of 3.3 has “seasons”. Based on the current titles, it is hard to figure out which part in Section 3 actually discusses “seasonal variations”.
4. In section 3, there are some sentences that are repetitive. For example, lines 266-268, and lines 280-282. Section 3 should be integrated in a better way. After the results from previous studies are moved to other places, Section 3 can be more focused and better integrated.
5. It seems the organic carbon and elemental carbon are missing in Figure 2. See the figure caption, (d).
6. Equation 1: Nccn/Ncn should be replaced with AR, to be consistent with the use of AR in Equation 4.
7. Equation 2: the two formula should be put in separate lines.
8. Line 448: “in winter, the increasing trend…” should be changed to “in winter, the decreasing trend”.
9. Line 39: “impact of PNSD on AR was greater than on aerosol hygroscopicity in summer” should be changed to “impact of PNSD on AR was greater than aerosol hygroscopicity in summer”. In addition, “vice versa” is not a good expression in this sentence.

Citation: https://doi.org/10.5194/egusphere-2024-956-RC2
- AC2: 'Reply on RC2', Mingfu Cai, 31 Jul 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-956/egusphere-2024-956-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-956-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-956', Anonymous Referee #1, 26 Jun 2024

Please find the reviewer comments below.;

Citation: https://doi.org/10.5194/egusphere-2024-956-RC1
- AC1: 'Reply on RC1', Mingfu Cai, 31 Jul 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-956/egusphere-2024-956-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-956-AC1
RC2:
'Comment on egusphere-2024-956', Anonymous Referee #2, 27 Jun 2024

This manuscript investigates the aerosol and CCN properties over the South China Sea area. The manuscript generally provides some interesting results regarding the seasonal variation and the anthropogenic influences in this area. However, the writing of the manuscript needs a lot of improvements. The focus of the manuscript may also need some changes. Below are some suggestions:
1. I find it very distracting when results from this study are mixed with a lot of results from previous studies in Section 3. It is very difficult to get the point of this study when it is mixed with other studies. For example, lines 227-234, some measurements of particle number concentration are listed. It actually doesn’t mean much if only to compare which one is higher and which one is lower. I would suggest adding a table to summarize these measurements so that it is a lot easier for the readers to see which one is higher and which one is lower. Alternatively, results from previous studies can be organized into the Introduction section so that the readers can have a better background from the beginning. The comparison between the previous results and this study can also be organized into a new Discussion section. Basically I would prefer that Section 3 focuses on the results only from this study. Similarly, lines 236-238, lines 249-251, lines 256-265, lines 298-308, lines 321-323, lines 344-345, lines 362-367, lines 374-377, lines 380-388, and lines 392-396 are all results from previous studies. Please put these previous results in a table, or put them into Introduction or a new Discussion section. This would help the readers to integrate the results from this study.
2. It is very interesting to see that aerosol and CCN properties are quite different in summer and winter. This indicates that the seasonal variations of aerosol and CCN properties should be considered in regional or climate models when studying aerosol-cloud interaction for this area. I especially agree that particle composition and kappa are quite different in summer and winter. However, it is not very clear if particle number concentration is significantly different in summer and winter. The manuscript emphasizes that summer has much higher number concentration when the marine atmosphere is influenced by terrestrial air masses (lines 226-227). I agree. But how about the average number concentration in the whole observed period in summer? Is it still much higher than that in winter? For many days when the atmosphere is influenced by mixed air masses, particle number concentration seems to be similar in summer and winter. So please check if the number concentration in the whole summer period is on average much higher than that in winter. The panel d in Figure 2 cannot provide such information because summer and winter are not plotted with the same scale. It would help if the properties are plotted in the same scale for summer and winter in Figure 2.
In addition, regarding the dominant mode in PNSD, it is said in line 30 that PNSD has a dominance of Aitken mode in summer and a dominance of accumulation mode in winter. But based on Figure 2 and Figure 3, I would say that both Aitken mode and accumulation mode are important in winter. It is not appropriate to conclude that the dominant mode in winter is accumulation mode. So I would see more evidence regarding the dominant mode. Maybe you could calculate the total number concentration in Aitken mode and in accumulation mode and compare to see which one is dominant.
3. I think the size-resolved AR should be shown, especially because D50 is determined by fitting the AR and dry diameter at each supersaturation.
4. The method in 2.2.1 (equation 1) and 2.2.2 (equation 4) seem to be in conflict. In equation 1, I assume that the activation ratio is size-resolved? However, in Equation 4, the activation ratio is the bulk activation ratio? So please clarify whether AR represents the size-resolved or the bulk activation ratio.
5. Regarding the size-dependent kappa value in lines 282-283, please clarify the reasons why kappa value is size-dependent.
6. Regarding the AR ratio in lines 390-391 in Section 3.3, what does “beyond D50” mean? The meaning of this sentence is not clear. Please revise. This is very important for understanding the sensitivity tests afterwards. I think it’s quite interesting that PNSD is the most important factor influencing Nccn in summer, whereas hygroscopicity is the most important factor in winter (lines 416-417). This is based on the sensitivity tests performed in this study. I wonder if the authors can provide any underlying physical reasons for this.
7. Section 3.4 seems to have conflicting results with Section 3.3. It is shown in Section 3.3 that PNSD determines Nccn in summer and hygroscopicity determines Nccn in winter. However, in Section 3.4, it is shown that PNSD is important for Nccn in both summer and winter. I think Section 3.3 and Section 3.4 should be better integrated. The writing should be more concise and focused.
Minor points:
1. Please provide a little discussion on cloud climatology for the studied area. It would be good to see that there is a relatively high cloud fraction, especially warm cloud in the studied area.
2. Lines 431-433 are very similar to lines 448-450. The writing should be improved.
3. The manuscript title and the titles in Section 3 are kind of confusing. A lot of “impact of … on….” Or “influence of … on …” are seen in the titles. For example,
Title of the manuscript: “anthropogenic influence on CCN activation”
Title of 3.2: Impact of chemical composition on hygroscopicity
Title of 3.2.1: impact of inorganic components
Title of 3.2.2: impact of organic components
Title of 3.4: influence of spatial distribution of particle properties on NCCN
In addition, the title of 3.1 is too simple. This title does not provide much information.
There are also some inconsistency in the titles. For example, I can see that seasonal variation is a focus of this study based on the title of the manuscript. However, only the title of 3.3 has “seasons”. Based on the current titles, it is hard to figure out which part in Section 3 actually discusses “seasonal variations”.
4. In section 3, there are some sentences that are repetitive. For example, lines 266-268, and lines 280-282. Section 3 should be integrated in a better way. After the results from previous studies are moved to other places, Section 3 can be more focused and better integrated.
5. It seems the organic carbon and elemental carbon are missing in Figure 2. See the figure caption, (d).
6. Equation 1: Nccn/Ncn should be replaced with AR, to be consistent with the use of AR in Equation 4.
7. Equation 2: the two formula should be put in separate lines.
8. Line 448: “in winter, the increasing trend…” should be changed to “in winter, the decreasing trend”.
9. Line 39: “impact of PNSD on AR was greater than on aerosol hygroscopicity in summer” should be changed to “impact of PNSD on AR was greater than aerosol hygroscopicity in summer”. In addition, “vice versa” is not a good expression in this sentence.

Citation: https://doi.org/10.5194/egusphere-2024-956-RC2
- AC2: 'Reply on RC2', Mingfu Cai, 31 Jul 2024
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-956/egusphere-2024-956-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2024-956-AC2

Peer review completion

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

AR by Mingfu Cai on behalf of the Authors (31 Jul 2024) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (31 Jul 2024) by Armin Sorooshian

RR by Anonymous Referee #2 (14 Aug 2024)

RR by Anonymous Referee #3 (02 Sep 2024)

ED: Reconsider after major revisions (02 Sep 2024) by Armin Sorooshian

AR by Mingfu Cai on behalf of the Authors (05 Oct 2024) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (08 Oct 2024) by Armin Sorooshian

RR by Anonymous Referee #4 (22 Oct 2024)

RR by Anonymous Referee #5 (07 Nov 2024)

ED: Reconsider after major revisions (07 Nov 2024) by Armin Sorooshian

AR by Mingfu Cai on behalf of the Authors (05 Dec 2024) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (05 Dec 2024) by Armin Sorooshian

RR by Anonymous Referee #5 (02 Jan 2025)

ED: Publish subject to minor revisions (review by editor) (02 Jan 2025) by Armin Sorooshian

AR by Mingfu Cai on behalf of the Authors (06 Jan 2025) Author's response Author's tracked changes Manuscript

ED: Publish subject to minor revisions (review by editor) (06 Jan 2025) by Armin Sorooshian

AR by Mingfu Cai on behalf of the Authors (07 Jan 2025) Author's response Author's tracked changes Manuscript

ED: Publish as is (07 Jan 2025) by Armin Sorooshian

AR by Mingfu Cai on behalf of the Authors (08 Jan 2025)

Journal article(s) based on this preprint

27 Feb 2025

Measurement report: Cloud condensation nuclei (CCN) activity in the South China Sea from shipborne observations during the summer and winter of 2021 – seasonal variation and anthropogenic influence

Hengjia Ou, Mingfu Cai, Yongyun Zhang, Xue Ni, Baoling Liang, Qibin Sun, Shixin Mai, Cuizhi Sun, Shengzhen Zhou, Haichao Wang, Jiaren Sun, and Jun Zhao

Atmos. Chem. Phys., 25, 2495–2513, https://doi.org/10.5194/acp-25-2495-2025,https://doi.org/10.5194/acp-25-2495-2025, 2025

Short summary

Hengjia Ou, Mingfu Cai, Yongyun Zhang, Xue Ni, Baoling Liang, Qibin Sun, Shixin Mai, Cuizhi Sun, Shengzhen Zhou, Haichao Wang, Jiaren Sun, and Jun Zhao

Supplement

https://doi.org/10.5194/egusphere-2024-956-supplement

Data sets

Measurement Report: Seasonal variation and anthropogenic influence on cloud condensation nuclei (CCN) activity in the South China Sea: Insights from shipborne observations during summer and winter of 2021 [dataset] Hengjia Ou https://doi.org/10.6084/m9.figshare.25472545

Hengjia Ou, Mingfu Cai, Yongyun Zhang, Xue Ni, Baoling Liang, Qibin Sun, Shixin Mai, Cuizhi Sun, Shengzhen Zhou, Haichao Wang, Jiaren Sun, and Jun Zhao

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Two shipborne observations in the South China Sea (SCS) during the summer and winter of 2021 were conducted. Our study found that aerosol hygroscopicity is higher in SCS in summer than in winter, with significant influences from various terrestrial air masses. Aerosol size distribution had a stronger effect on activation ratio (AR) than aerosol hygroscopicity in summer and vice versa in winter. Our study provides valuable information to enhance our understanding of CCN activities in the SCS.

Measurement Report: Seasonal variation and anthropogenic influence on cloud condensation nuclei (CCN) activity in the South China Sea: Insights from shipborne observations during summer and winter of 2021

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