Hygroscopic growth obscures actual variation in anthropogenic aerosol optical depth over central China during 2010&ndash;2024

He, Yun; Jing, Dongzhe; Yin, Zhenping; Müller, Detlef; Liu, Fuchao; Zhang, Yunpeng; Yi, Yang; Huang, Kaiming; Yi, Fan

doi:10.5194/egusphere-2025-6360

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https://doi.org/10.5194/egusphere-2025-6360

Preprints

04 Jan 2026

| 04 Jan 2026

Hygroscopic growth obscures actual variation in anthropogenic aerosol optical depth over central China during 2010–2024

Yun He, Dongzhe Jing, Zhenping Yin, Detlef Müller, Fuchao Liu, Yunpeng Zhang, Yang Yi, Kaiming Huang, and Fan Yi

Abstract. Particle bulk optical property parameters play an essential role in evaluating air quality, however, both parameters can be substantially enhanced under humid atmospheric conditions via hygroscopic growth. Here we use 532-nm polarization lidar observations and ERA5 humidity data during 2010–2024 to retrieve vertical profiles of ambient and dry aerosol backscatter and extinction coefficients of anthropogenic pollution over central China. Particle hygroscopic growth led to enhanced particle backscatter coefficient by 11–46% below 2 km on an annual basis for the considered time frame. Anthropogenic Aerosol Optical Depth (AOD) was 30.7% higher under ambient atmospheric conditions. We found values of AOD_amb=0.404 and AOD_dry=0.309. During China’s rapid air-cleaning period of 2010–2017, AOD_amb declined significantly by −0.068 yr^-1; in contrast, the rate of decrease of AOD_dry was −0.049 yr^-1 which is 28% slower, but the decrease of the dry aerosols more accurately captures aerosol emission reductions. Hygroscopic-growth-induced net AOD ( ΔAOD_RH) dropped sharply in 2011–2014, most likely as a result of emission mitigation and drier atmospheric conditions, then rebounded in 2014–2019 as rising humidity conditions and the presence of hydrophilic aerosols. Since 2020, ΔAOD_RH has remained high attributing to rising humidity conditions but weakening hygroscopicity. While AOD_amb suggests peak pollution in summer, AOD_dry identifies winter as the true air-pollution maximum. These results highlight the significant impact of aerosol water uptake on its optical properties; therefore, it must be accounted for to ensure accurate air quality assessments.

Received: 19 Dec 2025 – Discussion started: 04 Jan 2026

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Journal article(s) based on this preprint

14 Apr 2026

Hygroscopic growth obscures actual variation in anthropogenic aerosol optical depth over central China during 2010–2024

Yun He, Dongzhe Jing, Zhenping Yin, Detlef Müller, Fuchao Liu, Yunpeng Zhang, Yang Yi, Kaiming Huang, and Fan Yi

Atmos. Chem. Phys., 26, 4937–4951, https://doi.org/10.5194/acp-26-4937-2026,https://doi.org/10.5194/acp-26-4937-2026, 2026

Short summary

Yun He, Dongzhe Jing, Zhenping Yin, Detlef Müller, Fuchao Liu, Yunpeng Zhang, Yang Yi, Kaiming Huang, and Fan Yi

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-6360', Anonymous Referee #1, 29 Jan 2026

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2025-6360/egusphere-2025-6360-RC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2025-6360-RC1
- AC1: 'Reply on RC1', Yun He, 15 Feb 2026
  
  We appreciate the reviewer's thorough review. Please see our response as attached.
  
  Citation: https://doi.org/10.5194/egusphere-2025-6360-AC1
RC2:
'Comment on egusphere-2025-6360', Anonymous Referee #2, 30 Jan 2026

The paper of He et al. has too much similarity with the paper of Jing et al. (2026) (https://doi.org/10.5194/amt-19-389-2026)., which is not properly disclaimed. Thus, it cannot be accepted. Thus, my decision is to reject the current manuscript, but encourage the authors to work on the structure and then re-submit. Further details are given below.
Many results are given which seem to come from the current study, but in fact they come from the paper of Jing et al. (2026), however, this it is not always clearly stated.
One example: In the abstract you state:
"During China’s rapid air-cleaning period of 2010-2017, AODamb declined significantly by -0.068 yr-1; in contrast, the rate of decrease of AODdry was -0.049 yr-1 which is 28% slower, but the decrease of the dry aerosols more accurately captures aerosol emission reductions."
But the -0.068 per year do come from the study of Jing et al. (2026) (where you are of course co-authoring) and only the -0.049 per year are the result the novel study which I review here.
This is just one example, but is valid for most of the manuscript. You need to make clear, what is new in this studyà this is investigation of the dry AOD over a longer time and the differences and so on. Everything which was resulting from Jing et al, should be clearly stated and not repeated until really needed.
You could, for example, state in the abstract:” Jing et al. (2026), found a decrease of the ambient AOD by -0.068 per year. We used the same lidar data set to estimate the dry AOD and contrast it to the ambient AOD. Doing so, we find a decrease of -0.049 per year”. Or similar.
One more example:
Figure 3a of He et al. is completely similar to Fig. 5a of Jing et al. (2026), but also here this is not properly stated and also not needed for this work.
As a consequence, I would propose the authors rework on the manuscript, which has indeed interesting and new results, but clearly make it a follow-up paper from Jing et al. (2026), stating that they use the same data set and build on the results of the previous publication.
Due to these severe issues, I also did not yet review the results part, because a clear restructuring of the manuscript needs to be done first.
However, some few comments already:
The authors need to discuss the uncertainty introduced by applying one fixed lidar ratio of 50 sr for all aerosols and all humidity conditions.
Figure 2 is not clear to me. For example, in my understanding beta_nd is needed also in the grey box, but this is not shown in this figure. Thus, please properly overwork the flowchart. Also, state when you sue radiosonde data and when ERA5.
Reference:
Jing, D., He, Y., Yin, Z., Müller, D., Huang, K., and Yi, F.: Hygroscopic growth characteristics of anthropogenic aerosols over central China revealed by lidar observations, Atmos. Meas. Tech., 19, 389–403, https://doi.org/10.5194/amt-19-389-2026, 2026.

Citation: https://doi.org/10.5194/egusphere-2025-6360-RC2
- AC2: 'Reply on RC2', Yun He, 15 Feb 2026
  
  We appreciate the reviewer's thorough review. Please see our response as attached.
  
  Citation: https://doi.org/10.5194/egusphere-2025-6360-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-6360', Anonymous Referee #1, 29 Jan 2026

The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2025-6360/egusphere-2025-6360-RC1-supplement.pdf

Citation: https://doi.org/10.5194/egusphere-2025-6360-RC1
- AC1: 'Reply on RC1', Yun He, 15 Feb 2026
  
  We appreciate the reviewer's thorough review. Please see our response as attached.
  
  Citation: https://doi.org/10.5194/egusphere-2025-6360-AC1
RC2:
'Comment on egusphere-2025-6360', Anonymous Referee #2, 30 Jan 2026

The paper of He et al. has too much similarity with the paper of Jing et al. (2026) (https://doi.org/10.5194/amt-19-389-2026)., which is not properly disclaimed. Thus, it cannot be accepted. Thus, my decision is to reject the current manuscript, but encourage the authors to work on the structure and then re-submit. Further details are given below.
Many results are given which seem to come from the current study, but in fact they come from the paper of Jing et al. (2026), however, this it is not always clearly stated.
One example: In the abstract you state:
"During China’s rapid air-cleaning period of 2010-2017, AODamb declined significantly by -0.068 yr-1; in contrast, the rate of decrease of AODdry was -0.049 yr-1 which is 28% slower, but the decrease of the dry aerosols more accurately captures aerosol emission reductions."
But the -0.068 per year do come from the study of Jing et al. (2026) (where you are of course co-authoring) and only the -0.049 per year are the result the novel study which I review here.
This is just one example, but is valid for most of the manuscript. You need to make clear, what is new in this studyà this is investigation of the dry AOD over a longer time and the differences and so on. Everything which was resulting from Jing et al, should be clearly stated and not repeated until really needed.
You could, for example, state in the abstract:” Jing et al. (2026), found a decrease of the ambient AOD by -0.068 per year. We used the same lidar data set to estimate the dry AOD and contrast it to the ambient AOD. Doing so, we find a decrease of -0.049 per year”. Or similar.
One more example:
Figure 3a of He et al. is completely similar to Fig. 5a of Jing et al. (2026), but also here this is not properly stated and also not needed for this work.
As a consequence, I would propose the authors rework on the manuscript, which has indeed interesting and new results, but clearly make it a follow-up paper from Jing et al. (2026), stating that they use the same data set and build on the results of the previous publication.
Due to these severe issues, I also did not yet review the results part, because a clear restructuring of the manuscript needs to be done first.
However, some few comments already:
The authors need to discuss the uncertainty introduced by applying one fixed lidar ratio of 50 sr for all aerosols and all humidity conditions.
Figure 2 is not clear to me. For example, in my understanding beta_nd is needed also in the grey box, but this is not shown in this figure. Thus, please properly overwork the flowchart. Also, state when you sue radiosonde data and when ERA5.
Reference:
Jing, D., He, Y., Yin, Z., Müller, D., Huang, K., and Yi, F.: Hygroscopic growth characteristics of anthropogenic aerosols over central China revealed by lidar observations, Atmos. Meas. Tech., 19, 389–403, https://doi.org/10.5194/amt-19-389-2026, 2026.

Citation: https://doi.org/10.5194/egusphere-2025-6360-RC2
- AC2: 'Reply on RC2', Yun He, 15 Feb 2026
  
  We appreciate the reviewer's thorough review. Please see our response as attached.
  
  Citation: https://doi.org/10.5194/egusphere-2025-6360-AC2

Peer review completion

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

AR by Yun He on behalf of the Authors (16 Feb 2026) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (11 Mar 2026) by Silke Gross

RR by Anonymous Referee #2 (27 Mar 2026)

Suggestions for revision or reasons for rejection

The authors adequately discussed the previous referees' remarks and adapted the manuscript accordingly.
Especially, the uncertainties introduced by choosing a fixed lidar ratio are now discussed in sufficient detail.
This is of particular importance since this issue was brought up by both previous referees.
Also, the highly critical originality concerns are now clarified by clearly stating the follow-up nature of this study.
I therefore think, after some minor, in my opinion, technical revisions, this manuscript can be accepted for publication in Atmos. Chem. Phys.

I would like to mention two minor points which still could be discussed in more detail (Lines correspond to the originally submitted manuscript):

Line 220: "This result points to a higher content of water vapor in the atmosphere, which thereby leads to stronger particle hygroscopic growth."
Without having read Kallihosur et al. (2024), could not stronger pollution levels and/or different aerosol chemical composition be other possible reasons for that? Please, explain that in a bit more detail or modify the sentence.

Line 274: "a concurrent shift toward a drier atmosphere".
Only in those years (and the mentioned extraordinary drought)? Did it get wetter later again? Is this shown in this manuscript (via RS or ERA5)? Or is it shown in Jing et al. (2025 or 2026)? I think it needs either a reference or some more explanation.

Furthermore, some minor textual and style suggestions to be potentially implemented follow here (Lines correspond to the originally submitted manuscript, some might be already changed in the revised version):
Line 17: Use -- for periods always, (2010--2017), as you do just above for percentages, see several suggestions below.
Line 22: "attributed" instead of "attributing".
Line 37: PM2.5 is an abbreviation and needs introduction.
Line 43: "fine-mode particles" instead of "fine-mode particle".
Line 45: "aerosol chemical composition" instead of "aerosol chemistry composition".
Line 75/76 and 77: "~kg~m$^{-1}$~s$^{-1}$" instead of "kg m-1 s-1".
Line 84: space, "2014 (Yin" instead of "2014(Yin".
Line 97: "30--80" instead of "30-80".
Line 113: Maybe, refer here to Sect. 2.3 with regard to the gamma parameter e.g.. "(see Sect. 2.3)".
Line 137: Avoid \cdot in units, or use it everywhere.
Line 179: "ERA5" instead of "EAR5".
Line 181: "0520--0639" instead of "0520-0639".
Line 183: "1--2 km" instead of "1-2 km".
Line 191: "(0--7 km)" instead of "(0-7 km)".
Line 199: "11--46%" instead of "11-46 %" (furthermore, consistently use either no space or \, (as Copernicus does) before \%.
Line 214: "0.30--0.50" instead of "0.30-0.50".
Line 215: "0.30--0.35" instead of "0.30-0.35".
Line 222: "2010--2024" instead of "2010-2024".
Line 224: "2010--2017" instead of "2010-2017".
Line 227: "ERA5" instead of "EAR5".
Line 244/245 "2010--2017" and "2018--2024" instead of "2010-2017" and "2018-2024".
Line 250: "Fig. 6b" instead of "Figure 6b", and "2--5" instead of "2-5".
Line 252: "2011--2013" instead of "2011-2013".
Line 261/262: "2014--2018", "2019--2024", and "0.02--0.04" instead of "2014-2018", "2019-2024" and "0.02-0.04".
Line 269: "Fig. 7a" instead of "Figure 7a".
Line 273: "2011--2014" instead of "2011-2014".
Line 280: "20--50%" instead of "20-50%".
Line 285: "15--19%" and "7--10%" instead of "15-19%" and "7-10%".
Line 311: "2010--2024" instead of "2010-2024".
Line 315: "ERA5" instead of "EAR5".
Line 324: "2--5" instead of "2-5".
Line 327/329: "2011--2014" and "2014--2019" instead of "2011-2014" and "2014-2019".
Line 330/331: "15--19%" and "7--10%" instead of "15-19%" and "7-10%".
Line 364: add "and" instead of or additional to comma "for ERA5 reanalysis data(,) and the University of Wyoming"
Line 399/511: Use the same journal abbreviation name consistently, "J. Geophys. Res. Atmos." vs "J. Geophys. Res.-Atmos". (e.g., on Line 407). I think the latter is the chosen style by Copernicus.
Line 407: Provide page-like article number ("D16203") here as well, as you do it elsewhere too.
Line 418: Hänel has a doi, please provide it: "https://doi.org/10.1016/S0065-2687(08)60142-9".
Line 443: Jing et al. (2025b) is now available as final version. ->already adapted in the revised version.
Line 456: "Nat. Commun." instead of "Nat. Commu."
Line 463: Provide page-like article number ("e2020GL090167") here as well, as you do it elsewhere too.
Line 497: add volume and page-like article number: "npj Clim. Atmos. Sci., 9, 3".
Line 536: "J. Clim." instead of "J. Climate".
Line 543: Rethink the citation style (proceedings) and at least provide the doi: "https://doi.org/10.1117/12.417040".
Line 544: Page-like article number is "1897" and not "3--1"
Line 547: Pages are 13,370–13,387 and not 13--370.
Line 557: "npj Clim. Atmos. Sci." instead of "npj Clim. Atmos. Sc."
Line 573: "Cheng, J." instead of "Cheng, j."

In the revised manuscript, also some of the new references still need to be adapted:
Brooks et al. (2002): provide page-like article number: "1917" and not "23--1".
Müller et al. (2007): provide page-like article number: "D16202".
Wise et al. (2007): provide page-like article number: "D10224".

Hide

ED: Publish subject to technical corrections (02 Apr 2026) by Silke Gross

AR by Yun He on behalf of the Authors (03 Apr 2026) Author's response Manuscript

Journal article(s) based on this preprint

14 Apr 2026

Hygroscopic growth obscures actual variation in anthropogenic aerosol optical depth over central China during 2010–2024

Yun He, Dongzhe Jing, Zhenping Yin, Detlef Müller, Fuchao Liu, Yunpeng Zhang, Yang Yi, Kaiming Huang, and Fan Yi

Atmos. Chem. Phys., 26, 4937–4951, https://doi.org/10.5194/acp-26-4937-2026,https://doi.org/10.5194/acp-26-4937-2026, 2026

Short summary

Yun He, Dongzhe Jing, Zhenping Yin, Detlef Müller, Fuchao Liu, Yunpeng Zhang, Yang Yi, Kaiming Huang, and Fan Yi

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Using ground-based polarization lidar observations during 2010–2024, we retrieve the vertical profiles of aerosol backscatter and extinction coefficients of anthropogenic pollution under dry and ambient atmospheric conditions over central China. The year-to-year and seasonal variations of optical parameters are very different after removing hygroscopic growth effect.


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