The evolution of cloud and aerosol microphysics at the summit of Mt. Tai, China

Li, Jiarong; Zhu, Chao; Chen, Hui; Zhao, Defeng; Xue, Likun; Wang, Xinfeng; Li, Hongyong; Liu, Pengfei; Liu, Junfeng; Zhang, Chenglong; Mu, Yujing; Zhang, Wenjin; Zhang, Luming; Herrmann, Hartmut; Li, Kai; Liu, Min; Chen, Jianmin

doi:https://doi.org/10.5194/acp-20-13735-2020

Articles | Volume 20, issue 22

https://doi.org/10.5194/acp-20-13735-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-20-13735-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 20, issue 22

Research article

|

16 Nov 2020

Research article |

| 16 Nov 2020

The evolution of cloud and aerosol microphysics at the summit of Mt. Tai, China

Jiarong Li, Chao Zhu, Hui Chen, Defeng Zhao, Likun Xue, Xinfeng Wang, Hongyong Li, Pengfei Liu, Junfeng Liu, Chenglong Zhang, Yujing Mu, Wenjin Zhang, Luming Zhang, Hartmut Herrmann, Kai Li, Min Liu, and Jianmin Chen

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Final revised paper (published on 16 Nov 2020)
Supplement to the final revised paper
Preprint (discussion started on 14 Aug 2019)
Supplement to the preprint

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC1: 'Review of: The evolution of cloud microphysics upon aerosol interaction at the summit of Mt. Tai, China', Anonymous Referee #1, 12 Oct 2019
- AC1: 'Reply to comments from Anonymous Referee #1', Jianmin Chen, 26 Dec 2019
RC2: 'Review of the manuscript "The evolution of cloud microphysics upon aerosol interaction at the summit of Mt. Tai, China"', Kevin Noone, 21 Nov 2019
- AC2: 'Reply to comments from Anonymous Referee #2', Jianmin Chen, 26 Dec 2019

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

AR by Jianmin Chen on behalf of the Authors (26 Dec 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (10 Feb 2020) by Ilona Riipinen

RR by Anonymous Referee #3 (06 Apr 2020)

Suggestions for revision or reasons for rejection

Comments on “The evolution of cloud microphysics upon aerosol interaction at the summit of Mt. Tai, China” by Li et al.

The authors have greatly improved the quality of this paper compared to the last version. I would recomend its publication if the authors could address my following concerns.

Compared to results in earlier studies is an important approach to generalize your finding, or find new questions. Thus, such comparison should end up with concluding remarks. I would suggest the authors to revise the manuscript accordingly. Here are a few examples:

Page 7 line 21 “The number concentration of cloud droplets at Mt. Tai both in the present study and in 2014 can reach 2000-3000 # cm-3 (Li et al., 2017a), which is much higher than those values (with a range 25 of 10–700 # cm-3) for city fogs and convective and orographic clouds”, so?
Page 7 line 27, “When compared with previous orographic clouds, LWC at Mt. Tai appeared to show a larger range. We monitored the high values, which are comparable with convective clouds, and the low values, which are similar to city fogs.” This seems to be the conclusion of this paragraph, so?

Figure 1, can you explain the meaning of lines? “The dashed and solid shapes indicated the airborne and land observation, respectively.” What’s the meaning of the position, area of these rectangles?

Page 8 line 2, “As opposed to convective clouds studied by research aircraft...” In last version,
The authors seems that suggest measurements at a fixed location better than aircraft measurements because the site is fixed. The revise manuscript has clarified this.

Page 9 line 5, “the increase of PM2.5, Np and Ta decreased cloud droplet sizes (Rosenfeld et al., 2014a), decreased the ambient supersaturation, enhanced the evaporation of small droplets (Ackerman et al., 2004), and finally caused the cloud events to vanish (Mazoyer et al., 2019).”
Here the authors claimed that aerosols enhanced evaporation and caused cloud events to vanish by referring to early studies. This statement, however, is in contrast to the authors’ statement in the abstract “we find that the albedo can increase 36.4% if the cloud gets to be disturbed by aerosols. This may induce a cooling effect on the local climate system”. Has this lifetime effect been considered in your calculation?

Page 8 line 25 “During SP1 and SP2, the perturbation through particles occurred. Dramatic increase of Nc, and decrease of reff and LWC/NC”. Here the authors seem to attributed all changes to aerosol perturbation. However, the sharp shift of size distributions in Fig. 2 can also be a result of change of air masses. This has been known to strongly influence the diurnal variation of pollutants at mountain site. Thus, another explanation could be that it is not a controlled aerosol perturbation of a certain air mass, but rather snapshots of several different air masses. Then, the following classification could also be problematic. “Each cloud event of CP-2 was separated into activation stage (S1), collision-coalescence stage (S2), stable stage (S3), and dissipation stage (S4) (Fig. 3a)”.

Sect 3.2.1. Why using ss= 02% rather than other ss? The more relevant CCN would be those activated at the same ss as in the cloud events. Could you estimate the activation ss to support this or include other ss into discussion?

Page 9 line 30 “In the study of Mazoyer et al. and Asmi et al. (2012), both of them found that high NCCN/Np was associated with high κ at a given SS ... It indicates that the difference of aerosol organic chemical compositions during CP-1 and CP-2 might influence the k of aerosols and further affect the NCCN/NP ratio during this two cloud processes”

Here the authors cited earlier studies reporting different correlations of activation fraction with aerosol hygroscopicity, and volatile organic aerosol fraction. Since correlation doesn’t imply causation. I don’t think these are the best examples to support your argument. The Kohler theory and kappa-Kohler equation themselves are already sufficient to show the importance of chemical compositions. Note that variability of particle size often matters more chemical compositions (Dusek et al. 2006).
Ref: Dusek et al., Size Matters More Than Chemistry for Cloud-Nucleating Ability of Aerosol Particles. Science 312, 1375-1378 (2006).

In Figure 4, the R2 of 0.282 and 0.05 is too low to derive a statistically meaningful linear dependence, and thus the calculation of FIE_N is questionable.

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RR by Anonymous Referee #4 (02 Jun 2020)

Suggestions for revision or reasons for rejection

This manuscript describes a potentially interesting data set of microphysical cloud properties conducted simultaneously with aerosol particle size distribution, CCN, and PM2.5 measurements. The authors have already revised the manuscript once based on the recommendations from two sets of reviews, resulting in some improvements of the original manuscript. There remains, however, several important issues that still need to be addressed before the manuscript can be considered for publication within ACP.

General / major issues:

1. The most important shortcoming of the manuscript has to do with causal inference where the data available cannot be use to conclude causality between aerosol and cloud droplet concentrations and properties. This issue was already raised in the first round of reviews, and the authors made the effort of estimating the upper limits of the updrafts that the airmasses observed had likely experienced together with the cloud base heights. These were certainly steps to the right direction, but there are still some specific aspects of the analysis that need to be improved.

I would recommend revising the whole manuscript to focus more on displaying simultaneous observations of the cloud droplet and aerosol microphysics, and focus less on drawing strong conclusions about their interactions because the latter is very difficult to do unambiguously with the present data set and was not directly observed although the current manuscript gives this impression. Also, I would recommend making too strong statements about direct climate implications of these observations. Here are some examples (although this is probably not an exhaustive list):

- Title: I would replace "evolution of cloud microphysics upon aerosol interaction" with "evolution of cloud and aerosol microphysics"

- Abstract, line 23: Replace ", the aerosol-cloud interactions, and the possible climate effect during cloud cycles..." with ", simultaneous variations in aerosol microphysics and their potential interactions..."

- Abstract, line 35: replace "...and will help to reduce the uncertainties in climate models when predicting climate responses to cloud-aerosol interactions in North China plain" with e.g. "that can enhance our understanding on cloud and aerosol properties along with their potential interactions in North China plain". The way from the results presented here to reducing uncertainties in climate models is too long and winding to mention this in the abstract.

- p. 2, line 29: replace "results" with "can result"

- p. 3, line 21: replace "upon aerosol interaction" with "coupled to simultaneous monitoring of aerosol size distributions, PM2.5 mass and CCN concentrations"

- p. 3, line 24: remove "for the aerosol impact" and add "and their potential links to aerosol concentrations and size distribution" to the end of the sentence.

- p. 3, line 24: replace the last sentence with "Implications of cloud and aerosol microphysics for cloud albedo and climate are discussed."

- P. 6, Sect 2.7 and throughout the manuscript: Please remove the term "First indirect effect or FIE" and replace it with something more suitable. The parameters calculated are not the first indirect effect (which would be the effect of adding or removing aerosol particles when everything else would be kept constant). The parameters calculated in this study are simply approximations of the derivatives of the effective diameter or Nd with respect to changes in aerosol concentrations - which can be a result of covariation as well as a consequence of the aerosol perturbation. They should be renamed to reflect the reality.

- In several places throughout the manuscript (especially Sects. 3.2, 3.2.1) the authors suggest that during "CP-2", the increase in PM2.5 (or Np) would "break off" the cloud in the way that there would be some causal relationship between decreasing aerosol concentrations and increasing cloud droplet concentrations. The data presented in the paper does not support such conclusion. Rather, it seems likely that the increase in PM2.5 that coincides with the dissipation of the cloud (and vice versa) is a consequence of cloud-aerosol interaction - i.e. the scavenging effect that the cloud has on the PM2.5. In other words, the PM2.5 increases in the absence of a cloud because in this situation a major sink of the PM2.5 is absent. Or do the authors have a specific reason to believe otherwise? Please revise / specify accordingly.

- I would recommend refraining from using the term "perturbation" throughout the manuscript when talking about time-dependent changes. This makes the reader think about a controlled perturbation to aerosol concentrations when everything else would be kept constant. Instead I would use terms like "increase / decrease in aerosol concentrations".

2. The second major issue is related to the presentation quality. Although the authors have made an effort to correct the language throughout the manuscript, the text is still very difficult to follow at times, due to grammatical errors and problems with the structures of the sentences, logical order etc. The issues are so numerous that the editorial work becomes too substantial to take care of as a reviewer / editor. The authors should therefore consult e.g. colleagues (or even co-authors) who are fluent enough in English to make sure that the presentation of the manuscript reaches the standards of ACP.

3. My third major / general comment has to do with the comparisons that the authors make to observations at other sites and of other cloud types. In many places the authors compare their results to e.g. other orographic clouds. I do not see the point of this comparison since the microphysical properties of ororgraphic clouds can depend drastically on the topography, atmospheric dynamics, aerosol and water sources related to a specific measurement site. I do not see any reason why one would expect e.g. a given range of droplet sizes etc. that would be specific for orographic clouds. I would recommend revising this discussion throughout the manuscript.

Specific comments:

- Please make sure to use italics for variables throughout the text.

- P. 4, line 25: please modify to ..."could provide an estimate of the vertical wind field (updraft velocity, v_up)" and remove the remainder of the sentence.

- P. 5, lines 2-5: The results of the v_up analysis should go under Results - or at least CP-1 and CP-2 should not be cited before they are introduced. Furthermore, instead of citing just the average values, the authors should present e.g. histograms or time series of the estimated updraft velocities to justify their assumption on the updraft being relatively constant.

- P. 5, lines 11-15, the text starting with "Through calculation...": Please specify how this piece of text relates to the previous sentence. The contents of this text need to understandable stand-alone, i.e. without the reader needing to find the Spiegel et al. reference (also it is not clear what the following "As can be seen" refers to ... seen from where? Fig. 7 in Spiegel et al.?). Please revise accordingly.

- P. 5, lines 26-28: I would recommend removing the sentence starting with "In the present study...". It does not add anything new, since the two parameters were not really "combined" in the sense of e.g. deriving a new parameter that combines information from both PM2.5 and Np.

- P. 6, line 11: Please specify how the Tai'an station relates geographically to the summit measurement site. It is representative for the air masses arriving at the mountain station?

- Generally throughout the manuscript: Please make sure to cite all the figures in order and move all the measurement or analysis results to the "Results" section.

- P. 7 from line 22 onwards to the end of the section: The authors discuss LWP for different cloud types and altitudes, but Fig. 1 does not specify the cloud types or altitudes in the different studies. Please revise. Also, please revise this whole paragraph accounting for the fact that LWP does not depend only on r_eff, N_c or even updraft (which is also not explicitly mentioned although it should be in relation to the different cloud types), but also the amount of water vapor available. This is an important aspect that is hardly discussed throughout the manuscript, while in reality obviously being a key factor in determining the formation and microphysics of clouds.

- P. 8, lines 2-6: I would recommend removing this text and clarifying the point of it. The purpose of the comparison between convective and orographic clouds is unclear, as is the argument as to why the cloud events at Mt. Tai would be "more easily affected by locally transferred airmass".

- P. 8, lines 12-13: I would replace "However, the perturbation of particles did not break off teh cloud, which made CP-1 be the longest cloud process and persist 74 hours in the present study" with just "CP-1 persisted for 74 h, making it the longest cloud event during the present campaign."

- P. 9, Sect. 3.2.1, first paragraph: Here the authors start with a statement that in my view they cannot prove based on the presented data. The relationship between Np and Nc can be a result of also other things than competition on water vapor, like scavenging of particles by cloud droplets or new particles being formed through the same mechanisms that are responsible for creating the water supersaturation etc. Please revise this discussion to be more comprehensive and systematic with respect to the relationships between cloud droplets and aerosol particles. Later in the same paragraph, the authors discuss "high" and "low" LWC/Nc regimes without referring to any quantitative results or clearly relating to their own work. This results in confusion on whether they are describing something they infer from their own data or on more general terms. As a summary, I feel that this whole section needs to be revised to be 1) more systematic in its discussion of the different mechanisms that may be behind covariation of Np and Nc; 2) more specific in its relation to the presented results.

- P. 9, Sect. 3.2.1, second paragraph: Here the authors discuss the CCN measurements and state that measurements of the hygroscopicity parameter kappa is not available. Would it not be possible to calculate an approximate kappa from the CCN data by assuming homogeneous composition throughout the size distribution and reporting that value? Later in the last sentence of the paragraph, the authors speculate that the chemical composition of CP-1 and CP-2 might be different due to different CCN to total particle number ratios. Looking at Fig. 2, however, it appears that the average size of the particles was also smaller during CP-1 as compared with CP-2. Is this not part of the explanation? Please clarify.

- P. 13, line 5. Here the authors state that "At the dissipation stage of S4, the clouds vanish due to mixing with the dry ambient air". Wouldn't this be contradictory with the speculations of increasing aerosol concentrations "breaking-off" the cloud mentioned earlier?

- P. 13, line 19: "The thickness of orographic cloud is usually very thin". This is a very vague statement. Thin compared to what? Also, can something like this be said about all orographic clouds in general - wouldn't this depend a lot on the specific topography and environmental conditions? Please revise.

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ED: Reconsider after major revisions (02 Jun 2020) by Ilona Riipinen

AR by Jianmin Chen on behalf of the Authors (26 Jun 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (07 Jul 2020) by Ilona Riipinen

RR by Anonymous Referee #3 (11 Jul 2020)

ED: Publish subject to minor revisions (review by editor) (04 Aug 2020) by Ilona Riipinen

AR by Jianmin Chen on behalf of the Authors (07 Aug 2020) Author's response Manuscript

ED: Publish subject to technical corrections (20 Sep 2020) by Ilona Riipinen

- Page 1, line 31: please add ”we find that” between ”droplets,” and ”particles”

- Page 1, line 34: please replace “tanking no account of the cloud lifetime” with “ignoring any lifetime effects”

- Page 2, line 1: please replace “on” with “of”

- Page 2, line 7: please remove “would”

- Page 3, line 11: please replace “the” with “this”

- Page 4, line 3: please replace “presented” with “found that”

- Page 4, line 6: please replace “was” with “is”

- Page 4, line 7: please replace “is” with “was”

- Page 6, line 24: please replace “have been” with “were”

- Page 7, line 1: please replace “represented” with “suggested that”

- Page 7, line 11: please remove “but”

- Page 7, line 15: please replace “on” with “of”

- Page 7, line 17: please replace “was” with “were”

- Page 7, line 20: please replace “with” with “with respect to”

- Page 7, lines 21-22: please replace the following text “The influence of topography and updraft velocity(vup) on Fog Monitor during CP-1 and CP-2 could be ignored. The detailed 21 information could be found in the Supplement (Table S2, Fig. S3 and Fig. S4) and was briefly introduced here.” with “The variations in updraft velocity v_up on cloud microphysics during CP 1 and CP were ignored for simplicity (see Supplementary Information, Table S2, Fig. S3 and Fig. S4)”.

- Page 7, line 24: please add “of the fog monitor” between “efficiency” and “were”

- Page 8, line 27: please replace “simultaneously” with “consistent”

- Page 8, line 29: please add “could” in front of “cause”

- Page 8, line 20: please replace “would” with “could”

- Page 9, line 9: I would suggest to replace the following sentence “Relative
higher LWC/N C value indicating water was sufficient for new cloud droplet formation.” with “The relatively higher LWC/N_c values could indicate conditions where the amount of water vapor was not limiting cloud droplet formation.”

- Page 9, line 10: Please replace “relative” with “relatively”

- Page 9, line 24: Please remove “the”

- Page 9, line 25: Please replace “represented” with “suggested that”

- Page 9, line 28: Please replace “scatter” with “scattered”

- Page 9, line 29: Please replace “settled” with “chosen”

- Page 9, line 30: Please add “were” between “CP-2” and “distributed”

- Page 10, line 13: Please replace “covariance” with “to covary”

- Page 10, line 17: Please replace “it was indicated” with “our results suggested”

- Page 10, line 17: Please replace “are” with “were”

- Page 10, lines 17-18: Please replace “under smaller aerosol amount conditions” with “under conditions with lower aerosol concentrations”

- Page 10, line 22: Please replace “caused” with “could be a cause of”

- Page 10, line 25. Please remove “It verified that cloud droplets in CP-2 were little influenced by aerosols.In the previous studies, both observation and modelling”. This information is given at the end of the manuscript, and the low correlation coefficients do not necessarily verify the lack of any influence from the aerosols.

- Page 11, line 8: Please replace “was” with “is”.

- Page 11, line 11: Please replace “Talbe” with “Table”

- Page 13, line 27: Please replace “was” with “can be”

- Page 13, line 15: Please replace “were” with “to be”

- Page 13, line 21: Please replace “regardless the cloud lifetime” with “disregarding any cloud lifetime effects”

- Page 13, line 24: Please replace “are employed to show” with “were used to study”

- Page 13, lines 25-26: I would suggest replacing the following sentence “Cloud droplets with smaller r_eff and lower LWC are observed at Mt. Tai, which are similar to urban fogs.” eith “Cloud events with small r_eff and low LWC similar to urban fogs were also observed at Mt. Tai.”

- Page 13, line 27: Please replace “are” with “were”

- Page 13, line 30: Please replace “are” with “were”

- Page 14, line 1: Please replace “dramatically increased with a factor of three” with “was found to dramatically increase”

- Page 14, line 5: Please replace “periodically” with “periodical”

- Page 14, line 6: Please replace “have been” with “were”

- Page 14, line 9: Please replace “represents” with “suggests”

- Page 14, line 18: Please replace “regardless the cloud lifetime” with “disregarding any cloud lifetime effects”

- Page 22, line 2: Please replace “the literatures” with “literature”

- Page 22, line 3: Please replace “represented” with “represent”

- Page 22, line 4: Please replace “represented” with “represent”

- Page 23, line 4: Please replace “volumn” with “volume”

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AR by Jianmin Chen on behalf of the Authors (25 Sep 2020) Author's response Manuscript

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Short summary

Based on a field study at Mt. Tai, China, the simultaneous variations of cloud microphysics, aerosol microphysics and their potential interactions during cloud life cycles were discussed. Results demonstrated that clouds on clean days were more susceptible to the concentrations of particle number, while clouds formed on polluted days might be more sensitive to meteorological parameters. Particles larger than 150 nm played important roles in forming cloud droplets with sizes of 5–10 μm.