|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.
- 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.