Measurement report: Atmospheric Ice Nuclei at Changbai Mountain (2623 m a.s.l.) in Northeastern Asia

Sun, Yue; Zhu, Yujiao; Qi, Yanbin; Chen, Lanxiadi; Mu, Jiangshan; Shan, Ye; Yang, Yu; Nie, Yanqiu; Liu, Ping; Cui, Can; Zhang, Ji; Liu, Mingxuan; Zhang, Lingli; Wang, Yufei; Wang, Xinfeng; Tang, Mingjin; Wang, Wenxing; Xue, Likun

doi:https://doi.org/10.5194/egusphere-2023-925

Preprints

https://doi.org/10.5194/egusphere-2023-925

Preprints

15 Jun 2023

| 15 Jun 2023

Measurement report: Atmospheric Ice Nuclei at Changbai Mountain (2623 m a.s.l.) in Northeastern Asia

Yue Sun, Yujiao Zhu, Yanbin Qi, Lanxiadi Chen, Jiangshan Mu, Ye Shan, Yu Yang, Yanqiu Nie, Ping Liu, Can Cui, Ji Zhang, Mingxuan Liu, Lingli Zhang, Yufei Wang, Xinfeng Wang, Mingjin Tang, Wenxing Wang, and Likun Xue

Abstract. Atmospheric ice nucleation plays an important role in modifying the global hydrological cycle and atmospheric radiation balance. To date, few comprehensive field observations of ice nuclei have been carried out at high-altitude sites, which is close to the height of mixed-phase cloud formation. In this study, we measured the concentrations of ice-nucleating particles (INPs) in the immersion freezing mode at the summit of Changbai Mountain (2623 m above sea level), Northeast Asia, in summer 2021. The cumulative number concentration of INPs varied from 3.8 × 10⁻³ L⁻¹ to 2.3 L⁻¹ over the temperature range from −20.5 °C to −5.5 °C. Proteinaceous-based biological materials accounted for the majority of INPs, with the proportion of biological INPs (bio-INPs) exceeding 75 % across the entire freezing temperature range, with this proportion even exceeding 90 % above −13.0 °C. At freezing temperatures ranging from −11 °C to −8 °C, bio-INPs were found to significantly correlate with wind speed and Ca²⁺, and weakly correlate with isoprene and its oxidation products (isoprene × O₃), suggesting that biological aerosols may attach to soil dust surfaces and contribute to INPs. During the daytime, bio-INPs showed a positive correlation with the planetary boundary layer height, with the valley breezes from southwestern mountainous regions also influencing the concentration of INPs. Moreover, the long-distance transport of air mass from the Japan Sea and South Korea significantly contributed to the high concentrations of bio-INPs. Our study emphasizes the important role of biological sources of INPs in the high-altitude atmosphere of northeastern Asia, as well as the significant contribution of long-range transport to the INPs concentrations in this region.

Received: 06 May 2023 – Discussion started: 15 Jun 2023

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15 Mar 2024

Measurement report: Atmospheric ice nuclei in the Changbai Mountains (2623 m a.s.l.) in northeastern Asia

Atmos. Chem. Phys., 24, 3241–3256, https://doi.org/10.5194/acp-24-3241-2024,https://doi.org/10.5194/acp-24-3241-2024, 2024

Short summary

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-925', Anonymous Referee #3, 17 Jul 2023

General comments
The manuscript by Sun et al. reports INP measurements at Changbai Summit in the summer of 2021. Using results from heat and H2O2 treatments, the authors distinguish between biological INPs, other organic INPs, and inorganic INPs and conclude that the majority of INPs in the temperature range studied were of biological origin. It is an interesting study that provides new information about biological INPs. They discuss correlations of biological INPs with meteorological data as well as with some chemical tracers, suggesting that biological INPs may originate from soil dust. In addition, possible sources and transport mechanisms of INPs are discussed based on knowledge of the height of the planetary boundary layer and the concentration-weighted backward trajectories of air masses. The authors have made an effort to explain their data, but given the small number of samples (22 in total, half of which were collected during the day and the other at night) and the lack of sample dilutions to extend the freezing spectra to lower temperatures, some sections require substantial revision in my opinion. I have major and minor comments that I hope will be helpful to the authors and can be addressed during the review process.

Specific comments
Abstract
Line 12: “modifying” is maybe not the right word here.
Lines 22-24: While this insight into atmospheric dynamics is welcome, I would note that this positive correlation between biological INPs with planetary boundary layer height is based on 7 data points only. 2 outliers were excluded and 2 missing data points were not mentioned. It is not stated which correlation analysis was done, something that persists throughout the study. Furthermore, it is unclear for the reviewer how these two cases of high concentrations of biological INPs differ from the other samples in terms of long-range transport. These results need thorough review, discussions about them need to be clarified, and the relevant conclusions probably need to be revised.

Introduction
The reviewer thinks that some parts of the introduction should be worded more precisely.
Line 40 and line 52: Please use “etc” carefully. Try to list fully instead.
Line 40: There are also efficient proteinaceous cell-free INPs (Pummer et al., 2015) that are not embedded in cell membranes. Please, reformulate the sentence.
Line 45: I am unsure what is meant by “and [in] agricultural soils”. Do you mean a site, where presumably many INPs come from particles from agricultural soils? Please reformulate.
Line 68: The tree sites that are referred to are not all located in the Swiss Alps, but are located across Switzerland.
Lines 70-71: Instead of “one order of magnitude”, you could keep the same units as in the previous sentence. Maybe summarize in percent per kilometer.
Line 72: The “atmosphere” can only be in singular.
Lines 72-75: Please mention that Schrod et al. 2017 findings were obtained during specific events, i.e., a series of elevated Saharan dust plumes.
Lines 75-77: The citation Conen et al. 2022 is missing at the end of the sentence. I would suggest adding here the following specification: “under free-tropospheric conditions”. Study could have been mentioned in L. 44-45 instead/as well.
Line 87: “INPs measurements” --> “INP measurements”

Methods
The reviewer found that the methods are well described, and that it was helpful that the authors provided the raw data for the reviewers.
Line 119: Please specify that your times are meant in local time or mention the correct time zone.
Line 120: A total of 24 samples were collected for INP analysis. The results of only 22 samples were reported in the provided data file. Could the authors please explain why the results of two samples are missing? Could it maybe be that 22 samples and 2 background filters were collected?
Line 130: It would be interesting to know how far the weather station is from the measurement site.
Lines 178-186: Please be more precise how you generated the air mass backwards trajectories and add information about starting time as well as number of trajectories per sample.
Line 188: Which data product from the Climate Data Store did you use for the PBL data?

Results and Discussion
The reviewer found that some parts of the results and discussion need thorough revision and much clearer statements.
Line 208 and lines 210-211: Wieder et al. (2022) contains INP concentrations from a mountain site called Weissfluhjoch (2693 m a.s.l.) and a valley site called Wolfgangpass (1631 m a.s.l.). The two sites in the Swiss Alps are only 4 km apart and are not necessarily representative of the entire Swiss Alps. Please be more specific: a) Swiss Alps and not any Alps, b) add the name of the site(s) you mean.
Lines 208-211: Please provide the time spans for collection and averaging for these other studies. For example, Wieder et al. (2022) collected samples over short time spans (i.e., 20 minutes) and averaged them into 2-hour bins. They found a peak at 19 h UTC (i.e., 21 h CET), which is defined as nighttime based on the definition used in this manuscript, if I am not mistaken. A possible diurnal cycle at Changbai Mountain may have been averaged out due to the long sampling time of 11 hours. Please mention specifically for Changbai Mountain only the comparison of daytime and nighttime, since only two samples are taken per day. In my opinion, a conclusion over the entire diurnal cycle cannot be made here.
Line 213: What is meant by “the temperature spectra showed a wider range”?
Line 217: What is meant by “the N_INP value was much larger at Mt. Huang than our results”? Can't the difference between both sites be explained by the fact that your results cover a warmer temperature range than the results from Mt. Huang? Please mention the freezing temperatures while comparing INP concentrations.
Line 256: Shouldn’t it be “bio-INP” instead of “INP”?
Line 254-256: A mean increase in F_INP-biofrom 0.8 to 0.9 with decreasing temperatures between -16.5 °C and -20 °C doesn’t make much sense and could be due to the way the data were processed here. It looks like some untreated and heat-treated samples already reached the upper detection limit at about -15 °C or -16 °C. In order to draw conclusions about the proportion of bio-INPs, other org-INPs, and inorganic INPs below -15 °C, I believe dilutions of the untreated and heat-treated samples would have been required. The number of data points of F_INP-biofrom maybe around -18 °C and lower is likely too low to draw any conclusions below that temperature threshold.
Lines 277-281: What about biological INPs originating from plants and oceans? Please discuss.
Lines 279-281: Maybe instead of citing the review, authors could cite the original studies e.g. Hill et al. 2016 or others.
Line 301: Maybe instead of citing the review, authors could cite the original studies.
Lines 315-321: Could the authors elaborate how the inclusion of these points would change the results and conclusion?
Line 320: Please indicate here that the “freezing” temperature is meant.
Lines 323-325: How does the CWT analysis on August 18 and 25 differ from the other days?

Conclusion
The reviewer believes that some rewording needs to be done, especially in the last paragraph.
Lines 365-368: A decreasing trend in F_INP-biowith decreasing temperature suggests that other organic or inorganic INPs become more important with decreasing temperatures. It does not suggest that the ice nucleation activity of bio-INPs decreases. In addition, due to the lack of data points in the low temperature regime, no conclusions can be drawn regarding F_INP-biofor that temperature range, in my opinion. Dilutions would have been required, as mentioned above.
Line 379: Did you mean to write that the INP number concentration is lower than the ice crystal number concentration, especially in the warm temperature range?
Line 381: Is there a word missing between “…is second only to…”?
Line 383: Please delete “through various collisions with pre-existing ice”. There are several multiplication processes, and they involve many more processes than only ice-ice collision. More information can be found for example in Korolev and Leisner, 2020.
Line 385: Bio-INPs do not impact secondary ice formation directly, please reformulate.

Figures
Fig.2(b)
Please indicate in the figure and legend the name of the mountain in the Swiss Alps from which the data originate similar to what you did with the Mt. Huang dataset.
Should the y-axis perhaps be extended to lower values to see the lower limit of the error bar?

Fig. 3(a)
Why are the error bars for N_INP-H2O2 below -15 °C extending to values outside the graph?
Please use the same axes in Fig. 3a than in Fig. 3b and Fig. 2b.

Fig.3(c)
I appreciate that there is an indication of the number of data points included in the analysis. Since the upper detection limit of about 2 INPs per liter is reached around -15 °C for N_INP-bio, dilutions would have been necessary to extend the plot from -15 to -20 °C as mentioned above.
How can the median fraction of inorganic INPs above -12 °C be more than 0.0 if the median fraction of bio-INPs is 1.0?

Fig.4
What kind of correlation analysis did you do? Please specify.

Fig.5(a-c)
What does “r” stand for? Please also describe what the red lines and the purple circles represent.
Is the x-axis showing the mean PBL height?
Maybe add “freezing” between “three” and “temperatures”.

Fig.5 (d-f)
Trajectories of which samples were included in the CWT analysis? Are the trajectories of all the samples included or only those of the daytime samples? Were the trajectories of the two outliers excluded or included here? Please be more specific.
Also describe in the legend what the star and triangle represent.

Fig. S1
Please describe in the legend precisely what is shown and what is meant by "R". Is the large "R" here similar to the small "r" in Fig. 5?

Fig. S2
Authors could add the star and the triangle in these maps, similar to Fig. 5 (d-f).

References:
Conen, F., Einbock, A., Mignani, C., and Hüglin, C.: Measurement report: Ice-nucleating particles active ≥ −15 °C in free tropospheric air over western Europe, Atmos. Chem. Phys., 22, 3433–3444, https://doi.org/10.5194/acp-22-3433-2022, 2022.
Korolev, A. and Leisner, T.: Review of experimental studies of secondary ice production, Atmos. Chem. Phys., 20, 11767–11797, https://doi.org/10.5194/acp-20-11767-2020, 2020.
Hill, T. C. J., DeMott, P. J., Tobo, Y., Fröhlich-Nowoisky, J., Moffett, B. F., Franc, G. D., and Kreidenweis, S. M.: Sources of organic ice nucleating particles in soils, Atmos. Chem. Phys., 16, 7195–7211, https://doi.org/10.5194/acp-16-7195-2016, 2016.
Pummer, B. G., Budke, C., Augustin-Bauditz, S., Niedermeier, D., Felgitsch, L., Kampf, C. J., Huber, R. G., Liedl, K. R., Loerting, T., Moschen, T., Schauperl, M., Tollinger, M., Morris, C. E., Wex, H., Grothe, H., Pöschl, U., Koop, T., and Fröhlich-Nowoisky, J.: Ice nucleation by water-soluble macromolecules, Atmos. Chem. Phys., 15, 4077–4091, https://doi.org/10.5194/acp-15-4077-2015, 2015.
Schrod, J., Weber, D., Drucke, J., Keleshis, C., Pikridas, M., Ebert, M., Cvetkovic, B., Nickovic, S., Marinou, E., Baars, H., Ansmann, A., Vrekoussis, M., Mihalopoulos, N., Sciare, J., Curtius, J., and Bingemer, H. G.: Ice nucleating particles over the Eastern Mediterranean measured by unmanned aircraft systems, Atmos Chem Phys, 17, 4817-4835, https://doi.org/10.5194/acp-17-4817-2017, 2017.
Wieder, J., Mignani, C., Schär, M., Roth, L., Sprenger, M., Henneberger, J., Lohmann, U., Brunner, C., and Kanji, Z. A.: Unveiling atmospheric transport and mixing mechanisms of ice-nucleating particles over the Alps, Atmos. Chem. Phys., 22, 3111–3130, https://doi.org/10.5194/acp-22-3111-2022, 2022.

Citation: https://doi.org/10.5194/egusphere-2023-925-RC1
- AC1: 'Reply on RC1', Yujiao Zhu, 04 Oct 2023
  
  We would like to thank the reviewer for the constructive comments and suggestions. We have addressed specific comments and revised the manuscript accordingly. Please see the supplement for our detailed response.
  
  Citation: https://doi.org/10.5194/egusphere-2023-925-AC1
RC2:
'Comment on egusphere-2023-925', Anonymous Referee #1, 31 Jul 2023

Review of Sun et al. 2023: Measurement report: Atmospheric Ice Nuclei ar Changbai Mountain (2623 m a.s.l.) in Northeastern Asia
Sun et al. 2023 present INP measurement results from the Changbai mountain in summer 2021. Changes in INP concentration are investigated towards diurnal variability, composition, source, and transport mechanism. It is an interesting study given the location of the measurement site, methodology and efforts taken in the analysis. However, major adjustments are needed to streamline and support the claims of the manuscript.

General Comments:
Major doubts concern the influence of the PBL height to Changbai mountain in Section 3.4. To the reviewer the analysis and interpretation are inconclusive. Especially it is not entirely traceable how the PBL height was derived and the involved error. Given the points raised below, the reviewer is not entirely sure if some claims need to be removed if not being support by further evidence from in-situ observations. In addition, the local wind system and dynamics should be better described or referenced.
Overall, it appears that frequently there are statements in the manuscript that should be supported by a reference. The authors may want to consider this aspect, while working through the manuscript. In addition, the figures of the manuscript could also be linked to the made statements more often. Furthermore, there appear some side information at some point, which not necessarily add to the flow of the manuscript. The authors may want to critically read through the paper, deciding which information is needed to reach the presented conclusions.
Some strong statements are made without reference or presenting data. For additional support of some of the made claims particle size measurements may be helpful. Have there not particle size measurements been available for the study?
Changbai mountain is referred as 2623 m a.s.l. (Tianchi site) and 2740 m a.s.l. (highest point). To avoid confusion the two locations and heights should be consistently appear combined.
For deeper explanations, see specific comments below.

Specific Comments:
Introduction
L29: ‘As most precipitation in clouds initiates via the ice phase’, this statement could be refined in regard of which cloud types and regions are affected and direct studies could be cited.
L63: ‘At present, it is unclear whether…’, in the reviewer’s opinion the current knowledge gap is not whether but to which extend and through which transport pathway INPs are brought to MPC relevant heights.
L68: One station in Conen et al. 2017 was located outside the Swiss Alps.
L71: Wieder et al. 2022 sampled frequently for short time spans throughout the day, whereas Conen et al. 2017 used filters sampling over longer timespans. Wieder et al. 2022 observed also a diurnal cycle with INP concentrations seeming to equilibrate over the course of a day. Further it may be important to point out to the reader that this was only observed in a wind direction where the topography promoted vertical transport of air masses from lower elevation.
L75-77: “For example, at the Jungfraujoch station (3580 m a.s.l.) in the Swiss Alps, approximately 80% of INPs were biological aerosols at freezing temperatures above −15 °C” – add reference.
L81-82: “… and establishing a parametric equation that depends on temperature and ice supersaturation for predicting the INPs concentration” – this information seems irrelevant for the current study.
L83: Here, Changbai mountain is attributed with a height of 2740 m a.s.l., whereas in L87 a height of 2623 m a.s.l. is given. If understood correct, the latter height refers to the INP measurement station of the current study. To avoid confusion the distinction between the peak and the measurement station should be made (also throughout the manuscript).

Methods
L102: Shouldn’t the elevations around the mountain decrease to all directions?
L104: Is 150m correct? Looking at maps it seems like more.
L106-112: Adding a timeseries plot (appendix or supplement) of the general meteorological parameters throughout the campaign including exemplary INP concentration would be helpful to understand the sampling conditions.
L112: What about touristic activities?
L114: How was differentiated whether the sampling site was in the free troposphere or influenced by the PBL? Please elaborate and add data or reference.
L116: A dedicated reader may be interested in a picture of the setup (also possibly in the appendix or supplement)
L117: Was there any pretreatment of the PCTE filters?
L117-124: For clarity, maybe specify what each filter sample type was used for, i.e. PCTE for INP analysis, PM2.5 for chemical composition.
L120: There were 24 samples taken covering roughly 30% of the entire measurement campaign. The authors may want to comment on the underlying measurement strategy and providing more concrete information under which meteorological conditions samples were taken.
L120: The chemical analysis was conducted on the samples collected using a PM2.5 inlet. Can the authors estimate the number of particles larger than 2.5 µm which contributed to the INP analysis samples, but would not be covered in the chemical analysis? Has there been any parallel size measurements supporting that claim?
L130: For consistency, specify the type of weather station.
L153: above -> at
L158: What was the value of V_air?
L159: If the INP concentrations were given in standard liters, the reviewer would advise to indicate this by using e.g., sL^-1, or stdL^-1 in Equation 3 and corresponding INP data plots.
L178: Which PBL data product was used? The reviewer could not find a unique record. Furthermore, what is the uncertainty and sensitivity of the PBL data product? Is Changbai mountain centered in a grid box that data was taken from or were different adjacent grid boxes averaged? Given the complex terrain of the mountainous region, how reliable does a 25km x 20km grid box represent the PBL height? Generally, the reviewer is a bit skeptical of the representativeness for the presented application. The authors should elaborate why this data is applicable. In addition, are there any direct meteorological (especially wind) observations along the mountain slope that would support the later claim of vertical transport due to orographic lifting?
L184: The authors may want to briefly describe the principle of CWT.

Results and Discussion
L190: “characterize situation of droplet freezing” sounds odd.
L192: As there are only two MilliQ water backgrounds displayed, rephrase to “were -30°C and -28.5°C”.
L193-196: This seems contradicting. If the contaminants could be ignored, one would not need to correct for it.
L195-196: Were averaged concentrations at each temperature step of the two blank filter samples subtracted as correction – please specify. As two samples are not many, the authors may want to comment on the overall obtained repeatability of blank filter measurements obtained which are not presented in this study.
L199: -26.0°C -> -20°C
L200: What it the values of T₅₀? -13°C from above? The authors should repeat this value here, or introduce another variable to avoid the nomenclature confusion of T₅₀representing the result of one sample (L191) or the average of all samples (L194).
L201: It is not necessarily the diversity of different INPs but could also just relate to different emission strengths.
L202: What would that local source be?
L205-206: This statement cannot be made, as it seems that there have no dilutions of samples been made. This sets the upper limit in detectable N_INP = 1/V_airi.e., all droplets frozen.
L206: To the reviewer, the temperature dependence results especially from the fact that N_INPis cumulative. A direct connection to the complexity of sources cannot be made.
L207: What test was used to check for differences between daytime and nighttime samples?
L207-211: It remains questionable if the sampling intervals used in the study (maximally two per day, 20 samples total spread out unknown over a month) allow for the detection of a diurnal cycle. It is conceivable that if, e.g., the minimum in INP concentration occurs at 6:00 and the maximum at 18:00, no difference would be observed on the filters. The described scenario could be likely if the transport is facilitated by convection. In addition, are there any potential local sources located on Changbai mountain, e.g., from the lake, which could cover up a potential diurnal cycle? The authors should elaborate on these aspects.
L212-226: In the following discussion, references to the data figure could be beneficial. Furthermore, when discussing the obtained results to previous studies, more precision is needed, what is the difference between “narrowly” (L214) and “much narrower” (L216)? More quantitative expressions are needed. In addition, the present study motivated the need for measurements on high altitude sites. It is not entirely clear, how the sites of Cerro Mirador and Beijing relate to this. Maybe an extra motivation for this comparison would be needed. Studies from high altitude stations like Storm Peak (US), Jungfraujoch (Switzerland), or Altzomoni (Mexico) might be interesting additions, which could also complement Figure 2b, but the reviewer leaves this up to the authors.
L213: Precise to Swiss Alps.
L214: Shouldn’t it be high-temperature and low-concentration region and vice versa?
Section 3.2: The reviewer perceived the usage of the abbreviations bio-INPs, other org-INPs, and inorg-INPs at times a bit odd. If the authors want to keep them, they may want to consider introducing them already in the introduction.
L236: Specify type of H₂O₂
L254-256: Was this increase significant and isn’t it rather a bias due to the measurement limitations (no dilutions)?
L264: Add the actual number of samples that make up 50% (also in the caption of Fig. 3).
L269-270: Again, how significant was this increase and is the decrease to low temperatures owed to a measurement bias?
Section 3.3: The data used in this section is unavailable. As the raw data for creating Figure 4 is already quite digested in Figure 4, the authors may want to add a table with the data written out per sample in the appendix. In addition, the found correlations are described as “good” or “weak”. As the definitions for these terms may vary, the value and type of used correlation should be named throughout the manuscript.
L278-279: Even though the authors selected a mild formulation for their interpretation, this statement should be toned down a little bit more for having only found a good correlation with one element. Furthermore, could there be other sources as well?
L281: Kanji et al. 2017 is a summary, maybe use direct study for this reference.
L288-289: Is there reference for this methodology? What was the used threshold in concentration to come to this conclusion?
L306-309: Despite being textbook knowledge, the authors may want to give a reference to read up in these topics. Furthermore, a short description of the essential processes for Changbai mountain could be given in the introduction.
L313: Specify “moderate-to-good”.
L315: “exceptionally high N_INP-bio values” add e.g., ‘as discussed below’ for readability.
L315-316: Even though being only a suggestion, in the reviewer’s opinion this statement cannot be made given too many assumptions and misinterpretation. First, the two high INP cases are excluded and given the argument should coincide with height. Is that an indication for a potential strong but infrequent local source? This might well be pure coincidence, but given the dates being a week apart, was there some periodic event near the measurement site? Second, while the correlation (which type of coefficient?) for some temperature is comparably large, there does not seem to be a significant increase in INP concentration. In addition, if the transport of bio-INP was the underlaying process, one could expect that the correlation should be expressed at a broad range of INP concentrations at a wide range of temperature in the HTR – has this been observed and could the correlation at all temperature been shown, e.g., in a table? Lastly, the PBL height never extends to the mountain top. For transport there is further evidence needed like wind speed and direction along the slope to support this claim. Ultimately, the analysis also bases only on 6-9 datapoints and the uncertainty in the PBL product remains undiscussed.
L316-319: For this claim, data should be presented.
L328: Add reference for phytoplankton blooms occurrence.
L348: Were there still enough datapoints available below
L357-358: Following Figure S1, it appears to the reviewer, that the correlations for other org-INPs seem similarly or even more consistent throughout the temperature range than for the presented bio-INPs data.

Conclusion
L364-371: Maybe repeat introduced variables such as F_INP-bio, LTR, WS.
L377-378: “With larger contributions observed from local and oceanic sources” - was this shown in the results section?
L379-389: The reviewer is unsure whether diving in to the topic of secondary ice formation in the last paragraph without any prior mention of the topic is within the scope of this publication.
L384: “confirm” seems to be the wrong word, the statement should be weakened.

Figures
Figure 1: Is it essential to indicate Beijing? If so, it should be named in the caption. To stay consistent between (b) and (a) it could be beneficial to indicate Changbai mountain (check spelling in figure) in red in (a).
Figure 2a: What is the error in T and f?
Figure 2b: Specify the data of Wieder et al. 2022 to Weissfluhjoch instead of Alps. The data of Wieder et al. 2022 is not fully visible. Beijing data is hard to read. For better comparability, maybe an average or median of each data set could be added.
Figure 3a and 3b: Using thin lines instead of dots per spectrum may enhance the readability.
Figure 3a: Error bars extend beyond axis limits. As N_INP, N_INP-heat, and N_INP-H2O2 are only used to calculate N_INP-bio, N_{INP-other org}, and N_INP-inorg Figure 3a could be moved to appendix to focus on the essential plots 3b and 3c.
Figure 3b: Are all the calculated differences in concentration significant? Could (exemplary) error bars be added?
Figure 4a: Figure missing.
Figure 4: As all other figures temperature increases to the right, the x axis of Figure 4 could be flipped for consistency. Which correlation coefficient was used? Specify in caption.
Figure 5: What is the red star? Is there a specific reason for the y-axis not being logarithmic in contrast to the other plots of INP concentrations?

References
Conen, F., Yakutin, M. V., Yttri, K. E., and Hüglin, C.: Ice nucleating particle concentrations increase when leaves fall in autumn, Atmosphere, 8, 202, https://doi.org/10.3390/atmos8100202, 2017.
Kanji, Z. A., Ladino, L. A., Wex, H., Boose, Y., Burkert-Kohn, M., Cziczo, D. J., and Krämer, M.: Overview of Ice 525 Nucleating Particles, Meteorological Monographs, 58, 1.1-1.33, https://doi.org/10.1175/amsmonographs-d-16-0006.1, 2017.
Wieder, J., Mignani, C., Schär, M., Roth, L., Sprenger, M., Henneberger, J., Lohmann, U., Brunner, C., and Kanji, Z. A.: Unveiling atmospheric transport and mixing mechanisms of ice-nucleating particles over the Alps, Atmos. Chem. Phys., 22, 3111–3130, https://doi.org/10.5194/acp-22-3111-2022, 2022.

Citation: https://doi.org/10.5194/egusphere-2023-925-RC2
- AC2: 'Reply on RC2', Yujiao Zhu, 04 Oct 2023
  
  We would like to thank the reviewer for the constructive comments and suggestions. We have addressed specific comments and revised the manuscript accordingly. Please see the supplement for our detailed response.
  
  Citation: https://doi.org/10.5194/egusphere-2023-925-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2023-925', Anonymous Referee #3, 17 Jul 2023

General comments
The manuscript by Sun et al. reports INP measurements at Changbai Summit in the summer of 2021. Using results from heat and H2O2 treatments, the authors distinguish between biological INPs, other organic INPs, and inorganic INPs and conclude that the majority of INPs in the temperature range studied were of biological origin. It is an interesting study that provides new information about biological INPs. They discuss correlations of biological INPs with meteorological data as well as with some chemical tracers, suggesting that biological INPs may originate from soil dust. In addition, possible sources and transport mechanisms of INPs are discussed based on knowledge of the height of the planetary boundary layer and the concentration-weighted backward trajectories of air masses. The authors have made an effort to explain their data, but given the small number of samples (22 in total, half of which were collected during the day and the other at night) and the lack of sample dilutions to extend the freezing spectra to lower temperatures, some sections require substantial revision in my opinion. I have major and minor comments that I hope will be helpful to the authors and can be addressed during the review process.

Specific comments
Abstract
Line 12: “modifying” is maybe not the right word here.
Lines 22-24: While this insight into atmospheric dynamics is welcome, I would note that this positive correlation between biological INPs with planetary boundary layer height is based on 7 data points only. 2 outliers were excluded and 2 missing data points were not mentioned. It is not stated which correlation analysis was done, something that persists throughout the study. Furthermore, it is unclear for the reviewer how these two cases of high concentrations of biological INPs differ from the other samples in terms of long-range transport. These results need thorough review, discussions about them need to be clarified, and the relevant conclusions probably need to be revised.

Introduction
The reviewer thinks that some parts of the introduction should be worded more precisely.
Line 40 and line 52: Please use “etc” carefully. Try to list fully instead.
Line 40: There are also efficient proteinaceous cell-free INPs (Pummer et al., 2015) that are not embedded in cell membranes. Please, reformulate the sentence.
Line 45: I am unsure what is meant by “and [in] agricultural soils”. Do you mean a site, where presumably many INPs come from particles from agricultural soils? Please reformulate.
Line 68: The tree sites that are referred to are not all located in the Swiss Alps, but are located across Switzerland.
Lines 70-71: Instead of “one order of magnitude”, you could keep the same units as in the previous sentence. Maybe summarize in percent per kilometer.
Line 72: The “atmosphere” can only be in singular.
Lines 72-75: Please mention that Schrod et al. 2017 findings were obtained during specific events, i.e., a series of elevated Saharan dust plumes.
Lines 75-77: The citation Conen et al. 2022 is missing at the end of the sentence. I would suggest adding here the following specification: “under free-tropospheric conditions”. Study could have been mentioned in L. 44-45 instead/as well.
Line 87: “INPs measurements” --> “INP measurements”

Methods
The reviewer found that the methods are well described, and that it was helpful that the authors provided the raw data for the reviewers.
Line 119: Please specify that your times are meant in local time or mention the correct time zone.
Line 120: A total of 24 samples were collected for INP analysis. The results of only 22 samples were reported in the provided data file. Could the authors please explain why the results of two samples are missing? Could it maybe be that 22 samples and 2 background filters were collected?
Line 130: It would be interesting to know how far the weather station is from the measurement site.
Lines 178-186: Please be more precise how you generated the air mass backwards trajectories and add information about starting time as well as number of trajectories per sample.
Line 188: Which data product from the Climate Data Store did you use for the PBL data?

Results and Discussion
The reviewer found that some parts of the results and discussion need thorough revision and much clearer statements.
Line 208 and lines 210-211: Wieder et al. (2022) contains INP concentrations from a mountain site called Weissfluhjoch (2693 m a.s.l.) and a valley site called Wolfgangpass (1631 m a.s.l.). The two sites in the Swiss Alps are only 4 km apart and are not necessarily representative of the entire Swiss Alps. Please be more specific: a) Swiss Alps and not any Alps, b) add the name of the site(s) you mean.
Lines 208-211: Please provide the time spans for collection and averaging for these other studies. For example, Wieder et al. (2022) collected samples over short time spans (i.e., 20 minutes) and averaged them into 2-hour bins. They found a peak at 19 h UTC (i.e., 21 h CET), which is defined as nighttime based on the definition used in this manuscript, if I am not mistaken. A possible diurnal cycle at Changbai Mountain may have been averaged out due to the long sampling time of 11 hours. Please mention specifically for Changbai Mountain only the comparison of daytime and nighttime, since only two samples are taken per day. In my opinion, a conclusion over the entire diurnal cycle cannot be made here.
Line 213: What is meant by “the temperature spectra showed a wider range”?
Line 217: What is meant by “the N_INP value was much larger at Mt. Huang than our results”? Can't the difference between both sites be explained by the fact that your results cover a warmer temperature range than the results from Mt. Huang? Please mention the freezing temperatures while comparing INP concentrations.
Line 256: Shouldn’t it be “bio-INP” instead of “INP”?
Line 254-256: A mean increase in F_INP-biofrom 0.8 to 0.9 with decreasing temperatures between -16.5 °C and -20 °C doesn’t make much sense and could be due to the way the data were processed here. It looks like some untreated and heat-treated samples already reached the upper detection limit at about -15 °C or -16 °C. In order to draw conclusions about the proportion of bio-INPs, other org-INPs, and inorganic INPs below -15 °C, I believe dilutions of the untreated and heat-treated samples would have been required. The number of data points of F_INP-biofrom maybe around -18 °C and lower is likely too low to draw any conclusions below that temperature threshold.
Lines 277-281: What about biological INPs originating from plants and oceans? Please discuss.
Lines 279-281: Maybe instead of citing the review, authors could cite the original studies e.g. Hill et al. 2016 or others.
Line 301: Maybe instead of citing the review, authors could cite the original studies.
Lines 315-321: Could the authors elaborate how the inclusion of these points would change the results and conclusion?
Line 320: Please indicate here that the “freezing” temperature is meant.
Lines 323-325: How does the CWT analysis on August 18 and 25 differ from the other days?

Conclusion
The reviewer believes that some rewording needs to be done, especially in the last paragraph.
Lines 365-368: A decreasing trend in F_INP-biowith decreasing temperature suggests that other organic or inorganic INPs become more important with decreasing temperatures. It does not suggest that the ice nucleation activity of bio-INPs decreases. In addition, due to the lack of data points in the low temperature regime, no conclusions can be drawn regarding F_INP-biofor that temperature range, in my opinion. Dilutions would have been required, as mentioned above.
Line 379: Did you mean to write that the INP number concentration is lower than the ice crystal number concentration, especially in the warm temperature range?
Line 381: Is there a word missing between “…is second only to…”?
Line 383: Please delete “through various collisions with pre-existing ice”. There are several multiplication processes, and they involve many more processes than only ice-ice collision. More information can be found for example in Korolev and Leisner, 2020.
Line 385: Bio-INPs do not impact secondary ice formation directly, please reformulate.

Figures
Fig.2(b)
Please indicate in the figure and legend the name of the mountain in the Swiss Alps from which the data originate similar to what you did with the Mt. Huang dataset.
Should the y-axis perhaps be extended to lower values to see the lower limit of the error bar?

Fig. 3(a)
Why are the error bars for N_INP-H2O2 below -15 °C extending to values outside the graph?
Please use the same axes in Fig. 3a than in Fig. 3b and Fig. 2b.

Fig.3(c)
I appreciate that there is an indication of the number of data points included in the analysis. Since the upper detection limit of about 2 INPs per liter is reached around -15 °C for N_INP-bio, dilutions would have been necessary to extend the plot from -15 to -20 °C as mentioned above.
How can the median fraction of inorganic INPs above -12 °C be more than 0.0 if the median fraction of bio-INPs is 1.0?

Fig.4
What kind of correlation analysis did you do? Please specify.

Fig.5(a-c)
What does “r” stand for? Please also describe what the red lines and the purple circles represent.
Is the x-axis showing the mean PBL height?
Maybe add “freezing” between “three” and “temperatures”.

Fig.5 (d-f)
Trajectories of which samples were included in the CWT analysis? Are the trajectories of all the samples included or only those of the daytime samples? Were the trajectories of the two outliers excluded or included here? Please be more specific.
Also describe in the legend what the star and triangle represent.

Fig. S1
Please describe in the legend precisely what is shown and what is meant by "R". Is the large "R" here similar to the small "r" in Fig. 5?

Fig. S2
Authors could add the star and the triangle in these maps, similar to Fig. 5 (d-f).

References:
Conen, F., Einbock, A., Mignani, C., and Hüglin, C.: Measurement report: Ice-nucleating particles active ≥ −15 °C in free tropospheric air over western Europe, Atmos. Chem. Phys., 22, 3433–3444, https://doi.org/10.5194/acp-22-3433-2022, 2022.
Korolev, A. and Leisner, T.: Review of experimental studies of secondary ice production, Atmos. Chem. Phys., 20, 11767–11797, https://doi.org/10.5194/acp-20-11767-2020, 2020.
Hill, T. C. J., DeMott, P. J., Tobo, Y., Fröhlich-Nowoisky, J., Moffett, B. F., Franc, G. D., and Kreidenweis, S. M.: Sources of organic ice nucleating particles in soils, Atmos. Chem. Phys., 16, 7195–7211, https://doi.org/10.5194/acp-16-7195-2016, 2016.
Pummer, B. G., Budke, C., Augustin-Bauditz, S., Niedermeier, D., Felgitsch, L., Kampf, C. J., Huber, R. G., Liedl, K. R., Loerting, T., Moschen, T., Schauperl, M., Tollinger, M., Morris, C. E., Wex, H., Grothe, H., Pöschl, U., Koop, T., and Fröhlich-Nowoisky, J.: Ice nucleation by water-soluble macromolecules, Atmos. Chem. Phys., 15, 4077–4091, https://doi.org/10.5194/acp-15-4077-2015, 2015.
Schrod, J., Weber, D., Drucke, J., Keleshis, C., Pikridas, M., Ebert, M., Cvetkovic, B., Nickovic, S., Marinou, E., Baars, H., Ansmann, A., Vrekoussis, M., Mihalopoulos, N., Sciare, J., Curtius, J., and Bingemer, H. G.: Ice nucleating particles over the Eastern Mediterranean measured by unmanned aircraft systems, Atmos Chem Phys, 17, 4817-4835, https://doi.org/10.5194/acp-17-4817-2017, 2017.
Wieder, J., Mignani, C., Schär, M., Roth, L., Sprenger, M., Henneberger, J., Lohmann, U., Brunner, C., and Kanji, Z. A.: Unveiling atmospheric transport and mixing mechanisms of ice-nucleating particles over the Alps, Atmos. Chem. Phys., 22, 3111–3130, https://doi.org/10.5194/acp-22-3111-2022, 2022.

Citation: https://doi.org/10.5194/egusphere-2023-925-RC1
- AC1: 'Reply on RC1', Yujiao Zhu, 04 Oct 2023
  
  We would like to thank the reviewer for the constructive comments and suggestions. We have addressed specific comments and revised the manuscript accordingly. Please see the supplement for our detailed response.
  
  Citation: https://doi.org/10.5194/egusphere-2023-925-AC1
RC2:
'Comment on egusphere-2023-925', Anonymous Referee #1, 31 Jul 2023

Review of Sun et al. 2023: Measurement report: Atmospheric Ice Nuclei ar Changbai Mountain (2623 m a.s.l.) in Northeastern Asia
Sun et al. 2023 present INP measurement results from the Changbai mountain in summer 2021. Changes in INP concentration are investigated towards diurnal variability, composition, source, and transport mechanism. It is an interesting study given the location of the measurement site, methodology and efforts taken in the analysis. However, major adjustments are needed to streamline and support the claims of the manuscript.

General Comments:
Major doubts concern the influence of the PBL height to Changbai mountain in Section 3.4. To the reviewer the analysis and interpretation are inconclusive. Especially it is not entirely traceable how the PBL height was derived and the involved error. Given the points raised below, the reviewer is not entirely sure if some claims need to be removed if not being support by further evidence from in-situ observations. In addition, the local wind system and dynamics should be better described or referenced.
Overall, it appears that frequently there are statements in the manuscript that should be supported by a reference. The authors may want to consider this aspect, while working through the manuscript. In addition, the figures of the manuscript could also be linked to the made statements more often. Furthermore, there appear some side information at some point, which not necessarily add to the flow of the manuscript. The authors may want to critically read through the paper, deciding which information is needed to reach the presented conclusions.
Some strong statements are made without reference or presenting data. For additional support of some of the made claims particle size measurements may be helpful. Have there not particle size measurements been available for the study?
Changbai mountain is referred as 2623 m a.s.l. (Tianchi site) and 2740 m a.s.l. (highest point). To avoid confusion the two locations and heights should be consistently appear combined.
For deeper explanations, see specific comments below.

Specific Comments:
Introduction
L29: ‘As most precipitation in clouds initiates via the ice phase’, this statement could be refined in regard of which cloud types and regions are affected and direct studies could be cited.
L63: ‘At present, it is unclear whether…’, in the reviewer’s opinion the current knowledge gap is not whether but to which extend and through which transport pathway INPs are brought to MPC relevant heights.
L68: One station in Conen et al. 2017 was located outside the Swiss Alps.
L71: Wieder et al. 2022 sampled frequently for short time spans throughout the day, whereas Conen et al. 2017 used filters sampling over longer timespans. Wieder et al. 2022 observed also a diurnal cycle with INP concentrations seeming to equilibrate over the course of a day. Further it may be important to point out to the reader that this was only observed in a wind direction where the topography promoted vertical transport of air masses from lower elevation.
L75-77: “For example, at the Jungfraujoch station (3580 m a.s.l.) in the Swiss Alps, approximately 80% of INPs were biological aerosols at freezing temperatures above −15 °C” – add reference.
L81-82: “… and establishing a parametric equation that depends on temperature and ice supersaturation for predicting the INPs concentration” – this information seems irrelevant for the current study.
L83: Here, Changbai mountain is attributed with a height of 2740 m a.s.l., whereas in L87 a height of 2623 m a.s.l. is given. If understood correct, the latter height refers to the INP measurement station of the current study. To avoid confusion the distinction between the peak and the measurement station should be made (also throughout the manuscript).

Methods
L102: Shouldn’t the elevations around the mountain decrease to all directions?
L104: Is 150m correct? Looking at maps it seems like more.
L106-112: Adding a timeseries plot (appendix or supplement) of the general meteorological parameters throughout the campaign including exemplary INP concentration would be helpful to understand the sampling conditions.
L112: What about touristic activities?
L114: How was differentiated whether the sampling site was in the free troposphere or influenced by the PBL? Please elaborate and add data or reference.
L116: A dedicated reader may be interested in a picture of the setup (also possibly in the appendix or supplement)
L117: Was there any pretreatment of the PCTE filters?
L117-124: For clarity, maybe specify what each filter sample type was used for, i.e. PCTE for INP analysis, PM2.5 for chemical composition.
L120: There were 24 samples taken covering roughly 30% of the entire measurement campaign. The authors may want to comment on the underlying measurement strategy and providing more concrete information under which meteorological conditions samples were taken.
L120: The chemical analysis was conducted on the samples collected using a PM2.5 inlet. Can the authors estimate the number of particles larger than 2.5 µm which contributed to the INP analysis samples, but would not be covered in the chemical analysis? Has there been any parallel size measurements supporting that claim?
L130: For consistency, specify the type of weather station.
L153: above -> at
L158: What was the value of V_air?
L159: If the INP concentrations were given in standard liters, the reviewer would advise to indicate this by using e.g., sL^-1, or stdL^-1 in Equation 3 and corresponding INP data plots.
L178: Which PBL data product was used? The reviewer could not find a unique record. Furthermore, what is the uncertainty and sensitivity of the PBL data product? Is Changbai mountain centered in a grid box that data was taken from or were different adjacent grid boxes averaged? Given the complex terrain of the mountainous region, how reliable does a 25km x 20km grid box represent the PBL height? Generally, the reviewer is a bit skeptical of the representativeness for the presented application. The authors should elaborate why this data is applicable. In addition, are there any direct meteorological (especially wind) observations along the mountain slope that would support the later claim of vertical transport due to orographic lifting?
L184: The authors may want to briefly describe the principle of CWT.

Results and Discussion
L190: “characterize situation of droplet freezing” sounds odd.
L192: As there are only two MilliQ water backgrounds displayed, rephrase to “were -30°C and -28.5°C”.
L193-196: This seems contradicting. If the contaminants could be ignored, one would not need to correct for it.
L195-196: Were averaged concentrations at each temperature step of the two blank filter samples subtracted as correction – please specify. As two samples are not many, the authors may want to comment on the overall obtained repeatability of blank filter measurements obtained which are not presented in this study.
L199: -26.0°C -> -20°C
L200: What it the values of T₅₀? -13°C from above? The authors should repeat this value here, or introduce another variable to avoid the nomenclature confusion of T₅₀representing the result of one sample (L191) or the average of all samples (L194).
L201: It is not necessarily the diversity of different INPs but could also just relate to different emission strengths.
L202: What would that local source be?
L205-206: This statement cannot be made, as it seems that there have no dilutions of samples been made. This sets the upper limit in detectable N_INP = 1/V_airi.e., all droplets frozen.
L206: To the reviewer, the temperature dependence results especially from the fact that N_INPis cumulative. A direct connection to the complexity of sources cannot be made.
L207: What test was used to check for differences between daytime and nighttime samples?
L207-211: It remains questionable if the sampling intervals used in the study (maximally two per day, 20 samples total spread out unknown over a month) allow for the detection of a diurnal cycle. It is conceivable that if, e.g., the minimum in INP concentration occurs at 6:00 and the maximum at 18:00, no difference would be observed on the filters. The described scenario could be likely if the transport is facilitated by convection. In addition, are there any potential local sources located on Changbai mountain, e.g., from the lake, which could cover up a potential diurnal cycle? The authors should elaborate on these aspects.
L212-226: In the following discussion, references to the data figure could be beneficial. Furthermore, when discussing the obtained results to previous studies, more precision is needed, what is the difference between “narrowly” (L214) and “much narrower” (L216)? More quantitative expressions are needed. In addition, the present study motivated the need for measurements on high altitude sites. It is not entirely clear, how the sites of Cerro Mirador and Beijing relate to this. Maybe an extra motivation for this comparison would be needed. Studies from high altitude stations like Storm Peak (US), Jungfraujoch (Switzerland), or Altzomoni (Mexico) might be interesting additions, which could also complement Figure 2b, but the reviewer leaves this up to the authors.
L213: Precise to Swiss Alps.
L214: Shouldn’t it be high-temperature and low-concentration region and vice versa?
Section 3.2: The reviewer perceived the usage of the abbreviations bio-INPs, other org-INPs, and inorg-INPs at times a bit odd. If the authors want to keep them, they may want to consider introducing them already in the introduction.
L236: Specify type of H₂O₂
L254-256: Was this increase significant and isn’t it rather a bias due to the measurement limitations (no dilutions)?
L264: Add the actual number of samples that make up 50% (also in the caption of Fig. 3).
L269-270: Again, how significant was this increase and is the decrease to low temperatures owed to a measurement bias?
Section 3.3: The data used in this section is unavailable. As the raw data for creating Figure 4 is already quite digested in Figure 4, the authors may want to add a table with the data written out per sample in the appendix. In addition, the found correlations are described as “good” or “weak”. As the definitions for these terms may vary, the value and type of used correlation should be named throughout the manuscript.
L278-279: Even though the authors selected a mild formulation for their interpretation, this statement should be toned down a little bit more for having only found a good correlation with one element. Furthermore, could there be other sources as well?
L281: Kanji et al. 2017 is a summary, maybe use direct study for this reference.
L288-289: Is there reference for this methodology? What was the used threshold in concentration to come to this conclusion?
L306-309: Despite being textbook knowledge, the authors may want to give a reference to read up in these topics. Furthermore, a short description of the essential processes for Changbai mountain could be given in the introduction.
L313: Specify “moderate-to-good”.
L315: “exceptionally high N_INP-bio values” add e.g., ‘as discussed below’ for readability.
L315-316: Even though being only a suggestion, in the reviewer’s opinion this statement cannot be made given too many assumptions and misinterpretation. First, the two high INP cases are excluded and given the argument should coincide with height. Is that an indication for a potential strong but infrequent local source? This might well be pure coincidence, but given the dates being a week apart, was there some periodic event near the measurement site? Second, while the correlation (which type of coefficient?) for some temperature is comparably large, there does not seem to be a significant increase in INP concentration. In addition, if the transport of bio-INP was the underlaying process, one could expect that the correlation should be expressed at a broad range of INP concentrations at a wide range of temperature in the HTR – has this been observed and could the correlation at all temperature been shown, e.g., in a table? Lastly, the PBL height never extends to the mountain top. For transport there is further evidence needed like wind speed and direction along the slope to support this claim. Ultimately, the analysis also bases only on 6-9 datapoints and the uncertainty in the PBL product remains undiscussed.
L316-319: For this claim, data should be presented.
L328: Add reference for phytoplankton blooms occurrence.
L348: Were there still enough datapoints available below
L357-358: Following Figure S1, it appears to the reviewer, that the correlations for other org-INPs seem similarly or even more consistent throughout the temperature range than for the presented bio-INPs data.

Conclusion
L364-371: Maybe repeat introduced variables such as F_INP-bio, LTR, WS.
L377-378: “With larger contributions observed from local and oceanic sources” - was this shown in the results section?
L379-389: The reviewer is unsure whether diving in to the topic of secondary ice formation in the last paragraph without any prior mention of the topic is within the scope of this publication.
L384: “confirm” seems to be the wrong word, the statement should be weakened.

Figures
Figure 1: Is it essential to indicate Beijing? If so, it should be named in the caption. To stay consistent between (b) and (a) it could be beneficial to indicate Changbai mountain (check spelling in figure) in red in (a).
Figure 2a: What is the error in T and f?
Figure 2b: Specify the data of Wieder et al. 2022 to Weissfluhjoch instead of Alps. The data of Wieder et al. 2022 is not fully visible. Beijing data is hard to read. For better comparability, maybe an average or median of each data set could be added.
Figure 3a and 3b: Using thin lines instead of dots per spectrum may enhance the readability.
Figure 3a: Error bars extend beyond axis limits. As N_INP, N_INP-heat, and N_INP-H2O2 are only used to calculate N_INP-bio, N_{INP-other org}, and N_INP-inorg Figure 3a could be moved to appendix to focus on the essential plots 3b and 3c.
Figure 3b: Are all the calculated differences in concentration significant? Could (exemplary) error bars be added?
Figure 4a: Figure missing.
Figure 4: As all other figures temperature increases to the right, the x axis of Figure 4 could be flipped for consistency. Which correlation coefficient was used? Specify in caption.
Figure 5: What is the red star? Is there a specific reason for the y-axis not being logarithmic in contrast to the other plots of INP concentrations?

References
Conen, F., Yakutin, M. V., Yttri, K. E., and Hüglin, C.: Ice nucleating particle concentrations increase when leaves fall in autumn, Atmosphere, 8, 202, https://doi.org/10.3390/atmos8100202, 2017.
Kanji, Z. A., Ladino, L. A., Wex, H., Boose, Y., Burkert-Kohn, M., Cziczo, D. J., and Krämer, M.: Overview of Ice 525 Nucleating Particles, Meteorological Monographs, 58, 1.1-1.33, https://doi.org/10.1175/amsmonographs-d-16-0006.1, 2017.
Wieder, J., Mignani, C., Schär, M., Roth, L., Sprenger, M., Henneberger, J., Lohmann, U., Brunner, C., and Kanji, Z. A.: Unveiling atmospheric transport and mixing mechanisms of ice-nucleating particles over the Alps, Atmos. Chem. Phys., 22, 3111–3130, https://doi.org/10.5194/acp-22-3111-2022, 2022.

Citation: https://doi.org/10.5194/egusphere-2023-925-RC2
- AC2: 'Reply on RC2', Yujiao Zhu, 04 Oct 2023
  
  We would like to thank the reviewer for the constructive comments and suggestions. We have addressed specific comments and revised the manuscript accordingly. Please see the supplement for our detailed response.
  
  Citation: https://doi.org/10.5194/egusphere-2023-925-AC2

Peer review completion

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

AR by Yujiao Zhu on behalf of the Authors (27 Oct 2023) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (03 Nov 2023) by Luis A. Ladino

RR by Anonymous Referee #2 (03 Nov 2023)

RR by Anonymous Referee #4 (26 Nov 2023)

ED: Publish subject to minor revisions (review by editor) (11 Dec 2023) by Luis A. Ladino

I thank the authors for addressing most of the comments and suggestions provided by Reviewers #1 and #3; however, the two additional reviewers are concerned about the readability of the manuscript. Additionally, Reviewer #4 has several Major, Specific, and Technical comments and I also added a list of Minor/Technical comments. Please improve the grammar of entire manuscript and properly address each comment listed below.

Reviewer #2:
Please carefully go through the manuscript to meet the standard of ACP.

Reviewer #4:
Review of “Measurement report: Atmospheric Ice Nuclei at Changbai Mountain (2623 m a.s.l.) in Northeastern Asia” by Sun et al.
The paper reports on the outcome of a one-month field campaign conducted at the Tianchi site on Mt. Changbai during the summer of 2021. Filter samples collected during 10 days at the end of the campaign are used to measure the concentration of immersion freezing INPs and additional heat treatment and H2O2 degradation of the sample are used to infer the contribution of biological INP to the INP concentration. In addition, the INP concentration data is correlated to axillary meteorological data, bulk aerosol composition and trace gas concentration, and back trajectories are used to find potential source regions of INP active in a certain temperature regime. The authors find that biological INP contribute the majority to the INP concentration and stress the importance of soil dust as a regional source as well as long range transport of biological marine INP and biological INP from vegetation.
While the conducted measurements and analysis are state of the art, the interpretation is mostly speculative and not explained clear enough. Instead of deducing conclusions from signals in the current data the reader is pointed to literature sources to back up interpretations. An additional shortcoming is the very limited number of samples collected, making it more of a preliminary study hinting at several interesting aspects on the sources of INPs in Northeast Asia that deserve deeper investigation. The authors have given insightful replies to some of the comments in the previous round of review but have not managed to implement all necessary clarifications and improvements into the manuscript. On some occasions the changes the authors mention in the reply have not been transferred to the revised manuscript, for example reply to question 5 of Referee #3.
Because the manuscript has not been substantially improved in reply to the previous round of review and the many additional comments below, I recommend major revision before the manuscript can be considered for publication. I also recommend a thorough language check by a native English speaker to avoid misunderstandings of the scientific content due to poor phrasing.

Major comments:
The surrounding of Tianchi station next to Tianchi Lake, inside a crater could have a major impact on the measured NINP. Provide an explain in the manuscript how the contribution of long-distant transport can be clearly distinguished from local or regional sources of INP.
The influence of fog and precipitation at the sampling site on the measured NINP should be analysed in more detail. In addition, the influence of precipitation along trajectories should be considered in the CWT analysis. For INPs to form ice in mixed-phase clouds they need to act as cloud condensation nuclei as well. Cloud formation and precipitation along trajectories should therefore wash them out preventing their lon-grange transport.
As pointed out in the previous round of reviews, the appropriateness of the PBL height from ERA5 for the Tianchi station site is questionable and needs further confirmation. The authors acknowledged in their response, that the GDAS topography in the region is off by over 900m. Also, complex effects from the mountain and its crater on the formation of the boundary layer cannot be neglected. Are additional measurements for example from balloon soundings available to provide evidence that the PBL height from ERA5 are representative for the location?
Specific comments:
1) Line 21: explain why correlation to windspeed, Ca2+ and isoprene suggests bio aerosol is attached to soil dust and act as INP.
2) Line 22ff: Provide an explanation why PBL height could be positively correlated to NINP. The opposite could be expected because of dilution of aerosol concentration with increasing PBL height. Explain based on what data it is found that valley breeze influences NINP.
3) Line 33ff: inappropriate citations. Koop et al., 2000, Murray et al., 2010, Cziczo et al., 2013 report on homogeneous ice nucleation and ice nucleation under cirrus cloud conditions not immersion freezing. For example, Murray et al., 2012 would be a better reference.
4) Line 37ff: By definition, mixed-phase clouds contain droplets and therefore only exist at water saturated conditions. Water saturation is not a prerequisite for ice formation. Reformulate.
5) Line 43ff: Not corrected as mentioned in response to Referee#3 question 5. Implement correction.
6) Line 45: Can lichen be considered biological aerosol? As I understand they are a symbiotic organism attached to surfaces.
7) Line 48: Double check if it is correct that pollen is non-proteinaceous. I find they contain about 30% protein.
8) Line 51: add a citation for the activity temperature of mineral dust and sea spray.
9) Line 55: inappropriate citations: references are for deposition ice nucleation, replace with references relevant for immersion freezing.
10) Line 59-62: Provide references for “numerous studies”, “spatial distribution heterogeneity”, and the altitude of mixed-phase clouds.
11) Line 69f: INP sources are not in the atmosphere but on the surface. Reformulate.
12) Line 74ff: JFJ station is not a good example for having high vegetation coverage. It is surrounded by bare rock and ice. Reformulate.
13) Line 83f: Clarify what is meant by “impact of bio INP on cloud droplets and their contribution to formation of precipitation”.
14) Line 91: Explain what boundaries are meant by “transboundary transport of air mass”.
15) Line 98: provide a reference for pollution transport to the Arctic from this region.
16) Line 112: Extend the discussion on weather conditions. What is meant by humid weather? Was it raining, or was there fog? Fog and rain can have an impact on the sampling as well as on the transport of INP. Potential evidence for this impact can be seen from the anticorrelation of NINP in the LTR with RH in Fig.4.
17) Line 116f: Elaborate on the potential impact of the surrounding (lake, dense vegetation) on NINP and other variables, for example isoprene concentrations.
18) Line 121ff: Provide characteristics on the sampler inlet cut-off. Is it a total inlet? As RH was high during the campaign and often at 100%, was there fog or precipitation? Does the sampler collect cloud droplets as well?
19) Line 123: Table S1 lists 25 sample intervals. Was the filter not changes for the two intervals during nighttime on the 11.8.? If not, maybe the 6min gap in sampling can be neglected and doesn’t need to be listed. Otherwise specify what happened.
20) Line 124, Tab.S1: The sample duration in Tab.S1 do not agree with the time difference between start to end time. Where does the duration come from? Does the sampler turn off if the pressure-drop over the filter is too high? The sample volume has been calculated using the set flow rate and start to end time. Does the sampler not provide a more precise measurement of the sample volume? If possible, use measured and not calculated sample volume to calculate NINP.
21) Line 126: provide model number for the PM2.5 sampler.
22) Explain how auxiliary data was averaged for the correlation analysis with NINP.
23) Line 139: is the enclosed droplet chamber part of the LTS120 cold stage?
24) Line 147ff: Clarify if sample droplets rest inside the oil or if the oil is between the cold stage and the glass slide? Are droplets in contact with the aluminium spacer? Revise the step-by-step description in the manuscript.
25) Line 148: “filled” might be the wrong word to describe the procedure. Do you mean covered?
26) Line 160 and Eq.2: As Equation 2 is irrelevant for the rest of the manuscript I suggest deleting it. If you want to keep it in, define K(T) in the text and explain what is meant by “cumulative concentration of each droplet above K(T)”. Add how Vair is calculated from the sample volume, volume of washing water and droplet volume. Add the equation how the background signal is subtracted.
27) Line 183-184: As pointed out by Referee#1 comment 22. in the previous round of reviews, the authors should elaborate in the text why the ERA5 PBL height data is applicable specific to their analysis.
28) Figure 2a: add dilution data to this figure to show that measurements were not affected by the water background instead of having an additional Figure S2.
29) Line 209: As pointed out above, add equation to Sec.2.3. how the background was subtracted and refer to the equation here.
30) Line 241f: You could cite Kanji et al.,2020, here. Correct sentence structure. There are significant correlations between BC and NINP below -20°C shown in Fig.4 not supporting this statement. The discrepancy to literature is worth adding a discussion of these data here or line 300.
31) Line 271f: The fraction of bio-INP is affected by the concentration of these INP and much less by their moderate or high ice activity. Reformulate.
32) Line 287f: Specify where these previous studies were conducted and provide references.
33) Line 295f, 309f: Please justify speculations by explaining the deductive chain of logical steps that lead to them. It is not obvious to me here. Is Ca2+ a proxy for soil dust? Are there sources of soil dust downwind of the sampling site? Considering the weather situation, wouldn’t soil be wet and therefore not prone to wind erosion? Isn’t soil covered by vegetation in this season that prevents erosion? Clarify in the text. Is it realistic that particle concentrations below 0.1 L-1 (NINP in the -8°C to -11°C range) influence the measured Ca2° concentration?
34) Line 298f: Provide an explanation for the correlation of NINP to ambient temperature and RH. 3
5) Line 313f: Explain why a correlation with WS and ambient temperature indicates local sources.
36) Line 316f, Line 396: Oxidation products of isoprene should be water soluble and not contribute to immersion freezing. Correlation does not imply direct causation.
37) Line 318: It could be expected that SOA activate as CCN when RH>100%. Did the sampler also collect cloud droplets? An anticorrelation to RH could provide a hint if the INP are also CCN. For INP to generate ice in mixed-phase clouds CCN activation is a prerequisite. I encourage a reanalysis of the data considering the weather situation at the time of sampling.
38) Line 323: The NINP was measured in this study not the IN activity. Reformulate.
39) Line 338f: Provide a reasonable explanation how PBL height can be positively correlated to NINP. The opposite could be expected due to dilution of air with increasing PBL height. Total particle concentration is usually anticorrelated to PBL height.
40) Line 341f: This is not supported by the data. If valley breeze transported INPs to the station during daytime, why is there not a difference between night and day NINP?
41) Line 350f: Clarify how NINP is related to phytoplankton bloom and growth. The Japanese Sea experiences a phytoplankton bloom twice a year, one in spring and one in fall (Wang et al., 2022). Clarify the relevance for the current observations.
42) Line 352-355, Figure 5: It is surprising that two distinct origins for HTR and LTR bio INPs are found, as it could be assumed that for cumulative NINP the occurrence of high NINP at -10.5°C is correlated to high NINP at -20°C. Is this not the case? Could there be an artifact from the measuring range? For example, how were samples with a frozen fraction =1 at temperatures above -20°C included in the CWT analysis in the LTR? Did you use the data of their dilutions? The NINP colour scale indicates that dilutions were not included.
43) Line 370ff: Explain how it can be concluded that long-range bio-INP were less prominent in your measurements? It seems contradictory to say there was no qualitative or quantitative analysis of bio INP and then state that they were less prominent from long-range transport.
44) Line 376: Clarify the interpretation between PBL height and local sources or long-range transport. Are you inferring that long-range transport contribution to NINP occurs exclusively by night and as soon as the boundary layer forms exclusively local sources contribute to NINP? This seems a critical assumption for your analysis and should be discussed in more detail and supported by stronger evidence.
45) Line 381ff: There was no diurnal cycle of NINP observed in this study. Explain how conclusions can still be drawn about a diurnal cycle.
46) Line 385f: The methods applied in this study do not allow to explore properties of INPs. Only their abundance was measured. Reformulate.
47) Line 393: An increase in bio NINP indicates that the concentration of bio-INP increased, not the activity. The type of measurements does not provide information if, for example, 1% or 100% of a certain INP type was active at a certain temperature. Reformulate.
48) Line 398ff: Please resolve the apparent contradiction between local soil dust sources and CWT pointing to long range transport by clarifying how long-distance sources can be disentangled from local sources. In addition, would the CWT analysis reveal different patterns for the nighttime NINP measurements, or at -10°C and -20°C? Would the correlation analysis, for example with Ca2+ differ if done separately for daytime and nighttime samples?
49) Figure S5: replace with Fig. R3 from the Author’s Response and include the reply to question 22 from Referee #1 explaining how airmasses approach the measurement site and why the trajectory endpoint was chosen at 967m a.g.l.
50) Figure S6: Specify if only daytime or all samples were used to create this figure.

Technical corrections:
1) misspelled citations: DeMott, O’Sullivan, McCluskey, in several instances.
2) there is no “the” needed before Switzerland. Also, in Figure 2.b) remove “The” in front of Weissfluhjoch and Jungfraujoch.
3) Line 110: Maybe use standard error of the mean instead of standard deviation to avoid range of RH (92.4%+11.8%=104,2%) to extend beyond the range of measurement. Also, line 309: 0.5ugm-3 – 1.0ugm-3 = - 0.5ugm-3 is unphysical.
4) Line 166-168: It is unclear what is explained here. Reformulate.
5) Line 173: Do you mean: …, which is 1.96 for a 95% confidence interval? Reformulate.
6) Line 191ff: Incomprehensible sentence. Reformulate.
7) Line 198: define nij in the text.
8) Line 213: replace “three” with “up to 5” to be consistent with what is stated in the conclusion.
9) Line 233-235: Incomprehensible sentence. Reformulate.
10) Line 237: Reformulate. …magnitude at temperatures from -26.0°C to -3.0°C.
11) Line 288: replace INPs with NINP
12) Line 321: define SNA.
13) Line 329: replace INPs with NINP.
14) Line 336: Define HLR. Do you mean HTR?
15) Line 347: “under immersion mode” do you mean “in the immersion mode”?
16) Line 352: “occurred in” do you mean “coming from”?
17) Line 363: define “the middle layer”.
18) When reporting NINP ranges and consecutive the temperature range, I suggest giving the temperature range from high to low temperature if the NINP range is given from low to high, so that the first number in the NINP range corresponds to the first number in the temperature range.
19) Specify whenever you mean “ambient temperature” to avoid confusion to experimental temperature of IN experiments. In particular: line 299, 313.

References:
Kanji, Z. A., Welti, A., Corbin, J. C., & Mensah, A. A. (2020). Black carbon particles do not matter for immersion mode ice nucleation. Geophysical Research Letters, 46, e2019GL086764. https://doi.org/10.1029/2019GL086764
Wang D, Fang G, Jiang S, Xu Q, Wang G, Wei Z, Wang Y and Xu T (2022). Satellite-detected phytoplankton blooms in the Japan/East Sea during the past two decades: Magnitude and timing. Front. Mar. Sci. 9:1065066. doi: 10.3389/fmars.2022.1065066

Editor:
L14: Replace “concentrations” with “concentration”
L20-L21: Replace “not significant correlate with isoprene” with “not significant correlation was found with isoprene”
L42: Replace “al., 2009), volcanic ashes” with “al., 2009), and volcanic ashes”
L43: I think “such as” should be “from”
L47: Delete “For the”
L59: I think “atmosphere” should be “atmospheric”
L62: What do the authors mean with “INPs can be extended”?
L65: Add a reference after “site”.
L70: Replace “high-altitude atmosphere” with “high-altitudes”
L71: Delete “In contrast”
L81: Replace “mountains” with “high-altitude sites”
L81: Replace “m a.s.l.), Wuling” with “m a.s.l.), and Wuling”
L82: I suggest replacing “Dinghu Mountain (1000 m a.s.l.), and found that the initiated freezing temperature” with “Dinghu Mountain (1000 m a.s.l.). The authors found that the onset freezing temperature was...”
L84: “cloud droplets”? Do the authors mean “ice formation”?
L89: Add a reference after “yields”
L89 and along the text: “high altitude”. Either use “high altitude” or “high-altitude”
L91: Replace “air mass” with “air masses”
L93: Replace “pathways of INPs” with “pathways on the INP population”
L93: Replace “understanding of INPs sources” with “understanding of their sources”
L94: I think “clouds” should be “mixed-phase clouds”
L98: Add a reference after “Arctic”
L110: Replace “field measurements” with “field campaign”
L113: Should “national nature reserve” be “national natural reserve”?
L114-115: Replace “Due to the emergence of novel coronavirus (COVID-19) cases, strict” with something like “Due to the COVID-19 pandemic, strict”
L115: Replace “measures have been implemented” with “measures were implemented”
L124: Replace “analysis and detailed” with “analysis with the detailed”
L124: Delete “is” in “information is provided”
L133: Replace “frequency increased to every 3 h during” with “frequency was increased from 2h to 3h”
L135: “national meteorological station”. Please add the model and manufacturer.
L135: Replace “from” with “away from”
L140: Replace “Germany), a charge-coupled” with “Germany), and a charge-coupled”
L140-141: “The Imaging Source, 140 Bremen, Germany), a ring LED light, and a computer system” is unclear.
L144: Replace “wash off particles” with “wash off the particles”
L146: Replace “spectra” with “a spectrum”
L147: “Figure S3”. This figure cannot be called before Figure S2. Please reorganize the order of the figures to call them sequentially
L149: Replace “and the particle suspension” with something like “and the suspension containing the particles”
L160-161: “the unit volume of sampled air”. This is unclear.
L185: Replace “during our sampling” with “during the sampling”
L203: Delete “A metric was applied to evaluate the freezing of droplets, i.e.,”
L204: Replace “frozen (T50)” with “frozen (T50) was calculated for each sample”
L207: “(for which T50 was −17.0 ± 4.1 ℃).” Please double check this. From figure 2 it seems that the average T50 is round -14C with T50 values as warm as -10C
L212: Replace “The freezing of” with “The onset freezing of”
L214: Should “freezing temperatures above T50” be “freezing temperatures above the average T50”?
L225-226: “and the limited dataset size and low sampling frequency may have contributed to the absence of diurnal variations.” Is this related to the present study?
L228: Units are missing.
L237: Should “magnitude during the measured” be “magnitude at similar”
L240: Replace “nuclei” with “INP”
L272: Replace “ice nuclei” with “INP”
L288: Replace “atmospheres” with “environments”
L293: Replace “with temperature range from −11.0 ℃ to −9.0 ℃.” With “at temperatures ranging between -11.0C and -9.0C”
L296: Replace “within the range of” with “between”
L299: Replace “with temperature” with “with ambient air temperature”
L303: Replace “And a significant” with “A significant”
L303: Replace “was showed” with “was found”
L303-307: Improve the grammar in this paragraph.
L308: Replace “with average” with “with an average”
L309: “metal ions with Ca2+”. This is unclear
L313: Replace “did observe that” with “observed”
L316: Add a reference after “aerosols”
L322: Replace “role in INPs formation” with “role as INPs”
L322-323: “2016). Note that PM2.5 chemical composition was used in this study, which may lead to uncertainties in the interpretation of the bulk IN activities”. This is unclear
L334: Replace “significant spanning temperatures from” with “at temperatures ranging between xx and xx.”
L335: Replace “observed when the” with “observed at the”
L338: Replace “discussed in the following paragraph” with “discussed below”
L341: Figure S5. This figure cannot be called before S4.
L357: “as −2~−5 ℃”. Please fix this.
L358-359: Replace “with biological aerosols produced there able to reach our sampling site through long-distance transport” with “with a high potential to emit biological aerosols those of which may be able to reach our sampling site through long-distance transport.”
L365: Should “In global transmission” be “On a global scale”?
L366: Add a reference after “ocean”
L369: What do the authors mean with “aerosol transmission”
L369-370: Replace “with the ice nucleation activity of dust significantly enhanced” with “enhancing the ice nucleation activity of dust significantly”
L371-272: “activity. Although long-range transported bio-INPs were less prominent in our study”. What do the authors mean and how is this supported?
L375: Replace “However, when” with “However, at”
L378: Replace “But” with “However”
L382: Replace “influence the diurnal cycles of INPs” with “influence the diurnal INPs”
L390-931: Please improve the grammar.
Figure S1. Why there is not INP data between 2021/7/24 and 2021/8/11?
Figure 1: Replace “(b) This map shows the three-dimensional shape of the sampling site, which was obtained from Google Earth. (c) The ice nuclei sampler (The TH-150D medium flow sampler, Wuhan Tianhong Corporation, China).” With “(b) Map with the three-dimensional shape of the sampling site, which was obtained from Google Earth. (c) The INP sampler (The TH-150D medium flow sampler, Wuhan Tianhong Corporation, China).”
Figure 2: Replace “(b) NINP was measured during the daytime and nighttime. The dark gray shaded area represents the upper and lower limits of NINP over the Weissfluhjoch (2693 m a.s.l.) (Wieder et al., 2022). The yellow shaded area represents the atmospheric NINP ranges at Mt. Huang (1840 m a.s.l) (Jiang et al., 2015). The purple square represents the median NINP at −15 ℃ and −10 ℃ in the Jungfraujoch (3580 m a.s.l.) (Conen et al., 2022). And the black” with “(b) NINP measured during the daytime and nighttime. The dark gray shaded area represents the upper and lower limits of NINP over the Weissfluhjoch (2693 m a.s.l.) (Wieder et al., 2022), the yellow shaded area represents the atmospheric NINP ranges at Mt. Huang (1840 m a.s.l) (Jiang et al., 2015), the purple square represents the median NINP at −15 ℃ and −10 ℃ in the Jungfraujoch (3580 m a.s.l.) (Conen et al., 2022), and the black”
Figure 3: Replace “dots). The point plot represents the median value. The shadow area represents” with “dots). Each point represents the median value and the shadow area represents”
Figure 4: Replace “and meteorological parameters, chemical compositions, as functions of temperature.” With “with meteorological parameters and chemical compositions as functions of temperature.”

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AR by Yujiao Zhu on behalf of the Authors (21 Dec 2023) Author's response Author's tracked changes Manuscript

ED: Publish as is (15 Jan 2024) by Luis A. Ladino

AR by Yujiao Zhu on behalf of the Authors (23 Jan 2024) Manuscript

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Measurement report: Atmospheric ice nuclei in the Changbai Mountains (2623 m a.s.l.) in northeastern Asia

Atmos. Chem. Phys., 24, 3241–3256, https://doi.org/10.5194/acp-24-3241-2024,https://doi.org/10.5194/acp-24-3241-2024, 2024

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Field observations were conducted at the top of Changbai Mountain in Northeast Asia. Our findings indicate that the ice-nucleating particles (INPs) were mainly dominated by biological sources, accounting for over 90 % above the freezing temperature of −13.0 °C. Biological INPs were found to attached to soil dust surfaces, and their concentrations influenced by a combination of factors, such as the planetary boundary layer height, valley breezes, and long-distance transport of air mass.


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Measurement report: Atmospheric Ice Nuclei at Changbai Mountain (2623 m a.s.l.) in Northeastern Asia

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