the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Oct 2025
Measurement report: Role of Organic Coating and Chemical Composition on Ice Nucleation Potential of Atmospheric Particles in European Arctic
Abstract. Understanding the ice nucleation (IN) potential of Arctic aerosols is critical for predicting their influence on cloud formation and water cycles in this vulnerable region. This study investigates the role of particle composition, organic coatings, and aerosol sources in modulating IN activity across five aerosol samples collected at the Gruvebadet Observatory Station in Ny-Ålesund, Svalbard. The IN potential of Arctic aerosol particles was studied by investigating chemical, morphological, and ice activity measurements. Single-particle analyses revealed distinct differences in mixing state, organic volume fraction (OVF), and organic coating morphology across samples. OVF distributions were linked to particle origin, with marine-influenced Na-rich particles often exhibiting thin organic coatings, while long-range transported particles showed thicker organic coatings. Biogenic contributions, though variable, were linked to heat-sensitive INPs, suggesting a role for labile biological macromolecules under certain meteorological conditions. Pearson correlation analysis between particle composition and immersion-mode ice-nucleating particle (INP) concentrations at two freezing temperatures indicated that organic-rich and Na-rich particles were positively associated with enhanced ice activity. However, discrepancies in INP activity were observed for particles with thicker organic coatings, where the morphological configuration of the organic material may play a role. The results highlight that Arctic INP variability is governed not only by chemical composition but also by the morphological configuration of organic material, which can either enhance or inhibit ice nucleation depending on its abundance, distribution, thickness, and mixing state. These findings underscore the combined influence of source regions, atmospheric processing, and organic–inorganic interactions in shaping Arctic aerosol freezing behavior.
Competing interests: Some authors are members of the editorial board of journal ACP.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: open (until 02 Dec 2025)
- RC1: 'Comment on egusphere-2025-4866', Anonymous Referee #1, 13 Nov 2025 reply
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RC2: 'Comment on egusphere-2025-4866', Anonymous Referee #2, 30 Nov 2025
reply
This manuscript presented a case study on the impacts of aerosol physiochemical characteristics on the ice nucleation activity. They conducted micro-spectroscopic single-particle analysis and derived the ice nucleation concentrations from droplet freezing experiments. Although with limited number of samples analyzed, the manuscript shows the complexity of interaction between particle mixing state and ice nucleation activity. The topic of this study fits the scope of this journal. There are several issues need to be addressed before it can be considered for publication.
Major issues:
- Missing information on the methods for (1) INP concentration calculation, (2) fraction of heat liable stable INP, (3) FLEXPART back-trajectory analysis. Brief descriptions are important to readers and reviewers for judgement on the methodology.
- The focus of this manuscript is connecting the particle physiochemical properties to ice nucleation activity, however, this a mismatch in particle size and sampling duration between the samples used for particle characterization and ice nucleation experiments. In addition, some organic or salt components are soluble, it is very tricky when discuss the impacts of organics what like contain soluble components on the immersion freezing ability of particles. Please comment on these and make this clear or add a few sentences to discuss these potential artifacts in the manuscript when possible.
- Ice nucleation ability (INA) and ice nucleation concentration are different concepts. Ice nucleation concentration is not only depended on the ice nucleation ability of particles but also on the total particle surface area in the sample. To compare the INA of different particle samples, it would be better to use normalized parameters, for example, ice nucleation active site density (over particle surface area or mass). Is there particle surface or mass measurements or estimation that can be used for this purpose? This is also related to previous comment. In addition, frozen fraction and freezing temperature (e.g., median freezing temperature) are usually presented in ice nucleation references. These are missing here.
- The descriptions and discussion in the differences for five samples are inconsistent, for example, in the Line 277-283, L305, it claims they are similar; however, in Line 307, 321-326, the discussion assumes that five samples have different INA. Please provide quantitative comparison with uncertainties on this comparison.
Technical comments:
- L119, for the HYSPLIT analysis, using 50 m maybe too low, 100 or 200, 500m which are usually used. Please comment on this.
- L280, the mean is 0.3 but the range is between 0.1-0.3? these numbers don’t match.
- Figure 5, how do you calculate the percentage of heat liable INPs? In this figure, are these averaged over different temperatures?
- Figure 8, how many data points were used for this analysis? How about the significance level?
Citation: https://doi.org/10.5194/egusphere-2025-4866-RC2
Data sets
Data set for Measurement report: Role of Organic Coating and Chemical Composition on Ice Nucleation Potential of Atmospheric Particles in European Arctic N. N. Lata et al. https://doi.org/10.5281/zenodo.17373230
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- 1
Lata et al. present in their manuscript "Measurement report: Role of Organic Coating and Chemical Composition on Ice Nucleation Potential of Atmospheric Particles in European Arctic" results of STXM/NEXAFS, SEM-EDX, and INP measurements of samples collected on Svalbard during the winter season of 2020/2021. They found indications that the properties of the organic coating influence the ice nucleation activity of their samples. While this study only features five samples, which of course limits the statistical significance of the results, one must recognize the labor that went into the analyis of these samples. STXM/NEXAFS measurements of so many individual particles are no small feat. Furthermore, STXM/NEXAFS is rarely used in studies of ambient aerosol samples in conjunction with ice-nucleating particle measurements, which makes these results valuable. Considering the limited scope of the study due to the small sample size and the value of the results, I think the publication as a measurement report is appropriate after making some revisions.
Please see my comments and suggestions below. Some comments are marked with "***"; these are the ones I deem more important and that need to be addressed. There is also a list of technical comments (typos, etc.) at the end.
Comments and suggestions
L51
Immersion freezing is mentioned for the first time without further explanation. I suggest adding one or two sentences to the previous paragraph to explain that there are different freezing modes and describe immersion freezing, stating that it is the most relevant mode for MPCs.
L62
Since the em dash is now often seen as a sign of AI usage, I recommend removing it and rephrasing the sentence if AI was not actually used. Using AI is generally fine, but according to the ACP submission guidelines, if AI was used to prepare the manuscript, its use must be described in the Methods section or the Acknowledgments.
L91 - L94
Also specify the distance between the Gruvebadet and the AWIPEV station.
L95
Introduce the disdrometer properly (see the 2nd technical comment for details)
L96
What is "Pluvio total"? Does it simply mean that the precipitation volume is derived from the OTT Pluvio² L regardless of the phase determined by the OTT Parsivel²?
L98 - L99
Do I understand correctly that the sampling for the INP analysis is continuous, but co-located samples for the single particle analysis were collected only on five occasions? Or were co-located samples always taken, but only five were analyzed? In either case, the text should mention the criteria used to select these five occasions.
*** Particle sizes
I am a bit surprised by the large number of supermicron particles you found on the TEM grids (Fig. 3). The TEM grids should mainly contain particles with an aerodynamic diameter between 250 and 500 nm, because you only used the last impactor stage with d50 = 250 nm and the previous stage has d50 = 500 nm. Of course, AED and aerodynamic diameter are not identical, and it is known that the AED is on average larger than the geometric diameter and also that the aerodynamic diameter is typically larger than the geometric diameter (Huang et al., 2021). But knowing this and considering typical shape factors and density of SSA, I find it hard to imagine a scenario where many particles with a significantly larger AED than aerodynamic diameter occur.
Do you have an explanation for the large number of supermicron particles? Was e.g., the impactor operated with the correct flow rate?
L108
I assume these filters are made of polycarbonate
L110
The citation in parentheses is not needed if the same papers are cited within the sentence
L111 - L112
Does that mean that some of the samples are measured in regular intervals in Ny-Ålesund, but most samples are analyzed at the authors' home institutes? Why are not all samples measured on-site? Is it the lack of manpower or is on-site only a rudimentary freezing array setup to ensure sample integrity? Even though you cite Li et al. (2023), an additional sentence describing these on-site verification measurements would not hurt.
Section 2.2.
Later, you present results from the FLEXPART back trajectory analysis. Why did you choose to use HYSPLIT to characterize the air masses and identify potential source regions, given that one could argue FLEXPART is better suited for studying aerosol particles?
L116
While it is known that back trajectories become significantly less accurate the farther back in time they go, and every trajectory going back more than five days should be viewed critically, 48 hours is rather short and might not reveal the full picture.
I suggest reproducing Fig. 2 with five-day back trajectories for the supplement.
Additionally, I suggest reproducing Fig. 2 with color-coded heights so readers can assess which regions sources close to the surface might be important in.
L135
How does the computer identify the particles? Is it by a brightness threshold of the BSE image? If so, do you think biological particles (i.e., C-rich particles), which appear less bright in the BSE image, could be undercounted? Is there also a lower size limit for what the computer recognizes as a particle? Please mention these things in the manuscript.
L139
Please provide more information about the EDX measurement, such as how long the spectrum was collected and whether it was measured at only one central spot or if the beam scanned across the detected particle.
***L151
You write that STXM/NEXAFS was performed on a subset of particles that were already analysed with CCSEM/EDX. If you measure a particle twice, isn't it possible that a particle received beam damage, which might alter the STXM/NEXAFS results?
L165
I suppose that also at the ALS the STXM/NEXAFS measurements do not provide the convenience of computer controlled measurements such as those of the SEM. Therefore, it is valid to mention (somewhere in this paragraph) that the nearly 2000 particles were measured manually to emphasize the effort involved in these measurements.
L170
What is the upper detection limit of WT-CRAFT?
L177
Are the "< 3%" calculated in the fice or NINP space? I would also recommend showing the field blank and, if available, pure MilliQ water measurements in the supplement.
L181
I would not talk about "airborne samples" as this as this gives the impression of samples collected on aircrafts, balloons, drones etc.
Figure 1
A cyclic colormap would be better suited for color-coding the wind direction.
Please also consider making as "zoomed in" version of this figure for the supplement, showing only the sampling periods
Figure 2
It would be great if the sea ice concentration or at least the sea ice edge is shown in these maps.
L212
Where does the information about turbulence come from? If the statement is based on measurements, they should be also be part of the manuscript.
L217
Can you elaborate on the possible enhanced atmospheric processing for this event? Is the cause for that primarily the farther transport (hence more time for the aging to take place), the presence of reactive species that do not exist at higher latitudes, or the availability of solar radiation?
Figure 3 and 4
Instead of a separate figure for CCSEM and STXM results, I think it would be better to have CCSEM and STXM sample wise side by side, eliminating the need to scroll through the document when a reader wants to asses the chemical composition of a specific sample.
Section 3.3 first paragraph
It is of course good to provide context and show what others have found, but I am missing the connection to your specific samples. Since you only have five samples from four distinct meteorological scenarios, you can directly compare your findings during, for example, the warm air intrusion with studies that also measured during a warm air intrusion.
L291
This statement should be removed. The 0.2 INP/L is simply the upper detection limit of the achievable with the used droplet freezing array. During the same expedition, also a CFDC (operated in immersion mode) was deployed and at -28°C, a max. INP concentrations of around 100 L-1 were measured, which can be seen in the cited overview publication by Welti et al. (2020), but also in more detail in the expedition related publication by Hartmann et al. (2021) (which you also already cite). If you look into the latter study more carefully, you will also notice, that the name of the campaign was PASCAL, Polarstern is the name of the research vessel and PS106 is the the consecutive expedition identifier asssigned by the operator of the vessel. Hence you might want to change "[...] from the Arctic expedition (Polarstern) - PS 106) [...]" accordingly so that a reader can more easily find information on that expedition online.
L295 - L297
I suggest removing all sentences referring to the dynamic filter processing chamber measurements in the Rinaldi study. You measured immersion freezing, not condensation freezing; therefore, these results are not relevant here. Also, the discrepancy between the dynamic filter processing chamber and the droplet freezing assay is a separate topic, and mentioning it here only distracts from your work.
L298
To which cold air outbreak are you referring? Was it during the Rinaldi study or yours? From the phrasing, this is unclear.
L301
It is not clear what the difference between the preparation techniques is. If you wash off the particle, you also end up with a particle suspension.
***L307
How do you come to the conclusion that the SML contributed? This has to be explained.
Figure S1
While potential readers are likely aware of the location of Svalbard, they may not know where Gruvebadet is located within the archipelago. Therefore, I suggest marking the study site on a map of Svalbard instead of the current map (or adding it to a separate panel, for example).
Table S3
How do you define open ice?
*** Heat sensitivity
1. Somewhere, the calculation of the percentage of heat-labile INPs should be explained.
2. I doubt that a percentage accurately captures the logarithmic nature of INPs.
3. Your calculation method is skewing the results since it is based on an unsound assumption. You assume that the concentration of heat-stable INPs is zero when it is simply below the detection limit of your setup. It is not only very unlikely that the concentration of heat-stable INPs goes immediately to zero when below the detection limit, but it is also not good scientific practice to make this assumption without mentioning it in the manuscript.
Unfortunately, there is no established, scientifically sound way to report the heat-labile fraction. One uncritical approach would be to report only values where the INP spectra of the heated and unheated samples overlap (see Gong et al., 2022). The disadvantage is that, especially at higher temperatures, it is not possible to report any values.
I suggest calculating the heat-labile fraction in a conservative, robust way by replacing values below the detection limit with the lowest detectable value. This method provides a conservative estimate of the heat-labile fraction that represents the case with the least amount of heat-labile INPs. Along with your existing values, which represent the maximum amount of heat-labile INPs, you can report a range for the heat-labile fraction of a sample. In my view, this is a better representation of the sample since it is impossible to determine the true value.
L307
What are you basing the statement that SA2 and SA4 exhibit high INA on? At -25°C, these two samples appear to have higher NINP. However, at higher temperatures (>-15°C), this does not seem to be the case. Therefore, labeling them as high INA seems inaccurate.
***L309 - L311
The phrasing is this sentence gives the impression that the cold conditions are one of the indicators pointing towards INPs that are internal mixtures of organic/biological and Na-rich particles. If that is what you meant, then this needs explanation, as I do not understand how cold conditions alone are an indicator for this. If this is not what you meant, then the sentence needs rephrasing.
L315 - L316
It is certainly possible that the SML contributes biological INPs, but can you exclude other sources that are often discussed in this context, like low-INA dust acting as carrier for high-INA biological INPs? If you can, then this is also worth mentioning in the text.
L324
Do you expect the biogenic part to be from local sources or from long-range transport as well?
L332
Please rephrase this statement. Polysaccharidic INP certainly can be enriched in the SML, but are rather heat-resistent, so the heat treatment does not indicate their presence (see Hartmann et al., 2025).
L343
Tab. S1 contains the precipitation at the measurement site. However, for your statement, the precipitation along the airmass trajectory is more important. Since precipitation is one of the HYSPLIT output variables, I recommend reporting the average accumulated precipitation along the airmass trajectory for each sample in the supplement to emphasize your point.
L351
At least a reference should be added to explain how the OVF is determined. Even better would be a few sentences describing it.
L371 - L372
Are these "overall OVF values" the mean of all the individual OVF values of all the particles in a sample? If yes, would not the median be a more appropriate measure? I would also recommend adding these numbers to Fig. 7.
L372 - L373
In general I would recommend the use of the Spearman rank coefficient instead of the Pearson correlation coefficient, because it does not assume linearity and is not easily affected by outliers. Regardless of Pearson or Spearman, five data points are of course not a very solid basis to determine correlation. For that reason I would recommend to remove figure 8 from the main manuscript, because it highlights too much results with weak statistical basis. It can still be shown in the supplement and the values can be reported in the text, but the reader should be reminded of the small sample size and hence assess these values carefully. Also a scatter plot matrix could be shown in the supplement, as this allows the reader to assess correlation themselves.
L373
While I am not aware of fixed rules for the descriptive words used for the strength of a correlation, I never seen anyone to refer to an R of 0.5 as strong. Generally, this would be considered a moderate positive correlation.
L394
I do not see how "promoting heterogeneous freezing via organic-induced deliquescence or restructuring" can be directly inferred from your measurements. You can of course mention this as a possible mechanism that could take place, but then the respective literature has to be cited and sentences that explain the mechanism need to be added.
L402
I have not seen where you show and discuss potential influence of the morphology. You should either add this or remove "morphology" from this sentence.
L402-403
Can this statement be supported quantitatively? Could you derive a mean organic layer thickness for the particles in a sample? Is there an existing metric for "patchiness" that could be applied to your measurements?
L413 - 421
In the first sentence you basically only state that there was a case of many Na-rich particles with a thin organic coating and that they had only moderate INA. I do not understand why this finding underscores the critical role of biological INPs, nor is the connection to mild, humid conditions clear.
Then, you discuss the particles from cold and dry cases, which I assume are SA2 and SA5. You state that these particles have enhanced INA. However, this is not entirely consistent with what you wrote in the Results section. In L282-283, you wrote that SA1 and SA5 are less ice-active than SA2, SA3, and SA4.
Fig S3
The airmass sampled on SA5 seems to have experienced the highest BC concentrations of all samples. BC emissions are also typically accompanied by the emission of sulphate species, but SA5 hardly contains sulphate in the CCSEM/EDX measurements. Do you have an explanation for this?
Summary & Conclusion
With only five samples it might be a viable idea to have summary table, which contains for each sample the central results from your analysis like: meteo. conditions, dominant particles classes (EDX), mixing state, OVF, organic coating thickness/patchiness, N_INP at a high and low temperature, N_INP of heat stable INPs also at a high and low temperature.
Technical comments
L93
missing spaces: "[...] GVB(Mazzola et al., 2016) [...]" and "[...] (Pluvio2 L 400 RH)(Ebell et al., 2025) [...]"
L93
"OTT Pluvio (Pluvio2 L 400 RH)"
It is not clear what is the company name and what is the instruments name. Please follow common conventions of citing instruments. E.g., OTT Pluvio² L (OTT HydroMet GmbH, Kempten, Germany). After that, please refer to the instrument by its correct name or introduce an abbreviation properly: "OTT Pluvio² L (OTT HydroMet GmbH, Kempten, Germany, hereafter referred to as Pluvio2, ...)"
L94
Typo "Ny-Aalesund" should be "Ny-Ålesund"
L94
missing article "OTT Pluvio2L weighing gauge [...]" should be "The OTT Pluvio2L weighing gauge [...]"
L96
remove "So,"
L99
Plural: "[...] 5 pairs of filter samples was collected [...]" should be "[...] 5 pairs of filter samples were collected [...]"
Table 1
The headers are aligned differently. One is centered and the other is left-aligned. Please use consistent formatting. Additionally, I recommend that the authors take a look at the "APA Style manuals" and consider revising their tables. These manuals provide good guidelines for creating appealing, readable scientific tables.
L135
"figures out" sounds colloquial. Suggestion: "determines"
L138
missing space "[...] behavior(Lata et al., 2021, 2023)." should be "[...] behavior (Lata et al., 2021, 2023)."
L246
Write "back trajectory" consitently with or without hyphen throughout the document.
L286
too many parentheses "[...] range (e.g., (Hill et al. [...]", should be "[...] range (e.g., Hill et al. [...]"
L287
missing space "[...] NINPmeasured [...]" should be "[...] NINP measured [...]"
L295
citation in parentheses is unnecessary since the study is already cited within the sentence
L309
Plural. Suggestion: "Though SA2 and SA4 contain 16.1 and 12% OC-rich particles, respectively."
L331
There seems to be a space at the beginning of this line.
Use consistent panel identifier throughout the manuscript (Fig. 1, 2, 3 used "(a), (b), etc."; Fig. 4 used "a), b), etc."; Fig. 5 used "a., b., etc.")
Use consistent parameter abbreviations: Fig. 5 denotes the INP concentration with a lower case "n" (n_INP), while the text uses the upper case letter (N_INP)
References
Huang, Y., Adebiyi, A. A., Formenti, P., & Kok, J. F. (2021). Linking the different diameter types of aspherical desert dust indicates that models underestimate coarse dust emission. Geophysical Research Letters, 48, e2020GL092054. https://doi.org/10.1029/2020GL092054