From the journal Environmental Science: Atmospheres Peer review history

19-Jan-2022

Dear Dr Bertram:

Manuscript ID: EA-ART-12-2021-000101
TITLE: Ice nucleating properties of airborne dust from an actively retreating glacier in Yukon, Canada

Thank you for your submission to Environmental Science: Atmospheres, published by the Royal Society of Chemistry. I sent your manuscript to reviewers and I have now received their reports which are copied below.

I have carefully evaluated your manuscript and the reviewers’ reports, and the reports indicate that major revisions are necessary. Reviewer 1 in particular raised important concerns about the representativeness of the 4 INP samples, and whether those samples can provide meaningful conclusions about the nucleating properties of dust from retreating glacier areas. Please carefully address these concerns.

Please submit a revised manuscript which addresses all of the reviewers’ comments. Further peer review of your revised manuscript may be needed. When you submit your revised manuscript please include a point by point response to the reviewers’ comments and highlight the changes you have made. Full details of the files you need to submit are listed at the end of this email.

Please submit your revised manuscript as soon as possible using this link:

*** PLEASE NOTE: This is a two-step process. After clicking on the link, you will be directed to a webpage to confirm. ***

https://mc.manuscriptcentral.com/esatmos?link_removed

(This link goes straight to your account, without the need to log on to the system. For your account security you should not share this link with others.)

Alternatively, you can login to your account (https://mc.manuscriptcentral.com/esatmos) where you will need your case-sensitive USER ID and password.

You should submit your revised manuscript as soon as possible; please note you will receive a series of automatic reminders. If your revisions will take a significant length of time, please contact me. If I do not hear from you, I may withdraw your manuscript from consideration and you will have to resubmit. Any resubmission will receive a new submission date.

The Royal Society of Chemistry requires all submitting authors to provide their ORCID iD when they submit a revised manuscript. This is quick and easy to do as part of the revised manuscript submission process. We will publish this information with the article, and you may choose to have your ORCID record updated automatically with details of the publication.

Please also encourage your co-authors to sign up for their own ORCID account and associate it with their account on our manuscript submission system. For further information see: https://www.rsc.org/journals-books-databases/journal-authors-reviewers/processes-policies/#attribution-id

Environmental Science: Atmospheres strongly encourages authors of research articles to include an ‘Author contributions’ section in their manuscript, for publication in the final article. This should appear immediately above the ‘Conflict of interest’ and ‘Acknowledgement’ sections. I strongly recommend you use CRediT (the Contributor Roles Taxonomy from CASRAI, https://casrai.org/credit/) for standardised contribution descriptions. All authors should have agreed to their individual contributions ahead of submission and these should accurately reflect contributions to the work. Please refer to our general author guidelines http://www.rsc.org/journals-books-databases/journal-authors-reviewers/author-responsibilities/ for more information.

I look forward to receiving your revised manuscript.

Yours sincerely,
Dr Tzung-May Fu
Associate Editor
Environmental Science: Atmospheres
Royal Society of Chemistry

************

Reviewer 1

This study tries to focus on the ice nucleating properties of airborne dust from an actively retreating glacier in North America (Yukon, Canada). Because North America is thought to be one of the significant sources of high-latitude dusts, field INP data in this region is very valuable. On the other hand, a weak point of this study is that the key conclusion is based on only four INP data, which were probably collected under high dust conditions (May 15, 16, 22 and 24 in 2018). In addition, it seems that these four INP data indicate the ice nucleating ability of total aerosol particles, rather than local dust particles from glacial outwash plains in Yukon. I could not understand why the authors did not report the ice nucleating ability of dust samples collected at the ground surface of the glacial outwash plains in Yukon, Canada.

Despite the limited data and evidence, the authors conclude that “the ice nucleating ability of the airborne dust (in Yukon, Canada) was significantly worse than the glacial outwash sediments collected in Svalbard by Tobo et al. (2019)”. In my impression, this conclusion is challenging, because this means that the ice nucleating ability of dust particles from Yukon is much lower than that of Alaska (Creamean et al., 2020) located in North America (i.e., similar location to Yukon), but is almost comparable that of Iceland dust of volcanic origin (Sanchez-Marroquin et al., 2020). I think that more detailed data analysis and discussion would be required to quantify the ice nucleating properties of airborne dust from an actively retreating glacier in the Yukon region. I would like to suggest reconsidering whether the authors’ conclusion is indeed reasonable after checking the following comments.

Major Comments

1) It would not be appropriate to directly compare the ice nucleating ability of high-latitude dusts in Svalbard (Tobo et al., 2019) with those of Yukon reported in this study. Tobo et al. (2019) reported the ice nucleating ability of glacial outwash sediments collected at the ground surface, while this study measured the ice nucleating ability of total aerosol particles (the aerosol composition is not quantified) collected on filters. The authors should evaluate the ice nucleating ability of glacial outwash sediments collected from the ground surface of Yukon if they want to demonstrate that the ice nucleating ability of high-latitude dusts in Yukon was significantly worse than those in Svalbard.

2) I doubt if the authors indeed examined the ice nucleating ability of pure airborne dust from glacial out wash plains in Yukon. When calculating the ice nucleating ability of aerosol particles (i.e., aerosol composition is not quantified) collected on filters, I think that the authors determined the mass of “total aerosol samples” gravimetrically after drying (Section 2.1 and 2.3). The total aerosol population would be characterized by local and long-range transported dust particles, other insoluble particles (e.g., black carbon, primary biological aerosol particles, insoluble organics), and water-soluble particles (e.g., sea salt, sulfate, nitrate, water soluble organics). The authors should evaluate the composition of the particles collected on filters to quantify the fraction of local dust particles in the total aerosol particles. Then, the authors might need to evaluate the ice nucleating ability of airborne local dust isolated from the total aerosol particles.

3) A reason of Comments 1 and 2 is that the results in Yukon (this study) are quite different from those of Creamean et al. (2020). I would like to suggest checking Creamean et al. (2020) and discuss the possible difference between this work and their work. Creamean et al. (2020) reported the ice nucleating ability of dust samples collected from the ground surface in Alaska (active layer and permafrost) and demonstrate that the results in Alaska are almost comparable to that of glacial outwash samples collected in Svalbard (Tobo et al., 2019). If the conclusion of this manuscript is true, it means that the ice nucleating ability of the glacial dust in Yukon was significantly worse than those of Alaska, despite the fact that Alaska is located in North America and is relatively close to Yukon. The authors would need to evaluate the ice nucleating ability of dust particles collected in Yukon more carefully (see Comments 1 and 2).

4) Why did the authors collect only 4 samples for INP analysis under relatively similar conditions? Why didn’t you measure the INP number concentrations when the influence of local dust emissions would be relatively small? (see also Comments 5and 6)

5) It is not clear whether dust concentrations were indeed well above background levels (e.g., Abstract). First, the authors should explain the details on how to measure dust concentrations in the Method section. In addition, the authors should show the background dust concentrations at the measurement site and then demonstrate that the dust concentrations of 500 to 1400 ug/m^3 (Section 3.1, Table 1, Figure 4) are indeed well above background levels. It is also necessary to explain that such high dust concentrations in May 2018 would be mainly caused by local dust emissions in Yukon and/or its adjacent areas, rather than dust emissions from other high-latitude sources or long-range transport of dust from low-mid latitudes.

6) As for Comment 5, it is also important to explain that the quality of dust simulation in GEOS-Chem model, because the authors use the GEOS-Chem model to indicate that dust concentrations at the measurement site in May 2018 were higher than those caused by long-range transported dusts from low latitude mineral dust sources and anthropogenic sources (Section 3.3). The authors need to verify that the GEOS-Chem model would be useful to quantify the influence of long-range transported dusts from low latitude mineral dust sources and anthropogenic sources. For example, please explain that the GEOS-Chem model can successfully simulate dust concentrations over Yukon during periods when high-latitude dust emission is not expected (e.g., wintertime).

Specific Comments

7) Section 2.1: How did you dry the aerosol samples collected on filters?

8) Equation 3: I doubt if this method is not appropriate, because the n_m value is determined based on the mass of the total aerosol particles (i.e., both water-soluble and insoluble particles), while the S_p value represents the geometric surface area of only insoluble particles contained in the suspension. If the authors need to calculate the number of INP per unit surface area of total aerosol particles, they should use the geometric surface area of total aerosol particles measured in the atmosphere and not in the suspension.

9) Equation 4: I think the authors can calculate the number of INP per volume of air using a more straightforward way. The authors first calculated the n_m values of dried ambient aerosol samples using equation (1) and then converted it into the number of INP per volume of air using equation (4) (the description like “MassConc_Dust” in equation (4) might not be appropriate, because it represents the mass concentration of “total aerosol particles” and not “dust particles only”). Many other studies have calculated the number of INP per volume of air using a more simplified equation (e.g., see Tobo et al., 2019; Wex et al., 2019; Sanchez-Marroquin et al., 2020), because the information on the mass of material collected on the filters would not be required when calculating the number of INP per volume of air.

10) Section 3.2.1 (Second paragraph): To support this discussion, the authors would need to measure the organic content of aerosol samples collected on filters or glacial outwash sediments collected at the Yukon site.

11) Section 3.3: Please explain the details of PM10 measurements in the Method section. In addition, please explain whether PM10 concentrations are different from dust concentrations or not.

12) Figure 2 (Caption): Field samples => Initial suspension (or undiluted)?

13) Figure 3: Please explain how the range of the concentrations measured ah high latitudes over Arctics is quantified. If this range is originally determined by the authors, please show a figure comparing this range and the INP data presented in references (6-13, 67-72) in the Supplementary Information.

14) Figure 3 caption: Glacier dust samples => Field samples (or Yukon samples)?

15) Figure 4 (data points at -20 degreeC): Why are there 5 data points?

16) Figure 4 (x-axis): Does it represent the mass concentrations of “airborne dust” and not “total aerosol particles”?

17) Figure 5: It might be reasonable to add the data reported by Creamean et al. (2020) (n_m for dust samples collected in Alaska) for comparison.

References
Creamean et al. (2020), https://doi.org/10.1088/1748-9326/ab87d3
Sanchez-Marroquin et al. (2020), https://doi.org/10.1126/sciadv.aba8137
Tobo et al. (2019), https://doi.org/10.1038/s41561-019-0314-x
Wex et al. (2019), https://doi.org/10.5194/acp-19-5293-2019

Reviewer 2

I recommend publication of this manuscript after considering major changes, see attached file.

Dear Dr. Tzung-May Fu,

Thank you for your assessment of our manuscript. Below we provide detailed responses to all the reviewer’s comments. We have numbered the individual reviewer comments by reviewer number and comment number for ease of cross reference, e.g., “R1C1” denotes reviewer 1 comment 1.

**************
REVIEWER REPORT(S):
Referee: 1

Comments to the Author
This study tries to focus on the ice nucleating properties of airborne dust from an actively retreating glacier in North America (Yukon, Canada). Because North America is thought to be one of the significant sources of high-latitude dusts, field INP data in this region is very valuable. On the other hand, a weak point of this study is that the key conclusion is based on only four INP data, which were probably collected under high dust conditions (May 15, 16, 22 and 24 in 2018). In addition, it seems that these four INP data indicate the ice nucleating ability of total aerosol particles, rather than local dust particles from glacial outwash plains in Yukon. I could not understand why the authors did not report the ice nucleating ability of dust samples collected at the ground surface of the glacial outwash plains in Yukon, Canada.

Despite the limited data and evidence, the authors conclude that “the ice nucleating ability of the airborne dust (in Yukon, Canada) was significantly worse than the glacial outwash sediments collected in Svalbard by Tobo et al. (2019)”. In my impression, this conclusion is challenging, because this means that the ice nucleating ability of dust particles from Yukon is much lower than that of Alaska (Creamean et al., 2020) located in North America (i.e., similar location to Yukon), but is almost comparable that of Iceland dust of volcanic origin (Sanchez-Marroquin et al., 2020). I think that more detailed data analysis and discussion would be required to quantify the ice nucleating properties of airborne dust from an actively retreating glacier in the Yukon region. I would like to suggest reconsidering whether the authors’ conclusion is indeed reasonable after checking the following comments.

Major Comments

RIC1: It would not be appropriate to directly compare the ice nucleating ability of high-latitude dusts in Svalbard (Tobo et al., 2019) with those of Yukon reported in this study. Tobo et al. (2019) reported the ice nucleating ability of glacial outwash sediments collected at the ground surface, while this study measured the ice nucleating ability of total aerosol particles (the aerosol composition is not quantified) collected on filters. The authors should evaluate the ice nucleating ability of glacial outwash sediments collected from the ground surface of Yukon if they want to demonstrate that the ice nucleating ability of high-latitude dusts in Yukon was significantly worse than those in Svalbard.

***
The referee is correct that we studied the ice nucleating ability of total aerosol. In a previous publication (Bachelder et al. 2020), we have shown the total aerosol population sampled was dominated by local mineral dust from glacial outwash sediments in the region. To address the referee’s comment, we have added a new section to the manuscript where we discuss the evidence that suggests the total aerosol population was dominated by local mineral dust from glacial outwash plains in the region (see response to R1C2 below). Since our results correspond to local mineral dust from glacial outwash sediments, we think that a comparison with the results from Tobo et al. is reasonable. In the revised manuscript, we have tried to make it clearer, that the samples in the current study were from aerosolized samples, and the studies from Tobo et al. were from glacial outwash sediments collected on the ground.

Note, in the current manuscript, we choose to study the ice nucleating ability of aerosolized glacial outwash sediments rather than glacial outwash sediments collected on the ground, since the aerosol sample may be different from the sample collected on the ground. For example, Bachelder et al. 2020 showed that PM10 elemental composition was distinct from surface-collected glacial outwash sediments, most likely due to the saltation/sandblasting mechanism of dust emissions. To make this point clear, in the revised manuscript we added the following text to the Introduction.

"To illustrate, Bachelder et al. showed that the elemental composition of aerosolized samples was distinct from surface-collected glacial outwash sediments near the Kaskawulsh Glacier in Yukon, Canada, most likely due to the saltation/sandblasting mechanism of dust emissions."
***

R1C2: I doubt if the authors indeed examined the ice nucleating ability of pure airborne dust from glacial out wash plains in Yukon. When calculating the ice nucleating ability of aerosol particles (i.e., aerosol composition is not quantified) collected on filters, I think that the authors determined the mass of “total aerosol samples” gravimetrically after drying (Section 2.1 and 2.3). The total aerosol population would be characterized by local and long-range transported dust particles, other insoluble particles (e.g., black carbon, primary biological aerosol particles, insoluble organics), and water-soluble particles (e.g., sea salt, sulfate, nitrate, water soluble organics). The authors should evaluate the composition of the particles collected on filters to quantify the fraction of local dust particles in the total aerosol particles. Then, the authors might need to evaluate the ice nucleating ability of airborne local dust isolated from the total aerosol particles.

***
Thank you for the comment. In a previous publication (Bachelder et al. 2020) we have shown the total aerosol population sampled was dominated by local mineral dust from glacial outwash sediments in the region. Evidence to support this claim includes the following:

First, all the days that filter samples were collected correspond to extreme dust events if we use the 24-hr average WHO health standard for PM10 (50 µg/m3) as the criteria for an extreme dust event, as done previously. Second, the mass concentrations at the Down Valley site were substantially higher than that at the nearby Visitor’s Center site for all days except one, suggesting a local dust source near the Down Valley site. Note, the Down Valley site was near the center of the exposed A’ą̈y Chù delta, whereas the Visitor’s Center site was off to the side of the exposed delta. Third, the vertical aerosol flux at the Down Valley site was positive for all the days that samples were collected and vertical aerosol flux measurements were made, confirming that the glacial outwash sediments were an emission source at the Down Valley site for these days. Fourth, the maximum in the mass size distribution of the total aerosol population at the Down Valley site for the sampling days was approximately 3.25 µm, based on previous measurements, consistent with a local mineral dust source. Fifth, only mineral dust particles were detected in samples collected from the Down Valley site during the same month and year and for similar PM10 levels (but on a different day) based on SEM/EDX measurements, with the caveat that carbonaceous or semi-volatile materials could not be detected with the SEM/EDX measurements.

Based on the information above, we assumed that the ice nucleating ability of the samples was due to local mineral dust from glacier outwash sediments. The correlation between the concentration of INPs measured in this study and the total mass of the aerosol samples is consistent with this assumption.

To address the referee’s comments, we have added a new section to the manuscript (see Section 3.1 in the revised manuscript) where we discuss the evidence above that suggests the total aerosol population sampled was dominated by local mineral dust from glacial outwash sediments.
***

R1C3: A reason of Comments 1 and 2 is that the results in Yukon (this study) are quite different from those of Creamean et al. (2020). I would like to suggest checking Creamean et al. (2020) and discuss the possible difference between this work and their work. Creamean et al. (2020) reported the ice nucleating ability of dust samples collected from the ground surface in Alaska (active layer and permafrost) and demonstrate that the results in Alaska are almost comparable to that of glacial outwash samples collected in Svalbard (Tobo et al., 2019). If the conclusion of this manuscript is true, it means that the ice nucleating ability of the glacial dust in Yukon was significantly worse than those of Alaska, despite the fact that Alaska is located in North America and is relatively close to Yukon. The authors would need to evaluate the ice nucleating ability of dust particles collected in Yukon more carefully (see Comments 1 and 2).

***
In the revised manuscript we have added the results for the active layer from Creamean et al. (the most relevant results from their study) to revised Figure 5, and we have discussed possible reasons for the difference between our results and the active layer samples from Creamean et al. See discussion below.

“Also included in Fig. 5 are n_m values for the active layer (samples collected 0.15 m below the surface) from Fairbanks, Alaska, USA during August 2019 55. The n_m values of the airborne dust in the current study was also approximately 0-2 orders of magnitude lower than that of the active layer collected from Alaska. Several reasons could explain these differences. For example, the differences could be due to differences between aerosolized samples and samples collected below the surface. In addition, the differences could be due to differences in mineralogy and biology at the Yukon site compared to the Fairbanks site for various reasons, such as different microclimates and different mineral formation mechanisms in the different regions.”
***

R1C4: Why did the authors collect only 4 samples for INP analysis under relatively similar conditions? Why didn’t you measure the INP number concentrations when the influence of local dust emissions would be relatively small? (see also Comments 5and 6)

***
To address the referee’s comment, we have carried ice nucleation measurements on 3 additional airborne dust samples, bringing the total number of airborne dust samples analyzed to 7.
***

R1C5: It is not clear whether dust concentrations were indeed well above background levels (e.g., Abstract). First, the authors should explain the details on how to measure dust concentrations in the Method section. In addition, the authors should show the background dust concentrations at the measurement site and then demonstrate that the dust concentrations of 500 to 1400 ug/m^3 (Section 3.1, Table 1, Figure 4) are indeed well above background levels. It is also necessary to explain that such high dust concentrations in May 2018 would be mainly caused by local dust emissions in Yukon and/or its adjacent areas, rather than dust emissions from other high-latitude sources or long-range transport of dust from low-mid latitudes.

***
To address the referee’s comments, we have added details to the Methods section on how the dust concentrations were measured. In addition, we added a new section to the manuscript that illustrates that such high dust concentrations in May 2018 are most likely dominated by local mineral dust from glacial outwash sediments in the region (See response to R1C2 above).
***

R1C6: As for Comment 5, it is also important to explain that the quality of dust simulation in GEOS-Chem model, because the authors use the GEOS-Chem model to indicate that dust concentrations at the measurement site in May 2018 were higher than those caused by long-range transported dusts from low latitude mineral dust sources and anthropogenic sources (Section 3.3). The authors need to verify that the GEOS-Chem model would be useful to quantify the influence of long-range transported dusts from low latitude mineral dust sources and anthropogenic sources. For example, please explain that the GEOS-Chem model can successfully simulate dust concentrations over Yukon during periods when high-latitude dust emission is not expected (e.g., wintertime).

***
To address the referee’s comments, we have added the following text to the manuscript:

“Simulations of dust using GEOS-Chem have previously been found to be in good agreement with surface observations at Trapper Creek, Alaska spanning a full year (Breider et al., 2014) and CALIOP retrievals in the Arctic during the spring haze period (Di Pierro et al., 2011).”

Breider, Thomas J, Loretta J. Mickley, Daniel J. Jacob, Qiaoqiao Wang, Jenny A. Fisher, Rachel Y.-W. Chang, and Becky Alexander. “Annual Distributions and Sources of Arctic Aerosol Components, Aerosol Optical Depth, and Aerosol Absorption.” Journal of Geophysical Research: Atmospheres 119, no. 7 (2014): 4207–4124. https://doi.org/10.1002/2013JD020996.

Di Pierro, M., L. Jaeglé, and T. L. Anderson. “Satellite Observations of Aerosol Transport from East Asia to the Arctic: Three Case Studies.” Atmospheric Chemistry and Physics 11, no. 5 (March 11, 2011): 2225–43. https://doi.org/10.5194/acp-11-2225-2011.
***

Specific Comments

R1C7: Section 2.1: How did you dry the aerosol samples collected on filters?

***
This information has been added to the revised manuscript. Specifically, the following text was added to revised manuscript:

“After collection, the filters were dried for 24 h in a desiccator and then the mass collected on each filter was determined gravimetrically.”
***

R1C8: Equation 3: I doubt if this method is not appropriate, because the n_m value is determined based on the mass of the total aerosol particles (i.e., both water-soluble and insoluble particles), while the S_p value represents the geometric surface area of only insoluble particles contained in the suspension. If the authors need to calculate the number of INP per unit surface area of total aerosol particles, they should use the geometric surface area of total aerosol particles measured in the atmosphere and not in the suspension.

***
As discussed above, the total aerosol population sampled was dominated by local mineral dust from glacial outwash sediments in the region, and hence water-soluble particles should only represent a very small fraction of the total aerosol surface area (see responses to R1C2 above). Under these conditions Equation 3 (Equation 4 in revised version) should be a reasonable assumption. To address the referee’s comment, we added the following text to the manuscript:

“Equation 4 assumes that the amount of water-soluble material in the collected samples was minor, which should be a reasonable assumption since the collected samples were most likely dominated by local mineral dust from glacial outwash sediments in the region (see below for details).”
***

R1C9: Equation 4: I think the authors can calculate the number of INP per volume of air using a more straightforward way. The authors first calculated the n_m values of dried ambient aerosol samples using equation (1) and then converted it into the number of INP per volume of air using equation (4) (the description like “MassConc_Dust” in equation (4) might not be appropriate, because it represents the mass concentration of “total aerosol particles” and not “dust particles only”). Many other studies have calculated the number of INP per volume of air using a more simplified equation (e.g., see Tobo et al., 2019; Wex et al., 2019; Sanchez-Marroquin et al., 2020), because the information on the mass of material collected on the filters would not be required when calculating the number of INP per volume of air.

***
To calculate the INP per volume of air for the field samples, we switched to a simpler equation, consistent with the suggestion by the referee. In the revised manuscript, we have replaced Equation 4 with the simpler equation (Equation 2 in revised version) used to calculate the INP per volume of air for the field samples.
***

R1C10: Section 3.2.1 (Second paragraph): To support this discussion, the authors would need to measure the organic content of aerosol samples collected on filters or glacial outwash sediments collected at the Yukon site.

***
We agree that measurements of the organic content of the aerosol samples would be interesting. Unfortunately, these measurements have not been made. In the revised manuscript, at the end of Section 3.2.1 we have added the following text:

“Measurements of the amount of organic material in the airborne dust at the Yukon site, as well as the ice nucleating ability of surface-collected glacier outwash sediments at the Yukon site, would be useful to understand these differences.”
***

R1C11: Section 3.3: Please explain the details of PM10 measurements in the Method section. In addition, please explain whether PM10 concentrations are different from dust concentrations or not.

***
The details of the PM10 measurements were added to the Method section as suggested. The PM10 measurements are most likely the same as the dust concentrations (see responses to R1C2 above).
***

R1C12: Figure 2 (Caption): Field samples => Initial suspension (or undiluted)?

***
We have changed “field samples” to “suspensions of field samples” in the caption.
***

R1C13: Figure 3: Please explain how the range of the concentrations measured ah high latitudes over Arctics is quantified. If this range is originally determined by the authors, please show a figure comparing this range and the INP data presented in references (6-13, 67-72) in the Supplementary Information.

***
As suggested, we have added a figure to the SI that compares the estimated ranges in Figure 3 and the INP data presented in references (6-13, 67-72).
***

R1C14: Figure 3 caption: Glacier dust samples => Field samples (or Yukon samples)?

***
We have changed “glacier dust samples” to “Yukon field samples” to address the referee’s comments.
***

R1C15: Figure 4 (data points at -20 degreeC): Why are there 5 data points?

***
One of the points corresponded to (0,0). We have removed this point in the revised manuscript.
***

R1C16: Figure 4 (x-axis): Does it represent the mass concentrations of “airborne dust” and not “total aerosol particles”?

***
In the revised manuscript, we have changed “mass concentration” to “PM10 concentration” for cases like this.
***

R1C17: Figure 5: It might be reasonable to add the data reported by Creamean et al. (2020) (n_m for dust samples collected in Alaska) for comparison.

***
Done.
***

Referee: 2

Comments to the Author
I recommend publication of this manuscript after considering major changes, see attached file.

Summary

Xi et al. present INP concentration measurements of glacial outwash sediments, which are a potential high-latitude dust source and therefore relevant for the climatic impact of clouds in this region. The filter-based measurements are airborne collected, and are therefore more representative for ambient INP concentrations as compared to ground-collected samples. The authors find that the glacial dust sediments cause freezing between -6°C and -23°C. Below -15°C, the nucleation ability of their samples are comparable to Icelandic dust and k-feldspar, and above -15°C the INPs were likely of biological origin. While the topic of the study is very relevant, a major drawback is the small number of collected samples. Only four airborne dust samples were taken within 9 days, which makes a correlation coefficient analysis problematic. For example, no samples were collected during low-dust or no-dust periods, which could give information about the freezing ability of the natural non-dust background aerosol, and might impact the observed relation to the aerosol mass. Therefore, major conclusions drawn from this correlation method, e.g., INP concentration estimates based on the derived parameterization, are not reliable. However, given the relevance of such glacial airborne samples, I still recommend publication, after considering major changes.

R2C1: First, I suggest that the statements based on the correlation analysis are weakened or that the uncertainty related to this analysis are emphasized better.

***
To strengthen our analysis, we have carried ice nucleation measurements on 3 additional airborne dust samples, bringing the total number of airborne dust samples analyzed to 7. In addition, in the revised manuscript we weakened our statements based on the correlation analysis. The following is the revised text related to the correlation analysis:

“On days when filter samples were collected, the INP concentrations at the site were correlated with the PM10 concentrations of the aerosols at the site (compared Fig. 2a and Fig. 2c). Correlation coefficients (R2) were 0.8559, 0.7937, and 0.7004 and p-values were 0.003, 0.007, and 0.019 for freezing temperatures of 10, 15, and 20 °C, respectively. The correlation between the concentration of INPs and PM10 concentrations are consistent with the aerosol particles collected at the Down Valley site being dominated by mineral dust from glacial outwash sediments in the region.”
***

R2C2: Second, I have some concerns about the suitability of the model calculations. You do not use high-latitude dust emission sources in your model, but connect desert and anthropogenic dust emission calculations to your parameterization based on glacial dust, which is clearly reflecting a high-latitude dust source. In my opinion that does not make sense, as the ice nucleation ability of such non-high-latitude dust sources can be different, and also the emission calculations are not reflecting high-latitude dust sources. In order to make conclusions about a missing dust source in high-latitudes, shouldn’t you have connected the dust concentration model results with the ice nucleation ability of desert and anthropogenic dust?

***
This is a very good point. To address the referee’s comment, in the revised manuscript, we re-ran the model calculations incorporating only natural desert dust from low-latitude regions. To determine the INP concentrations for this natural desert dust, we used an ice nucleation parameterization specifically developed for natural desert dust from low-latitudes.
***

In general, the study is very well written and incorporates some interesting methods such at the size distribution measurements in solution, and the ammonium sulfate freezing assay.

***
Thank you for the positive comments!
***

General comments

Introduction

R2C3: References 3-5: You could consider including the study of Fan et al. (2017) here.

***
We have added this reference.
***

R2C4: References 6 – 13: Murray et al. (2021) also show that clouds in high latitudes are especially sensitive to INPs, therefore this study could be included here.

***
We have added this reference.
***

R2C5: You could consider to quantify the ice nucleation abilities of the studies of Tobo et al., Paramonov et al., and Sanchez-Marroquin et al. in terms of the onset temperature of nucleation, and INP number concentration at specific temperatures.

***
As suggested, we have added information on the number of INP per mass or per surface area at specific temperatures.
***

Methods

R2C6: Were all samples collected during times when ambient dust concentrations were high? How do you know that the high INP concentrations are steming from the dust, if you don’t have a reference/non-dust period?

***
See response to R1C2 above.
***

R2C7: Could you provide a short description about the basic working principle of the Coulter Counter?

***
A short description of principle of the Coulter Counter has been to Section 2.3:

“The Coulter Counter is a device designed for determining the concentration and size distributions of particles suspended in an electrolyte solution. As particles are drawn through microchannels that separate two chambers containing the electrolyte solution, each particle causes a brief change in the resistance of the liquid. The relationship between the measured change in electrical resistance and the size of the particles is used to determine the size of the particles (DeBlois and Bean, 1970).”

R. W. DeBlois and C. P. Bean, Counting and Sizing of Submicron Particles by the Resistive Pulse Technique, Rev. Sci. Instrum., 1970, 41, 909–916.
***

R2C8: What is the uncertainty of the total geometric surface area, based on the measurements of the Coulter Counter? And how can this uncertainty impact your calculation of the surface area and respective interpretation of the ice nucleation ability of the glacial dust sample?

***
The uncertainty is two standard deviations based on triplicate runs, which was not included in Fig. S1 for clarity. The uncertainty has been included when calculating the uncertainty of the ns values.
***

Results

R2C9: The difference to the sediments from Svalbard could also be explained by a difference in mineralogical composition, couldn’t it?

***
Good point. We have added this possible explanation to the revised document.
***

R2C10: The interpretation of the ns and nm results are based on the assumption that the aerosol population is only composed of glacial dust (see also previous comment). However, other aerosol particles could be present in ambient air. Please elaborate on this topic.

***
See response to R1C2 above.
***

Conclusion

R2C11: “…the INP concentrations at the site were correlated with the high concentrations of airborne dust at the sites” is inprecise; you observed a high correlation with the aerosol mass, see previous comment.

***
We have modified this text to be more precise. The following is the new text added.

"Several pieces of evidence suggest that the aerosol particles sampled on these days were dominated by local mineral dust from glacial outwash sediments in the region."
***

24-Apr-2022

Dear Dr Bertram:

Manuscript ID: EA-ART-12-2021-000101.R1
TITLE: Ice nucleating properties of airborne dust from an actively retreating glacier in Yukon, Canada

Thank you for your submission to Environmental Science: Atmospheres, published by the Royal Society of Chemistry. I sent your manuscript to reviewers and I have now received their reports which are copied below.

After careful evaluation of your manuscript and the reviewers’ reports. One reviewer still has some concerns about the manuscript, which I think are legitimate. I will be pleased to accept your manuscript for publication after a minor revision to address those concerns.

Please revise your manuscript to fully address the reviewers’ comments. When you submit your revised manuscript please include a point by point response to the reviewers’ comments and highlight the changes you have made. Full details of the files you need to submit are listed at the end of this email.

Please submit your revised manuscript as soon as possible using this link :

*** PLEASE NOTE: This is a two-step process. After clicking on the link, you will be directed to a webpage to confirm. ***

https://mc.manuscriptcentral.com/esatmos?link_removed

(This link goes straight to your account, without the need to log in to the system. For your account security you should not share this link with others.)

Alternatively, you can login to your account (https://mc.manuscriptcentral.com/esatmos) where you will need your case-sensitive USER ID and password.

You should submit your revised manuscript as soon as possible; please note you will receive a series of automatic reminders. If your revisions will take a significant length of time, please contact me. If I do not hear from you, I may withdraw your manuscript from consideration and you will have to resubmit. Any resubmission will receive a new submission date.

The Royal Society of Chemistry requires all submitting authors to provide their ORCID iD when they submit a revised manuscript. This is quick and easy to do as part of the revised manuscript submission process. We will publish this information with the article, and you may choose to have your ORCID record updated automatically with details of the publication.

Please also encourage your co-authors to sign up for their own ORCID account and associate it with their account on our manuscript submission system. For further information see: https://www.rsc.org/journals-books-databases/journal-authors-reviewers/processes-policies/#attribution-id

Environmental Science: Atmospheres strongly encourages authors of research articles to include an ‘Author contributions’ section in their manuscript, for publication in the final article. This should appear immediately above the ‘Conflict of interest’ and ‘Acknowledgement’ sections. I strongly recommend you use CRediT (the Contributor Roles Taxonomy from CASRAI, https://casrai.org/credit/) for standardised contribution descriptions. All authors should have agreed to their individual contributions ahead of submission and these should accurately reflect contributions to the work. Please refer to our general author guidelines http://www.rsc.org/journals-books-databases/journal-authors-reviewers/author-responsibilities/ for more information.

I look forward to receiving your revised manuscript.

Yours sincerely,
Dr Tzung-May Fu
Associate Editor
Environmental Science: Atmospheres
Royal Society of Chemistry

************

Reviewer 1

I think that the authors have answered the most parts of the reviewer’s comments appropriately. In the revised manuscript, they have newly added 3 samples for INP analysis (7 samples in total now) and it helps to improve this work. Although it is still unfortunate that they did not report on the ice nucleating ability of glacial outwash sediments collected at the ground surfaces, I could understand that it would be difficult to obtain such samples located at glacial outwash plains. I still have some additional comments on R1C1, R1C2, R1C14, R1C15, and R1C17; however, I would like to support the publication of this work if they could answer the following comments.

[Additional Comment on R1C1]
It is hard to understand the authors’ explanation that “<i>Bachelder et al. showed that the elemental composition of aerosolized samples was distinct from surface-collected glacial outwash sediments near the Kaskawulsh Glacier in Yukon, Canada, most likely due to the saltation/sandblasting mechanism of dust emissions</i>”. What do you mean by this sentence? Please give some more detailed explanations in the manuscript.

[Additional Comment on R1C2]
I could not understand the fourth explanation that “<i>the maximum in the mass size distribution of the total aerosol population at the Down Valley site for the sampling days was approximately 3.25 μm, based on previous measurements, consistent with a local mineral dust source</i>”. Can you show evidence that the mass size distribution of other aerosols (for example, long-range transported mineral dust particles) is different from that of mineral dust particles from a local source? What is the typical maximum in the mass size distribution of the total aerosol population at the Down Valley site under background conditions (i.e., non-dusty conditions)?

[Additional Comment on R1C14]
The caption of new Figure 3: “Field samples” => “Yukon field samples”?

[Additional Comment on R1C15]
Did you remove this figure itself? If so, please explain the reason why you decided to remove it from the revised manuscript.

[Additional Comment on R1C17]
Please cite Creamean et al. (2020) in the legend of Figure 5 appropriately.

Reviewer 2

The authors addressed all my major concerns and the manuscript improved significantly. Therefore, I recommend that the manuscript is published.

Dr. Tzung-May Fu
Associate Editor
Environmental Science: Atmospheres
Royal Society of Chemistry

Dear Dr. Tzung-May Fu,

Thank you for your assessment of our manuscript. Below we provide detailed responses to the final comments from the referees. We have numbered the individual reviewer comments by reviewer number and comment number for ease of cross reference, e.g., “R1C1” denotes reviewer 1 comment 1.

******
REVIEWER REPORT(S):
Referee: 1

R1C1: It is hard to understand the authors’ explanation that “<i>Bachelder et al. showed that the elemental composition of aerosolized samples was distinct from surface-collected glacial outwash sediments near the Kaskawulsh Glacier in Yukon, Canada, most likely due to the saltation/sandblasting mechanism of dust emissions</i>”. What do you mean by this sentence? Please give some more detailed explanations in the manuscript.

Thank you for the question. Bachelder et al. showed that PM10 elemental composition was enriched in trace elements as compared to bulk soil samples and the fine soil fractions (d < 53 µm). They proposed that this difference was because the primary mechanisms for dust emission at the site was rupture of clay coatings on particles or the release of resident fine particulate matter trapped within sand particles. To address the referee’s comments, we have added this text to the revised manuscript. Specifically, the following text has been added to the Introduction (Section 1):

“To illustrate, Bachelder et al. showed that PM10 elemental composition was enriched in trace elements as compared to bulk soil samples and the fine soil fractions (diameter < 53 µm) near the Kaskawulsh Glacier in Yukon, Canada. They proposed that this difference was because the primary mechanisms for dust emission at the site was rupture of clay coatings on particles or the release of resident fine particulate matter trapped within sand particles.”

R1C2: I could not understand the fourth explanation that “<i>the maximum in the mass size distribution of the total aerosol population at the Down Valley site for the sampling days was approximately 3.25 μm, based on previous measurements, consistent with a local mineral dust source</i>”. Can you show evidence that the mass size distribution of other aerosols (for example, long-range transported mineral dust particles) is different from that of mineral dust particles from a local source? What is the typical maximum in the mass size distribution of the total aerosol population at the Down Valley site under background conditions (i.e., non-dusty conditions)?

The work from Bachelder et al. showed that the temporally averaged particle size distributions of PM10 were very fine (maximum in the mass size distribution of 3.25 µm). This is very fine compared to measurements at more well-characterized, low-latitude dust sources. For example, results compiled by Huang et al. 2019 showed that the maximum of the volume size distribution for PM10 collected from low-latitude dust sources to be closer to 10 µm. To address the referee’s comments, we have added this text to the revised manuscript. Specifically, the following text has been added to Section 3.1:

“This is very fine compared to measurements at more well-characterized, low-latitude dust sources. For example, results compiled by Huang et al. showed that the maximum of the volume size distribution for PM10 collected from low-latitude dust sources was closer to 10 µm (Huang et al., 2019).”

R1C3: The caption of new Figure 3: “Field samples” => “Yukon field samples”?

This change has been made.

R1C4: Additional comment on R1C15 from the first round of comments. Did you remove this figure itself? If so, please explain the reason why you decided to remove it from the revised manuscript.

Yes, we removed this figure to partially address a comment from the Referee 2 during the last round of comments. Specifically, Referee 2 recommended that the we should deemphasize the correlation analysis (R2C1 from last round of comments).

R1C5: Please cite Creamean et al. (2020) in the legend of Figure 5 appropriately.

We have changed the citation in the figure caption of Figure 5 to address the referee’s comment.

Referee: 2

R2C1: The authors addressed all my major concerns and the manuscript improved significantly. Therefore, I recommend that the manuscript is published.

Thank you!

10-May-2022

Dear Dr Bertram:

Manuscript ID: EA-ART-12-2021-000101.R2
TITLE: Ice nucleating properties of airborne dust from an actively retreating glacier in Yukon, Canada

Thank you for your submission to Environmental Science: Atmospheres, published by the Royal Society of Chemistry. I sent your manuscript to reviewers and I have now received their reports which are copied below.

The Reviewer raised one important concern about the revised manuscript, which I deem legitimate. As such, I will be pleased to accept your manuscript for publication after a minor revision specifically to address this concern.

Please revise your manuscript to fully address the reviewers’ comments. When you submit your revised manuscript please include a point by point response to the reviewers’ comments and highlight the changes you have made. Full details of the files you need to submit are listed at the end of this email.

Please submit your revised manuscript as soon as possible using this link :

*** PLEASE NOTE: This is a two-step process. After clicking on the link, you will be directed to a webpage to confirm. ***

https://mc.manuscriptcentral.com/esatmos?link_removed

(This link goes straight to your account, without the need to log in to the system. For your account security you should not share this link with others.)

Alternatively, you can login to your account (https://mc.manuscriptcentral.com/esatmos) where you will need your case-sensitive USER ID and password.

You should submit your revised manuscript as soon as possible; please note you will receive a series of automatic reminders. If your revisions will take a significant length of time, please contact me. If I do not hear from you, I may withdraw your manuscript from consideration and you will have to resubmit. Any resubmission will receive a new submission date.

The Royal Society of Chemistry requires all submitting authors to provide their ORCID iD when they submit a revised manuscript. This is quick and easy to do as part of the revised manuscript submission process. We will publish this information with the article, and you may choose to have your ORCID record updated automatically with details of the publication.

Please also encourage your co-authors to sign up for their own ORCID account and associate it with their account on our manuscript submission system. For further information see: https://www.rsc.org/journals-books-databases/journal-authors-reviewers/processes-policies/#attribution-id

Environmental Science: Atmospheres strongly encourages authors of research articles to include an ‘Author contributions’ section in their manuscript, for publication in the final article. This should appear immediately above the ‘Conflict of interest’ and ‘Acknowledgement’ sections. I strongly recommend you use CRediT (the Contributor Roles Taxonomy from CASRAI, https://casrai.org/credit/) for standardised contribution descriptions. All authors should have agreed to their individual contributions ahead of submission and these should accurately reflect contributions to the work. Please refer to our general author guidelines http://www.rsc.org/journals-books-databases/journal-authors-reviewers/author-responsibilities/ for more information.

I look forward to receiving your revised manuscript.

Yours sincerely,
Dr Tzung-May Fu
Associate Editor
Environmental Science: Atmospheres
Royal Society of Chemistry

************

Reviewer 1

I think that the authors have answered all the reviewer’s comments, except R1C2.

As for R1C2, I do not think that the fourth explanation and the citation of Huang et al. (2019) are reasonable. Do you think that the maximum of the volume size distribution for the long-range transported aerosol population from low low-latitude dust sources to the Down Valley site is still close to 10 μm? It is hard to believe, and I cannot accept this explanation. If you cannot show evidence that the mass size distribution of long-range transported dust particles (from low-latitude sources to the Down Valley site) is different from that of dust particles from a local source, I think the authors should delete the fourth explanation.

Dr. Tzung-May Fu
Associate Editor
Environmental Science: Atmospheres
Royal Society of Chemistry

Dear Dr. Tzung-May Fu,

Thank you for your assessment of our manuscript. Below is our response to the remaining comment from Referee 1.

Sincerely,
Allan Bertram
Professor of Chemistry
University of British Columbia

****
REVIEWER REPORT(S):
Referee: 1

Comments to the Author
I think that the authors have answered all the reviewer’s comments, except R1C2.

As for R1C2, I do not think that the fourth explanation and the citation of Huang et al. (2019) are reasonable. Do you think that the maximum of the volume size distribution for the long-range transported aerosol population from low low-latitude dust sources to the Down Valley site is still close to 10 μm? It is hard to believe, and I cannot accept this explanation. If you cannot show evidence that the mass size distribution of long-range transported dust particles (from low-latitude sources to the Down Valley site) is different from that of dust particles from a local source, I think the authors should delete the fourth explanation.

Response:

To address the referee’s comment, we have deleted the fourth explanation, as suggested. Thank you for your help.

14-May-2022

Dear Dr Bertram:

Manuscript ID: EA-ART-12-2021-000101.R3
TITLE: Ice nucleating properties of airborne dust from an actively retreating glacier in Yukon, Canada

Thank you for submitting your revised manuscript to Environmental Science: Atmospheres. I am pleased to accept your manuscript for publication in its current form. I have copied any final comments from the reviewer(s) below.

You will shortly receive a separate email from us requesting you to submit a licence to publish for your article, so that we can proceed with the preparation and publication of your manuscript.

You can highlight your article and the work of your group on the back cover of Environmental Science: Atmospheres. If you are interested in this opportunity please contact the editorial office for more information.

Promote your research, accelerate its impact – find out more about our article promotion services here: https://rsc.li/promoteyourresearch.

We will publicise your paper on our Twitter account @EnvSciRSC – to aid our publicity of your work please fill out this form: https://form.jotform.com/211263048265047

How was your experience with us? Let us know your feedback by completing our short 5 minute survey: https://www.smartsurvey.co.uk/s/RSC-author-satisfaction-energyenvironment/

By publishing your article in Environmental Science: Atmospheres, you are supporting the Royal Society of Chemistry to help the chemical science community make the world a better place.

With best wishes,

Dr Tzung-May Fu
Associate Editor
Environmental Science: Atmospheres
Royal Society of Chemistry