Mapping ice formation to mineral-surface topography using a micro mixing chamber with video and atomic-force microscopy

Friddle, Raymond W.; Thürmer, Konrad

doi:https://doi.org/10.5194/amt-13-2209-2020

Articles | Volume 13, issue 5

https://doi.org/10.5194/amt-13-2209-2020

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

https://doi.org/10.5194/amt-13-2209-2020

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

Articles | Volume 13, issue 5

Research article

|

07 May 2020

Research article |

| 07 May 2020

Mapping ice formation to mineral-surface topography using a micro mixing chamber with video and atomic-force microscopy

Raymond W. Friddle and Konrad Thürmer

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Final revised paper (published on 07 May 2020)
Preprint (discussion started on 24 Sep 2019)

Interactive discussion

Status: closed

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

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- Supplement

EC1: 'Editor's comment', Mingjin Tang, 24 Sep 2019
RC1: 'Review of Friddle and Thurmer 2019', Anonymous Referee #1, 19 Oct 2019
- AC1: 'Reply to Referee 1', Raymond Friddle, 18 Dec 2019
RC2: 'Review', Anonymous Referee #2, 22 Oct 2019
- AC2: 'Reply to Referee 2', Raymond Friddle, 18 Dec 2019

Peer-review completion

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

AR by Anna Mirena Feist-Polner on behalf of the Authors (09 Jan 2020) Author's response

ED: Referee Nomination & Report Request started (09 Jan 2020) by Mingjin Tang

RR by Anonymous Referee #1 (29 Jan 2020)

RR by Thorsten Bartels-Rausch (11 Feb 2020)

Suggestions for revision or reasons for rejection

The manuscript by Friddle and Thürmer presents the development of a method to observe ice formation on well characterized surfaces under controlled temperature and humidity settings. The ice formation is then related to the observed surface features such as steps and defects.

The manuscript has two foci, it presents and characterized the novel set-up and it discusses whether or not ice formation is triggered on specific surface sites or not. I understand that this is an instrumental paper presenting a novel measurement approach. The discussion on ice formation serves as proof of concept. I therefore judge the manuscript mainly on how rigorous the set-up and procedure is described and tested. Also because, the novelty and uniqueness of the scientific discussion compared to the submitted manuscript Friddle 2019a is not possible to assess. That said, I find that the presentation of the set-up and approach lacks crucial information and supporting data.

The manuscript is well written and easy to follow. The length is appropriate while the level of details might be increased. The topic fits perfectly to the scope of the journal. The described approach further tackles a key question in atmospheric science presenting a possibility to relate surface structure to ice forming ability. What keeps me from accepting the manuscript in its current form is
• the missing detailed characterization of temperature and relative humidity in the cell. Temperature and water vapor pressure are crucial for ice nucleation and growth behavior and I fell that both issues require additional discussion and/or reference measurements.
• That I don’t understand how observation of ice larger in size than the defects/surface features says anything about the ice nucleating or forming at the defect. It could just have nucleated next to the defect and grow over it. I think there might be an issue with resolution to draw sound conclusions. In this respect, I suggest to at least mention Knopf, npj Climate and Atmospheric Science, 2020 in the manuscript.

Detailed comments:

Page 1, Line 6: “cloud like atmosphere”: What is the operational range of your set-up both for temperature and for water vapour pressure that you have tested. Please specify the conditions.
Page 1, Line 9: “relate the likelihood of ice formation to nanoscale properties of a mineral substrate”. This is true but misleading. Surface features can be resolved down to a nanometer scale, but the smallest ice patch is a few um in diameter (Figure 6). I would strongly argue that the lower resolution determines the overall performance of the approach which would be um and not nanometer in this case. However, please specify the resolution of both methods in the abstract.
Page 2, line 4 (and throughout the manuscript): relative humidity to what? Water or ice? Please specify.
Pae 2, line 16: “Meanwhile at RH …. Just 6 ms.” Interesting fact about the set-up. Please move to the discussion and expand.
Page 2 line 30: I miss a introduction to surface features/defects with focus on typical sizes and a discussion on which of these have been found to nucleate ice or foster the formation of ice.
Page 3, line 10 “The humidity of the … ThermoWorks). Taken that relative humidity has such a profound impact on ice nucleation, growth and stability; I think that this short statement is not enough.
• What is the precision of the sensor?
• Do you achieve equilibrium vapor pressure in the bubbler filled with water? This could be achieved by dispersing smaller droplets; then you could calculate the RH based on the water temperature. From my experience this is much more reliable than sensors.
• Have you cross-checked the sensor with a dew-point sensor? That would be another option to verify.
Page 3, line 13: What is real time? Please specify sample rate.
Page 3, line 26: Which range of gas flows can be explored. Please specify.
Section 2.1.2
May I ask you to specify the temperature distribution and trend with time more detailed. The temperature at any location in the chamber is basically given by the cooling and heat flux. Isolating materials add complexity to this as their cooling rate is slow. Nevertheless, if you constantly cool your chamber with cold N2 gas, at some point the whole chamber will reach the temperature of the gas unless you actively heat from the outside. In your case, heating comes from the outside air. Given this complexity, I can’t follow your arguments on why your set-up guarantees that the coldest spot is the sample. Can you specify and give some experimental proof. One possibility might be to set the partial pressure of water to lets’ say 1 mbar which corresponds to the the vapour pressure of ice at -20°C, set T(sample) to -30°C to trigger ice growth, then to -20°C (or close to). Now, if you keep this running for hours, the ice will only remain or cover all parts that are at -20°C. Warmer parts will not be ice covered. Thus the spread of ice will show you which parts of the set-up are at -20°C and wich are warmer.

Page 3, Line 28-31. All this is a result and should be moved to the results/discussion section.
Page 3 line 37. If you switch off the the flow of water vapour, do you then not change the mixing ratio of cold to warm gas (as the water vapour flow is part of the warm gas) and thus change the temperature? Please specify the “consant temperature” in line 37.
Page 4, line 14-16. “note that … values”. This is correct and does not need the “can be” before the “much lower”. Once you have ice in the chamber, its temperature determines the partial pressure of water in the cell which is always 100% relative to ice near the ice. If AHin is larger ,the ice growths.
Page 4 line 17 – 20. I’m sorry, but I can’t follow you here. Any onset of condensation might be kinetically hindered. Wouldn’t it be better to perform this calibration at equilibrium conditions.
Page 5 line 5: Please detail why you expect liquid below 0°C. This comes a little abrupt and might sound odd to those not familiar with freezing point depression by inverse Kelvin effect which I assume you refer to here.
Page 6 line 25 “ice is more likely to form” should that not be ice is more likely to grow.
Discussion. Please discuss and mention temperature gradients along the sample. Can you rule out that those set the direction into which the ice grows or the locations where the ice forms. I’m convinced you can, but please specify.

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ED: Reconsider after major revisions (13 Feb 2020) by Mingjin Tang

AR by Raymond Friddle on behalf of the Authors (27 Mar 2020) Author's response Manuscript

ED: Publish as is (31 Mar 2020) by Mingjin Tang

Short summary

An obstacle to predicting ice content in mixed-phase clouds is the inability to directly view atmospheric ice nucleation at the nanoscale, where this process occurs. Here we show how a cloud-like environment can be created in a small atomic-force microscopy (AFM) sample cell. By colocating video microscopy of ice formation with high-resolution AFM images, we quantitatively show how the surface topography, down to nanometer-length scales, can determine the preferential locations of ice formation.