Deposition freezing, pore condensation freezing and adsorption: three processes one description?
Abstract. Heterogeneous ice nucleation impacts the hydrological cycle and climate through affecting cloud microphyiscal state and radiative properties. Despite decades of research, a quantitative description and understanding of heterogeneous ice nucleation remains elusive. Parameterizations are either fully empirical or heavily rely on classical nucleation theory (CNT), which does not consider molecular level properties of the ice nucleating particles - which can alter ice nucleation rates by orders of magnitude through impacting pre-critical stages of ice nucleation. The Adsorption Nucleation Theory (ANT) of heterogeneous droplet nucleation has the potential to remedy this caveat and provide quantitative expressions in particular for heterogeneous freezing in the deposition mode (the existence of which has even been questioned recently). In this paper we use molecular simulations to understand the mechanism of deposition freezing and compare it with pore condensation freezing and adsorption. We put forward the plausibility of extending the ANT framework to ice nucleation (using black carbon as a case study) based on the following findings: i) The quasi-liquid layer at the free surface of the adsorbed droplet remains practically intact throughout the entire adsorption and freezing process, therefore the attachment of further water vapor to the growing ice particles occurs through a disordered phase, similar to liquid water adsorption. ii) The interaction energies that determine the input parameters of ANT (the parameters of the adsorption isotherm) are not strongly impacted by the phase state of the adsorbed phase. Thus, not only the extension of ANT to the treatment of ice nucleation is possible, but the input parameters are also potentially transferable across phase states of the nucleating phase.
Maria Lbadaoui-Darvas et al.
Status: final response (author comments only)
- RC1: 'Comment on egusphere-2023-644', Anonymous Referee #1, 05 May 2023
- RC2: 'Comment on egusphere-2023-644', Anonymous Referee #2, 18 May 2023
- CC1: 'Comment on Lbadaoui-Darvas et al.', Claudia Marcolli, 23 May 2023
Maria Lbadaoui-Darvas et al.
Maria Lbadaoui-Darvas et al.
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This is the review of the manuscript entitled “Deposition freezing, pore condensation freezing and adsorption: three processes one description?” by Mária Lbadaoui-Darvas, Ari Laaksonen, and Athanasios Nenes. This study aims to gain a deeper understanding of deposition ice nucleation by means of molecular simulations. Deposition ice nucleation is mechanistically compared to the recently suggested pore condensation freezing (PCF) and how it is related to adsorption. The results of this study support the application of the so-called adsorption nucleation theory (ANT) to describe deposition ice nucleation in place of classical nucleation theory (CNT), PCF, and other parameterizations. A black carbon substrate, with and without pores, serves as a surrogate of an ice nucleating substrate. The simulations show that a quasi-liquid layer remains on the water cluster on the surface, i.e., adsorption and ice nucleation occur in a disordered phase. Also, the input parameters for ANT that describe the interaction between water or ice and black carbon are very similar suggesting that an ANT description might hold for the water nucleation (adsorption) as well as for deposition ice nucleation.
Further fundamental understanding of ice nucleation is crucial, and this study nicely fills this gap. Hence, in terms of topic and theme it fits in the scope of the journal Atmospheric Chemistry and Physics. In general, I am in support of publishing this study. However, I have a couple of revision requests the authors should address.
I think it should be stressed that the terminology/definition of deposition ice nucleation is historically macroscopically defined (before the application of in situ microscopy and MD simulations). For many current experimental techniques, this still has validity. Though on a molecular level this may not be true. Following the conventional definition, it is “deposition ice nucleation” and not “deposition freezing”. Liquid (macroscopic) water freezes, but deposition ice nucleation does not involve (following convention) bulk liquid water. If the authors by purpose mix these two definitions and generate a novel terminology, since they observe deposition ice nucleation to originate from a liquid-like water cluster, then this has to be discussed. However, this seems not to be the case since this term is readily used. Also, I would not challenge the conventional definition based on one simulation study only. Hence, “deposition freezing” should be exchanged for deposition ice nucleation throughout the manuscript.
The other issue regarding terminology is to call the water clusters “droplets”, “dropletwise”, etc. I see that the authors struggle with this issue as well, trying also “nanodroplets” or “nanophase”. In this community droplets are usually defined to be 10s of micron in size. The “nanodroplets” forming inside the pore are about 2 nm or smaller. Typically, we call those entities clusters. It may not even be clear if this cluster size possesses bulk-liquid water properties (surface tension, etc.)? I am also not entirely sure how to name those condensed nanometer-sized islands of water but naming those “droplets” is unfortunate and ambiguous. Liquid-like or ice-like water clusters may be an idea. Maybe “nanodroplets” works to convey the idea but I feel this is not ideal either.
From the abstract and introduction, one would expect some analysis using ANT, i.e., deriving ice nucleation rates, etc. However, this study makes the case that ANT can be applied to deposition ice nucleation based on the simulation results. As written, this fact may not be so clear, and the overall confidence is only supported by this study looking at one idealized substrate. Maybe in some instances the text could convey a more exploratory study. I do not disagree with the authors; I suggest being a bit more conservative. Especially when reading the model methods. Many caveats are discussed (which I appreciate, and this does not minimize the impact of the study) but it feels a bit counter (i.e., weaker) to the introduction. This is maybe something the authors could consider.
Line 22: The authors could cite here the recent review by (Knopf and Alpert, 2023).
Line 30: I doubt that (DeMott et al., 2010) discuss in detail nucleation theory and rates relevant for this paper and they do not discuss specifically deposition ice nucleation. Other literature would be needed in this place.
Line 37: “…adsorbed water can exist….”
Line 40: At this point it is not clear what you mean by “whereas other locations that collect pre-critical clusters might have an opposite effect.” Why do they have an opposing effect?
Line 47: Here it suddenly switches to immersion freezing. I recommend keeping the focus on deposition ice nucleation throughout the introduction. Also, I am not sure if I agree with this statement. When CNT is expressed in terms of water activity, intrinsic parameters like contact angle, interfaces, etc. are considered. See, e.g., the work by Knopf and Barahona groups. In fact (Knopf and Alpert, 2023) show that deposition ice nucleation may be well described using water activity as for the case of homogeneous ice nucleation and immersion freezing.
Line 55-57: Missing words, empty brackets?
Line 73-75: As mentioned above, considering water activity in CNT descriptions might account for these issues (Knopf and Alpert, 2023; Koop et al., 2000; Barahona, 2015, 2014; Knopf and Alpert, 2013).
Line 81: Period missing?
Line 81-86: A long sentence, maybe too long. Also, this statement is too general. Careful literature review will show that there are several studies (some employ nanoscale resolution) which do not corroborate PCF occurring in observed deposition ice nucleation experiments, e.g. (Wang et al., 2016). I would avoid “in reality” and write “…’freezing’ could be pore condensation…”.
Line 112: It is crucial to conduct atomistic and coarse-grained molecular simulations as discussed in (Knopf and Alpert, 2023) and shown in (Roudsari et al., 2022). They can yield different results while atomistic simulations are likely the preferred method, if feasible.
Line 127: What do you mean by energetic background? This is not a thermodynamic expression. Maybe just state the parameters you assess?
Line 146-147: Could you please elaborate here. The target vapor pressure corresponds to the adsorption layer structure”? At such high vapor pressure, one would have multiple layers of water? I assume, this is what you want?
Line 159: What do you mean by “deterministic dynamics”?
Line 168: Figure 1 instead 4?
Line 170-175: Long sentence with a lot of information. Again, a rather strong caveat. Maybe split up this information.
Line 194: sigma parameter has no units?
Line 242: What is “dropletwise phase”? Does this expression exist? See also general comment.
Line 247: You discuss Fig. 5 before Fig. 4?
Figure 3: Panel (b) is missing?
Line 277: Does this statement depend on pore size? Is it correct to generalize this?
Line 281: Maybe semicolon after “point I.” to make this easier to follow?
Line 287: “In neither case is complete pore filling required for freezing.” I think this is a very interesting and important finding of this study. It challenges the PCF mechanism. I am wondering why this is not mentioned in the abstract.
Figure caption 4: I am not sure what is the difference between freezing onset and initial stage. Onset is an “initial’ condition in a way. Not sure how to better (unambiguously) define this. Panel (b) is not described? And panel indicator “(b)” in caption text should be “(c)”?
Line 319-320: Several MD studies suggest that the critical nucleus forms in second water layer, e.g., (Cox et al., 2013). I assume the nucleus attaches after it forms?
Line 324-327: This sentence could be split in two to make understanding easier. From where comes the insight that layer-by-layer ice growth (is it growth or nucleation?) represents barrierless freezing? Please add references. Though if it is growth, then we talk about other energies than that needed for nucleation?
Line 327: What do you mean with “it shifted to the left”?
Line 360: What is meant by (kal)?
Line 361 -362: The A-values have no units?
Line 458: Clearly these 2 nm clusters are not supercooled droplets in the conventional application of terminology.
Line 479: empty citation?
Line 489: Was ITIM defined previously?
Line 493: (kal)?
Line 18: omit first “of”
Line 39: superfluous space
Line 55: “…implemented in regional…”
Line 102: solid-vapor phase? I suggest to use hyphens for expressing interfaces.
Line 117: Omit “even”.
Line 195: superfluous space
Line 205: space missing
Figure caption 2: Shaded areas not visible in my pdf file.
Line 231: double citation.
Line 282: superfluous space
Line 318: “dropletwise”?
Line 325: reach
Line 393: space needed before “for”
Line 442: adsorption
Line 444: …superior compared to that on…
Line 470: proven
Line 480: superfluous space
Line 480: molecules, respectively,
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Barahona, D.: Thermodynamic derivation of the activation energy for ice nucleation, Atmos. Chem. Phys., 15, 13819-13831, 10.5194/acp-15-13819-2015, 2015.
Cox, S. J., Raza, Z., Kathmann, S. M., Slater, B., and Michaelides, A.: The microscopic features of heterogeneous ice nucleation may affect the macroscopic morphology of atmospheric ice crystals, Faraday Discuss., 167, 389-403, 10.1039/c3fd00059a, 2013.
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Roudsari, G., Pakarinen, O. H., Reischl, B., and Vehkamaki, H.: Atomistic and coarse-grained simulations reveal increased ice nucleation activity on silver iodide surfaces in slit and wedge geometries, Atmos. Chem. Phys., 22, 10099-10114, 10.5194/acp-22-10099-2022, 2022.
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