| 18 Feb 2026
Revisiting the Parameterization of Ice Nucleation of Dust Particles under Mixed-Phase Cloud Conditions from Laboratory Measurements
Abstract. Dust aerosol plays a key role in cloud formation and evolution due to its high atmospheric abundance and efficient ice nucleation abilities (INA). However, a generalized parameterization of dust-induced ice formation in climate models remains challenging, because dust INA varies substantially with mineral composition, measurement methods, and atmospheric aging processes. In this study, we revisited the INA of dust particles under mixed- phase cloud conditions (MPC, -38 < T < 0 °C) compiled from previous laboratory studies. Our results indicate that measurement methods, whether particles are dry-dispersed or wet- suspended introduce the largest variability in reported dust INA, represented by ππ (ice active site surface density), showing a difference of 1−6 orders of magnitude at -38 < π < -18 °C. This discrepancy likely arises from different water-particle interactions between the two methods, including particle coagulation at artificially high particle concentration and surface modification by water. Aging generally reduces dust INA, with chemical reactions inducing the strongest reduction, followed by thermal treatments and water/aqueous aging. Based on these findings, we developed a suite of ππ − based parameterizations to represent INA of dust particles with mixed and specific mineral composition. To overcome the variability introduced by measurement methods, we also developed parameterizations based on π·π (spherical equivalent particle diameter within a droplet), which predict droplet freezing across the full MPC temperature range using a single expression. The developed parameterizations provide a physically grounded approach for representing dust INA and are expected to improve the accuracy of predictions of dust-induced cloud formation in climate models.
This manuscript describes meta-analysis of a wide range of recently published INP characterizations of mineral dust samples analyzed by several different techniques. Data is reanalyzed to create comparable quantities, and discrepancies between the different datasets are discussed, with a focus on 1) different materials, 2) different measurement techniques, and 3) different sample ageing conditions. Particle coagulation and wet ageing processes are considered for the source of discrepancies between different measurement techniques. Parameterizations are constructed for aggregate data, divided by measurement technique and sample ageing conditions.
There is a lot of interesting data and discussion within this paper, however there are significant weaknesses that prevent any strong conclusions from being made.
Foremost: aggregate equivalent diameters are constructed to examine possible impacts of aggregation on measured freezing temperatures. This is an interesting idea, with some interesting data. In the manuscript it is taken as proof of extensive aggregation, however, which does not logically follow from any of the data or discussion. One of the following needs to happen: 1) Compelling evidence needs to introduced that extensive aggregation is occurring in droplet freezing measurements or 2) much of the manuscript needs to be rewritten to remove the unwarranted conclusion.
Second: Many strong conclusions and atmospheric implications are made without strong, or any, evidence, these need to be walked back or better supported. See comments on lines 500+ below.
Despite these issues, I think there is a lot of interesting analysis and work that has gone into this paper, and I think it will be publishable and of broad interest with the right framing and revised discussion, but extensive revisions are required.
Specific comments:
Section 2.2: In this section it was unclear to me if you are using equations 1-6 and applying them to literature datasets, or simply explaining how these quantities might be calculated and using literature values that have already been calculated. I think it would be much more clear to move this information to the supplemental and expand the discussion to be more explicit about which quantities were used from each dataset to calculate each derived quantity. Right now it feels like there is enough information to make a few guesses but not enough information to be sure what you have actually done. Perhaps a very brief explanation should stay in the main manuscript and point to the supplemental.
Line 232 or thereabout: There is a lot of discussion of feldspar ice nucleation, and the variability in mineral dust ice nucleation properties, and I feel that inclusion of Whale 2017 would greatly benefit this section. In that work, for feldspar samples measured using the same technique, there are >5 orders of magnitude difference in ns, in a similar manner to the combined data within your manuscript. This certainly seems relevant for understanding the origin of the variability and should be discussed.
Line 253: I donβt think it is fair to say β1-8 orders of magnitude higherβ when some of the aerosol and suspension points overlap, maybe 0-8?
Line 270: similar to above, maybe β0-6 ordersββ¦ or βup to 6 ordersβ might sound better. Also shows up line 428 and 565.
Line 276: My understanding based on the equations included, is that the way you are estimating Jhet will shift ns values in an identical way based on experimental cooling rate or residence time, is that correct? Such that any relative change between the relative ordering of experiments in ns and jhet is due to cooling rate changes? Some discussion of this would be helpful I think. I also think that more explicit discussion (related to my comments on section 2.2) surrounding what assumptions go into this estimation of jhet and their validity would be helpful.
Line 283: The βtwo step temperature dependenceβ is weakest in natural dust samples, and doesnβt appear for the aerosol samples. Iβm not convinced that this statement is well-supported by the data presented thus far.
Line 310: referencing eq. 1 and 3 here seems worse than just redefining the terms β Sp is the surface area of a single aerosol and Sd is the total surface area of all suspended aerosol in a droplet.
Line 312: Why are you choosing different definitions for βfreezing temperatureβ for suspension and aerosol measurements? That needs to be justified.
Lines 315-330: So you have constructed an equivalent diameter for all particles in solution drops and compared to actual aerosol diameters, after briefly discussing coagulation. I donβt understand quite how you think these comparisons are meaningful, however. It certainly doesnβt seem to follow that droplet freezing measurements are only relevant to >10 micron single particles within the atmosphere, when you have only constructed a βwhat if everything coagulatesβ product with no evidence that coagulation is actually occurring in these measurementsβ¦
Related to this, droplet freezing measurements often use serial dilutions to access different INP concentration ranges, with the most dilute samples differing by >1000 fold. In most cases there is overlap in INP concentration between dilutions, which would not be the case if the degree of aggregation were changing with concentrations. Some discussion of this is relevant and warranted in this section.
Lines 367: The transition to parameterizations seems abrupt, especially immediately following a teaser for discussing relevant β|water-ageingβ processes. Maybe this belongs elsewhere in the manuscript, or perhaps it just needs to be tied together better.
Figure 5: The aged and fresh data for aerosol/suspension look so similar, can you do significance testing to see if there are population level differences? Maybe a simple thing would be to see how well the best fit lines for fresh populations fit the aged data (calculating R^2 values). There are lots of fancier ways to check for significance between the two populations at a given temperature, or across all temperatures (which should probably be restricted to where you have data for both, i.e. >-27C for suspensions).
Line 575: you arenβt really accounting for the variability in composition and measurement methods, are you? Just fitting the aggregate data separately for the two techniques. You havenβt synthesized them together in any way thoughβ¦
Β Line 616-621: Do you actually know that dry-dispersed measurements are more representative of freshly emitted aerosol? I donβt think there is strong evidence in your analysis that this is the case, and I also donβt think it is well-supported by your citations. I think more realistically, we still have two different techniques with discrepancies in what theyΒ measure but we donβt know which is more representative of ambient concentrations or aerosol-cloud interactions.
Line 626: I donβt think you have shown that De based parameters are atmospherically relevant in any ways, and this discussion seems poorly supportedβ¦
References:
Whale, T. F., Holden, M. A., Kulak, A. N., Kim, Y.-Y., Meldrum, F. C., Christenson, H. K., and Murray, B. J.: The role of phase separation and related topography in the exceptional ice-nucleating ability of alkali feldspars, Phys. Chem. Chem. Phys., 19, 31186β31193, https://doi.org/10.1039/C7CP04898J, 2017.