Influence of granulometry on the ice-nucleating efficiency of alkali feldspars

Mixed-phase clouds represent a major source of uncertainty in the representation of cloud microphysical processes in climate models. These clouds, consisting of supercooled liquid droplets and ice crystals, strongly influence precipitation formation and cloud radiative properties. Ice formation in mixed-phase clouds occurs predominantly via heterogeneous ice nucleation, enabling freezing at temperatures well above the homogeneous freezing limit of pure water [1].Aerosol particles suspended in clouds can act as ice-nucleating particles (INPs), promoting heterogeneous ice formation through interactions between water molecules and particle surfaces. Numerous studies have shown that ice-nucleating (IN) activity [2] is governed by surface properties that influence the structure of interfacial water. Among atmospheric INPs, feldspars have received particular attention due to their high IN efficiency relative to other mineral dust components, especially alkali feldspars [3]. This efficiency has been linked to feldspar surface properties such as surface chemistry, crystallographic structure, and morphology [4].Feldspar IN activity is not static but evolves in response to environmental and physicochemical processing. Here, we investigate the effect of mechanical comminution on the immersion freezing behavior of feldspars. Powdered feldspar samples were ground using different mortars and grinding durations, producing particle populations with distinct size distributions and specific surface areas. Our results demonstrate that changes in granulometry significantly affect ice-nucleating activity, indicating that particle size and surface state play an important role in controlling ice nucleation.  [1] Burrows, S. M., McCluskey, C. S., Cornwell, G., Steinke, I., Zhang, K., Zhao, B., Zawadowicz, M., Raman, A., Kulkarni, G., China, S., Zelenyuk, A., and DeMott, P. J.: Ice-Nucleating Particles That Impact Clouds and Climate: Observational and Modeling Research Needs, Rev. Geophys., 60, e2021RG000745, https://doi.org/10.1029/2021RG000745, 2022.[2] Shimizu, T. K., Maier, S., Verdaguer, A., Velasco-Velez, J. J., and Salmeron, M.: Water at surfaces and interfaces: From molecules to ice and bulk liquid, Prog. Surf. Sci., 93, 87-107, https://doi.org/10.1016/j.progsurf.2018.09.004, 2018.[3] Canet, J., Rodríguez, L., Renzer, G., Alfonso, P., Bonn, M., Meister, K., Garcia-Valles, M., Verdaguer, A.: Measurement report: Ice nucleation ability of perthite feldspar powder, EGU [preprint], https://doi.org/10.5194/egusphere-2025-5014, December 2025.[4] Pach, E. and Verdaguer, A.: Pores Dominate Ice Nucleation on Feldspars, J. Phys. Chem. C, 123, 20998-21004, https://doi.org/10.1021/acs.jpcc.9b05845, 2019.