Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 16, 8915-8937, 2016
https://doi.org/10.5194/acp-16-8915-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Review article
19 Jul 2016
Ice nucleation efficiency of AgI: review and new insights
Claudia Marcolli1,2, Baban Nagare1, André Welti1,3, and Ulrike Lohmann1 1Institute for Atmospheric and Climate Science, ETH Zurich, Zurich, Switzerland
2Marcolli Chemistry and Physics Consulting GmbH, Zurich, Switzerland
3Leibniz Institute for Tropospheric Research (TROPOS), Leipzig, Germany
Abstract. AgI is one of the best-investigated ice-nucleating substances. It has relevance for the atmosphere since it is used for glaciogenic cloud seeding. Theoretical and experimental studies over the last 60 years provide a complex picture of silver iodide as an ice-nucleating agent with conflicting and inconsistent results. This review compares experimental ice nucleation studies in order to analyze the factors that influence the ice nucleation ability of AgI. The following picture emerges from this analysis: the ice nucleation ability of AgI seems to be enhanced when the AgI particle is on the surface of a droplet, which is indeed the position that a particle takes when it can freely move in a droplet. The ice nucleation by particles with surfaces exposed to air depends on water adsorption. AgI surfaces seem to be most efficient at nucleating ice when they are exposed to relative humidity at or even above water saturation. For AgI particles that are completely immersed in water, the freezing temperature increases with increasing AgI surface area. Higher threshold freezing temperatures seem to correlate with improved lattice matches as can be seen for AgI–AgCl solid solutions and 3AgI·NH4I·6H2O, which have slightly better lattice matches with ice than AgI and also higher threshold freezing temperatures. However, the effect of a good lattice match is annihilated when the surfaces have charges. Also, the ice nucleation ability seems to decrease during dissolution of AgI particles. This introduces an additional history and time dependence for ice nucleation in cloud chambers with short residence times.

Citation: Marcolli, C., Nagare, B., Welti, A., and Lohmann, U.: Ice nucleation efficiency of AgI: review and new insights, Atmos. Chem. Phys., 16, 8915-8937, https://doi.org/10.5194/acp-16-8915-2016, 2016.
Publications Copernicus
Short summary
Silver iodide is one of the best-investigated ice nuclei. It has relevance for the atmosphere since it is used for glaciogenic cloud seeding. Nevertheless, many open questions remain. This paper gives an overview of silver iodide as an ice nucleus and tries to identify the factors that influence the ice nucleation ability of silver iodide.
Silver iodide is one of the best-investigated ice nuclei. It has relevance for the atmosphere...
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