Ice nucleation efficiency of AgI: review and new insights
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...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/16/8915/2016/acp-16-8915-2016.pdf |
| Summary: | 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·NH<sub>4</sub>I·6H<sub>2</sub>O, 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. |
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| ISSN: | 1680-7316 1680-7324 |