WMOD00300

• Title: Characterization of Silver Iodide-Sodium Iodide Ice Nuclei Using Chemical Kinetic Methodology
• Date: 5/1/1985
• State: CO
• Weather Modification - Doc Type: Report

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injecting them into a mixing oloud chamber. No drying of the sample was
done before introduot1on into the chamber, so water supersaturation can
be expected to oocur whioh is proportional to the relative humidity of
the sample. Results 1ndioate that when the aerosol is preoonditioned
above a water vapor pressure of 12mm Hs, yield of 10e crystals 1noreased
in direct proportion to the vapor pressure. Yield increased by a factor
of three when the sample was oondit1oned at 25mm Hs.
The possib1le existence of transient water super saturations was
generally not considered in most research involving ioe nucleation by
AgI and Agl-Hal. Mossop (1968) recognized it in bis work and
recommended that tuture researchers should avoid supersaturations.
Garvey (1'75) made a conscious effort to avoid supersaturations, by
modifying the cloud ohamber andcaretully diluting aerosol samples with
clean, dry (-300C dew point temperature) air.
The chemical nature of AgI-HaI partioles as affeoted by high water
supersaturation was briefly examined by Johnson and Davis (1972). They
noted the temporary, metastable existence of the hydrated AgI'Nal
complex in high, non-equilibrium humidities. After a time, which is
governed by the kinetic rate of chemical transformation, these oomplexes
were observed to break down, resulting in the appearenoe of solid AgI
particles in Hal solution envelopes. Solid AgI appeared more quiokly
when the dry partiole beoame embedded into a cloud droplet.
Adiabatic and pseudo-adiabatic temperature and humidity ohanges oan
create water supersaturated environments. Chen, et ale (1'72) noted
that when temperature and humidity changes are suffiCiently rapid,
certain complex phases of the Agl-Hal-H20 system oan effectively be
bypassed. This may have been demonstrated by Garvey, et ale (1976) in

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