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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error of the data. Furthermore, activation energy, Ea' of the Arrhenius
equation is related to AHt of the aotivated complex theory.
AHt - Ea - RT. U.l.15)

3.2 Kinetic Reaction Mechanisms of Ice Nucleation

A ohemical kinetic interpretation of heterogeneous ice nucleation

via four modes, or mechanisms is disoussed in DeMott (1'82) and DeMott,

et ale (1983). The four modes are 1) vapor deposition, 2) condensation

to aqueous embryos followed by freezing, 3) condensation to droplets
followed by freezing, and 4) oontaot freezing. Experimental evidence of

the contact freezing and vapor deposi tion modes of ice nucleation by

hydrophobic aerosol particles given in these papers indicate the

applicability of the kinetic methodology to phase change processes. The

seoond and third forms of ioe nucleation above, generically termed

condensation-freezing processes, will be emphasized here.

Reaction equations tor the condensation-freezing processes can be

expressed as follows.

condensa tion to embryos followed by freezing:
. k k k
N + V -~ AE ~ IE + V -~ Ie

<3.2.1)

condensation to droplets followed by freezing
k k k
H + V -=4 DSD -~ FD + V -~ Ie

<3.2.2)

Specific species are as follows: H is an ioe nuoleus, V is water vapor,

Ie is ice orystal, AE is aqueous embryo, IE is ioe embryo, DSD is dilute

solution droplet, and FD is frozen droplet. Eaoh arrow or step in the

prooesses has a rate constant, kn, unique to that step. Both processes

individually are examples of oonseoutive reactions. Both prooesses can

also occur simultaneously.