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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />ABSTRACT OF THESIS <br /> <br />CHARACTERIZATION OF SILVER IODIDE-SODIUM IODIDE ICE NUCLEI <br />USING CHEMICAL KINEnC METHODOLOGY <br /> <br />Ice nucleation by aerosol particles generated from combustion of <br /> <br />acetone solutions of silver iodide and sodium iodide has been <br /> <br />characterized in the CSU Isothermal Cloud Chamber using the techniques <br /> <br />of chemical kinetics. The mec~ani~~~~f ice nucle~~ion has b~~n~o~~~_ ~o <br />be primarily condensation-freezing ice nucleation.~ Two sePar~te <br />____,,__.~___.~-'_..-. .~_~__~. ~_ __ _'~o_<--~__.~r_'._"___:_.. ___'_'.__"'_'._-=--~ -~'- ~ ___.--'"'--"~--_. <br /> <br />mechanisms_~f ice nucleation have been observed. One mechanism. <br />~-~-~-'---~--' ----.~_.--~.-_.,~--_...-) <br /> <br />!denti!,!_~d ~ a~_~ondensat10n to droplets followe~~~_ freezing. ~~~~s _at <br />water saturation and is a characteristi~a.~!y slow process. with a hal! <br /> <br />life on the order of 10-30 minutes. The other mechanism. identified as <br /> <br />condensation to aqu~()us embryos fop.owed byfree.zing--.u-occurs_at-l@t~L <br /> <br />~'~_-""--=C-~~""'~ <br /> <br />supersaturated conditions. is characteristically fast. requiring less <br />.......-..... ',' .... .. :." F ~_~~_~__...._~A--'_ --.. ____ ~'_",_--,__....~_._...__ 4 <br /> <br />than a minute for~~ollt~~!tiOD:"_1 ~~_. r~~~~~,~~n. a higher yield of ice <br />crystals than the slow mechanism. The mechanisms are dependent on <br />.~_.,_ _.._.,_-,,-".7;'-;..z'~' ,",,_~-c..-'-,_,"-.-__,__ <br /> <br />temperature and water vapor ooncentration, respectively. and are <br />......-~~_.__.- <br /> <br />independent of the liquid water content of the cloud. Contact of the <br /> <br />----..___~d _~_' ._.,,:...~..,~~~-<.'--'''~' .'->~ <br /> <br />aerosol particles with cloud droplets has also been observed at high <br /> <br />liquid water contents to be a mechanism of ice nucleation by silver <br /> <br />iodide-sodium iodide aerosol particles. <br /> <br />The energy of activation for the slow mechanism of condensation to <br /> <br />droplets followed by freezing. has been found to be three times the <br /> <br />latent heat of condensation of water. This is believed to be related to <br /> <br />the extent of hydration of the silver iodide-sodium iodide complex. <br /> <br />ii1 <br />