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<br />I <br />I <br />.1 <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 />17 <br /> <br />flares tested, which produoed~hYdr~bo.bic _~~~rt.101es,_~JS!l~edno olear <br />---------.,.....-----_.......-~ . . -, --~-~--..._--- .>~- <br /> <br />temperature dependence for the half lives. <br /> <br />Hy~rf:)~t!9bicQYc:l.'~ gene!'ally <br /> <br />function by a oontact meohan1sm(DeMott, et al., 1'83). <br /> <br />The nuolei particles used by Edwards and Evans (1960), apparently <br />functioned at two different rates depending on the initial environmental <br /> <br />conditions in the mixing oloud chamber used. The cloud chamber was <br /> <br />maintained at constant temperature and at water saturation. In one set <br /> <br />of experiments, the aerosol sample was at room temperature and 1001. <br /> <br />relative humidity. Injection of tbe sample into the bottom of the cold <br /> <br />chamber temporarily produced significant supersaturation with respeot to <br /> <br />water. Ice crystal production and fallout was observed to be rapid, <br /> <br />being oomplete within one IIl1nute. 'l'be aerosol was also introduoed into <br /> <br />the chamber witb dry air (relative humidity not stated). Ice crystal <br /> <br />produotion in tbis oase was observed to be 'prolonged', requiring ~re <br /> <br />than five minutes to complete. Experiments oonducted in a small rapid <br /> <br />expansion chamber, where supersaturations were estimated, support tbe <br /> <br />above observations. Edwards and Evans suggested that additional <br /> <br />meohanisms involved in the 'prolonged' nucleation were aovement, by <br /> <br />conveotion, of tbe aerosol to more humid regions of the chamber and <br /> <br />contact of aerosol partioles with droplets. <br /> <br />Experiments were conduoted in a 'dynamio', slow expansion oloud <br /> <br />obamber, whioh simulates the temperature and pressure changes of <br /> <br />adiabatic and pseudo-adiabatio expansion of an air parcel (Garvey, et <br /> <br />al., 1976). AgI-NaI aerosol particles from acetone combustion appeared <br /> <br />to exhibit different rates of ice nucleation depending on the initial <br /> <br />conditions of the aerosol. When Agl-HaI aerosol was introduoed into <br /> <br />ohamber air that was warmer than tbat of the lifting oondensation level <br /> <br />- <br /> <br />