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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 />19 <br /> <br />TWo sampling procedures were used by Edwards and Evans (1960) in <br />their examination or hygroscopic aerosol particles. In one prooedure, <br />aerosol at 1001 relative humidity at room temperature was injected into <br />a oloud chamber whioh was apprOXimately water saturated. This aerosol <br />was termed 'wet'. The other prooedure involved injeotion of aerosol <br />from a signifioantly drier environment into the oloud chamber. The <br />extent of supersaturation oaused by the 'wet' aerosol was not <br />determined. Results indicated that the yield of ice nuoleation by 'wet' <br />aerosol was approximately an order of magnitude greater than the yield <br />of ice nucleation by 'dry' aerosol at all temperatures. Additionally, <br />'wet' aerosol was observed to nucleate rapidly, within one minute, while <br />'dry' aerosol was observed to nucleate for prolonged amounts of time. <br />They attributed the differenoe in ice nuoleation behavior to a <br />oombination of faotors including looation of sample injeotion, <br />oonveotion in the chamber and subsequent migration of nuclei to zones of <br />water supersaturation and high liquid water, and over~eeding. <br />Water supersaturatioDS were induced in the cloud chamber used by <br />Mossop (1968) where a semi-permeable membrane oontaining warm water was <br />used for humidifioation and cloud formation in the cold box. TWo <br />humidifier temperatures were used, 350C and 450C, to produce two <br />relatively ditferent water vapor conditions. Increases in yield were <br />noted for Agl-Nal ioe nuolei of about a half order of magnitUde at <br />temperatures warmer than -160C. <br />Preoonditioning AgI-Hal ioe nuclei in a moist environment resulted <br />in similar ice nucleation behavior. St. Louis and Steele (1'68) allowed <br />Agl-Hal aerosol partioles produced from acetone combustion to <br />eqUilibrate in environments of varying relative humidities before <br />