Carbon Dioxide (CO2) particles exiting from a variety of feed tube and shroud configurations, and in combination with varying volumetric flow rates of purge air were measured using a laser diffraction device. CO2 particles were then injected into the stilling chamber of two open-circuit blow down supersonic wind tunnels to obtain PIV measurements. A ten degree ramp placed in the test section of one wind tunnel produced a shock wave which allowed for the characterization of the time response of the CO2 particles as they crossed the shock wave. This time response was compared with theoretical time responses of varying diameter CO2 particles in order to characterize the spherical diameter of the actual CO2 particles. Purge air was used to demonstrate the ability to alter the size of particles by altering the time response of the particles across the shock wave. A scale up was performed to demonstrate the applicability of the clean seeding technique to different size wind tunnels. Initial particle measurements demonstrate the ability to control the size of CO2 particles which is backed up by actual PIV measurements confirming size characterization.