Abstract:Two formulations (WMC IN 001 and WMC IN 002) of high efficient AgI pyrotechnics used in weather modification have been obtained after a number of screen tests were carried out in CAMS 1 m3 isothermal cloud chamber. The effectiveness can reach to 1014 g-1 AgI at temperatures of -7℃ and colder for WMC IN 001, and it can reach up to 1015 g-1 AgI at -15℃. The foreign pyrotechnic was made according to the formulation of silver spare (USSR). The ice nucleating properties of silver spare and other five formulations of AgI pyrotechnics in the marketplace in 2011 was tested in the same chamber for comparison with the new pyrotechnics. The results show that the nucleating rates are very low for WMC IN 001 and WMC IN 002, and change less (in 40-55 min) in the temperature range between -7 and -20℃. The aerosol particles produced by WMC IN 001 are identified by environmental scanning electron microscope (ESEM) and energy disperse spectroscopy (EDS). The particle sizes are within 0.02-0.60 μm in diameter, and the mean cube root diameter is 0.2472 μm. WMC IN 001 aerosol has a pronounced bimodal size distribution with particles in the small diameter mode between 0.02-0.10 μm and particles constituting the mode between 0.20-0.55 μm. The relatively large particle size may be one cause for the low nucleating rates.