tall in the atmosphere,ice crystals are born in thin, wispy cirrus. Most of this ice birthing, or what researchers call ice nucleation,is initiated on particles of soot, dust, or compounds,or other droplets. Researchers at Pacific Northwest National Laboratory, Michigan Technological University, or Los Alamos National Laboratory studied a variety of soot particles they produced from a diesel generator. They emulated soot-ice nucleation in super-cold temperatures found in cirrus,up to -50° C (-122° F). The research showed that all the particles were similarly efficient at nucleating ice, but that altering the properties of soot changes the ice crystal concentration observed in clouds.
Source: phys.org