“Chemtrails” When stratospheric air is very clean and stable it may contain MORE water vapour than it does when it is described as having 100% Relative Humidity. The slightest disturbance to it will cause ice crystals to precipitate out of it. It cannot go into super-saturation if there are ANY nucleative materials of any sort in this air. Here is just such a case, which occurs on occasion in the sub-tropical stratosphere. The trail forms by “burst condensation” into super-cooled droplets which are microscopic initially and can refract sunlight byinterference. Over a small space of time these droplets grow progressively as water vapour deposits more supercooled water into them. As they progressively increase their size they run through a progression of light frequencies which they interfere with. This is NOT a refraction effect.