Falconer 1
let's assume the atmospheric conditions described in these phenomena have been around for a long while..
Actually I recall reading a study that was trying to quantify why the size of super-cooled water droplets was increasing. Speculation was that it was due to several things, one of them being the decrease in particulate matter in the atmosphere due to lower levels of certain types of pollution. The end result from our perspective was that the icing models that had been used to certify a/c deicing systems were no longer valid and would have to be reevaluated. A link to the study when I can locate it again.