For a while now I've followed the chemtrail versus contrail ideology with interest. Actually, with amused interest. From the plausibility standpoint alone, assuming that the USAF really is delivering a potentially harmful agent from, say, thirty or forty thousand feet, it isn’t a very efficient method. The dilution factor from that height WOULD BE ENORMOUS. Maybe they're utilizing a homeopathic principal? Crop dusters would do a much better job!