HAARP is the big thing nowadays. The airborne chemical tests were more of a 1970's thing, when declassified documents prove that "harmless" bacterial agents were dispersed over NYC, Chicago, and LA to test the spread of these biological agents in the cities. The harmless bacteria cause flu-like outbreaks in some sensetive people and at least three reported deaths.
I can't discredit the chemtrail theory completely, as I've seen some myself. I documented some of it in this thread:
http://www.tfproject.org/tfp/showthr...threadid=38268