Your coworker must be an Art Bell fan.
First off "chemtrails" look like contrails because they are contrails. Contrail is from condensation trail. A good article on them can be found here http://asd-www.larc.nasa.gov/SCOOL/contrails.html
Now, conspiricy theorists insiste that the US gov't is sparying citizens with chemicals/viruses surepticiously. That's right, the United States Government. The same government who couldn't hide a blow-job in the oval office. The same government who have continually failed to keep their nuclear secrets a secret. The same government unable to keep a few microphones in a hotel secret. The same government who couldn't even succesfully sell arms to a third world nation without getting in deep nfbsk! (end rant)(
The first point I want to make is that the contrails are very high up. Usually they occur behind aircraft with a flight level in excess of 30,000 feet. This is a very ineffective altitude to spary *anything* at because: 1) If it is a liquid, it will become vaperous at the speed they are traveling. The liquid will then follow whatever whims the weather has in store for it, but typically it would get locked into the prevailing winds at that altitude and (if it comes down at all) would come down in the atlantic. 2) If it is a solid, the dispersion would be nearly impossible to controll.
Other points. The 'Highflyers" making the contrails are actually fairly easy to identify. Buy a scanner and tune in to the local air traffic controll frequency. You can essentially play a game "plane spotting". In almost every case, you'll find that the "chemtrails" are comming from regular passanger flights.
You're more likely to see contrails when it is fairly warm out (i.e. you're sitting in the effects of an upper ridge). This, at the least, suggests that the trails are weather dependant.
Finally, clouds are not in any way solid. They wouldn't effect anything you're trying to drop or spray. If it made it down that far, it would fall through the cloud. Given that, and given that the millitary is sometimes smart... Wouldn't you think it would be logical to, if you are trying to be secretive about things, spray your chemicals when there is a blanket of low cloud that would prevent people from noticing?
Chemtrails are contrails. Contrails are condensation trails. They are, essentially, vapour comming off the engine and turning to small ice crystals which hang in the air. Basically, they're clouds.
Jon Up North