In the quest for the truth regarding Chemtrails, one must sort through information and disinformation.
Disinformation: Contrails don't form below 30,000 ft.
This is a commonly cited oversimplification. Contrails can form as low as ground-level, if the atmospheric conditions are correct, as can occur in Anartica. In Houston, TX, for example, my research shows that contrails typically are seen at altitudes of 33,000 ft. to 43,000 ft. The 43,000 ft. upper limit is probably due to maximum altitude of typical airtraffic, not a physical limit, although a temperature inversion can cap the upper altitude extent of contrails. So the observed altitude thresholds vary geographically.
Disinformation: Contrails don't last longer than 30 seconds.
Normal jet traffic can leave trails that persist for quite some time given atmospheric conditions that are favorable. In my studies, contrails from commercial and passenger jets have left contrails that persisted for as much as two minutes, on one occasion more than 20 minutes. Normal contrails can persist even more if they fly through a pre-existing persistent trail, cloud or other high mosture zone.
Disinformation: Shiptrails are Chemtrails sprayed by jets over the ocean.
The phenomenon known as shiptrails, which are observed over the oceans in some satellite images have been purported to actually be Chemtrails sprayed by jets, however a simple examination of the formation of these trails in timelapse satellite images shows they are created by very slow craft averaging less than 30 MPH. Read more
Disinformation: "It's just commercial traffic!".
Before my trail research was conducted, it was often stated by debunkers that the trails reported by Chemtrailers were just contrails from commercial jets. Research conducted showed that commercial traffic was responsible for contrails that averaged less than a minute of persistence. None of the dozens of commercial observations ever produced the highly-persistent trails that were observed coming from unidentified (military) jets averaging hours of persistence.
Disinformation: The 'Mechanic's Statement'.
This hoax was created by a Chemtrail 'debunker' who uses the online name SprayplanePilot. It supposedly is a statement by an airline mechanic who stumbles upon extra pipes and tanks on a commercial plane, gets in trouble with management for not minding his business, and shares his story as a "concerned citizen". At the time of this writing, this hoax is posted at Carnicom's site, linked