Chemtrails aren't real, they are just conspiracy theory nonsense that discredits real environmentalists and genuine issues of toxic aircraft emissions.

 http://en.wikipedia.org/wiki/Chemtrail

Have fun...

 http://contrailscience.com/how-to-debunk-chemtrails/

Meteorology 101

When you are shown pictures of purported "chemtrails" call attention to the vague whispiness in the sk near them. That's a sign that the air aloft is superstaurated. Water vapor wants to condense into droplets (cloud) but can't do that as fast as it would like for lack of "seeds" (surfaces on which to condense).

Under dry (far from saturated conditions aloft) when an airplane flies through depositing in its wake fine droplets of water from the burned fuel (the H in the fuel has burned to H2O) these would revaporate to water vapor and the contrail fade away behind the plane. But when the air through which the plane is flying is saturated or super saturated with water vapor these droplets serve as seed for cloud formation. In which case the contrails persist or even grow into those linear clouds being misidentified as "chem trails".

PLEASE NOTE: This is not (nor is it intended to be) a disclaimer about the existence or non-existence of substance trails being intentionally deposited by aircrft. However note that there is NO good reason to suppose any such real chemtrails would be visible to the eye. Very few chemicals would result in visible trails. This is just about the "evidence" being presented by believers in chemtrails.