its a popular conspiracy theory that poses that the trails of condensation left by high-flying aircrafts are actually made of chemicals that can do everything from poison crops to control the weather.
According to the chemtrail conspiracy theory, long-lasting trails left in the sky by high-flying aircraft are chemical or biological agents deliberately sprayed for sinister purposes undisclosed to the general public. (control the masses)
Jet engines spew out very hot air. Because water vapor is one of the byproducts of the exhaust, the air is also very humid. However, high in the atmosphere where these jets fly, the air is typically very cold - often lower than -40 degrees Fahrenheit. Additionally, the atmosphere up there is often of low vapor pressure, or the force exerted by a gas on the surrounding environment.
The "chemtrails" label is usually applied to these longer contrails, with their very persistence put forward as "evidence" that they cannot be normal contrails.