A new song by Lana Del Ray, called "Chemtrails Over the Country Club," through its popularity is making worse a misconception about the clouds left over from jet engine exhaust. Contrails (not chemtrails) happen when tiny pieces of carbon and other byproducts of combustion become nuclei for ice crystal formation at very high altitudes. When the weather up there is dry, the contrails dissipate quickly, but when it is humid up there, contrails can linger for hours.
A popular but misguided conspiracy theory holds that these lingering contrails are actually laced with chemicals by the Federal Government for nefarious purposes including mind control and chemical dependency of the general, unsuspecting population. They call these "chemtrails." Some people who have never heard of the conspiracy theory have managed to confuse the words and now refer to any jet trail as a chemtrail. Please, the word is "contrail."