By Henry Fountain
Conspiracy theories can be stubborn, particularly in the echo chamber of the internet.
One persistent belief in some quarters is that the government — or business, perhaps — is deploying a fleet of jet aircraft to spray chemicals into the sky to control the population, food supply or other things.
As evidence, they point to what they call “chemtrails,” which are more commonly known as contrails, or condensation trails, produced at high altitudes as water vapor in jet engine exhaust condenses and freezes.
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