Chemtrail conspiracy theory is an unproven suspicion that long-lasting trails, so-called “chemtrails”, are left in the sky by high-flying aircraft, and that they consist of chemical or biological agents deliberately sprayed for sinister purposes undisclosed to the general public. Believers in the theory argue that normal contrails dissipate relatively quickly, and contrails that do not dissipate must contain additional substances. These arguments have been dismissed by the scientific community: such trails are normal water-based contrails (condensation trails) that are routinely left by high-flying aircraft under certain atmospheric conditions. Although proponents have attempted to prove that the claimed chemical spraying does take place, their analyses have been flawed or based on misconceptions.
Because of the widespread popularity of the conspiracy theory, official agencies have received many inquiries from people demanding an explanation. Scientists and government officials around the world have repeatedly needed to confirm that supposed chemtrails are in fact normal contrails.
The term chemtrail is a portmanteau of the words chemical and trail, as contrail is a contraction of condensation trail. Believers in the conspiracy theory speculate that the purpose of the claimed chemical release may be solar radiation management, psychological manipulation, human population control, weather modification, or biological or chemical warfare, and that the trails are causing respiratory illnesses and other health problems. Contrails are formed at high altitudes (5–10 miles or 8–16 kilometers), and any chemicals released at such a height would disperse harmlessly and fall many hundreds of miles away, or degrade before touching the ground.