chemtrail

An Airbus A340's engines leaving a water condensation trail (contrail) – miniature clouds formed by the engine exhaust

The chemtrail conspiracy theory /ˈkɛmtreɪl/ is the erroneous belief that long-lasting condensation trails left in the sky by high-flying aircraft are actually "chemtrails" consisting of chemical or biological agents, sprayed for nefarious purposes undisclosed to the general public. Believers in this conspiracy theory say that while normal contrails dissipate relatively quickly, contrails that linger must contain additional substances. Those who subscribe to the theory speculate that the purpose of the chemical release may be solar radiation management, weather modification, psychological manipulation, human population control, biological or chemical warfare, or testing of biological or chemical agents on a population, and that the trails are causing respiratory illnesses and other health problems.