The chemtrail conspiracy theory posits the erroneous[1] belief that long-lasting condensation trails are "chemtrails" consisting of chemical or biological agents left in the sky by high-flying aircraft, sprayed for nefarious purposes undisclosed to the general public.[2] Believers in this conspiracy theory say that while normal contrails dissipate relatively quickly, contrails that linger must contain additional substances.[3][4] Those who subscribe to the theory speculate that the purpose of the chemical release may be solar radiation management,[3] 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.