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The chemtrail conspiracy theory posits that some trails left by aircraft are chemical or biological agents deliberately sprayed at high altitudes for purposes undisclosed to the general public and directed by various government officials. This theory is not accepted by the scientific community, which states that they are just normal contrails, as there is no scientific evidence supporting the chemtrail theory.
Because of the popularity of the conspiracy theory, official agencies have received thousands of complaints from people who have demanded an explanation. The existence of chemtrails has been repeatedly denied by scientists and government officials around the world, who say the trails are normal contrails.
The term chemtrail is a combination of the words "chemical" and "trail," just as contrail is a contraction of "condensation trail." The term does not refer to other forms of aerial spraying such as agricultural spraying ('crop dusting'), cloud seeding, skywriting, or aerial firefighting. The term specifically refers to aerial trails allegedly caused by the systematic high-altitude release of chemical substances not found in ordinary contrails, resulting in the appearance of characteristic sky tracks. Supporters of this conspiracy theory speculate that the purpose of the chemical release may be for solar radiation management, psychological manipulation, human population control, weather modification, or biological or chemical warfare, and that these trails are causing respiratory illnesses and other health problems.