Chemtrails
Chemtrails refers to a conspiracy theory that the government is using aircraft to secretly spray chemical or biological agents into the atmosphere for various nefarious purposes, such as mind control, sterilization or weather manipulation, and that these chemicals create visible plumes in the sky similar to aircraft condesation trials (contrails). Conspiracy theorists claim that these "chemtrails" are distinguishable from normal contrails because they do not dissipate as quickly. Such claims have frequently been debunked by the scientific community.