Why are some people afraid of contrails? Why would the appearance of water vapor in the exhaust of a jet inspire feelings of illness and dread? It all began in the 1990s when “investigative journalists” like William Thomas began describing purported plots by the government to inject poisons into the atmosphere via the exhaust trails of jet planes. Chemtrails are defined on the Web site of Internet pundit Jeff Rense

“…as author and airline pilot Patrick Smith tells readers, the contrails consist of not just ice crystals and water vapor but also other byproducts of engine exhaust. These include carbon dioxide, nitrogen oxides, sulfate particles and soot . Some point out that these, in addition to the extra cloud cover, can have negative environmental effects. And conspiracy theorists have nicknamed contrails “chemtrails” under the suspicion that the government is taking advantage of this scientific phenomenon to secretly release other substances into the atmosphere.”