evidence: Chemtrails: An Overview of The Phenomenon [...] The term contrail is a contraction of condensation and trail, as chemtrail is of chemical and trail. The first one is used to name trails left in the sky by aircrafts under certain atmospheric conditions. Some people argue that when contrails do not dissipate quickly is because contain substances added and sprayed for sinister purposes undisclosed to the population (weather modification and biological and/or chemical war are the most common). [...] official statements on the non-existence of chemtrails have not discouraged the proponents of the theory of chemtrails.