This EPA fact sheet explains that aircraft contrails are line-shaped clouds made of ice crystals formed when water vapor in jet engine exhaust mixes with cold air at high altitudes. Contrails are composed primarily of water and do not pose direct health risks, but persistent contrails can spread into cirrus cloud cover and may influence the Earth's climate by affecting atmospheric cloudiness. Scientists estimate that persistent contrails cover about 0.1 percent of the Earth's surface on average, with the highest concentrations occurring over heavily trafficked air corridors like Europe and the United States.Open full document
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This EPA factsheet describes the formation, occurrence, and climate effects of aircraft condensation trails (contrails). It explains how contrails form from water vapor in jet engine exhaust under cold, humid atmospheric conditions, and distinguishes between short-lived and persistent contrails. The document also addresses the potential climate impacts of persistent contrails and their relationship to aviation’s overall contribution to climate change.