Chem trails are visible vapor trails left in the sky behind an aircraft. Chem trails appear as white streaks in the sky and contain byproducts of the condensation left behind by aircrafts with jet engines.
Large jet engines release byproducts through their exhaust as they travel. Water vapor is one of the components of this extremely hot and humid air. The atmosphere where jets typically fly is cold, sometimes lower than negative 40 degrees, and has low vapor pressure. When jet engines release hot air into a cold atmosphere with low vapor pressure, condensation results. The water vapor released from the engine converts to water droplets, which becomes ice crystals. These crystals become what look like clouds forming behind the jet. These cloud-like streaks are called contrails, which is short for condensation trail.
Contrails do not just contain water vapor, however. Other byproducts, such as carbon monoxide, sulfates and nitrogen oxides, are mixed with the vapor, making them a possible cause of environmental effects in the atmosphere. Because these trails contain more than just condensation, they have been dubbed chem trails. Chem trails are an issue of mistrust in some people because some believe the government is releasing other substances along with them.