Chemtrail is actually a misnomer because there aren’t too many chemicals in them! They’re very similar to clouds and are mostly ice crystals that form from the exhaust of planes. The actual name for them is contrails, which is short for condensation trails.

It’s really cold at high altitudes where planes fly, so water in the air can freeze to form these trails. So you might ask why we only see this phenomena when planes pass by. The water that is in the air at high altitudes is super cooled, which means its temperature is below its freezing point, but it still hasn’t solidified. In order to solidify, it needs something to agitate it or act as a template (chemists call this a seed crystal) to begin the crystallization process. You can see this in the picture I attached where the seed crystal induces a crystallization of the chemicals in the beaker.

The soot that is produced from burning jetfuel is exhausted by planes and acts as this seed crystal for water vapor in the air. So there will be small amounts of chemicals that come from burning jetfuel (sulfates, soot, carbon dioxide, and nitrogen dioxide), but these chemicals are the same ones that are produced when a car burns gas for example.