Link (thanks Oliver)
Many theories say that the smoke released from these planes is poison, and others think it is a biological virus. What do you think?
Google has a research project about removing condensation trails, answering the question:
Contrails, short for condensation trails, are the line-shaped clouds that you sometimes see behind airplanes. They form when water vapor in the air condenses around tiny particles of soot and other pollutants emitted by airplane engines.Google Research