Condensation and chemical trails

A friend posed the question, what comes out of airplane engines? Con or Chem trails? It’s a question I can’t resist answering, I’m hopefully telling you something you already know?

Condensation trails are what comes out of plane engines. Water vapour from the engines condenses out onto dust particles in the upper atmosphere. They cause the characteristic long thin trails up high in the sky. On the other hand chem trails were the US using crystals of silver iodide which is a harmless salt. It acted as nucleation  point for water droplets and was washed out of the clouds it had been released into. They used it to make rain during droughts, I’m not sure if that is still the case.

There is a Kate Bush song about it which I’ve forgotten. We had to learn a few of them a few years ago I can’t remember which one.