Amen. But from a different angle.
 
 Any engine using fuel produces water vapor.  You see it in the tailpipes of cars in the winter especially.

Jet engines produce the same thing and you see it as a white trail.

Do you really think there are tanks of chemicals onboard commercial airlines and controlled by the pilot?

Where are these tanks in the airplane? 
 
Who orders them to dump chemicals?

 Where are they instructed to dump chemicals?

Why are the thousands of pilots who run these planes (and have been for decades) completely silent about such a thing?   Because it does not exist.

I have heard of cloud seeding to cause rain.  That is another operation completely and certainly do not use passenger planes.