I hope he is pulling our leg
A simple Spectrograph of these trails should tell of their composition. Anyone with access to a High School Physics Lab should have the necessary equipment.
Not that it is worth the time for such a silly thing.
Like I said above, if you want to dump chemicals on a target, spreading it out in the Stratosphere is not the way to do it. You would only succeed in it dispersing around the globe where it would take years for it to fall back to the Earth. By then, it would be so diluted, it would be ineffective.