If sulfur were to be used, it would be quickly apparent to everyone concerned.
Although the trails would appear the same, growing in the same manner as they fell, subsequent aircraft would be flying through them. Their occupants would be breathing in dilute sulfuric acid mist at a cabin pressure of 6000 feet. That wouldn't be endurable for more than a few seconds.
The basic oxide of aluminum is refractory, and its fine dust could be breathed in. It wouldn't be good for you in the same way that finely powdered glass isn't. Barium oxide is rather like quicklime. Less pleasant, and nearly as nasty as sulfuric acid mist.
I'm not guessing here. I have worked in petrochemical plants and have breathed most weird things at most times. My favorite is NaO. The one good thing I can say about that is it removes all traces of acne quite quickly.