I daresay that would be a lot less effective than you might expect. See the Moscow theater hostage situation[1][2] for what happens when trying to use it on a fixed target with ground level access. Imagine how much harder that would be from an air-drop, and the concentration gradient you'd end up with. Individual dispensers, cluster-bomb style might help a bit, but I still think you'd end up killing anyone close-by if you wanted it strong enough to permeate buildings.
Calling in a heavy smoke/CS drop and then retreating might be a sensible option, although I don't think there's nearly enough (public) information for anyone to judge definitively on the correct course of action in this instance.
[1] https://en.wikipedia.org/wiki/Moscow_theater_hostage_crisis