This spell is a part of the Air's Constant Flow spell chain and can be found in the Air's Constant Flow rune stone.
Wisps of Death showed the angered aeromancer what patience made possible - a single breath turned against a single target, quiet enough that no one else in the fight ever needed to know it had happened at all. Choking Gas is what happens when the anger stops being patient. This isn't a poison slipped carefully into one person's air anymore. It's the aeromancer flooding the air itself, all of it, all at once, and no longer particularly caring who happens to be standing in it when they do - the anger of the Tornado damaging all in its wake with no concern or notice as to who that might entail.
A putrid gas rolls out to fill a 4x4 space around the aeromancer, thick enough to choke on, indifferent to whose lungs it reaches. Ally and enemy alike take 5d12 damage every round they remain caught inside it - the aeromancer does not spare their own, not here, not this time. Only the aeromancer themself stands untouched, the one calm point in air that's turned against everyone else in it - the eye of the storm itself. Escaping the cloud, or waiting for it to finally disperse after 1d8 rounds, doesn't end the danger either - what's already been breathed in keeps working, 1d8 poison damage every round from there, until it's cured or the body simply gives out. Unlike Wisps of Death, at least this much can be undone, if someone with the means to cure it gets there in time.
It's a messier kind of anger than Wisps of Death ever was - louder, wider, less controlled - and the aeromancer knows it. But some rage doesn't leave room to aim carefully, and by the time Choking Gas is called for, aiming carefully was never really the point anymore.
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