Phiuhl

Not a true elemental, but what happens when one is killed and has its soul warped. The Phiuhl is a column of hot toxic vapours, often found the Bleak Eternity of Gehenna, the volcanic plane of evil and home of yugoloths.

Being a gaseous cloud, the Phiuhl is without true shape, though some who look into it claim to see faces of misery and sadism. The touch of this creature will leave burns, but this is among the weakest of its abilities. What's worse is to be trapped within the gas of the Phiuhl. As said before, it is extremly toxic, so the Phiuhl merely needs to casually hover around its victim for it to die within minutes.

I know that this creature's probably supposed to be some sort of physical embodiment of volcanic gases, but its description of being green and purple throws me off. Combine that with it gives off poisonous heat, I can only come up with one conclusion.

The Phiuhl is the radiation elemental.