Elemental Affinity requires electrified surface for Aerothurge. As we known, making electrified surface required at least 2 step ：
none->water/blood->electrified water/blood (not talking about the electrified cloud which required more steps).
But for other school magic, it's Elemental Affinity surface is easier to make with 1 step.
My suggestion is considering cloud surface as the Elemental Affinity surface for Aerothurge as well. Some Aerothurge magic are cloud related, and the cloud is a kind of air, it's reasonable.
Also this change will make some interesting combination of Aerothurge magic: Smoke Cover + Smoke Cover then cast long range Aerothurge magic inside the smoke while other can't see you inside the smoke.
