Graves Smokescreen to Tear Gas

This is just my two cents but I feel Graves' smokescreen is a little useless. Yes, it's good that you deny vision and slow champs that walk through it but what about those who just stand in it? Even while fighting in a teamfight it still barely does anything. I feel that this ability could be better, instead of Smokescreen how about Tear Gas?

Like smokescreen it will blind and slow but for those who stand in it the entire time or are CC'ed in it, breathing the gas will cause damage over time unless they leave the smoke. Making this ability better used in teamfight and in creep control. Otherwise they might as well take the mana cost down from smokescreen because it is pretty poor in damage OR increase the radius of the ability and leave mana cost as is because that too is just as poor.