Acid Fog

Acid fog creates a billowing mass of misty vapors like the solid fog spell. In addition to slowing down creatures and obscuring sight, this spell's vapors are highly acidic. When you first cast the spell and each round at the beginning of your turn, the fog deals 2d6 points of acid damage to each creature and object within it.

[For Reference]

Solid Fog: You create a 20-foot radius cloud of fog centered on a point you designate within range. In addition to obscuring sight, the solid fog is so thick that it impedes movement. Creatures moving through a solid fog move at half their normal speed and have disadvantage on all melee attacks inside the cloud. The vapors prevent effective ranged weapon attacks (except for magic rays and the like). A creature or object that falls into solid fog is slowed so that each 10 feet of vapor that it passes through reduces the falling damage by 1d6. A creature cannot take a 5-foot-step while in solid fog. Solid fog, and effects that work like solid fog, do not stack with each other in terms of slowed movement and attack penalties.

Unlike normal fog, only a severe wind (31+ mph) disperses these vapors, and it does so in 1 round.