You create a 20-foot-radius sphere of toxic smog centered on a point within range. The sphere spreads around corners, and its area is heavily obscured. It lasts for the duration or until a wind of moderate or greater speed (at least 10 miles per hour) disperses it.

When a creature enters the spell's area for the first time on a turn or starts its turn there, that creature must make a Constitution saving throw. On a failed save, a creature takes 3d6 poison damage and is poisoned for 1 minute. On a successful one, a creature take half as much damage and isn't poisoned. Creatures are not affected if they hold their breath or don't need to breathe. 

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d6 for each slot level above 3rd.