Volcanic Ash

You create a 20-foot-radius sphere of scorching ash 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 strong wind disperses it. Creatures starting their turn within the sphere take 2d6 fire damage. Any creatures ending their turn within the sphere must succeed a constitution saving throw or take 2d6 poison damage as choking ash clogs their lungs.

The ash ignites flammable objects not being worn or carried. 

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the radius increases by 10ft for each slot level above 4th.