Bubble

You create a large bubble of clean air in a 5-foot radius sphere. The bubble keeps all free flowing gasses and liquids from entering or exiting it, but solid objects, and magical effects are able to freely move through it. The quality of air at the time of the spell's casting is the quality within the bubble. The bubble has enough air to last a number of hours equal to its radius. If the spell is cast whilst completely submerged, then clean air is produced in the bubble at its casting. The radius of the sphere cannot be altered after casting.

As a bonus action, you can make the bubble travel up to 20 feet. If it travels more than 200 feet away from you, the spell ends.

If you cast this spell with a spell slot higher than 1st level, the radius of the sphere increases by 5 feet per spell slot level.