exterior vs open air

exterior and open air both are nouns.

Word	Noun	Adjective	Verb	Adverb
exterior	Yes	Yes	No	No
open air	Yes	No	No	No

As nouns, open air is a hyponym of exterior; that is, open air is a word with a more specific, narrower meaning than exterior:

Other hyponyms of exterior include open, out-of-doors, outdoors.

exterior (noun)	open air (noun)
the outer side or surface of something	where the air is unconfined
the region that is outside of something

exterior (adjective)	open air (adjective)
situated in or suitable for the outdoors or outside of a building