Definitions for open air
Random House Webster's College Dictionary
Origin of open air:
outdoors, out-of-doors, open air, open(adj)
where the air is unconfined
"he wanted to get outdoors a little"; "the concert was held in the open air"; "camping in the open"
in the open air
"an alfresco lunch"; "an open-air theater"
Kernerman English Learner's Dictionary
It felt great to be out in the open air.