open air; outside air
Refers to the air outdoors, often in contrast to indoor air. Common in contexts like ventilation, weather, or exposure to the elements.
Let's open the window and let in some fresh air.
The outside temperature is low, so I turned on the heater.
If you don't get some outside air for a while, you start to feel unwell.
These machine parts rust easily when exposed to outside air.
The air conditioner draws in outside air to refresh the air in the room.