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.
窓を開けて外気を取り入れましょう。
Let's open the window and let in some fresh air.
外気温が低いので暖房をつけた。
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.
The air conditioner draws in outside air to refresh the air in the room.
These machine parts rust easily when exposed to outside air.