空气 (kōngqì) is a noun meaning "air" or "atmosphere." It refers to the gaseous substance surrounding us and can also describe the mood or feeling of a place. For example, 房间的空气中 means "in the air of the room."
打开窗户,让新鲜空气进来吧。
Dǎkāi chuānghù, ràng xīnxiān kōngqì jìnlái ba.
Open the window and let some fresh air in.
房间里的空气有点闷,我们出去走走。
Fángjiān lǐ de kōngqì yǒudiǎn mèn, wǒmen chūqù zǒuzou.
The air in the room is a bit stuffy; let's go out for a walk.
今天的空气质量不太好,出门戴口罩吧。
Jīntiān de kōngqì zhìliàng bù tài hǎo, chūmén dài kǒuzhào ba.
The air quality today isn't very good; wear a mask when going out.