Define "air". Some people define it as a sense of space which can be achieved with a good room or hall reverb. Other people (especially those bottle-fed Mackie boards) define it as a boost around 16kHz.

A sense of space. Is what I am after.

Good room, detailed pres, reverb, boosting high freq.

several factors, dito, the recording art wrote:

Good room, detailed pres, reverb, boosting very* high freq.

plus a very good stereo placement can help to add the sense of overall "space"

* edited by me, in sensible amounts unless you hate dogs or want to mix for whales, LOL.