Air is also called Nitrogen, the advantage it is very stable and is not affected by outside temperatures.
The disadvantage is the bottles are more expensive and to get the number of shots you need much higher pressure than Co2.
You’ll see on a air system or tank figures such as 3000 PSI 48cu.
The 3000 relates to the amount of pressure the tank can hold and the 48 relates to the capacity inside the tank.
The system or tank can be brought either in aluminium or fibre wrap.
The aluminium is cheaper but heavier, the fibre is the opposite, dearer but lighter. The aluminium does not require a cover, the fibre wrap does.
To fill the air systems or tanks requires a scuba air fill station which attaches to a scuba tank which one can purchase from any scuba shop or second hand shop like cash converters when they’re available .