Air is a general term which can mean, among others:
1. The mixture of gases that make up the atmosphere ; 78% nitrogen and 21% oxygen with the balance consisting of smaller amounts of gases including argon, carbon dioxide, neon, helium, and other gases required for breathing;

AIR HANDLING UNIT (AHU): For purposes of this document refers to equipment that includes a blower or fan, heating and/or cooling coils, and related equipment such as controls, condensate drain pans, and air filters. Does not include ductwork, registers or grilles, or boilers and chillers.

AIR PASSAGES: Openings through or within walls, through floors and ceilings, and around chimney flues and plumbing chases, that permit air to move out of the conditioned spaces of the building.