Air refers to the mixture of gases that makes up the Earth's atmosphere. Air is composed primarily of nitrogen (78%), oxygen (21%), and trace amounts of other gases, such as carbon dioxide, water vapor, and argon.
Air is important in the aerospace industry because it is the medium through which aircraft and other aerospace vehicles move. It is also the source of oxygen that is necessary for the operation of many types of aircraft engines.
Air is also used in a variety of aerospace applications, such as pressurization, cooling, and cabin ventilation. In pressurized aircraft, air is used to maintain a constant atmospheric pressure inside the cabin, regardless of the altitude of the aircraft. Air is also used to cool the engines of some aircraft, and it is used to circulate fresh air through the cabin of an aircraft to provide a comfortable environment for passengers and crew.