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Air is a name for the mixture of gases present in the Earth's atmosphere.

Dry air is roughly 79% nitrogen, 20% oxygen, and 1% argon. Air may contain 0-7 % water vapor (the 79%, 20% and 1% become accordingly a little less), and less than 1% carbon dioxide. The composition of air changes with altitude; also exhaled air contains a greater percentage of carbon dioxide than what is inhaled, ca. 4.5%.

Pressure decreases with altitude; this is why aircraft have pressurised cabins. The air pressure inside aircraft cabins is maintained at a pressure higher than that outside, for the comfort of the passengers and crew, although for fuel efficiency reasons the pressure is still slightly lower than at ground level. With a decrease in total air pressure, the partial pressure of all the component gases (including oxygen) decreases. Mountain climbers must carry a supply of oxygen on their way up to the summit of high mountains to ensure the partial pressure of oxygen in their blood is maintained.

Compressed air is often used in scuba diving as a shallow water breathing gas and to inflate buoyancy devices. Compressed air is also used as a source of energy for pneumatic air tools.

Air is one of the classical elements, and is associated with many other concepts, such as the sword suit in the tarot.
Air is a French electronic music duo. Their acclaimed first album Moon Safari was followed by the releases Premiers Symptomes, 10,000 Hz Legend, The Virgin Suicides film soundtrack and Talkie Walkie.
To air an audiovisual production means to broadcast it.
Air is also the name of a well-known renai game by Key, which also created Kanon.