Air Definition in Science

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The term "air" refers to gas, but exactly which gas depends on the context in which the term is used. Learn about the modern definition of air in scientific disciplines and the earlier definition of the term.

Modern Air Definition

Air is the general name for the mixture of gases that makes up the Earth's atmosphere. On the Earth, this gas is primarily nitrogen (78 percent), with oxygen (21 percent), water vapor (variable), argon (0.9 percent), carbon dioxide (0.04 percent), and many trace gases. Pure air has no discernible scent and no color. Air typically contains dust, pollen, and spores. Other contaminants are referred to as air pollution. On another planet (e.g., Mars), the "air" would have a different composition. There is no air in space.

Older Air Definition

Air is also an early chemical term for a type of gas. Many individual "airs" made up the air we breathe. Vital air was later determined to be oxygen, phlogisticated air became nitrogen. An alchemist might refer to any gas released by a chemical reaction as its "air."