Because air is a mixture, not a compound, it can be separated into its components. Air can be compressed at the point of use for most practical applications. For most practical purposes, the air composition is taken to be 78 percent nitrogen and 21 percent oxygen by volume, and to be 75.5 percent nitrogen and 23.2 percent oxygen by weight. Trace impurity levels may vary with geographic locations or with proximity to industrial areas or highways carrying dense traffic. This composition remains relatively consistent in altitudes up to 70,000 feet.
Air meeting particular purity specifications has many important applications.
Some of these applications include medical, undersea, aerospace, and atomic energy fields. Air may be compressed from the atmosphere and purified by chemical and mechanical means. It may also be synthetically produced from already purified major components nitrogen and oxygen. Nonflammable Gas DOT ID No.