The air around us is a mixture of gases, mainly nitrogen and oxygen, but containing much smaller amounts of water vapor, argon, and carbon dioxide, and very small amounts of other gases. Air also contains suspended dust, spores, and bacteria. Because of the action of wind, the percent composition of air varies only slightly with altitude and location. The table indicates the composition of a typical sample of air after all water vapor and suspended particles have been removed. The amount of water in the air varies tremendously with location, temperature, and time.
Air is the commercial source for many of the gases it contains.
It is separated into its components by fractional distillation of liquefied air. Before air is liquefied, water vapor and carbon dioxide are removed, because these substances solidify when cooled and would clog the pipes of the air liquefaction plant. The dry, CO 2 -free air is compressed to about 200 atmospheres. This compression causes the air to become warm, and the heat is removed by passing the compressed air through radiators. The cooled, compressed air is then allowed to expand rapidly.