The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth creates pressure, absorbs most meteoroids and ultraviolet solar radiation, warms the surface through heat retention (greenhouse effect), and reduces temperature extremes between day and night (the diurnal temperature variation), maintaining conditions allowing life and liquid water to exist on the Earth's surface.

As of 2023, by mole fraction (i.e., by number of molecules), dry air contains 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.04% carbon dioxide, and small amounts of other gases.[8] Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere. Air composition, temperature, and atmospheric pressure vary with altitude. Within the atmosphere, air suitable for use in photosynthesis by terrestrial plants and breathing of terrestrial animals is found only in Earth's troposphere.

Cryogenic air separation on industrial scale started in the beginning of 20th century fostering the development of metallurgy and other branches of industry highly dependent on the availability of oxygen, nitrogen, and finally argon. Cryogenic air separation plants (ASP) are characterized by very good quality of the products, big capacities, and high reliabilities. In spite of other emerging technologies of air separation, cryogenics air separation technology remains the basic technology for oxygen production. Cryogenic air separation plants are most commonly used to produce high purity gaseous products. However, the use of this technology is restricted for the applications needing the gases in high quantities normally above several hundred tons of the separated gases per day. They can produce products as gases or liquids.

The cryogenic air separation technology utilizes difference in boiling points of gases for their separation. It is based on the fact that the different constituent gasses of air have different boiling points and by manipulating the immediate environment in terms of temperature and pressure, the air can be separated into its components. The boiling point of oxygen at a 1 atmosphere pressure and 0 deg C is minus 182.9 deg C and that at 6 atmosphere pressure and 0 deg C is minus 160.7 deg C. The corresponding boiling points of nitrogen are minus 195.8 deg C and minus 176.6 deg C, and those for argon are minus 185.8 deg C and minus 164.6 deg C respectively.

Cryogenic separation is most effective process when any of the three criteria need to be met namely (i) high purity oxygen is needed (higher than 99.5 %), (ii) high volumes of oxygen are needed (greater than 100 tons of oxygen / day), or (iii) high pressure oxygen is needed. Cryogenic air separators take more than an hour to start up. Additionally, since cryogenics can produce such a high purity of oxygen, the waste nitrogen stream is of a usable quality.