Terrestrial Air
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Air
1. The mixture of gases comprising the earth's atmosphere.
The percent by volume of those gases found in relatively constant amount in dry air near sea level in very nearly as follows:
|
ELEMENT |
% |
| nitrogen (N2) | 78.084 |
| oxygen (O2) | 20.9476 |
| argon (A) | 0.934 |
| carbon dioxide (CO2) | 0.0314 (variable) |
| neon (Ne) | 0.001818 |
| helium (He) | 0.000524 |
| methane (CH4) | 0.0002 (variable) |
| krypton (Kr) | 0.000114 |
| hydrogen (H2) | 0.00005 |
| nitruous oxide (N2O) | 0.00005 |
| xenon (Xe) | 0.0000087 |
This table is from the 1965 edition of the Aerospace Dictionary.
In addition to the above constituents there are many variable constituents. Chief of these is water vapor, which may vary from zero to volume percentages close to 4 percent. Ozone, sulfur dioxide, ammonia, carbon monoxide, iodine, and other trace gases occur in small and varying amounts.
The above composition of dry air is true to about 90 kilometers. See upper atmosphere.
2. The realm or medium in which aircraft operate.
References
This article is based on NASA's Dictionary of Technical Terms for Aerospace Use
