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Engineering ToolBox > Air Composition
Air is a mixture of gases, 78% nitrogen and 21% oxygen with traces of water vapor, carbon dioxide, argon, and various other components. We usually model air as a uniform (no variation or fluctuation) gas with properties that are averaged from all the individual components.
| Gas | Ratio compared to Dry Air (%) | Molecular Mass - M - (kg/kmol) | Chemical Symbol | Boiling Point | ||
| By volume | By weight | K | (oC) | |||
| Oxygen | 20.95 | 23.20 | 32.00 | O2 | 90.2 | -182.95 |
| Nitrogen | 78.09 | 75.47 | 28.02 | N2 | 77.4 | -195.79 |
| Carbon Dioxide | 0.03 | 0.046 | 44.01 | CO2 | 194.7 | -78.5 |
| Hydrogen | 0.00005 | ~ 0 | 2.02 | H2 | 20.3 | -252.87 |
| Argon | 0.933 | 1.28 | 39.94 | Ar | 84.2 | -186 |
| Neon | 0.0018 | 0.0012 | 20.18 | Ne | 27.2 | -246 |
| Helium | 0.0005 | 0.00007 | 4.00 | He | 4.2 | -269 |
| Krypton | 0.0001 | 0.0003 | 83.8 | Kr | 119.8 | -153.4 |
| Xenon | 9 10-6 | 0.00004 | 131.29 | Xe | 165.1 | -108.1 |
The water or vapor content in air varies. The maximum moisture carrying capacity of air depends primarily on the temperature.
The composition of air is unchanged until the height of approximately 10.000 m.
The average air temperature diminishes at the rate of about 0.6oC for each 100 m vertical height
"One Standard Atmosphere" is defined as the pressure equivalent to that exerted by a 760 mm column of mercury at 0oC sea level and at standard gravity (32.174 ft/sec2).
More about Temperature, Density, Specific heat, Thermal Conductivity - the properties of air.