Air Composition
Dry air is a mechanical mixture of nitrogen, oxygen, carbon dioxide and more
Air is a mixture of gases - 78% nitrogen and 21% oxygen - with traces of water vapor, carbon dioxide, argon, and various other components.
Air is usually modeled as a uniform (no variation or fluctuation) gas with properties averaged from 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 temperature
- The composition of air is unchanged until elevation of approximately 10.000 m
- The average air temperature diminishes at the rate of 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)
Other components in air
- Sulfur dioxide - SO2 - 1.0 parts/million (ppm)
- Methane - CH4 - 2.0 parts/million (ppm)
- Nitrous oxide - N2O - 0.5 parts/million (ppm)
- Ozone - O3 - 0 to 0.07 parts/million (ppm)
- Nitrogen dioxide - NO2 - 0.02 parts/million (ppm)
- Iodine - I2 - 0.01 parts/million (ppm)
- Carbon monoxide - CO - 0 to trace (ppm)
- Ammonia - NH3 - 0 to trace (ppm)
Common Pressure Units frequently used as alternative to "one Atmosphere"
- 76 Centimeters (760 mm) of Mercury
- 29.921 Inches of Mercury
- 10.332 Meters of Water
- 406.78 Inches of Water
- 33.899 Feet of Water
- 14.696 Pound-Force per Square Inch
- 2116.2 Pounds-Force per Square Foot
- 1.033 Kilograms-Force per Square Centimeter
- 101.33 kiloPascal
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