A mixture of individual gases. The gaseous mixture surrounding the earth. Standard density of dry air, free of carbon dioxide (0 °C, 101,325 kPa) is equal to 1,2928 g/L. (density of 1.2928 kg/m3 at a temperature of 273 °K and a pressure of 101.325 kPa).
It is mainly composed of three gases: nitrogen (about 78%), oxygen (about 21%), and argon (about 1%). Together, these three gases make up 99.96% of dry air. All three can be economically recovered as industrial gas products. Standard dry air also contains a small amount of carbon dioxide, and very small amounts of neon, helium, krypton, hydrogen and xenon (see table below).
Water vapor (humidity). The amount of water vapor in air at ground level can vary quite a bit – from almost zero to about 5 percent. Many factors influence the amount of humidity in the air at a given location and time.
Other constituents (which are usually present in trace amounts) which reflect local conditions
notes:
- (A) Mole fraction is sometimes referred to as volume fraction; these are identical for an ideal gas only.
- (B) ppm: parts per million by molecular count
- The total ppm above adds up to more than 1 million (currently 83.43 above it) due to experimental error.
- (C) The concentration of CO2 has been increasing in recent decades, as has that of CH4.
- (D) Water vapor is about 0.25% by mass over full atmosphere
- (E) Water vapor varies significantly locally