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The air is composed of a mixture of several gases and forms the Earth's atmosphere.
The composition of air[edit | edit source]
- Nitrogen: 78.08%
- Oxygen: 21%
- Argon: less than 1%
- Carbon dioxide (CO2): 0.038%, that is, 380 ppm (parts per million)
- Miscellaneous noble gases
The most important gas by quantity is nitrogen (more precisely dinitrogen, N2) which represents 78% or more than 3/4 of the air. It's an inert gas, which is to say that it cannot have a chemical reaction with other things, and only certain types of mushrooms can use it directly.
The next component is dioxygen (O2), more often called oxygen, which represents 21% of the air. It's the one we take in when we breathe. It also allows fire to burn: it's oxidising.
Argon (Ar) represents a bit less than 1%; carbon dioxide or carbonic gas, 0,038%. following up, there are other gases making up even smaller parts of the air
The quantity of CO2 was 0.028% before the Industrial Revolution started in Europe. Since it is a gas which contributes to the greenhouse effect, its increase is considered a main cause of the global warming, i.e. a long-term increase in average temperatures on Earth as measured over many decades.
The air also contains several rare gases. In decreasing percentages, these are: neon, helium, nitrogen monoxide, krypton, methane, dihydrogen, nitrogen protoxide, xenon, nitrogen dioxide, ozone, radon.
In addition to these "permanent" gases, there is water vapour in the air (between zero and 7%). Water vapour is no more visible than a gas. When we see it, for example as a cloud, then it means that the vapour actually turned into very small drops of liquid water (so it's no longer a gas).
The mass and weight of air[edit | edit source]
Air does have a mass, and for a large volume, this mass is very significant. Under ordinary conditions, the mass of a cubic meter of air is about 1.2 kg. This means that a room 3 meters wide, 4 meters long and 2.5 meters high contains 36 kg of air.
Air pressure[edit | edit source]
On Earth, the air is responsible for atmospheric pressure.