4.3. Chemical composition of the atmosphere

Chemical composition of the atmosphere

The atmosphere is made up of air (a homogeneous mixture of gases in different proportions), and atmospheric dust, small particles that float in the air (pollen, fine sand, volcanic ash, etc.).

The composition of the air is:

78.08% Nitrogen. It is an inert gas that does not react with almost any substance. It is an inert gas.
20.95% Oxygen. It combines with other substances by oxidizing them. Needed for respiration. It is soluble in water. It is generated in photosynthesis (plants, algae and some bacteria).
0.93 Argon.
0.03% CO₂. It is obtained from the combustion of fossil fuels and the respiration of living beings. Plants use it in photosynthesis.
Other gases (O₃, Neon, Hydrogen, Helium, Methane, Krypton, etc.).
Water vapor. It comes from the evaporation of surface water and the transpiration of plants.

By Nicolás Lichtmaier [Public domain], via Wikimedia Commons

Air density decreases at high altitudes. Most of the air mass is in the low-lying areas, attracted by the force of Earth's gravity. On the other hand, in the higher areas, the air is thinner and lighter, with less density.

Air density and atmospheric pressure decrease height.

Curiosity: Altitude sickness

Altitude sickness is caused by the non-adaptation of the body to the lack of oxygen with altitude. It usually occurs between 2400 meters and 8000 meters of altitude. It occurs more frequently among those under 50 years of age, and among those who usually live at less than 900 meters of altitude.

It can cause serious problems if the altitude is very high and you have climbed there at a high speed. If you descend to lower levels, the symptoms of altitude sickness disappear.

As atmospheric pressure decreases with altitude, there is less oxygen available to the body. Lhe pulmonary alveoli cannot oxygenate the same amount of blood as if it were at higher pressure. The body slowly adapts to these circumstances by producing more red blood cells so that they can carry the little oxygen that comes from the air.

Some athletes train at high altitude, especially if their competition is going to be in high areas, to produce a greater number of red blood cells. Other cheating athletes dope themselves by injecting the hormone erythropoietin (EPO) to achieve these effects.

Musical minutes

What do you think about the composition of the air that Mecano tells us in his song "Air"?

Retroalimentación

In the song it is said that the air is made up of oxygen, nitrogen and argon. Not bad, but do not forget that there are more gases in the composition of the air.

**Composition of the atmosphere free of water vapor, by volume**
Gas	Volume (%)
volume percentage
Nitrogen (N₂)	78,084
Oxygen (O₂)	20,946
Argon (Ar)	0.9340
Carbon dioxide (CO₂)	0.035
Neon (Ne)	0.001818
Helium (He)	0.000524
_{Methane (CH}4₎	0.000179
Krypton (Kr)	0.000114
Hydrogen (H₂)	0.000055
Nitrous oxide (N₂O)	0.00003
Carbon monoxide (CO)	0.00001
Xenon (Xe)	0.000009
Ozone (O₃)	0 to 7×10 ⁻⁶
Nitrogen dioxide (NO₂)	0.000002
Iodine (I₂)	0.000001
Ammonia (NH₃)	0.0003
Not included in dry air:
Water vapor (H₂O)	~0.40% in upper layers of the atmosphere; usually 1 to 4% on the surface.

Interactive Activity: Calculate the amount of different gases in your room.

Interpreting a graph: The elements of the atmosphere (click help).

Interactive Activity: Cyclists and Altitude.

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