O atmospheric air it consists of a mixture of different gases, such as the nitrogen, oxygen, carbon dioxide and noble gases. Oxygen and nitrogen are the most abundant gases, with the other gases found in smaller amounts. In addition to the aforementioned gases, atmospheric air also presents Steam (whose quantity depends on some factors such as climate, temperature and location), which is presented in the form of fog, clouds and rain. In the air we also find pollutants, dust, ash, microorganisms and pollen in suspension.
O oxygen(O2) present in the atmospheric air is extremely important for the maintenance of life on the planet, as it is the gas used in the breathing of all living beings and is also necessary for the combustion. Atmospheric air is estimated to be composed of approximately 21% oxygen.
O nitrogen(N2) it makes up approximately 78% of the atmospheric air, and is extremely important for all living beings, as it participates in the formation of various organic molecules necessary for its metabolism. Of all living organisms, only a few microorganisms are able to capture nitrogen (nitrogen cycle) available in the atmosphere and degrade it so that living beings can enjoy it.
O carbon dioxide(CO2) it is found in very small proportions in the atmosphere, contributing only 0.03% of the air composition. It is an extremely important gas for photosynthesis by plants, and it is released into the atmosphere through combustion and also through the breathing of animals.
Among the noble gases that are part of the composition of the air, we can mention: argon (Ar), neon (Ne), radon (Rn), helium (He), krypton (Kr) and xenon (Xe), being that they make up about 0.93% of the atmospheric air. These gases do not produce any type of chemical reaction with other substances and are therefore considered noble.
O Steam which also participates in the composition of the air comes from the evaporation of water from rivers, seas and lakes, breathing of beings living, plant transpiration, soil water evaporation and waste water evaporation (stool and urine from animals).
Source: Brazil School - https://brasilescola.uol.com.br/biologia/composicao-do-ar.htm