The most important gases in the atmosphere are nitrogen and oxygen, the others are considered as atmospheric pollutants. 1. Nitrogen: constitutes 78% of the volume of the air. It is made up of molecules that have two nitrogen atoms, so that their formula is N2. 2. Oxygen: represents 21% of the volume of the air. It is formed by molecules of two oxygen atoms and its formula is O2. It is a very reactive gas and most living beings need it to breathe. 3. Other gases: the most abundant is argon (Ar), which contributes 0.9% to the volume of air. It is a noble gas that does not react with any substance. 4. Carbon dioxide: is made up of molecules of a carbon atom and two oxygen atoms, so its formula is CO2. It represents 0.04% of the air volume.
