The air we breathe consists of a mixture of gases and solid and liquid particles. Its composition is not constant, it can in fact vary from place to place and over time. Leaving aside the water vapour, atmospheric dust and other variable components, we find that the composition of the air is practically constant. Nitrogen and oxygen, equal to 78.08% and 20.95% by volume, respectively, are the two main components of the atmosphere. The remaining 1% consists of:
- argon, equal to 0.93% by volume, an inert gas like nitrogen;
- carbon dioxide (CO2), equal to 0.03%, of natural and anthropogenic (i.e. generated by the activities carried out by man, such as combustion processes) origin, plays a key role in the greenhouse effect;
- other gases such as neon, krypton, xenon, hydrogen and others, which together make up only 0.01% by volume of the atmosphere.
