air

Above any other consideration, it is, together with water, one of the fluids that make life possible on Earth. The set of gases that make up the atmosphere. This gaseous mixture is formed by three main components: nitrogen (N₂), oxygen (O₂) - both in their molecular (diatomic) form - and argon (Ar), whose proportions remain constant in the lower atmosphere and in part of the upper atmosphere (up to about 80 kilometers of altitude, the homosphere). The small abundance of argon compared to nitrogen and oxygen makes it, by definition, a trace gas. In any sample of air we take, just over 99% of its volume is occupied by those three gases (N₂ –78%, O₂–21%, Ar–0.9%, in round numbers), while the rest is made up of trace gases - of highly variable proportions -, such as water vapor, ozone, carbon dioxide, methane, or nitrous oxide, among others, in addition to minuscule solid and liquid particles of different natures in suspension (aerosols). The terms air and atmosphere are frequently used interchangeably, and it is also quite common to identify air with wind.