Air density
The mass of air per unit volume, usually expressed in kg/m3. Along with pressure and temperature, it is one of the fundamental variables in the theoretical study of the atmosphere. At sea level and under the standard conditions established by the ISA atmosphere, it takes an approximate value of 1.225 kg/m3. Air density, like atmospheric pressure, decreases with altitude, its decrease being particularly marked when ascending through the troposphere and the stratosphere. The same does not happen with the proportion of nitrogen and oxygen (N2 /O2) making up the gaseous mixture, which remains approximately constant in the first 80 kilometers of atmosphere (homosphere). Its density decreases with altitude, but not its proportion. Above that elevation - within the domains of the ionosphere -, the air is highly rarefied, its density is very low, and stable molecules cease to exist, since at those atmospheric levels solar radiation arrives almost unattenuated, is highly energetic, and literally breaks apart the gaseous molecules. A kind of "electron cloud" forms up there, made up mostly of ions, which are good conductors of electricity.