Changes of the air composition

Considerable changes of the air composition may be observed depending on the height. The ratios between particular gaseous components in the atmosphere at different altitudes are governed by diffusion processes, temperature and pressure. 

The atmosphere layer which is characterized by the change from the turbulent mixing to the molecular diffusion is termed the turbopause below the turbopause and above it there are the homosphere and heterosphere, respectively (Fig. 5.1). 

In the heterosphere, a stratification of gases depending on molar masses, occurring by action of diffusion and gravitation, may be observed. It is possible to recognize 4 layers [10-20] as follows  

1st layer — contains prevalently molecular nitrogen. The change of its composition is affected mainly by the photodissociation of molecular oxygen (biatomic), which is present mostly in its atomic form at a height altitude of 120 km. As a result of molecular diffusion, the nitrogen content gradually decreases. 

2nd layer — contains prevalently atomic oxygen. This extends to an altitude of 1100 km. From this layer we consider the so-called exosphere, characterized by electrically neutral atoms which overcome the earth s gravitation and escape into cosmic space. 

---

The atmosphere structure may be considered from different standpoints. A classification frequently accepted is that connected with change in the vertical direction i.e. the vertical arrangement of the atmosphere in layers dependent on temperature, changes of the air composition at different altitudes, etc. 

---