Roberto, The composition of the atmosphere at different levels partially determines why there are different layers in the atmosphere. There is generally a greater concentration of ozone throughout the Stratosphere than in the Troposphere. The Stratosphere is either non-existent or very hard to detect at the poles. The other atmospheric components are about the same as in the Stratosphere.
Temperature increases with altitude.
The bulk of the air is nitrogen and monatomic oxygen. Above the Thermosphere is the Exosphere, where you can hardly say that there is any atmosphere. I might add that the depth of the atmosphere and it's layers varies with season and latitude, with the atmosphere being deeper and with better defined layers at the equator than at the poles. This is a very rare occurrence. Argonne National Laboratory, Division of Educational Programs, Harold Myron, Ph.D., Division Director.