Is relatively uniform because of mixing by strong winds. Tropopause marks the boundary with the stratosphere. Air temperature is stable or increases with altitude. Water vapor is lower but ozone levels are much higher than in the troposhere . Relatively calm with little mixing.
Contaminants can remain in suspension for many years.
Mesosphere - extends from about 50 km to about 80 km. Thermosphere - begins at about 80 km. Temperatures are very high due to constant bombardment of molecules by high-energy solar and cosmic radiation. Lower part of this layer is called the ionosphere. This is where the aurora borealis or northern lights appear.