Why do pscs occur at heights of 15-20 km? The long polar night produces temperature as low as 183 k(-90oC)at heights of 15 to 20 km The stratosphere contains a natural aerosol layer at altitudes of 12 to 30 kmWhy do PSCs occur at heights of 15-20 km? • The long polar night produces temperature as low as 183 k (-90oC) at heights of 15 to 20 km. • The stratosphere contains a natural aerosol layer at altitudes of 12 to 30 km