Important causes of are given below:
(i) Radiation Inversion
(ii) Subsidence Inversion
(iii) Adjective Inversion
(i) Radiation inversion:
During the day, the sun heats the earth and air near it. At night, the ground and the air near it cool faster than that high up, creating an inversion. This is more prominent in winter.
Radiation inversions generally start at dusk and with the progress of evening the inversion extends to a higher and higher elevation. At evening, the pollutants thus, get concentrated near the ground level.
Without sunlight the photochemical reactions cannot occur and the biggest problem is the accumulation of carbon monoxide (CO).
In the morning when the sun rises, inversion starts breaking up, although it may persist for few days in cold and cloudy weather and the pollutants that were trapped in the stable air mass are suddenly brought back to the earth through a process known as fumigation.
(ii) Subsidence inversion:
Subsidence inversion is associated with anticyclones (high pressure weather system). This kind of inversion results when the upper layer of air descends (subsides) during a developing anticyclone.
The high pressure compresses the upper layer of air, thereby heating it. The lower layer of air on the other hand, is relatively colder and denser. This cold air cannot rise up due to the lack of any driving force and the atmosphere becomes stable.
Thus, in this case of high level lid for pollutants, Causing Warm air/ them to accumulate and raise their concentration. Thus, if the subsidence inversion lasts for a long time, it will create a serious air pollution problem.
(iii) Adjective inversion:
This type of inversion occurs when warm air moves over cold air or a cold surface. Elevated adjective inversion occurs when a hill range forces a warm land breeze to flow at high levels and a cool sea breeze flows at low levels in just the opposite direction.