Thermal inversion is a typical meteorological phenomenon in industrial urban centers, which occurs when a layer of cold air, positioned over an industrial city, is suddenly covered by a layer of warm air, which imprisons it.
Thermal inversion usually takes place in the late morning and early morning, particularly on cold autumn or winter days.
When two air masses of different temperatures (one hot and one cold) collide and the hot air is forced to pass over the cold air, the normal situation is reversed. The cold air near the surface of the city cannot rise as it is denser, and the warm air above it cannot descend as it is less dense.
Cause of thermal inversion
Large cities are precisely the most favorable environments for the occurrence of thermal inversion, due to the fact that have a large built-up area, deforested and waterproofed, which absorb a huge amount of heat during the morning.
When solar radiation warms the soil, the trapped heat radiates, in turn, warming the lower layers of the atmosphere. At night, however, they lose heat quickly. This is exactly where the cause of the thermal inversion lies: with the concentration of cold air in the lower layers of the atmosphere, and of the air hot forming a layer, does not allow the gases and soot released by factories and automobiles to be carried by the winds.
When winds manage to horizontally displace the cold air layer, thus restoring vertical circulation between the hot and cold air layers, the heat inversion dissipates.
Consequences of thermal inversion
During colder periods, air pollution levels in large industrial cities tend to be more critical. At that time, the scarcity of winds and low atmospheric humidity favored the occurrence of thermal inversion, making the air quality inadequate, which ends up intoxicating people.
The closer to the ground the thermal inversion occurs, the worse, as the pollutants are concentrated closer to the surface. According to experts, when the inversion takes place at a height of 100 meters it becomes very dangerous. The main effects of this phenomenon on the health of the population are respiratory diseases, such as pneumonia, bronchitis, asthma, emphysema, headaches, itchy throat, eye irritation, and worsening heart disease.
See also
- Acid rain
