What is thermal inversion?
Thermal inversion makes it difficult to disperse polluted air. Understand how this phenomenon occurs
Thermal inversion is a phenomenon that hinders the dispersion of pollutants generated in urban centers. It is a consequence of the rapid heating and cooling of the surface and can occur naturally or be caused by the way the city is structured.
According to the UN, every year, thousands of people die from air pollution. The generation of pollutants and the impact on people's health depend not only on the existence of emission sources but also on the dispersion of gases. This dispersion is related to variables such as factory chimney position, site topography, wind direction and climate.
The main sources of air pollution are factories and means of transport. Transport pollutes due to the combustion of gasoline, diesel oil, alcohol, among others, which generates gases such as carbon monoxide, sulfur oxide, sulfur gases, in addition to several unburned hydrocarbons.
How does the thermal inversion take place?
The layers of the atmosphere have different distances and characteristics. The troposphere (layer closest to the ground) has the characteristic of presenting a decrease in temperature with increasing altitude. In this layer, the air tends to circulate in vertical movements (convection currents) due to the difference in temperature between the air from the lower layers and the air from the higher layers.Atmosphere layers
Due to the absorption of solar radiation, the air closer to the ground is usually warmer. Therefore, this air has the most agitated molecules, which occupy a greater volume with less weight (which makes the air less dense). The tendency of this less dense air mass is to undergo an upward movement. With this movement, the less dense mass takes the place of the mass that is at a lower (denser) temperature, moving it downwards. As the hot air mass rises, it cools down and continues the ascension process by encountering air masses that are denser than itself. This process causes the air mass that was close to the ground to rise and take with it the particles of pollutants that were in it. This is the typical functioning of air masses in the troposphere, and contributes to the dispersion of local pollution.
However, in a few days, there is a reversal of this process. This inversion occurs mainly during winter, when the nights are longer (less solar radiation) and humidity drops, which can create a layer of cold air close to the ground and below the first layer of warm air. Cold air, as it is denser, tends to get trapped below the hot layer, trapping all pollutants with it once the air is no longer circulating. This inversion of air masses is called a thermal inversion.
This phenomenon occurs mainly in urban centers, where currents trap polluted air close to the ground. Thermal inversion becomes a problem when the air has high concentrations of pollutants. This retention of pollutants in the atmosphere can cause or aggravate health problems, mainly related to respiratory tract diseases, such as pneumonia, bronchitis, asthma, etc.
Measures to reduce the emission of pollutants are essential to reduce the problem of air pollution aggravated by thermal inversion.
Attitudes such as exchanging individual car transport for collective transport or bicycles, reducing meat consumption (learn more about this topic in the article: "Reducing red meat consumption is more effective against greenhouse gases than not driving a car, experts say "), demand that factories and the automotive sector generate less gases, or less polluting gases, and consume consciously are examples of actions that can contribute to reducing the effects of this phenomenon.
