In the troposphere, temperatures decrease as we increase in altitude. Therefore, it is more normal for it to be colder in mountain areas than at sea level. However, there are some atmospheric phenomena that cause a change in this gradient that causes it to be reversed. It is known as thermal inversion. It is a process in which the temperature rises in altitude.
In this article we are going to tell you what thermal inversion is, how it originates and how it is related to air pollution.
What is thermal inversion
It is a process in which temperature increases with altitude. That is, in the lowest areas of a city, for example at sea level, we find lower temperatures than if we ascend a mountain. It is the opposite of what normally happens.
This temperature inversion is due to certain special situations in which cold air layers descend and remain stable. Let's review some basic concepts of atmospheric dynamics. When anticyclones exist, the air descends from higher layers, and in low pressure systems, it does the opposite. The air bar rises toward higher layers. Thermal inversion occurs under anticyclone conditions and with great atmospheric stability.
In a thermal inversion we can see how the cold air from the upper layers descends to the lower layers close to the earth's surface. This downward movement of cold air is known as SubsidenceAs it descends, the air becomes increasingly compressed, increasing its pressure and temperature. It also loses moisture, which is why there are no clouds. We can see how, when it reaches the surface, it expands and diverges. This causes it to spread across the entire surface, creating layers of stability.
How the thermal inversion is formed
Upward movements of air masses due to global warming are inhibited and with it the possibility of instability. The absence of these air movements prevents air masses of different temperatures from mixing. When night falls, the earth rapidly loses the temperature it has reached during the day thanks to solar radiation. This heat is transmitted to the air in contact with the earth. Cold air is much heavier and settles at the bottom of valleys, which is why temperatures are colder in the mornings.
It is important to remember that in these thermal inversion situations, the air descends from higher layers and warms up, so the warm air would remain above the cold air. This causes a plug or lid to formSince upward air movements are completely inhibited, as there are no winds due to the high stability, these masses of different characteristics do not mix, and thus the phenomenon of thermal inversion occurs.
The most normal thing is that the atmospheric temperature decreases with the height, but in this case there is the thermal inversion.
Why it occurs
For a temperature inversion to occur, several situations must occur. During the night, the Earth's surface cools rapidly, as it loses all the heat it has accumulated during the day. This layer of air has a lower temperature than the layer immediately above it. This means that the air has different densities, which prevents them from mixing. As the sun reappears, it begins to correct the temperature inversion and warms the Earth's surface again, restoring normal conditions.
This phenomenon occurs more frequently in valley areas, as radiative cooling is greater. If there is a high contrast between daytime and nighttime temperatures, a temperature inversion is more likely. When a temperature inversion exists, it is easily recognizable. This is due to the fact that the fog or smoke tends to concentrate in the vicinity of the earth's surface. and spreads horizontally. It is more common in maritime areas and valleys. It typically occurs in areas where, due to their morphology, normal air circulation is difficult.
How Inversion Affects Pollution
We have mentioned that during the thermal inversion process a layer of atmospheric stability is generated on the earth's surface. This layer is made up of cooler air that is denser and stays in the lower layer. This makes it impossible to mix the two layers of air that have different density when having different temperatures. Therefore, it is quite easy to conclude that one of the main effects that thermal inversion can cause is that pollution is trapped on the earth's surface without the possibility of dispersing into the atmosphere.
Normally, air tends to rise, allowing us to disperse atmospheric pollution from the lower reaches. However, in a thermal inversion, the higher temperature layer acts as a barrier to the colder air in contact with the ground surface. This is where a large amount of pollutants are stored. One of the immediate consequences is smog. This layer of pollution can be seen from several kilometers away and often leads to a drop in air quality levels.
The consequences of this phenomenon on human health translate into an increase in medical consultations due to respiratory and cardiovascular problems. It should be noted that breathing polluted air is particularly harmful to at-risk groups, such as the sick, the elderly, and children. Levels of nitrogen dioxide and sulfur dioxide accumulate during periods of thermal inversion. Furthermore, particles between 10 and 2.5 microns in size concentrate and penetrate the pulmonary alveoli.
I hope that with this information you can learn more about the phenomenon of thermal inversion.