In places like Los Angeles and Salt Lake City, this is a real problem because of all the emissions from vehicles, power plants, and other factories or heat sources
Besides trapping smog, inversions also trap sound waves. Because of this, the loud sounds of things like airplanes taking off will seem louder as the sound waves refract off the inversion layer and back down to the ground
But sound waves aren't the only thing that gets refracted by weather inversions. light can be bent by the inconsistency of the temperature. When an inversion is not present, but the ground temperature is significantly hotter than the air higher up like in the desert, the bending of light causes mirages in the form of thinking that there is a lake or puddle up ahead. Really, it is the sky reflecting off of the ground because of the extreme change in temperature
When there is a temperature inversion, the affect is just the opposite. If the inversion is strong enough, it can cause far off objects to look like they are floating above the ground. If things are far enough they are past the curvature of the earth, they may become visible. This reverse or "superior" mirage is called looming.
Subsidence Inversions Take pace in valleys or in places partially surrounded by hills or mountains.
When the air blows over the hills, it is heated as it is compressed into the side of the hills
When that warm air comes over the top, it is warmer than the cooler air of the valley.
Also, increasing the inversion, as the air comes over the top of the hill, it causes the air in the valley to be compressed, heating the cooler, valley air from the top down.
picture by Amber Smith
When this cool air is trapped and compressed, so is everything that is in the air, such as vehicle emissions, smoke, and smog in general. This is a big problem for cities located in valleys.