When the atmosphere warms up with height, a stable atmospheric condition is created. This is why pollutants are able to be trapped. A cooled atmospheric layer, in contrast, is an unstable atmospheric condition in which pollutants can disperse.
If air comes down from a high elevation to a low elevation, the air warms up due to compression. This air also tends to be dry. In this type of inversion, the air originated over dry land and lost any of its moisture when it rose over a mountain range. The warm air mixes with the cool air of the ocean and forms a layer over the top of the cool air.
Radiation inversions often occur in the winter season. Nights are cool and have relatively low wind and no clouds. The ground emits heat into space in the form of long wave radiation. When this happens, the dirt and land cools. The cool land takes the heat from the lowest atmospheric layer of air, causing this layer to become colder than the layer of air above it.
Air that is located over the ocean is cool and moist. This air can be blown towards lands by wind. Since cool air is more dense than warm air, it stays underneath the warm air. Since land heats up as the day goes on, the warm air rises and mixes with the cooler air from the ocean.
If you notice that the sky is exceptionally hazy, this may be due to a temperature inversion. This is because inversion layers trap pollutants and smog. For example, think of the air quality in Los Angeles, which often has a temperature inversion in the atmosphere. Also, extra-red sunsets often point to a temperature inversion. Inversions are possible when there is no wind current. Wind mixes up the air, typically preventing an inversion.