What does the term "inversion layer" refer to?

The term "inversion layer" specifically refers to a layer in the atmosphere where temperature increases with altitude, which creates a stable air mass that can trap pollutants and prevent them from dispersing. This phenomenon occurs when a warm layer of air sits above cooler air near the surface. Normally, air temperature decreases with altitude, allowing for the typical dispersion of pollutants as air mixes. However, when an inversion layer is present, the warm air acts as a cap that traps cooler air (and any pollutants contained therein) close to the ground. This situation can lead to increased concentrations of air pollution, especially in urban areas, as the trapped air does not rise and disperse. Thus, understanding inversion layers is crucial in atmospheric dispersion studies since they directly impact air quality and the behavior of emissions.