What occurs during a thermal inversion that affects air quality?

During a thermal inversion, warm air at higher altitudes traps cooler air near the ground. This phenomenon leads to a situation where the cooler air, which is often denser, becomes trapped underneath the warm layer. As a result, any pollutants emitted from ground-level sources, such as vehicles or factories, become concentrated in the cooler air. The inversion creates a stable atmosphere, preventing the normal mixing processes that would usually disperse these pollutants into the upper atmosphere.

Consequently, the buildup of pollutants can lead to deteriorating air quality, causing increased health problems and environmental issues. This phenomenon is particularly common in urban areas where pollution sources are abundant and can lead to smog formation, especially during warmer months when inversions are more likely to occur.

The other options discuss scenarios that do not accurately capture the dynamics of a thermal inversion. For instance, the idea that colder air traps warmer air on the ground misrepresents the layering effect, while claims about temperature stabilization leading to cleaner air contradict the reality of pollution concentration during an inversion. Humidity levels might influence pollutant behavior, but they do not prevent dispersion under inversion conditions.