Which factor contributes to reduced vertical mixing in the atmosphere?

Reduced vertical mixing in the atmosphere is primarily influenced by temperature inversions. A temperature inversion occurs when a layer of warm air traps cooler air at the surface. This phenomenon creates a stable atmosphere, preventing the cooler, denser air below from rising. Consequently, vertical mixing is inhibited, leading to stagnant air conditions and potentially higher concentrations of pollutants trapped within that layer.

In contrast, factors like increased wind speed typically enhance mixing by promoting turbulence in the atmosphere, while higher humidity levels and low atmospheric pressure do not have the same stabilizing effect as a temperature inversion. Therefore, the stabilization of the atmosphere due to a temperature inversion is what leads to reduced vertical mixing.