What phenomenon causes reduced visibility due to a layer of warm air trapping cooler air below?

The phenomenon that causes reduced visibility due to a layer of warm air trapping cooler air below is known as an inversion. In this situation, the typical temperature gradient of the atmosphere is altered; instead of temperature decreasing with altitude, warm air sits above cooler air near the ground. This creates a stable layer in which pollutants and moisture can accumulate, leading to reduced visibility, especially in urban areas. The warm air effectively acts as a lid, preventing the cooler air below from rising and dispersing, which can contribute to fog formation and haze due to the trapped moisture.

In contrast, other options describe different conditions. Radiation fog occurs when the ground cools overnight, leading to moisture condensing on cool surfaces. Wind shear relates to changes in wind speed or direction with altitude, which can create turbulence rather than visibility issues due to temperature gradients. Advection fog is formed when warm, moist air moves over cooler surfaces and cools, leading to condensation, but it does not specifically involve the trapped layer of warm air that characterizes an inversion.