What is typically the worst case stability class for daytime conditions?

In atmospheric science, stability classes are categorized based on the degree of vertical mixing within the atmosphere, which affects how pollutants disperse. Stability class D represents the most stable conditions during the daytime, characterized by limited vertical mixing. Under these conditions, the atmosphere tends to resist upward movement, trapping pollutants near the surface and allowing them to accumulate.

This stability class often arises on clear, sunny days when solar heating leads to temperature inversions, which stabilize the atmosphere. When the mixing is restricted, pollutants emitted from ground sources do not disperse effectively, leading to higher concentrations in the vicinity of the emission source.

In contrast, stability classes A, B, and C represent more unstable conditions conducive to better mixing and dispersion of pollutants. Therefore, class D is accurately identified as the worst-case scenario for dispersion during daytime conditions, because it typically leads to higher levels of air pollution exposure and potential negative impacts on air quality.