What phenomenon reduces the contrast between foreground objects and the distant horizon when the air is thick with pollutants?

Answer

Atmospheric perspective degradation

When the air is thick with pollutants or humidity, the air itself acts like a light veil, reducing the contrast between objects near and far. This reduction in clarity is termed atmospheric perspective degradation.

What phenomenon reduces the contrast between foreground objects and the distant horizon when the air is thick with pollutants?
appearanceskyatmospherechange