How does fog form near the ground?

Fog forms when air at ground level becomes saturated, usually because it cools overnight or moves over a colder surface. When the air reaches its dew point, water vapor condenses onto tiny particles such as dust or salt, creating suspended droplets. Radiation fog often forms on clear, calm nights, while advection fog develops when moist air moves over cooler land or water. Meteorologists usually call it fog when visibility is less than 1 kilometer; if visibility is greater, it is often called mist.