What are clouds made of?
Clouds are just condensed water vapor or ice crystals. Cloud droplets also require cloud condensation nuclei, however, which often consist of sulfate aerosols.
Meteorologically, fog can be classified into four general types according to the mechanism by which it is formed: advection, radiation, upslope, and precipitation.
Advection fog is formed whenever a current of relatively warm, moist air passes over a colder body of land or water. Fog of this type is frequent in the winter when snow is on the ground. It is also common over the ocean, as in the North Atlantic when winds blow across the warm Gulf Stream and reach the cold Labrador Current.
Radiation fog, formed only over land, is caused by the cooling of the earth by radiation. At night, radiation lowers water temperature comparatively slowly, but land cools rapidly, becoming cooler than the air above it; consequently a fog is formed. Such fog is seldom thick and usually �burns off� in the morning.