After condensation the water vapour or the moisture in the atmosphere takes one of the
following forms — dew, frost, fog and clouds.
Forms of condensation can be classified on the basis of temperature and location.
Condensation takes place when the dew point is lower than the freezing point as well as higher than the freezing point.
Dew
When the moisture is deposited in the form of water droplets on cooler surfaces of solid objects (rather than nuclei in air above the surface) such as stones, grass blades and plant leaves, it is known as dew.
The ideal conditions for its formation are clear sky, calm air, high relative humidity, and cold and long nights.
For the formation of dew, it is necessary that the dew point is above the freezing point.
Frost
Frost forms on cold surfaces when condensation takes place below freezing point (00C), i.e. the dew point is at or below the freezing point.
The excess moisture is deposited in the form of minute ice crystals instead of water droplets.
The ideal conditions for the formation of white frost are the same as those for the formation of dew, except that the air temperature must be at or below the freezing point.
Fog and Mist
When the temperature of an air mass containing a large quantity of water vapour falls all of a sudden, condensation takes place within itself on fine dust particles.
So, the fog is a cloud with its base at or very near to the ground.
Because of the fog and mist, the visibility becomes poor to zero.
In urban and industrial centres smoke provides plenty of nuclei which help the formation of fog and mist.
Such a condition when fog is mixed with smoke, is described as smog.
The only difference between the mist and fog is that mist contains more moisture than the fog.
In mist each nuceli contains a thicker layer of moisture.
Mists are frequent over mountains as the rising warm air up the slopes meets a cold surface.
Fogs are drier than mist and they are prevalent where warm currents of air come in contact with cold currents.
Fogs are mini clouds in which condensation takes place around nuclei provided by the dust, smoke, and the salt particles.
Fog occurs during calm or light wind conditions. It is more common in the areas near to the ocean due to the supply of more moisture by sea breeze. In the interior of the continents fog is formed due to reduction of temperature to extreme low during the winter nights.
Clouds
Cloud is a mass of minute water droplets or tiny crystals of ice formed by the condensation of the water vapour in free air at considerable elevations.
As the clouds are formed at some height over the surface of the earth, they take various shapes.
