7. Dew

When the relative humidity of the air is low, even a drop in temperature during the winter nights fails to saturate the air. Hence condensation does not take place in free air but on some solid objects like leaves, flowers, grass blades, pieces of rocks, etc., which become comparatively cool due to the quick radiation at night. When the cool air comes in contact with these objects, the dew point is reached and condensation takes place. The deposition of water droplets on these objects is called dew.

Some favourable conditions for the formation of dew are the following:

1) Long Nights: During long nights earth’s surface is cooled. With the coming into contact of

humid air with this surface, condensation occurs.

2) Cloudless Clear Sky: On account of cloudless and clear sky there is more heating during the day. Hence evaporation will also be more and also rapid cooling of surface at night due to terrestrial radiation.

3) Calm Air: Calm air remains in contact with the surface for longer duration. It is a favourable condition for condensation.

4) Relative Humidity: High relative humidity promotes more condensation. That is why condensation can be more in the months of August -September in India.