water can form on surfaces at night when the air is clear becase...?

Question

a) the air near the ground is colder than the ground.
b) the air is NOT saturated
c) the air near the ground cools to dew point
d) the relative humidity decreases



thanks for the homework help guys =]

Answer 1

The answer is 'c'.
On clear nights,earth's surface loses more energy by Infra-red radiation than it receives during the day from the solar radiation.In conditions of light wind,the downward transfer of water vapour( a little water vapour in the higher atmosphere is a required condition) from the atmosphere to the cooled surface occurs.If sufficient relative humidity is available near the ground and the air near the ground is cooled below the dew point,the condensation takes place over the ground.Incidentely this is the process of dew formation.

Answer 2

c There is always some moisture in the air. When the air cools, the water in it becomes water again...and that is dew