The relation between relative humidity & temperature

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Relative humidity is the ratio between the actual amount of water vapour present in the atmosphere at a given temperature & the maximum amount of water vapour that the atmosphere can retain at that temperature & is expressed as a percentage.
      We know, A.P.=K*D*T
where,A.P.=atmospheric pressure;K=constant=density & T=Temperature
temperature is the index of heat contained in a substance.thus,when temperature increases density of air mass decreases so does the atmospheric pressure.Since,we are concerned with water vapour so vapour pressure would be a more appropriate term,Hence,it is the actual vapour pressure expressed as the percentage of saturation vapour pressure which would be possible at the same temperature. It(relative Humidity) is concerned with 2 variables:-
a)actual water vapour in a given mass of air;
b)Temperature of that mass of air,since this determines the capacity of the air to hold water vapour.this implies high temperature which is indicative of high latent heat supply by water vapour which it contains to the amount of 2260 Joules/gram of water vapour.this results in volumetric expansion of the water vapour containing air mass as a result the actual vapour pressure decreases since the individual atoms/molecules of water vapour is exerting pressure over a large area rather than on a smaller surface area of the Earth's surface,which would have resulted in high actual vapour pressure.So,the gap or difference between actual vapour pressure & saturation vapour pressure increases resulting in low relative humidity.
Relative humidity is low during the day & high during the night. This is because the gravitational pull overpowers all other forces (resulting in expansion) & results in compression of water vapour molecules & low temperature minimal at night due to absence of sun favours the reduction of gap between actual vapour pressure & saturation vapour pressure, as a result relative humidity increases. The water molecules are now exerting pressure because of the small surface area over which it is operating than during the day time.

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