Posted by Steve on .
If the relative humidity is 66.8% in the middle of a spring day in auckland when the temperature is 15 degrees celsius, What will the relative humidity be in the evening when the temperature falls to 10 degrees celius (Assume the partial pressure of water in atmosphere remain as constant as possible) The saturated vapour pressure of water has values as follows:
Temp 5∘C 10∘C 15∘C 20∘C 25∘C
P(kPa) 0.87 1.19 1.69 2.33 3.17

physics 
drwls,
At 66.8% humidity on a 15C day, the air partial pressure is 66.8% of 1.69 kPa, or 1.13 kPa. That is 94.9% of the saturation pressure at 10 C.
Therefore the relative humidity becomes 94.9% when the temperature drops to 10C