Question

What does relative humidity describe about air?

Answer 1

The ratio of water vapor in the air compared to the amount of water vapor required to saturate the air.

Explanation:

Relative humidity is the water vapor in the air as a percent of the total amount of water vapor the air could hold at it's present temperature.

The above chart illustrates this by showing the maximum amount of water vapor or 100% relative humidity, with the red line and 50% relative humidity shown by the green line.

So at 20 degrees it shows that the air is saturated when it contains 16 grams of water vapor per kilogram of air. At the same temperature if the air had 8 grams it would therefore have 50% relative humidity.