Question

What makes air become more humid one day than it was the day before?

Answer 1

Either addition of water vapor or lowering of temperature.

Explanation:

Humidity is the relationship between the water vapor in the air as a percentage of the maximum amount of water vapor the air can hold. In order to change it then you either have to change the amount of water vapor, or change the maximum amount of water vapor it can hold. What determines the maximum amount of water the air can hold is temperature (warm air holds more water vapor). Therefore to increase the humidity you either have to A) add more water vapor or B) lower the temperature.