Daily Archives: April 7, 2025

Weather reports often include the dew point temperature and the relative humidity. These are just two of several ways to express the amount of water vapor in the atmosphere. Vapor pressure is another way. Each method has advantages and disadvantages.

Gas molecules exert a pressure when they collide with objects. The atmosphere is a mixture of gas molecules and each type of gas makes up a part of the total atmospheric pressure. The pressure the water molecules exert is another useful method of representing the amount of water vapor in the atmosphere. The pressure caused by these water vapor molecules is called the vapor pressure. Atmospheric vapor pressure is expressed in millibars (mb). Continue reading →