# relative humidity and dewpoint

In Glogpedia

by MrRepasy
Last updated 10 years ago

Discipline:
Science
Subject:
Cycles & Processes

RELATIVE HUMIDITY AND DEWPOINT

Humidity - the amount of water vapor in the airRelative Humidity - the amount of water vapor in the air "relative to the total amount of water vapor that it can hold at a particular temperatureDew Point - the temperature that the air would have to be in order to be saturated with water vapor (100% Relative Humidity)

WARM AIR HOLDS MORE WATER VAPOR THAN COLD AIR.Therefore, as the air temperature gets warmer, the same amount of water vapor is a "relatively" smaller percentage of the maximum amount of water vapor that the air could hold, and vice versa for colder air - it would be a "relatively" larger percentage. This is Relative Humidity (R.H.)

Notice that as the temperature of the air DECREASES the relative humidity INCREASES.....until it reaches 100%. At that point the air is saturated, meaning that it is holding the maximum amount of water vapor that it can at that temperature. The air temperature at which saturation occurs (R.H. = 100%) is called the DEWPOINT.

Relative humidity is calculated by taking taking the temperature difference between a dry thermometer bulb and a wet thermometer bulb and looking it up on a Relative Humidity Chart. If the air is very dry (low humidity) then there will be a lot of evaporation (cooling) from the wet bulb, and the difference between the two thermometers will be great, resulting in a small % Relative Humidity. If the air is very moist (high humidity) then there will be very little evaporatin (cooling) from the wet bulb, and the difference between the two thermometers will be less, resulting in a greater % Relative Humidity. To calculate the dewpoint, simply find the temperature at which a glass of ice water just begins to fog (collect dew) and you have found the dewpoint.