Aim: How can we explain relative humidity and dew point?

Saturation  When the air is holding as much moisture as it can, it is SATURATED  The WARMER the temperature, the MORE moisture it can hold  The COLDER the temperature, the LESS moisture it can hold  If the temperature is lowered enough, then the air will become saturated

Relative Humidity  Expresses how FULL of moisture the air is.  Compares how much moisture is in the air to how much the air COULD hold.  Air is SATURATED at 100% relative humidity

 With the same amount of water present:  The HIGHER the temperature goes, the LOWER the relative humidity becomes  The LOWER the temperature goes, the HIGHER the relative humidity become

Measuring Moisture  sling psychrometer  Two thermometers, one is dry called the “dry bulb” temperature  One is covered in a wick that has been moistened with water called the “wet bulb” temperature  Swing it around until the water from the wick evaporates so you can measure the “wet bulb” temperature. This temperature is always lower because of the evaporating water.  and charts on page 12 of your ESRT

How to find relative humidity: (1)Locate dry-bulb reading on the left- hand side of chart (2)Subtract wet-bulb reading from dry- bulb reading (3)Locate this difference on the top of chart (4)Follow top column down until you meet dry-bulb temp. on left

Dry-bulb is 14 o C and wet- bulb is 9 o C = 5

Dry-bulb is 28 o C and wet- bulb is 25 o C = 3

Dry-bulb is 10 o C and wet- bulb is 10 o C = 0

Humidity is 13% and dry bulb is 10. What is the wet bulb?

Dew Point  The temperature to which the air must be lowered to become saturated  If temp. falls below dew point condensation occurs!!!!  Can also sublimate directly to a solid (think of frost on grass!)

 The more water vapor in the air, the higher the dew point  The less water vapor in the air, the lower the dew point

How to find dew point:  Same as Relative Humidity…just make sure you use the DEW POINT CHART!!!!

Dry-Bulb is 20 o C and wet- bulb is 15 o C 20 – 15 = 5

Dry-Bulb is 0 o C and wet-bulb is -2 o C = 2

Dry-Bulb is 12 o C and wet- bulb is 5 o C 12 – 5 = 7

To say that the relative humidity on a given day is 70% means that the air (1)Is composed of 70% water vapor (2)Holds 70% of its water vapor capacity (3)Contains 70 parts of water to 100 parts of dry air (4)Contains the same amount of water that it would at 70 o F

If the amount of water vapor in the air increases, then the dew point of the air will (1)Decrease (2)Increase (3)Remain the same

As the air temperature rises, the relative humidity (1)Increases (2)Decreases (3)Remains the same