1. Bellwork 3/9 **We’re going outside for a bit…if you want a jacket, go grab it! **
How would you describe humidity in your own words?
Describe a setting/location in which humidity would be high. What about low?

2. How is heat measured?
Calorie = amount of heat required to raise the temperature of 1 gram of water 1⁰C
EX: When 10 calories are added to 1g of Water, the temperature increases 10⁰C

3. What happens when heat is added or subtracted from the atmosphere?
Changes of State of Water

5. Changes of State Energy is RELEASED Energy is ABSORBED
Liquid gas = Evaporation
Solid Liquid = melting
Gas Liquid = Condensation
Liquid  solid = freezing

6. Changes of State The “weird” ones…
Solid Gas = Sublimation
No liquid state
EX: Dry ice “smoke”, ice cubes shrinking in freezer
Gas Solid = Deposition
No liquid state
EX: Frost on grass/windows, frost in freezers

7. Now that we understand how water can change state, let’s look at how this plays a role in our atmosphere. First, we’ll focus on condensation & evaporation

8. Humidity Amount of water vapor in the air
Saturated air is air that is filled with water vapor to capacity
“Capacity” is temperature dependent – warm air can hold more water vapor
Water vapor adds pressure (called vapor pressure) to the air

9. Relative Humidity: Expressed as a percent Saturated air
Ratio of the air's actual water vapor content compared with the amount of water vapor required for saturation at that temperature (and pressure)
Expressed as a percent
Saturated air
Content equals capacity
Has a 100% relative humidity
Relative Humidity (RH) =

10. Relative Humidity continued…
Relative humidity can be changed in two ways
1. Adding or subtracting moisture
2. Changing the air temperature
Lowering the temperature raises the relative humidity

11. Adding/Subtracting Moisture

12. Change in Temperature

13. Typical daily variations in temperature and relative humidity

14. Dew Point Dew point temperature
Temperature to which air would need to be cooled to reach saturation
Cooling the air below the dew point causes condensation
dew, fog, or cloud formation

15. Measuring Humidity
Psychrometer - compares temperatures of wet-bulb thermometer and dry-bulb thermometer
If the air is saturated (100% relative humidity) then both thermometers read the same temperature
The greater the difference between the thermometer readings, the lower the relative humidity