1. Water & Humidity
Earth Science – S1

2. A. States of water Draw the diagram below:
Energy
Energy
Energy

3. B. Specific Humidity Actual amount of water vapor in air.
1. Warm air can hold more water vapor, because its molecules are further apart have more vacancy.

4. C. Relative Humidity
- actual amount of H2O vapor in air compared to the max amount the temperature of air can hold. (specific humidity) Actual amount of H2O vapor in the air. The capacity (amount of water vapor it can hold) is determined by the air’s temperature!

5. 1. Saturated air has a relative humidity of 100%
Relative Humidity for Air at 26.5°C (capacity 22 g)
Relative humidity= 5.5/22 = 25%
5.5 g
1. Saturated air has a relative humidity of 100%
Relative humidity= 11/22 = 50%
Specific Humidity
11 g
Relative humidity= 22/22 = 100%
22 g

6. 2. Finding relative humidity= psychrometer (evaporation causes cooling

7. The “Dry Bulb” Don’t let it fool you. It is just a thermometer.
It measures the air temperature.
20°C

8. The “Wet Bulb” Has a little wet cloth tied to the bottom.
Gets cool when water evaporates.
12°C
Wet Cloth

9. A Dry Day… A lot of moisture will evaporate.
The wet bulb will be a lot cooler than the dry bulb.
20°C
20°C
14°C
12°C
8°C
Difference between wet bulb & dry bulb is 12 °C.

10. A Humid Day… A little bit of moisture will evaporate.
The wet bulb will not be much cooler than the dry bulb.
20°C
14°C
Difference between wet bulb & dry bulb is 6 °C.

11. Dry-bulb temperature is your air temperature.
20 °C

12. Subtract (the difference) between the dry bulb and wet bulb

13. 20°C
14°C
20-14=6

14. 18°C
16°C
18-16=2

15. Put it all together
20°C
8°C
20-8=12
Relative Humidity = 11%

16. 14°C
10°C
14-10=4
Relative Humidity = 60%

17. D. Dew point
Dew- H2O vapor condenses on a surface (ex. Grass, car window etc.)
Dew point= temperature at which saturation (specific humidity = capacity) occurs.

18. 15.5
Capacity
Vapor
Temperature (°C) 10
Capacity
Vapor
Over capacity = DEW
4.5
Capacity
Vapor
0 g
4 g
8 g

19. Pre-Lab Questions Compare specific humidity vs. relative humidity.
What instrument is used to find relative humidity
Define dew point in your own terms.
The amount of dew decreases during the daytime. Explain why this occurs.
(Hint: think about what temperature holds more water and when dew forms.)