1. Water in the Atmosphere

2. Earth is called the “Water Planet”
71% of the earth’s surface is covered by water.
Water is essential for LIFE on earth.

3. Water on earth’s surface is easy to see…
Oceans
Lakes
Rivers
Glaciers
But what about water in earth’s atmosphere???

4. Water in the atmosphere
It’s less obvious than surface water, but there are many signs of water in the atmosphere:
Rain, Snow, Drizzle
Clouds & Fog
Hot days that feel “muggy” or “humid”
Dew on the grass in the morning

5. Water Cycle
The movement of water between the atmosphere and earth’s surface is the water cycle.

6. How does water get into the air?
EVAPORATION – is the process where liquid water molecules escape into the air as water vapor.
3 things affect how quickly water evaporates:
1) Temperature
2) Wind
3) Humidity of the air

7. How much water can air hold?
HUMIDITY is the measure of how much water vapor is in the air.
TEMPERATURE affects how much water vapor the air can hold…
Warm Air
Cold Air
holds MORE water vapor.
holds LESS water vapor.
That’s why air feels more “HUMID” on hot days!

8. What is the “Dew Point”?
As air cools, the amount of water vapor it can hold decreases.
At a certain temperature, the water vapor in the air will CONDENSE back into water droplets or ice.
This temperature is the “DEW POINT”.

9. What is the “Dew Point”?
So, when the air temperature equals the “Dew Point” temperature, the air cannot hold any more water.
That means relative humidity is 100%!

10. Ever wondered about why the grass (or a car windshield) is wet in the morning?
Overnight, the temperature dropped below the “dew point” temperature, and the water in the air condensed into water droplets on the grass.

11. Measuring Dew Point August 15, 2008
Question: At what temperature will the water vapor in the air turn back into liquid water droplets?
Hypothesis: Write your prediction.
Room Temperature is 23°C.
Data Collection: Create this data chart.
Temperature (°C) Condensation (yes/no)
23 °C no

12. Measuring Dew Point
Start with a cup of room temp. water and record its temperature.
Add 1 ice cube and stir with the thermometer until it melts.
Monitor the temperature continuously! Record in your data chart every 2-3°C.
Keep adding ice cubes one at a time until you see fog/dew form on the outside of the cup.
Remove the ice as soon as you see condensation on the cup.
This is the DEW POINT temperature!

13. Conclusion: What is “dew point” temperature in here?
Why do you think meteorologists would want to measure dew point?
What happens to water vapor that condenses at a temperature BELOW 0°C?
Would the dew point be the same if we did this experiment on a different day? Explain.

14. Watch the BrainPop video on “Humidity”. Write down 3 things you learned.