Chapter 12 Section 2 What is humidity? Objective: Explain how we measure the amount of water vapor in the air.

Key Terms capacity: amount of material something can hold saturated: filled to capacity specific humidity: actual amount of water in the air

Humidity The amount of water vapor in a particular parcel of air is its humidity. high humidity = large amount of water vapor low humidity = small amount of water vapor

DEFINE: What is humidity?

Capacity Capacity is the amount of matter something can hold. Air has a capacity for holding water vapor. Air’s capacity for holding water vapor changes with the air temperature. As the temperature of the air goes down, air’s capacity to hold water vapor goes down.

2. STATE: What affects the capacity of air to hold water?

Saturated Air Air can be saturated. When air is saturated, it holds all the water vapor it can at a certain temperature. As the temperature goes up, the capacity of air for holding water goes up.

3. INFER: At which temperature will air hold more water vapor, 5℃ or 25℃?

Specific Humidity The actual amount of water vapor that is in the air is called specific humidity. Expressed as the number of grams of water vapor in 1 kg of air. Does not change with temperature or pressure. Only adding more water vapor to the air can change the specific humidity

4. NAME: How is specific humidity expressed?

12-2 Classwork The amount of ___ in the air is its humidity. The amount of water vapor the air can hold is its ___. The actual amount of water vapor in the air is called ___. When air is ___, it holds all the water vapor it can at a given temperature. The amount of water vapor that air can hold changes with ___.

12-2 Classwork continued 6. INFER: The air temperature in Boise, Idaho, is 25℃. The air temperature in Austin, Texas, is 35℃. Which city’s air could hold more water vapor? Why? 7. COMPARE: How is a sponge similar to air in terms of capacity?