How does water get into the atmosphere? What is humidity? Units 12-1 and 12-2 Notes How does water get into the atmosphere? What is humidity?

12-1 Water Vapor Water vapor- water in the form of a gas. Water vapor droplets in the form of water/ice- clouds/fog. About 14 million tons of water vapor is in the air.

12-1 Evaporation Evaporation= changing of a liquid to a gas---water vapor in air. As water is evaporated from seas and oceans, winds carry water vapor all over the world.

12-1 Heat/Evaporation Molecules in a liquid= always moving. When heat is applied, some escape off the top and become part of the atmosphere and form a gas = evaporation.

12-1 Heat/Evaporation Substances being heated have these liquid molecules to escape faster and faster, and these change into gas molecules faster and faster = hotter= faster evaporation.

12-1 Living Things/Water Vapor Living things add H2O to the air. Respiration and perspiration add moisture to the air. Plants give off water through tiny holes in the leaves (stomata). This process is called transpiration.

12-1 Lesson Summary Water is in the air as water vapor. Evaporation= liquid to a gas. Most of water in the air is evaporated from oceans. All living things add water to the air- respiration, perspiration, and transpiration.

12-1 Class work Complete Checking Concepts and Thinking Critically on p. 279.

Humidity- amount of water vapor in the air. High humidity- lots of water vapor. Low humidity- little water vapor.

12-2 Capacity Capacity- amount of material something can hold- at its fullest level. Warm air can hold more water vapor than cold air. Warm air has MORE capacity.

Saturated- filled to capacity. 12-2 Saturated Air Saturated- filled to capacity. Air is saturated when it holds all the water vapor it can at a certain temp.

12-2 Saturated Air As temp. goes up, the capacity of air for holding water goes up. When temp. cools down, the capacity shrinks, and water vapor comes back out- dew, fog, clouds, etc.

12-2 Specific Humidity Specific humidity- the actual amount of water vapor that is in the air. Specific humidity is the number of grams of water vapor in 1 kilogram of air.- an ACTUAL COUNT. Specific humidity is not affected by temperature or air pressure changes.

12-2 Lesson Summary Humidity is the amount of water vapor in the air. Capacity is the amount something can hold. Capacity is affected by temperature changes.

12-2 Lesson Summary To be saturated is to be filled to capacity. Specific humidity is the exact number of water vapor molecules in the air.

Class Work Complete the Checking Concepts and Thinking Critically sections on p. 281. Read the “Meteorologist” section.