Water in the Air

Air has water vapor in it. Humidity- is the measure of water vapor in the air

Temperature affects how much water vapor the air can hold. Warm air can hold more water vapor than cooler air.

Relative Humidity Relative humidity is a ratio of how much water vapor the air is holding to how much water vapor it is capable of holding at a given temperature

Study the graph. The same amount of water vapor is in the air. The air is shown at different temperatures. As the temperature increases, what happens to the percent of relative humidity? Does it increase or decrease?

How to measure relative humidity: A hygrometer measures relative humidity.

A psychrometer is a simple type of hygrometer. A psychrometer is made of 2 thermometers. One is normal (dry bulb). One has a wet wick on the end (wet bulb).

The wet and dry bulb readings are compared using a table.

evaporation Evaporation is when liquid water becomes water vapor. Water changes from liquid to gas.

condensation Condensation is when water vapor becomes liquid water. Water changes from gas to liquid.

Dew point When air becomes cooler, it may reach a temperature where the air can no longer hold its water in vapor form. At that point condensation occurs. That temperature is called the dew point.

Air is saturated… …when the relative humidity is 100%. If the air continues to cool, condensation occurs.

Examples of condensation: Air in direct contact with your cold glass of ice water

Examples of condensation: Air during the night can cool below saturation and reach its dew point.

Examples of condensation: Condensation on small particles of dust in the atmosphere forms clouds.

Examples of condensation: Contrails are caused by water condensing on particles from the exhaust of jets.

precipitation Warm moist air rises and cools. Condensation in the atmosphere forms clouds. Eventually the condensation becomes too heavy to cling to dust particles in the air. Rain, snow or sleet is the result.

barometer A barometer measures air pressure. When air pressure drops, warmer air is rising and precipitation is predicted.

Look at current weather conditions in your area. Find the Temperature ASSIGNMENT Look at current weather conditions in your area. Find the Temperature Relative humidity Dew point Barometric pressure (air pressure)