Water in the Atmosphere

States of Matter Water vapor – gaseous form (0 to 4% by volume) Water – rain, dew, clouds, fog Ice – snow, hail, clouds

Changes in States of Matter Evaporation – process of changing a liquid to a gas Condensation – process of changing a gas to a liquid Sublimation – conversion of a solid directly to a gas Deposition – conversion of a gas to a solid

The process of changing state requires that energy is transferred in the form of heat. Latent heat – energy absorbed or released during a change of state

Humidity General term for the amount of water vapor in the atmosphere

Saturation the maximum amount of water vapor that the air can hold at a particular temperature and pressure

Relative Humidity A ratio of the air’s actual water vapor content compared with the amount of water vapor air can hold at saturation Depends upon water vapor content and temperature of the air

Amount of water vapor in the air Amount of water vapor at saturation Relative Humidity = X 100

Psychrometer Instrument used to measure relative humidity

Dew Point (temperature) The temperature needed for air to reach saturation At this temperature water condenses and dew, fog, or clouds form

Check for understanding Find relative humidity. The air contains 3 grams of water vapor. The air can hold 9 grams before it becomes saturated. What happens to the above relative humidity if the air is cooled? What are the two factors that influence relative humidity?

Check for understanding What does it mean if the air is saturated? What is the relative humidity at this point? What is dew point temperature? What is the relative humidity at this point? Sketch a graph to show the relationship between relative humidity and temperature.