Chapter 22 The Atmosphere

2 important functions served by our atmosphere are: it protects Earth’s surface from the sun’s radiation AND it helps regulate the temperature of Earth’s surface. Without our atmosphere, we would likely die from radiation or heat.

Composition of the Atmosphere Permanent: Nitrogen-78% Oxygen-21%, Others - 1% Variable: Water vapor (H2O) Carbon dioxide (CO2) Ozone (O3) Particulates (dust & pollution)

Oxygen comprises 21% of Earth’s atmosphere. Natural processes maintain the chemical balance of oxygen in the atmosphere. Oxygen is continuously being cycled. 6 ways oxygen is removed from the atmosphere 1. Animals, 2. bacteria, 3. plants remove it for life processes 4. Fires, 5. burning fuel, 6. chemical weathering of rocks

Parts of Atmosphere important to weather Water Vapor - as water evaporates from oceans, lakes, streams, and soil, it enters air as water vapor. Transpiration -the life process by which plants and animals give off water vapor Condensation & precipitation -removes water vapor as it enters the atmosphere 5

3 factors that affect the percentage of water vapor in the air Time of day Location Season Dry air has less than 1% water Moist air may contain up to 4% water

Water Vapor Imagery

Ozone Ozone high in the atmosphere is good Absorbs harmful UV rays Ozone here is formed naturally 3 oxygen molecules = O3 CFC’s break down good ozone and cause the hole in the ozone layer. This allows more of the sun’s radiation to heat the earth (global warming)

- Ozone low in the atmosphere is bad creates smog made by humans

Particulates - Volcanic dust, ash from fires, pollen - Absorb water and helps to form clouds - Absorbs/reflects sunlight

Atmospheric Pressure Holds gases of the atmosphere near Earth’s surface. The weight of the air above a point . Exerted equally in all directions. Measured with a barometer Standard Atmospheric Pressure = 1 atm or 760 mm of mercury or 1000mb 11

Earth’s gravity keeps 99% of the total mass of the atmosphere within 32km of Earth’s surface. Because the pull of gravity is not as strong as it is at higher altitudes, the air molecules are farther apart and exert less pressure. ***This is why atmospheric pressure changes with altitude!** As altitude increases, pressure decreases.

Besides altitude, two other factors that can cause changes in air pressure: Differences in temperature Amount of water in the air At sea level, when temperature increases, pressure decreases. Water molecules have less mass than nitrogen or oxygen. When air has a lot of water vapor in it, the mass of the water is less than the nitrogen/oxygen it displaced. This is why moist air is less dense than dry air is.

Atmospheric pressure variation with altitude

Measuring Pressure Mercurial Barometer -Tube filled with mercury -air pressure pushes on mercury from bottom -causes mercury to rise and fall

Aneroid Barometer Metal expands and contracts with changes in pressure Causes pointer to move so pressure can be read

Barograph Recording aneroid barometer Keeps track of pressure over several days

Layers of the Atmosphere

Troposphere Weather Sphere Lowest Layer Temperature decreases with height at constant rate Most clouds Most water vapor Most airplanes fly here TROPOPAUSE: upper boundary of troposphere

Stratosphere Ozone Layer Found between troposphere and mesosphere Increase Temp with height because ozone absorbs UV STRATOPAUSE – upper boundary of stratosphere

Mesosphere Coldest layer of atmosphere Temperature decreases to coldest point at the mesopause (upper boundary of mesosphere) (-90⁰C) Many meteors burn up in this layer.

Thermosphere Air is very thin. - Uppermost layer of atmosphere Temperature increases due to absorption of solar energy by nitrogen and oxygen Satellites orbit here MESOPAUSE: lower region of thermosphere

Ionosphere – part of the thermosphere Electrically charged layer AM radio waves reflect off of here Causes auroras – phenomena caused by interactions between solar radiation & ionosphere