Chapter 15The Atmosphere

I. Characteristics of the AtmosphereA. The Composition•Made up mostly of nitrogen gas• Oxygen makes up about 20% of the

atmosphere• Small particles, such as dust, volcanic ash,

sea salt, dirt, and smoke circulate the atmosphere•Water vapor is suspended and changes to

liquid rain and solid snow when atmospheric conditions change

B. Atmospheric Pressure and Temperature1. As Altitude Increases, Air Pressure Decreases• Gravity pulls molecules in the atmosphere toward

the Earth’s surface• Air pressure is the measure of the force of the

molecules pushing on a surface• Air pressure decreases the further from sea level

you move because there are less molecules above you

2. Atmospheric Composition Affects Air Temperature• Some parts of the atmosphere are warmer

because they contain a high percentage of gases that absorb solar energy

C. Layers of the Atmosphere• Based on temperature

changes1. The Troposphere• The layer in which we live• Densest atmospheric layer,

containing almost 90% of the atmosphere’s total mass• “tropo-” means “turning” or

“change”• Temperatures very greatly

causing gases to mix continuously

2. The Stratosphere• Home of the ozone layer• “Strato-” means “layer”• Gases are layered and do not mix much• Air is very thin and contains little moisture• Lower part of stratosphere is -60°C and rises

as altitude increases due to the ozone absorbing ultraviolet radiation from the sun

3. The Mesosphere• “Meso-” means “middle”• Coldest layer• Temperature decreases as altitude decreases• Top part of the mesosphere is -93°C

a. The Ionosphere- Upper part of the mesosphere- “iono-” means ions- Heat increases in the layer above the mesosphere

causing gas particles to become electrically charged- These electrically charged ions radiate shimmering

lights called auroras

4. The Thermosphere• The edge of the atmosphere• “thermo-” means “heat”• Temperature increases with altitude• Nitrogen and oxygen absorb solar radiation and

release thermal energy causing temperatures to exceed 1,000°C• Particles are less dense than particles in the

troposphere so heat, or thermal energy, is not transferred, so it does not feel hot

5. Exosphere• Outermost layer• “I Owe My Aunt Lucy Ten Outstanding

Strawberries. May I Taste ‘Em?Inner Core, Outer Core, Mesosphere,

Asthenosphere, Lithosphere, Troposphere, Ozone, Stratosphere, Mesosphere, Ionosphere,

Thermosphere, Exosphere

II. Atmospheric HeatingA. Energy in the Atmosphere

1. Radiation• Energy transferred by electromagnetic

waves• About 26% is scattered and reflected by

clouds and air• About 19% is absorbed by ozone, clouds,

and atmospheric gases

• About 51% is absorbed by Earth’s surface• About 4% is reflected by Earth’s surface

2. Conduction: Energy Transfer by Contact• Transfer of thermal energy through a material

from warm to cold areas• Air is heated near the Earth’s surface

3. Convection: Energy Transferred by Circulation• Transfer of thermal energy by the circulation, or

movement, of a liquid or gas• As air is heated, it becomes less dense and rises• Cool, denser air sinks• Cool air is heated by the Earth’s surface and begins

to rise again•Movement creates convection currents

4. The Greenhouse Effect• Energy that is absorbed by clouds and the Earth’s

surface is converted into thermal energy that warms the planet• Thermal energy is released into the atmosphere

but does not escape the outer limits of the atmosphere• The greenhouse effect is the process by which

gases in the atmosphere absorb thermal energy radiated from Earth- Allows solar energy to enter but prevents

thermal energy from escaping

5. Greenhouse Gases and Global Warming• Greenhouse gases are gases that absorb

thermal energy in the atmosphere and prevents the energy from escaping the atmosphere• An increase of greenhouse gases in the

atmosphere may be the cause of a warming trend

III. Global Winds and Local WindsA. Why Air Moves•Wind is the movement of air caused by

differences in air pressure• Differences in air pressure are generally

caused by unequal heating of the Earth

• The equator receives more direct solar energy than other latitudes- Air is warmer and less dense- Warm air rises and creates low pressure areas- Warm air flows toward the poles• Air at the poles is cooler and more dense

- Cool air sinks and creates high pressure areas- Cool air flows toward the equator

1. Pressure Belts- Bands of high pressure and low pressure

found about every 30° of latitude

B. Global Winds1. Polar Easterlies• Formed as cold, sinking air moves from the

poles toward 60° north and south latitude• Carry cold arctic air over the U.S., producing

snow and freezing weather

2. Westerlies•Wind belts between 30° and 60° latitude• Flow toward the poles from west to east• Carry moist air over the U.S., producing rain

and snow

3. Trade Winds• Blow from 30° latitude almost to the equator

4. The Doldrums• “dull” or “sluggish” winds• Little winds near the equator because the

warm, rising air creates an area of low pressure

5. The Horse Latitudes•Weak winds near 30° latitude because the

cool, sinking air creates an area of high pressure•Most of the world’s deserts are located at

these latitudes because the sinking air is very dry

6. Jet Streams• Narrow belts of high-speed winds that blow

in the upper troposphere and lower stratosphere• Do not follow regular paths around the Earth• Affect the movement of storms

C. Local Winds• Generally move short distances and can blow

from any direction1. Sea and Land Breezes

- Air over land is warmer and rises- Air over the ocean is cooler and flows to land,

producing a sea breeze- A land breeze flows over the ocean at night

due to warm air over the ocean

2. Mountain and Valley Breezes- Air above the mountain slopes is warm and

rises up the mountain, creating a valley breeze throughout the day

- Air cools at nightfall and falls back down the slopes, creating a mountain breeze

IV. Air PollutionA. Primary Pollutants• Put directly into the air by human or natural

activity1. Human

- Carbon monoxide, CO- Dust- Smoke- Vehicle exhaust

2. Natural- Sea salt- Volcanic ash- Smoke from forest fires- pollen

B. Secondary pollutants• Form when two primary

pollutants react• Ozone, O3, is an example

of a secondary pollutant- Ozone in the

stratosphere absorbs harmful radiation

- Ozone near the Earth’s surface, is a dangerous pollutant

C. Acid Precipitation• Sulfur dioxide and nitrogen oxide are

produced when fossil fuels are burned• Produce sulfuric acid and nitric acid when

mixed with water

1. Acid Precipitation and Plants- Acid precipitation can cause the acidity of soil

to increase- Nutrients become dissolved when soil acidity

increases and get washed away by rainwater

2. Acid Precipitation and Aquatic Ecosystems- Aquatic organisms have adapted to live in water

with a particular range of acidity- If acid precipitation increases the acidity of a

lake or stream, aquatic organisms may die- Effects are worse in the spring when acidic snow

starts to melt- Powdered lime, a base, is sprayed to neutralize

the acid in water

D. The Ozone Hole• Chemicals called CFCs cause the ozone, O3, to

break down into oxygen, O2

• Oxygen, O2, does not block the sun’s UV rays

1. Cooperation to Reduce the Ozone Holes- The use of CFCs have been banned and

alternatives have been developed- CFC molecules can remain active in the

stratosphere for 60 to 120 years - CFCs released 30 years ago are still

destroying ozone today

E. Cleaning Up Air Pollution• Clean Air Act was passed by Congress in 1970

that gives the Environmental Protection Agency (EPA) the authority to control the amount of air pollutants that can be released from any source