Chapter 15 The Atmosphere

I. Characteristics of the Atmosphere A. 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 Temperature 1. 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 changes 1. 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 Heating A. 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 Winds A. 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 Winds 1. 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 direction 1. 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 Pollution A. Primary Pollutants Put directly into the air by human or natural activity 1. 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, O 3, 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, O 3, to break down into oxygen, O 2 Oxygen, O 2, 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