1. The Atmosphere Chapter 12

2. The Air Around You Weather –The condition of Earth’s atmosphere at a particular time and place. Atmosphere –The envelope of gases that surrounds the planet.

3. The Air Around You Composition of the Atmosphere –Nitrogen –Oxygen –Carbon dioxide –Water vapor –Other gases –Particles of liquids and solids.

5. The Air Around You Mixtures of atoms and molecules make up the atmosphere. Atoms are the smallest unit of a chemical element that can exist by itself. Molecules are made up of two or more atoms.

6. The Air Around You Nitrogen –Most common gas in the atmosphere. –Makes up a little more than ¾ of the air we breathe. Oxygen –Second most abundant gas in the atmosphere. –Most oxygen molecules have two oxygen atoms. –Ozone is a form of oxygen that has three oxygen atoms in each molecule instead of the usual two.

7. The Air Around You Carbon Dioxide –Essential to life. Other Gases –Oxygen and nitrogen together make up 99 percent –Argon and carbon dioxide make up most of the other one percent. –Trace gases are the remaining gases which only a small amount are present.

8. The Air Around You Water Vapor –Water in the form of a gas. –Amount varies in the air greatly from place to place and from time to time. –Clouds form when water vapor condenses out of the air.

9. The Air Around You Particles –Pure air contains only gas. –Air we breathe also contains tiny solid and liquid particles of dust, smoke, salt, and other chemicals.

10. The Air Around You Importance of the Atmosphere –Makes conditions on Earth suitable for living things. –Contains oxygen and other gases that living things need to survive. –Protects living things from ultraviolet radiation from the sun. –Prevents Earth’s surface from being hit by most meteoroids.

11. The Air Around You Air Quality –Pollutants are harmful substances in the air, water, or soil. –Air pollution can affect the health of humans and other living things. Sources of Pollution –Some occurs naturally. –Result of burning fossil fuels, such as coal, oil, gasoline, and diesel fuel.

12. The Air Around You Smog and Acid Rain –The burning of fossils fuels can cause. –The brown haze that develops in sunny cities is called photochemical smog. Formed by actions of sunlight on pollutants such as hydrocarbons and nitrogen oxides. –Smog can irritate the eyes, throat, and lungs.

13. The Air Around You Acid Rain –Rain that contain more acid than normal. –The burning of coal that contains a lot of sulfur produces sulfur oxides, substances composed of oxygen and sulfur. –Forms when nitrogen oxides and sulfur oxides combine with water in the air to form nitric acid and sulfuric acid.

14. The Air Around You Improving Air Quality –Environmental Protection Agency (EPA) Monitors air pollutants in the United States.

15. Air Pressure Properties of Air –Air has mass, and other properties, including density and pressure. Density –Amount of mass in a given volume of air. Pressure –Force pushing on an area or surface. –The weight of the atmosphere exerts in a force on surface is known as air pressure. The result of the weight of a column of air pushing down on an area.

16. Air Pressure Measuring Air Pressure –Barometer An instrument that is used to measure air pressure. Two kinds –Mercury barometer –Aneroid barometer

17. Air Pressure Mercury Barometer –Consists of a glass tube open at the bottom end and partially filled with mercury.

18. Air Pressure Aneroid Barometers –Aneroid means “without liquid.” –Metal chamber is sensitive to changes in air pressure. –Pressure increase – push in –Pressure decrease – bulge out

19. Air Pressure Altitude and the Properties of Air –At the top of a mountain, the air pressure is less than the air pressure at sea level. –Altitude “elevation” is the distance above sea level, the average level of the surface of the oceans. –Air pressure decreases as altitude increases. As air pressure decreases, so does density.

21. Air Pressure Altitude Affects Air Pressure –Sea-level air has the weight of the whole atmosphere pressing on it. –So air pressure is greater at sea level. Altitude Also Affects Density –As you go up through the atmosphere, the density of the air decreases. –Since the air is less dense at a high altitude, there are fewer oxygen molecules to breathe in each cubic meter of air than at sea level.

23. Layers of the Atmosphere Scientists divide Earth’s atmosphere into four main layers classified according to changes in temperature. –Troposphere –Stratosphere –Mesosphere –Thermosphere

25. Layers of the Atmosphere The Troposphere –The inner, or lowest, layer of Earth’s atmosphere. –Tropo – means “turning” or “changing” –Conditions more variable –The layer in which Earth’s weather occurs. –The depth varies from 16 kilometers above the equator to less than 9 kilometers above the North and South poles. –Contains almost all of the mass of the atmosphere. –As altitude increases, the temperature decreases.

26. Layers of the Atmosphere The Stratosphere –Extends from the top of the troposphere to about 50 kilometers above Earth’s surface. –Strato – means “layer” or “spread out” –Second layer and contain ozone. –Lower level is cold and the upper level is warmer. –Middle portion contains a layer of air where there is much more ozone than in the rest of the atmosphere.

27. Layers of the Atmosphere The Mesophere –A drop in temperature above the stratosphere marks the beginning of this layer. –Meso – means “middle” –Begins 50 kilometers above Earth’s surface and ends at an altitude of 80 kilometers. –Protects Earth’s surface from being hit by most meteoroids.

28. Layers of the Atmosphere The Thermosphere –Outer most layer of the atmosphere. –Extends from 80 kilometers above Earth’s surface outward into space. –No definite outer limit, but blends gradually with outer space. –Thermo – means “heat.” –Divided into two layers. Ionosphere exophere

29. Layers of the Atmosphere Ionosphere –Lower layer –Energy from the sun causes gas molecules to become electrically charged particles called ions. –Brilliant light displays occur in this layer.

30. Layers of the Atmosphere Exosphere –Exo – means “outer.”

31. Energy in Earth’s Atmosphere Energy From the Sun –Nearly all the energy comes from the sun. –Energy travels to Earth as electromagnetic waves. –Electromagnetic waves are classified according to wavelength, or distance between waves. –Radiation is the direct transfer of energy by electromagnetic.

32. Energy in Earth’s Atmosphere Most of the energy from the sun travels to Earth in the form of visible light and infrared radiation. A small amount arrives as ultraviolet radiation.

33. Energy in Earth’s Atmosphere Visible Light ROYGBIV –Red –Orange –Yellow –Green –Blue –Indigo –Violet

34. Energy in Earth’s Atmosphere Non-Visible Radiation –Infrared radiation one form of electromagnetic energy has wavelengths that are longer than red light. not visible. –Ultraviolet Radiation Invisible form of energy with wavelengths that are shorter than violet light. Can cause sunburns.

35. Energy in Earth’s Atmosphere Energy in the Atmosphere –Some sunlight is absorbed or reflected by the atmosphere before it can reach the surface. –The rest passes through the atmosphere to the surface. –Dust particles and gases in the atmosphere reflect light in all directions in a process called scattering.

36. About 50 percent is absorbed by Earth’s surface. This energy heats the land and water. Some absorbed energy is radiated back into the atmosphere. 20 percent is absorbed by gases and particles in the atmosphere. About 25 percent of incoming sunlight is reflected by clouds, dust, and gases in the air. 5 percent is reflected by the surface back into the atmosphere.

37. Energy in Earth’s Atmosphere Energy at Earth’s Surface –When Earth’s surface is heated, it radiates most of the energy back into the atmosphere as infrared radiation. –The energy from the absorbed radiation heats the gases in the air. –These gases form a “blanket” around Earth that holds heat in the atmosphere. –The process by which gases hold heat in the air is called the greenhouse effect.