Suppose you dove into a pool. The deeper you went, the more water there would be above you. The weight of the water above causes the pressure to increase as you go deeper. Like water, air has weight, and pushes on you from all directions. Considering the example above, how do you think the pressure of the air above you would change if you climbed a mountain? How do air pressure and temperature vary in the atmosphere?

Greek Word Origins atmos Vapor, gas Atmosphere

Greek Word Origins exo- Out, outer Exosphere

Greek Word Origins Anemometer, barometer, thermometer meter Measure

Greek Word Origins photo- Light Photochemical

Greek Word Origins thermos Heat Thermosphere

Apply It! Review the Greek origins and meanings in the table. Then predict the meaning of exosphere. Revise your definition as needed. Sample: The exosphere is the outer layer or portion of the thermosphere; from Section 3.

End of Chapter Preview

Section 1: The Air Around You • What is the composition of Earth’s atmosphere? • How is the atmosphere important to living things? • What causes smog and acid rain?

Composition of the Atmosphere • Earth’s atmosphere is made up of nitrogen, oxygen, carbon dioxide, water vapor, and many other gases, as well as particles of liquids and solids.

Links on the Atmosphere • Click the SciLinks button for links on the atmosphere.

More on Air Pollution • Click the PHSchool.com button for an activityabout air pollution.

Oxygen • Click the Video button to watch a movie about oxygen.

End of Section: The Air Around You

Section 2: Air Pressure • What are some of the properties of air? • What instruments are used to measure air pressure? • How does increasing altitude affect air pressure and density?

Air Pressure • There is a column of air above you all the time. • The weight of the air in the atmosphere causes air pressure.

Measuring Air Pressure Activity • Click the Active Art button to open a browser window and access Active Art about measuring air pressure.

Measuring Air Pressure • Air pressure pushes down on the surface of the mercury in the dish, causing the mercury in the tube to rise. The air pressure is greater on the barometer on the right, so the mercury is higher in the tube.

Measuring Air Pressure • This diagram shows an aneroid barometer. Changes in air pressure cause the walls of the airtight metal chamber to flex in and out. The needle on the dial indicates the air pressure.

Air Pressure and Altitude • Air pressure decreases as altitude increases.

Altitude and Density • The density of air decreases as altitude increases. Air at sea level has more gas molecules in each cubic meter than air at the top of a mountain.

End of Section:Air Pressure

Section 3:Layers of the Atmosphere • What are the four main layers of the atmosphere? • What are the characteristics of each layer?

Layers of the Atmosphere • The atmosphere is divided into four main layers: the troposphere, the stratosphere, the mesosphere, and the thermosphere. The thermosphere is further divided into the ionosphere and the exosphere.

Changing Temperatures • The graph shows how temperatures in the atmosphere change with altitude. Use it to answer the questions that follow.

Temperature and altitude; degrees Celsius and kilometers Reading Graphs: What two variables are being graphed? In what unit is each measured? Changing Temperatures

Approximately –55ºC Reading Graphs: What is the temperature at the bottom of the stratosphere? Changing Temperatures

The thermosphere Interpreting Data: Which layer of the atmosphere has thelowest temperature? Changing Temperatures

Temperature decreases as altitude increases. Making Generalizations: Describe how temperature changes as altitude increases in the troposphere. Changing Temperatures

More on the Ozone Layer • Click the Planet Diary button for an activity aboutthe ozone layer.

End of Section:Layers of the Atmosphere

Section 4:Energy in Earth’s Atmosphere • In what form does energy from the sun travel to Earth? • What happens to the sun’s energy when it reaches Earth?

Energy From the Sun • 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.

Energy in the Atmosphere • Some sunlight is absorbed or reflected by the atmosphere. The rest passes through to the surface.

Greenhouse Effect • When Earth’s surface is heated, it radiates most of the energy back into the atmosphere as infrared radiation. Much of this energy is held by the atmosphere, warming it.

Links on Energy in Earth’s Atmosphere • Click the SciLinks button for links on energy in Earth’s atmosphere.

End of Section:Energy in Earth’s Atmosphere

Section 5:Heat Transfer in the Atmosphere • How is temperature measured? • In what three ways is heat transferred? • How is heat transferred in the troposphere?

Temperature and theMovement of Molecules • The iced tea is cold, so its molecules move slowly. The herbal tea is hot, so its molecules move faster than the molecules in the iced tea.

Temperatures in weather reports are usually given in Fahrenheit scale, but scientists use the Celsius scale. Temperature readings can be converted from the Fahrenheit scale to the Celsius scale using the following equation: If the temperature is 68ºF, what is the temperature in degrees Celsius? ºC = 20ºC Converting Units

Practice Problem Use the equation to convert the following temperature from Fahrenheit to Celsius. 35.0ºF 1.67ºC Converting Units

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