Pollution of the Atmosphere

Transcription

1 Pollution of the Atmosphere LESSON 2 Guiding Question: What are the sources of air pollution? Explain how both natural processes and human activities can cause air pollution. Describe how air pollutants affect human health. Explain what causes smog and how temperature inversions affect it and other forms of air pollution. Explain how acid deposition occurs and describe its effects. Reading Strategy Before you read, make a three-column KWL chart. In the first column, write what you already know about air pollution. In the second column, write what you want to learn. After reading, complete the chart by filling in what you have learned in the third column. Vocabulary air pollution, emission, fossil fuel, primary air pollutant, secondary air pollutant, smog, temperature inversion, acid deposition CROWDED TOGETHER, the horses in the parade seem to be fighting for space. The horse in the forefront is rearing, possibly frightened by the other horses and riders nearby. The rider, in contrast, appears calm as he looks off into the distance. Thousands of years ago, in ancient Athens, Greek sculptors created this parade in marble to go at the top of the Parthenon, a temple that honored the goddess Athena. Today the parade of warriors no longer graces the Parthenon. Instead, the sculptures are inside a museum in Athens. The sculptures were moved to protect them from more damage. One cause of damage was pollutants in the air. If you look carefully at Figure 10, you can see that some of the stone has been worn away LESSON PLAN PREVIEW Inquiry Students research the health effects of air pollutants. Real World Students predict how increasing public transportation use might affect a city s smog levels. Differentiated Instruction Less proficient readers organize information about the sources and effects of acid deposition RESOURCES Scientific Method Lab, Acid Rain and Seeds Outdoors Lab, What s in the Air? Lesson 15.2 Worksheets Lesson 15.2 Assessment Chapter 15 Overview Presentation GUIDING QUESTION FOCUS Divide the class into small groups and have each group sit in a circle. Have one student in each circle name a source of air pollution. Then, have the student to his or her right name another source. Have them continue around the circle naming different sources until the group runs out of ideas. FIGURE 10 Damage From Air Pollution Notice that the warriors faces have been worn away. The damage was caused partly by air pollution. The Atmosphere 461

2 FIGURE 11 Dust Storm Over a field in Africa, wind blows dust particles into the air. Sources of Air Pollution Air pollution can be caused by natural processes and human activities. The cars, trucks, and industries of modern Athens have released pollutants that have contributed to the damage to the Parthenon. Both human activities and natural processes cause outdoor air pollution, which is the release of damaging materials into the atmosphere. The substances released are called emissions. Some emissions, such as smoke and soot, consist of tiny particles, or particulate matter. Others are gases such as sulfur dioxide and carbon monoxide. BIG QUESTION How can we ensure everyone has clean air to breathe? Perspective After students have read about human sources of air pollution, reread the following sentence: Most air pollution comes, directly or indirectly, from the combustion of fossil fuels. Have students write a paragraph or two explaining how this statement affects their answer to the Big Question. Natural Processes Natural processes produce a great deal of the world s air pollution. Winds sweeping over dry land can create huge dust storms, as seen in Figure 11. Winds sometimes blow dust across oceans from one continent to another. Volcanic eruptions release tiny solid particles and gases into the atmosphere. Fires in forests and grasslands also produce smoke, soot, and gases. Human activities can make some natural pollution worse. For example, some farming and grazing practices strip most plants from the soil. When there are few plant roots to hold soil in place, wind erosion may occur. Wind erosion can lead to dust storms. Human Sources People s activities have influenced air quality. The way we live for example, our industries, the cars we drive, and the way we produce electricity has introduced many sources of air pollution. Air pollution can come from point sources or nonpoint sources. In London, power plants and factories act as point sources of emissions. Millions of cars and trucks together make up a moving nonpoint source. Most air pollution comes, directly or indirectly, from the combustion of fossil fuels. Fossil fuels are carbon-containing fuels that formed millions of years ago from the remains of living things. Motor vehicles, such as cars and trucks, run by burning fossil fuels. Motor vehicles release an enormous amount of pollutants into the air. 462 Lesson 2

3 Primary and Secondary Air Pollutants Pollutants may do harm directly, or they may cause chemical reactions that produce harmful compounds. Primary air pollutants, such as soot and carbon monoxide, are pollutants released directly into the troposphere. Primary air pollutants may cause damage themselves, or they may react with other products to cause damage. Harmful products produced when primary air pollutants react chemically with other substances are called secondary air pollutants. Secondary air pollutants include tropospheric ozone and sulfuric acid. The table in Figure 12 describes some primary and secondary air pollutants. FIGURE 12 Air Pollutants Primary air pollutants are released directly into the troposphere. Secondary air pollutants, in contrast, are the products of chemical reactions between primary air pollutants and other substances. Primary Air Pollutants Pollutant Carbon monoxide (CO A colorless, odorless gas Sulfur dioxide (SO 2 A colorless gas with a strong, unpleasant odor Nitrogen dioxide (NO 2 A foul-smelling, reddish-brown gas that belongs to a family of compounds called nitrogen oxides Volatile organic compounds (VOCs Carbon-containing chemicals that evaporate easily, producing fumes. Examples include methane, propane, butane, and benzene. Particulate matter Solid or liquid particles that are small enough to float in the atmosphere soot, dust, tiny bits of metals Lead A heavy metal that is one type of particulate matter Source The incomplete combustion (burning of fossil fuels by motor vehicles, industries, and other sources Burning of fossil fuels, especially coal, for electricity generation and industry A reaction between atmospheric nitrogen and oxygen in combustion engines and during the production of electricity Many sources, including vehicle engines, household cleaning products, some industrial processes, and natural processes Dust blown by wind; soot and chemicals produced by fires and combustion within engines; particles produced during construction and farming Industrial refinement of metals; in developing nations, gasoline contains lead Effect Binds to hemoglobin, the oxygencarrying chemical in blood; deprives cells of oxygen Produces secondary pollutants that are part of acid precipitation; causes lung irritation Can cause serious lung irritation; contributes to smog and acid precipitation Some can cause cancer; some interact with other chemicals to produce ozone in the troposphere. Can affect breathing and damage lungs Can damage body tissues, including those in the nervous system Pollutant Tropospheric ozone (O 3 A colorless gas with an unpleasant odor Sulfuric acid (H 2 SO 4 and nitric acid (HNO 3 Secondary Air Pollutants Source Results from the interaction of sunlight, heat, nitrogen oxides, and volatile organic compounds Produced when sulfur dioxide and nitrogen oxides combine with water in the atmosphere Effect Ozone in the stratosphere protects humans from radiation, but ozone in the troposphere can injure living tissues and cause respiratory problems. Components of acid precipitation The Atmosphere 463

4 FIGURE 13 Effects of Air Pollution A runner in the Beijing Olympic Games wears a mask to protect his respiratory system from air pollution. Beijing has severe air pollution. Before the 2008 Olympic Games, the city made a major effort to clean its air. How Air Pollutants Affect Your Health Air pollutants can damage the respiratory system, interfere with the body s uptake of oxygen, and cause cancer. Outdoor air pollution is a big health problem. Air pollutants can do serious harm to the respiratory system, which transports oxygen into your body and removes carbon dioxide. Some air pollutants can cause cancer. Respiratory System Problems Have you ever inhaled dust and then started coughing? Particles in the dust irritated your respiratory system, making you cough. Similarly, air pollutants irritate people s air passages and lungs. If people are exposed over and over to air pollution, they may develop harmful respiratory conditions. Asthma, bronchitis, and emphysema have all been linked to air pollutants. The Effect of Carbon Monoxide How do the cells of your body obtain the oxygen they need? The air that you inhale contains oxygen. This oxygen passes from the lungs into the bloodstream. There, oxygen binds to hemoglobin. Hemoglobin is a molecule in red blood cells that combines chemically with oxygen. The red blood cells then carry the oxygen to the cells of the body. However, if there is carbon monoxide in the air, the carbon monoxide will bind to hemoglobin, replacing some of the oxygen that the blood would normally carry. Therefore, carbon monoxide interferes with your body s ability to deliver oxygen to cells. This can cause headaches, tiredness, and nausea. Over time, carbon monoxide can damage the heart because the heart muscle has to work harder than normal to deliver oxygen to cells. In high concentrations, carbon monoxide can be fatal. Cancer Trace amounts of some air pollutants may contribute to cancer. Soot, for example, can cause cancer if it is inhaled frequently. Benzene, which is a volatile organic compound in gasoline, has also been linked to cancer. Exhaust from cars and trucks contains benzene. 464 Lesson 2

5 Smog and Temperature Inversions Temperature inversions may trap smog close to the surface of Earth, preventing the pollutants from dispersing. If you combine the words smoke and fog, you get the word smog. Smog is an unhealthy mixture of air pollutants that may form over cities and nearby areas. Industrial Smog The smog that covered London in 1952 was industrial smog. Industrial smog is produced when soot combines with sulfur compounds and water droplets in air. Because of government regulation, this type of smog is far less common in developed nations than it was years ago. However, the situation is different in developing nations, such as China and the nations of Eastern Europe. Industrial technologies in these nations are often older than those in developed nations, and have less ability to control pollution than do newer technologies. Also, there is less government regulation of air quality in these nations. Therefore, industrial smog continues to create health problems in many areas. Photochemical Smog A photochemical process is one that needs light. Photochemical smog is a thick, brownish haze that forms when sunlight acts on certain air pollutants, such as nitrogen oxides and chemicals called hydrocarbons. Tropospheric ozone is often the most abundant pollutant in photochemical smog. Ozone in the troposphere is chemically identical to ozone in the stratosphere. However, unlike ozone in the stratosphere, which protects living things by filtering ultraviolet light, tropospheric ozone can damage living tissue especially eye and lung tissues and plant leaves as well as other materials. The main source of the pollutants in photochemical smog is the exhaust released by cars and trucks. Governments are acting to reduce motor-vehicle emissions, which will reduce photochemical smog. For example, vehicle inspection programs make drivers fix cars and trucks that release high levels of pollutants. What Do you think? Should your city, or a city near you, start a congestion-charging program like London s? What are some of the pros and cons of such a program? ANSWERS What Do You Think? Answers will vary. Students should identify logical pros and cons. Reading Checkpoint For photochemical smog to form, light is necessary. Industrial smog can form without light. Figure 14 Burning coal FIGURE 14 Photochemical Smog Smog shrouds the borough of Manhattan in New York City. Relate Cause and Effect What was the main source of the pollutants that caused London s killer smog in 1952? Reading Checkpoint What is the difference between industrial smog and photochemical smog? The Atmosphere 465

6 ANSWERS Reading Checkpoint During a temperature inversion, the air at Earth s surface is colder than the air above it. Cold air has a greater density than warm air, so the cold air does not rise and mix with the air above it. Figure 15 A temperature inversion can trap pollutants, including those in smog, near the ground. FIGURE 15 Temperature Inversion Normally, tropospheric temperature decreases with height above the ground (a, and air at the surface mixes with air above it. In a temperature inversion (b, cool air stays near the ground, under a layer of warmer air, and little mixing occurs. Relate Cause and Effect Why can a temperature inversion, such as the one that occurred in London in 1952, make air pollution worse? Temperature Inversions Recall that in the troposphere, air temperature usually decreases as altitude increases. Earth s surface warms the air at low altitudes. Since warm air rises, any pollutants in the air are carried away from the surface and higher into the troposphere. This process removes pollutants from low altitudes and helps them disperse. The situation is different, however, when a temperature inversion occurs. A temperature inversion, or thermal inversion, is the condition in the troposphere in which a layer of cooler air is located beneath a layer of warmer air. Since cold air has a greater density than warm air, the air at Earth s surface does not rise and mix with the air higher up. Therefore, temperature inversions can keep air pollutants, including those found in smog, from going away. Figure 15 shows how a temperature inversion can worsen air pollution. It was a thermal inversion that caused London s killer smog of Inversions regularly cause smog buildup in some cities, such as Los Angeles and Mexico City. Reading Checkpoint High Altitude Altitude Low High Low Cool Temperature Warm Surface warmed by sun (a Normal Conditions Cool Warm Temperature Cool During a temperature inversion, why doesn t air at Earth s surface rise? Pollution trapped (b Thermal Inversion Vertical mixing Inversion layer 466 Lesson 2

7 Primary pollutants Secondary pollutants Sulfur dioxide (SO 2 Water (H 2 O, oxygen (O 2, and other substances Sulfuric acid (H 2 SO 4 Nitric oxide (NO Nitric acid (HNO 3 Acid precipitation Acid Deposition Acid deposition results when products of combustion combine with water, oxygen, and other substances in the atmosphere. When some pollutants combine with water, oxygen, and other chemicals in the atmosphere, they form compounds called acids. These acids may settle to the surface of Earth as acid deposition. Acid deposition may consist of solid or gaseous particles, or the acids may dissolve in fog or precipitation. Acid precipitation is sometimes called acid rain, but any kind of precipitation, such as snow or sleet, can contain acidic pollutants. FIGURE 16 Formation of Acid Precipitation Acid precipitation starts when sulfur dioxide and nitrogen oxides such as nitric oxide combine with water, oxygen, and other substances. Acid precipitation can affect areas a long way from the original source. The ph Scale and Precipitation The ph scale is used to measure whether solutions are acidic or alkaline. The values on the scale range from 0 to 14. A ph of 7 is neutral, that is, it is neither acidic nor alkaline. If a solution has a ph that is higher than 7, it is alkaline, or basic. An acid is a solution whose ph is lower than 7. The lower the ph number, the higher the acidity. The ph of precipitation varies. Normal precipitation is slightly acidic, with a ph of about 5.6. Acid precipitation has a lower ph. Some areas in the United States have precipitation with a ph as low as 4.3. Go Outside Is the Rainwater Acidic? 1 On a rainy day, put a clean plastic cup outside where it will collect rainwater. 2 Bring the collected rainwater indoors. Then use ph paper to measure the ph of the water. 3 Compare your results to those of other students. ANSWERS Go Outside 1. Answers will vary. Students should classify rainwater as acidic if its ph is lower than 5.6, the ph of normal precipitation. 2. Answers will vary. Analyze and Conclude 1. Analyze Data Is rainwater in your area more acidic than normal rainwater? Explain your answer. 2. Perform Error Analysis If other students obtained different results from yours, try to figure out why. The Atmosphere 467

8 Figure 17 Effects of Acid Deposition Notice that many trees no longer have any needles a result of acid deposition. ANSWERS Lesson 2 Assessment 1. Sulfur dioxide: primary pollutant; sulfuric acid: secondary pollutant. Sulfuric acid is the product of a reaction between sulfur dioxide and water. 2. To protect their respiratory system 3. In a temperature inversion, cooler, dense air is trapped near the ground. Since the air does not move, the pollutants that the air contains cannot mix with air higher up. 4. No; normal precipitation has a ph of about 5.6; acid precipitation has a ph lower than Developing nations are trying to industrialize. By restricting processes that produce smog, they might also slow economic progress. Sources of Acid Deposition Acid deposition starts mainly with sulfur dioxide and nitrogen oxides. These pollutants are produced largely through the burning of fossil fuels by automobiles, electric power plants, and industries. In the troposphere, these compounds can react with water, oxygen, and other substances to produce acids such as sulfuric acid and nitric acid. Wind can carry pollutants over long distances. Therefore, acid deposition may fall on areas that are far from where the pollutants were produced. For example, much of the pollution that is produced in Pennsylvania, Ohio, and Illinois falls out in states to the east, including New York, Vermont, and New Hampshire. Effects of Acid Deposition Acid deposition can harm ecosystems and structures that humans have built. For example, if the ph in lakes becomes too low, neither plants nor fishes can survive. Acid deposition can kill trees and destroy whole forests (Figure 17. When acid gets into the soil, harmful chemicals can be released. These chemicals can poison plants growing in the soil. Acid deposition can erode the surfaces of stone buildings and statues, such as the Parthenon sculptures. In addition, acid deposition can increase the acidity of the water that comes into your home. Water with increased acidity can pick up harmful chemicals from metal pipes and contaminate drinking water. Acid deposition is a problem, but it can be solved. People and governments have taken steps to eliminate or reduce air pollutants that cause acid deposition. The next lesson describes some of those steps Interpret Tables Sulfuric acid and sulfur dioxide are both air pollutants. Use Figure 12 to determine which is a primary pollutant and which is a secondary pollutant. What is the relationship between these two types of pollutants? 2. Infer When people work with volatile organic compounds, why should they wear special masks that cover their noses and mouths? 3. Relate Cause and Effect Why does a temperature inversion trap smog and prevent it from dispersing? 4. Apply Concepts The rain that falls in an area has a ph of 5.8. Is this acid precipitation? Explain your answer. 5. Explore the BIGQUESTION Why might developing nations be more reluctant than developed nations to take measures to control industrial smog? 468 Lesson 2