1. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Air Quality Issues Chapter 16 14 th Edition A Study of Interrelationships ENVIRONMENTAL SCIENCE 14 th Edition 1

2. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Outline 16.1 The Atmosphere 16.2 Pollution of the Atmosphere 16.3 Categories of Air Pollutants 16.4 Photochemical Smog 16.5 Acid Deposition 2

3. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Outline 16.6 Ozone Depletion 16.7 Control of Air Pollution 16.8 Air Pollution in the Developing World 16.9 Indoor Air Pollution 16.10 Noise Pollution 3

4. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 16.1 The Atmosphere The atmosphere is composed of 78.1% N, 20.9% O, and about 1% of other gases such as argon, carbon dioxide, methane, and water vapor. Most of the atmosphere is held close to the Earth by the pull of gravitational force, thus it gets less dense with increasing distance from the Earth. 4

5. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 16.1 The Atmosphere The troposphere extends from the Earth’s surface to about 10 km above the Earth. The stratosphere extends from the top of the troposphere to about 50 km above the Earth. Most ozone is located in a band between 15 and 30 km. The mesosphere extends from 50-80 km above the Earth. The thermosphere extends to about 300 km above the Earth. 5

6. Copyright © McGraw-Hill Education. Permission required for reproduction or display. The Atmosphere 6

7. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 16.1 The Atmosphere As the air absorbs heat from the Earth, it expands and rises. When heat is radiated into space, air cools, becomes more dense, and flows toward the Earth. As the air circulates vertically, it also moves horizontally as the Earth spins on its axis. The combination of all air movements creates the wind and weather patterns characteristic of different regions of the world. 7

8. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Global Wind Patterns 8

9. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 16.2 Pollution of the Atmosphere Pollution is any addition of matter or energy that degrades the environment for humans and other organisms. Because human actions are the major cause of pollution, we can do something to prevent it. Automobile emissions, chemical odors, factory smoke, and similar materials are considered air pollution. 9

10. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 16.2 Pollution of the Atmosphere Air pollution is directly related to the number of people living in an area and the kinds of activities in which they are involved. In urbanized, industrialized societies, there are dense concentrations of people that use large quantities of fossil fuels for manufacturing, transportation, and domestic purposes. These activities release large quantities of polluting byproducts into our environment. 10

11. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 16.2 Pollution of the Atmosphere In urbanized areas, pollution cannot be sufficiently diluted before the air reaches another city. Polluted air from Chicago is further polluted when it reaches Gary, Indiana; is supplemented by wastes of Detroit and Cleveland; and finally moves over southeastern Canada and New England to the ocean. Air pollution is not just an aesthetic problem; it also causes health problems. 11

12. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Air Pollution and Population Centers 12

13. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 16.2 Pollution of the Atmosphere Many of the megacities of the developing world have extremely poor air quality. The causes of this pollution are open fires, poorly maintained motor vehicles, and poorly regulated industrial plants. Air pollution increases the death rate and lowers the general health of the population. Chronic coughing and susceptibility to infections are common. 13

14. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 16.3 Categories of Air Pollutants Five major types of materials are released directly into the atmosphere in unmodified forms in sufficient quantities to pose a health risk. These are called primary air pollutants. They are: Carbon monoxide Volatile organic compounds (hydrocarbons) Particulate matter Sulfur dioxide Oxides of nitrogen 14

15. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 16.3 Categories of Air Pollutants Secondary air pollutants form under reaction of primary pollutants and water or sunlight. Ozone Criteria air pollutants are those pollutants for which specific air quality standards have been set. Nitrogen dioxide (NO 2 ) Ozone (O 3 ) Sulfur dioxide (SO 2 ) Particulate matter (PM) Carbon monoxide (CO) Lead (Pb) 15

16. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Carbon Monoxide Carbon monoxide is produced when organic materials are burned with insufficient oxygen. The single largest source is the automobile. 60% from vehicles driven on roads 20% from vehicles not used on roads Remainder from burning, i.e., power plants, leaves, etc. Carbon monoxide binds to hemoglobin in blood and makes the hemoglobin less able to carry oxygen. It is most dangerous in enclosed spaces; several hours of exposure to air containing only 0.001% CO can cause death. 16

17. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Carbon Monoxide Cigarette smoking is an important source because the person is inhaling CO directly. U.S. levels of CO have decreased by about 75% between 1970 and 2007. 17

18. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Carbon Monoxide 18

19. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Particulate Matter Particulate matter consists of minute pieces of solid materials (< 10 microns) and liquid droplets dispersed into the atmosphere. The EPA has set standards for particles smaller than 10 microns (PM 10 ) and 2.5 microns (PM 2.5 ). Larger than 2.5 microns are primary pollutants; smaller than 2.5 are mostly secondary pollutants. Particulates can accumulate in lungs and interfere with the ability of lungs to exchange gases. 19

20. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Particulate Matter Amount of PM 10 has decreased 28% between 1990 and 2007. U.S. EPA has been setting PM 2.5 standards for a shorter period of time. Amount decreased 11% between 2000 and 2007. Most communities now meet the standards set for PM 10 but exceed the standards set for PM 25. 20

21. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Particulate Matter 21

22. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Sulfur Dioxide Sulfur dioxide (SO 2 ) is a compound of sulfur and oxygen produced when sulfur-containing fossil fuels are burned. Burning coal releases SO 2. Today over 70% of SO 2 released into the atmosphere is from coal- burning power plants. U.S. levels of SO 2 decreased 56% between 1990 and 2007. Nearly all communities meet the SO 2 standards set by the U.S. EPA. 22

23. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Sulfur Dioxide 23

24. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Nitrogen Dioxide Oxides of nitrogen (NO x ) are formed when fossil fuels are burned. The nitrogen and oxygen molecules in the air combine with one another when subjected to the high temperatures of combustion. Nitrogen monoxide (NO) and nitrogen dioxide (NO 2 ) are the most common. Burning fossil fuels in internal combustion engines is the primary source of nitrogen oxides. Automobiles produce 38% Non-road motorized equipment produces 21% Electrical generations produces 22% 24

25. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Nitrogen Dioxide About 75% of the NO produced by an automobile engine is converted back into N 2 and O 2 by the catalytic converter. An increase in the number of cars and miles driven offsets the gains attributable to catalytic converters. Although all communities meet the EPA standards for nitrogen oxides, they remain a problem because they contribute to the development of photochemical smog. 25

26. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Nitrogen Dioxide 26

27. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Lead Lead (Pb) can enter the body through breathing airborne particles or consuming lead deposited on surfaces. Lead accumulates in the body and can cause mental retardation and kidney damage. Leaded gasoline was primary source. Almost all countries have phased out lead as an additive to gasoline. Nearly all gasoline is now unleaded. In the U.S. lead emissions peaked at about 258,000 tons per year. In 2007 they were about 1300 tons per year, a reduction of 99.5%, meeting EPA standards in the U.S. 27

28. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Volatile Organic Compounds Volatile organic compounds (VOCs) are organic compounds that readily evaporate and become pollutants in the air. Since they are composed primarily of carbon and hydrogen, they are often referred to as hydrocarbons. Sources of VOC air emissions include internal combustion engines (44%) and solvents (22%) VOCs are important in the processes that lead to the production of the secondary air pollutants found in smog. 28

29. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Volatile Organic Compounds (VOCs) 29

30. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Hazardous Air Pollutants Hundreds of other dangerous chemical compounds that can cause harm to human health or damage the environment are purposely or accidentally released into the air. These compounds are collectively known as hazardous air pollutants (HAP) or air toxics. Pesticides Benzene in gasoline Some consumer products such as glues and cleaners 30

31. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Hazardous Air Pollutants The majority of air toxics, however, are released as a result of manufacturing processes. Perchloroethylene is released from dry cleaning establishments, and toxic metals are released from smelters. The chemical and petroleum industries are the primary sources of hazardous air pollutants. Although air toxics are harmful to the entire public, their presence is most serious for people who are exposed on the job. 31

32. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 16.4 Photochemical Smog The pollutants discussed in the previous sections are primary air pollutants that are released directly into the air. Secondary air pollutants are those that are created in the air from preexisting pollutants. Photochemical smog involves the production of secondary air pollutants. 32

33. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 16.4 Photochemical Smog Photochemical smog is a mixture of pollutants. It forms when nitrogen dioxide and VOCs interact in primary pollutants interact under the influence of sunlight. Two most destructive components: Ozone Peroxyacetyl nitrates (PAN) 33

34. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 16.4 Photochemical Smog Ozone (O 3 ) is a molecule of three oxygen atoms bonded to one another. Ground-level ozone is a serious pollutant. Ultraviolet light can damage tissue and cause genetic mutations. However, in the upper atmosphere ozone serves to screens out ultraviolet light. 34

35. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Photochemical Smog 35

36. Copyright © McGraw-Hill Education. Permission required for reproduction or display. How Smog Forms For photochemical smog to develop, several ingredients are required: Nitrogen monoxide, nitrogen dioxide, and volatile organic compounds must be present. Sunlight and warm temperatures are important to support the chemical reactions involved. In most urban areas, nitrogen monoxide, nitrogen dioxide, and volatile organic compounds are present as by-products of the burning of fuel in vehicles and industrial processes. 36

37. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Major Steps in the Development of Photochemical Smog 37

38. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Daily Changes in Pollutants During a Photochemical Smog Incident 38

39. Copyright © McGraw-Hill Education. Permission required for reproduction or display. The Role of Climate and Geography Cities with warm climates and lots of sunlight are more prone to develop photochemical smog. Warm temperatures and sunlight are needed. Smog is more likely to be a problem in the summer with higher temperatures and longer days. Cities adjacent to mountains or in valleys tend to have trouble with photochemical smog because pollutants are trapped by thermal inversions. 39

40. Copyright © McGraw-Hill Education. Permission required for reproduction or display. The Role of Climate and Geography Thermal inversions occur when warm air becomes sandwiched between two layers of cold air and acts like a lid on a valley. Warm air cannot rise, causing smog accumulation. Ozone levels fell by about 12% from 1990 to 2012 and are still a problem, particularly in southern California and the U.S. Northeast. Since ozone is produced by VOCs and No x it is necessary to further reduce the levels of these two components to decrease the production of ozone. 40

41. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Thermal Inversion 41

42. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 16.5 Acid Deposition Acid deposition is the accumulation of potential acid- forming particles on a surface. When dry particles are deposited, an acid does not actually form until these materials mix with water. All of these sources of acid-forming particles are commonly referred to as acid rain. 42

43. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Causes of Acid Precipitation Acids in the atmosphere result from natural causes: Vegetation Volcanoes Lightning Human activities, such as the burning of coal and use of the internal combustion engine Acid rain is a worldwide problem. 43

44. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Sources of Acid Deposition 44

45. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Effects on Structures 45

46. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Effects on Terrestrial Ecosystems As lakes became more acidic, there is a progressive loss of many kinds of organisms: The food web becomes less complicated. Many organisms fail to reproduce, and many others die. Most healthy lakes have a pH above 6. At a pH of 5.5, many desirable species of fish are eliminated At a pH of 5, only a few starving fish may be found, and none is able to reproduce. Lakes with a pH of 4.5 are nearly sterile. 46

47. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Effects on Terrestrial Ecosystems The extent to which acid deposition affects an ecosystem depends on the nature of the bedrock in the area and the ecosystem’s proximity to acid-forming pollution sources. Eastern Canada and the U.S. Northeast are particularly susceptible to acid rain. 47

48. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Forest Decline 48

49. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Factors That Contribute to Acid Rain Damage 49

50. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Why Stratospheric Ozone is Important In 1985, it was discovered that a significant thinning of the ozone layer over the Antarctic occurred during the Southern Hemisphere spring. The stratosphere was being reduced, and this area became known as the “ozone hole.” Ozone in the outer layers of the atmosphere shields the Earth from the harmful effects of ultraviolet light radiation. 50

51. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Ozone Destruction Chlorofluorocarbons and similar compounds can release chlorine atoms which can lead to the destruction of ozone. It can take 10 to 20 years for chlorofluorocarbon molecules to get into the stratosphere. They can then react with the ozone for up to 120 years. 51

52. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Actions to Protect the Ozone Layer In 1987, several industrialized countries including Canada, the United States, the United Kingdom, Sweden, Norway, Netherlands, the Soviet Union, and West Germany agreed to freeze chlorofluorocarbon and halon (used in fire extinguishers) production and reduce production by 50% by 2000. This document, known as the Montreal Protocol, was ratified by Congress in 1988. As a result, emissions dropped 87% from their peak in 1988. 52

53. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Size of Antarctic Ozone Hole 53

54. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 16.7 Control of Air Pollution All of the air pollutants we have examined thus far are the result of human activity. That means their release into the atmosphere can be controlled. In the United States, implementation of the requirements of the Clean Air Act has been the primary means of controlling air pollution. 54

55. Copyright © McGraw-Hill Education. Permission required for reproduction or display. The Clean Air Act What is commonly called the Clean Air Act is in reality several pieces of legislation. The original Clean Air Act of 1970 was amended in 1977 and again in 1990. The EPA has a number of responsibilities under the original act of 1970 and its amendments. 55

56. Copyright © McGraw-Hill Education. Permission required for reproduction or display. The Clean Air Act EPA Responsibilities: Establishing air quality standards, developing strategies for meeting the standards, and ensuring that the standards are met. Conducting periodic reviews of the six criteria air pollutants that are considered harmful to public health and the environment. Reducing emissions of SO 2 and NO X that cause acid rain. 56

57. Copyright © McGraw-Hill Education. Permission required for reproduction or display. The Clean Air Act EPA Responsibilities (Continued): Reducing air pollutants such as PM, SO X, and NO X, which can reduce visibility across large regional areas. Ensuring that sources of toxic air pollutants are substantially reduced. Limiting the use of chemicals that damage the stratospheric ozone layer. 57

58. Copyright © McGraw-Hill Education. Permission required for reproduction or display. The Clean Air Act Implementation of the Clean Air Act and its amendments led to the establishment of a series of detailed control requirements to meet the goals of improving air quality: All industries are required to obtain permits to release materials into the air. All new and existing sources of air pollution are subject to national ambient air quality standards. Newly constructed facilities are subject to more stringent control technology and permitting requirements than are pre-existing facilities. 58

59. Copyright © McGraw-Hill Education. Permission required for reproduction or display. The Clean Air Act Clean Air Act Control Requirements (Continued): Hazardous air pollutants are specifically identified. Power plants are allowed to sell their sulfur dioxide release permits to other companies. The net result of this program has been a rapid reduction in sulfur dioxide emissions. A program for the phaseout of ozone-depleting substances (chlorofluorocarbons [CFCs], halons, carbon tetrachloride, and methyl chloroform) was established. 59

60. Copyright © McGraw-Hill Education. Permission required for reproduction or display. The Clean Air Act In 2007, the U.S. Supreme Court ruled that greenhouse gases like CO 2 could be considered pollutants and gave the Environmental Protection Agency the power to regulate them under the Clean Air Act. In 2011, the EPA established new regulations on the release of mercury and several other toxic substances. 60

61. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Actions That Have Reduced Air Pollution The improvement in air quality since the enactment of the Clean Air Act is a major success story. As a result of implementing the requirements of the Clean Air Act, a variety of pollution control mechanisms were effectively employed and air quality has improved significantly. 61

62. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Motor Vehicle Emissions Motor vehicles are the primary source of several important air pollutants: Carbon monoxide Volatile organic compounds Nitrogen oxides Ozone (secondary pollutant) Placing controls on the emissions from motor vehicles has resulted in a significant improvement in the air quality. 62

63. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Particulate Matter Emissions Particulate matter comes from a variety of sources: Road dust is the major source of PM 10 particles. Many industrial activities involve processes that produce dusts. Mining and other earth-moving activities, farming operations, and the transfer of grain or coal from one container to another all produce dust. Fires (forest fires, grass fires, leaf burning, and fires from fireplaces and woodstoves, etc.) are a significant source of particulate matter—particularly PM 2.5. Burning of fossil fuels is another major source of particulate matter. 63

64. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Power Plant Emissions The primary pollutants associated with electric power plants are particulates, sulfur dioxide (SO 2 ), and nitrogen oxides (NO X ). Most PM 10 emissions have been controlled with filters and other mechanical means. The control of sulfur dioxide requires more fundamental changes to the way electricity is produced. The EPA approached the problem by setting limits and allowing electric utilities to decide which options are the best for them. 64

65. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Power Plant Emissions Nitrogen oxides are produced wherever high temperature combustion occurs with air. Control of the release of nitrogen oxides typically involves processes that are technical and expensive. However, emissions of particulates, sulfur dioxide, and nitrogen oxides from power plants have been reduced significantly. 65

66. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 16.8 Air Pollution in the Developing World Although much of the economically developed world has made great strides in improving air quality, this is not true in the less developed countries of the world. In 2011 the World Health Organization published a study of the impact of outdoor air pollution on world health. The World Health Organization estimated that worldwide there were about 1.3 million premature deaths that could be attributed to outdoor air pollution. Over 800,000 of those premature deaths were in Asia and the Eastern Mediterranean areas that include many of the developing economies of the world. 66

67. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 16.8 Air Pollution in the Developing World Air pollution in much of the developing world it is dominated by poorly regulated industry and transportation sections of the economy. Economic development begins with the development of industry, which uses cheap labor and lax environmental regulations to manufacture products inexpensively. People and their governments are so eager to have the jobs and economic development that they are willing to accept the risks associated with poor environmental conditions. 67

68. Copyright © McGraw-Hill Education. Permission required for reproduction or display. World Air Pollution 68

69. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 16.9 Indoor Air Pollution Growing evidence indicates air within homes and other buildings can be more seriously polluted than outdoor air in the most industrialized cities. These pollutants are thought to have adverse effects on human health. Asbestos Formaldehyde (in many consumer products) Airborne pesticide residues Chloroform Perchloroethylene Paradichlorobenzene 69

70. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Sources of Indoor Air Pollutants Smoking is the most important pollutant. Weatherizing to increase efficiency slows air exchange and tends to trap pollutants. Movements to reduce indoor air pollution lag behind regulations governing outdoor air pollution. The EPA is conducting research to identify and rank the human health risks that result from exposure to individual indoor pollutants or mixtures of multiple indoor pollutants. 70

71. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Secondhand Smoke Secondhand smoke is exposure to environmental tobacco smoke as a result of living and working in places where people smoke. In July 1993, the EPA recommended several actions to prevent people from being exposed to secondhand indoor smoke: People not smoke in their homes or permit others to do so. All organizations that deal with children have policies that protect children from secondhand smoke. 71

72. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Secondhand Smoke Every company has a policy that protects employees from secondhand smoke. Today only 16 states do not have some kind of a statewide ban on smoking in public places. Even if a state does not have legislation, many cities and other jurisdictions within those states do. 72

73. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Sources of Indoor Air Pollutants Radon is an inert radioactive gas with a half-life of 3.8 days. It is formed as a byproduct of uranium-238 decay. It may undergo radioactive decay in human lungs when inhaled. Increased incidence of lung cancer is the only known health effect associated with radon decay products. 73

74. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Sources of Indoor Air Pollutants Radon usually diffuses up through rocks and soil and escapes harmlessly into the atmosphere, but it can diffuse into groundwater. It can enter a home through an open space in the foundation, from gaps around pipes, or from wells. The EPA and the U.S. surgeon general recommend that all Americans (with a few exceptions) test their homes for radon. If radon is detected, simple and inexpensive actions may be taken to lower the level in the home. 74

75. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Generalized Geologic Radon Potential of the United States 75

76. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 16.10 Noise Pollution Noise is unwanted sound. Research has shown that exposure to noise can cause physical as well as mental harm. The loudness of a sound is measured by decibels. The frequency or pitch of a sound is a factor in determining its degree of harm. Noise pollution is linked to a variety of ailments; research has shown it may also cause blood vessels to constrict, it disturbs unborn children, and sometimes causes seizures in epileptics. 76

77. Copyright © McGraw-Hill Education. Permission required for reproduction or display. 16.10 Noise Pollution The Noise Control Act of 1972 was the first major attempt in the U.S. to protect the public health and welfare from detrimental noise. Many European countries do more to control noise than the U.S. does. Several European countries have developed quiet construction equipment in conjunction with strongly enforced noise ordinances. 77

78. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Summary The atmosphere has a tremendous ability to disperse pollutants. Carbon monoxide, hydrocarbons, particulate matter, sulfur dioxide, and oxides of nitrogen are the primary air pollutants. The U.S. EPA establishes standards for six pollutants known as criteria air pollutants: carbon monoxide, nitrogen dioxide, sulfur dioxide, volatile organic compounds, ozone, and lead. 78

79. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Summary Acid rain is caused by emissions of sulfur dioxide and oxides of nitrogen in the upper atmosphere. These compounds form acids that are washed from the air when it rains or snows or settle as particles on surfaces. The control of acid rain requires the use of scrubbers, precipitators, and filters, or the removal of sulfur from fuels. 79

80. Copyright © McGraw-Hill Education. Permission required for reproduction or display. Summary Chlorofluorocarbons also lead to the destruction of ozone in the upper atmosphere, which results in increased amounts of ultraviolet light reaching Earth. Many commonly used materials release gases into closed spaces (indoor air pollution) where they cause health problems. The most important of these health problems are associated with tobacco smoking. 80