Ecological Issues. Air Pollution, Climate Change, and Ozone Depletion

Transcription

1 Ecological Issues Air Pollution, Climate Change, and Ozone Depletion

2 Fig. 15-1, p. 368

3 Asian Brown Cloud YK-2sDN4U SEJfpQLSI&NR=1&feature=fvwp

4 Core Case Study: South Asia s Massive Brown Cloud (1) Asian Brown Cloud India to Bangladesh to China s Pacific coast Pollutants from fires, cars, industry Skies permanently gray or brown

5 Core Case Study: South Asia s Massive Brown Cloud (2) Changing weather patterns 700,000 premature deaths per year Has traveled to the west coast of the U.S. Made worse by global warming

6 1: What is the Nature of the Atmosphere? Concept 1 The two innermost layers of the atmosphere are the troposphere, which supports life, and the stratosphere, which contains the protective ozone layer.

7 Earth s Atmosphere Troposphere Extends upward 5-11 miles above earth s surface Makes up 75 80% earth s air mass 78% N 2, 21% O 2 Weather and climate Stratosphere Ozone layer

8 Stratosphere Stratosphere Extends from miles above Earth s surface Volume of water vapor less than Troposphere Concentration of ozone much higher Ozone Layer Global sunscreen, keeps 95% of harmful UV radiation from reaching Earth s surface

9 Altitude (kilometers) Altitude (miles) Atmospheric pressure (millibars) ,000 Temperature Thermosphere Mesopause Mesosphere Stratopause Stratosphere Tropopause Ozone layer Pressure Troposphere 5 (Sea Level) Temperature ( C) Pressure = 1,000 Millibars at ground level Fig. 15-2, p. 370

10 2 What Are the Major Air Pollution Problems? (1) Concept 2A Three major outdoor air pollution problems are industrial smog from burning coal, photochemical smog from motor vehicle and industrial emissions, and acid deposition from coal burning and motor vehicle exhaust.

11 2 What Are the Major Air Pollution Problems? (2) Concept 2 The most threatening indoor air pollutants are smoke and soot from wood and coal fires (mostly in developing countries) and chemicals used in building materials and products.

12 Air pollution _ywfqvjt4&feature=related

13 Outdoor Air Pollution What is air pollution? Presence of chemicals in atmosphere in concentrations that are high enough to be harmful Stationary and mobile sources Primary pollutants-harmful chemicals emitted directly into the air Secondary pollutants- formed when primary pollutants react with one another and with other components of air to form new harmful chemicals

14 Types of Major Air Pollutants Carbon oxides (CO, CO 2 ) Nitrogen oxides and nitric acid (NO, NO 2, HNO 3 ) Sulfur dioxide and sulfuric acid (SO 2, H 2 SO 4) Particulates (SPM) Ozone (O 3 ) Volatile organic compounds (VOCs)

15 Carbon Oxides Carbon monoxide (CO) colorless, odorless and highly toxic gas that forms during incomplete combustion of carbon-containing materials Major sources: motor vehicle exhaust, burning of forests and grasslands, tobacco smoke, open fires/inefficient stoves for cooking Reacts with Hb in RBCs to decrease ability of blood to transport O2 to body cells and tissues

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17 Carbon dioxide (CO2) Colorless, odorless gas 93% of atmospheric CO2 result of natural carbon cycle Rest from burning fossil fuels, clearing forests and grasslands Now classified as air pollutant due to role in climate change

18 Nitrogen oxides and nitric acid Nitric oxide (NO) colorless gas forms when N and O react at high combustion temps in auto engines and coal-burning power/industrial plants In air NO reacts with O to form Nitrogen dioxide (NO2), reddish brown gas Collectively NO and NO2 called Nitrogen oxides (NOx)

19 Some NO2 reacts with water vapor to form nitric acid (HNO3) and nitrate salts (NO3-), components of acid deposition Both NO and NO2 play role in formation of photochemical smog: a mixture of chemicals formed under influence of sunlight in cities with heavy traffic

20 Nitrous oxide (N2O) greenhouse gas, emitted from fertilizers and animal wastes and produced by burning fossil fuels Nitrogen oxides can irritate eyes, nose, throat; aggravate lung ailments, suppress plant growth, and reduce visibility

21 Sulfur dioxide and sulfuric acid Sulfur dioxide (SO2) colorless gas with irritating odor 1/3 from natural sources, 2/3 from human sources such as combustion of sulfur containing coal and oil refining and smelting Can be converted to aerosols, microscopic suspended droplets of sulfuric acid (H2SO4) and suspended particles of sulfate (SO4) salts that return to Earth as component of acid deposition SO2, H2SO4 droplets, and suspended particles of sulfate reduce visibility; aggravate breathing problems; also damage crops, trees, soils and aquatic life, corrode metals, damage stone on buildings and statues Major component of Asian Brown Cloud

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24 Particulates Suspended particulate matter (SPM) Variety of solid particles and liquid droplets small and light enough to remain suspended in air for long periods 38% from human sources such as coal burning plants, motor vehicles, road construction, and tobacco smoke Major component of Asian Brown Cloud These particles can irritate nose, throat; damage lungs; aggravate asthma and bronchitis, and shorten life Also contains toxic particulates; can lead to mutations, reproductive problems, cancer Reduce visibility, corrode metals, discolor clothes and paints

25 Ozone Ozone (O3), colorless, highly reactive gas, major ingredient of photochemical smog Can cause coughing, breathing problems, aggravate lung and heart disease, reduce resistance to colds/ pnuemonia, irritate eyes, nose, throat damages plants, rubber in tires, fabrics, paints

26 Ozone in troposphere near ground level bad ozone Ozone in stratosphere good ozone b/c protects us from the sun s harmful UV radiation Same chemical Human activities decreasing good ozone increasing bad ozone

27 Volatile organic compounds (VOCs) VOC s are organic compounds that exist as gases in the atmosphere or that evaporate into the atmosphere Ex. hydrocarbons emitted by leaves of many plants and methane (CH4) a greenhouse gas 20 times more effective per molecule than CO2 is at warming atmosphere 1/3 from natural sources, 2/3 human sources; rice paddies, landfills, oil and natural gas wells, cows Other VOCs are liquids that evaporate into atmosphere ex. Benzene and other industrial solvents, dry cleaning fluids, components of gasoline, plastics, and other products

28 Sources and types of air pollutants Primary Pollutants CO CO 2 SO 2 NO NO 2 Most hydrocarbons Most suspended particles Sources Natural Stationary Secondary Pollutants SO 3 HNO 3 H 2 SO 4 H 2 O 2 O 3 PANs Most NO 3 and SO 2 4 salts Mobile Fig. 15-3, p. 371

29 In Class List the major outdoor air pollutants, describe, and give their harmful effects.

30 Describe the relationship in the graph below.

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32 Industrial Smog Burning coal Sulfur dioxide, sulfuric acid, suspended particles (gray air smog) Coal-burning a major contributor to Asian Brown Cloud Developed versus developing countries Air pollution control in the U.S. and Europe China, India, Ukraine

33 Photochemical Smog Photochemical reactions: chemical rxn activated by sunlight Photochemical smog: mixture of primary and secondary pollutants formed under the influence of UV radiation from the sun Brown-air smog (contains NO2) Sources Health effects Urban areas

34 Photochemcial smog in Santiago, Chile Fig. 15-4, p. 373

35 Natural Factors That Reduce Air Pollution Particles heavier than air Rain and snow Salty sea spray from oceans Winds Chemical reactions

36 Natural Factors That Increase Air Pollution Urban buildings Hills and mountains High temperatures VOC emissions from certain trees and plants Grasshopper effect Temperature inversions

37 -000F810F.5/Grasshopper%20effect.jpg

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39 Acid Deposition Sulfur dioxides and nitrogen oxides Wet and dry deposition Acid rain Regional air pollution Midwest coal-burning power plants Prevailing winds

40 Acid deposition: consists of rain, snow, dust, or gas with ph less than 5.6 Wind Transformation to sulfuric acid (H 2 SO 4 ) and nitric acid (HNO 3 ) Nitric oxide (NO) Sulfur dioxide (SO 2 ) and NO Windborne ammonia gas and some soil particles partially neutralize acids and form dry sulfate and nitrate salts Dry acid deposition (sulfur dioxide gas and particles of sulfate and nitrate salts) Wet acid deposition (droplets of H 2 SO 4 and HNO 3 dissolved in rain and snow) Acid fog Lakes in deep soil high in limestone are buffered Lakes in shallow soil low in limestone become acidic Fig. 15-5, p. 374

41 Regions where acid deposition is now a problem and regions with the potential to develop this problem Potential problem areas because of sensitive soils Potential problem areas because of air pollution: emissions leading to acid deposition Current problem areas (including lakes and rivers) Fig. 15-6, p. 375

42 Harmful Effects of Acid Deposition Structural damage Respiratory diseases in humans Toxic metal leaching Kills fish and other aquatic organisms Leaches plant nutrients from soil Acid clouds and fog at mountaintops

43 Solutions Acid Deposition Prevention Reduce coal use Burn low-sulfur coal Increase natural gas use Increase use of renewable energy resources Cleanup Add lime to neutralize acidified lakes Add phosphate fertilizer to neutralize acidified lakes Remove SO 2 particulates and NO x from smokestack gases Remove NO x from motor vehicular exhaust Tax emissions of SO 2 Reduce air pollution by improving energy efficiency Fig. 15-7, p. 376

44 Indoor Air Pollution According to WHO indoor air pollution is world s most serious air pollution problem especially for poor people Developing countries Indoor cooking and heating Often higher concentration in buildings and cars Most time is spent indoors or in cars EPA top cancer risk

45 Major Indoor Air Pollutants Tobacco smoke Formaldehyde Radioactive radon-222 gas Very small particles

46 Chloroform Source: Chlorine-treated water in hot showers Possible threat: Cancer 1,1,1-Trichloroethane Source: Aerosol sprays Threat: Dizziness, irregular breathing Nitrogen oxides Source: Unvented gas stoves and kerosene heaters, woodstoves Threat: Irritated lungs, children's colds, headaches Particulates Source: Pollen, pet dander, dust mites, cooking smoke particles Threat: Irritated lungs, asthma attacks, itchy eyes, runny nose, lung disease Asbestos Source: Pipe insulation, vinyl ceiling and floor tiles Threat: Lung disease, lung cancer Para-dichlorobenzene Source: Air fresheners, mothball crystals Threat: Cancer Carbon monoxide Source: Faulty furnaces, unvented gas stoves and kerosene heaters, woodstoves Threat: Headaches, drowsiness, irregular heartbeat, death Tetrachloroethylene Source: Dry-cleaning fluid fumes on clothes Threat: Nerve disorders, damage to liver and kidneys, possible cancer Tobacco smoke Source: Cigarettes Threat: Lung cancer, respiratory ailments, heart disease Methylene chloride Source: Paint strippers and thinners Threat: Nerve disorders, diabetes Formaldehyde Source: Furniture stuffing, paneling, particleboard, foam insulation Threat: Irritation of eyes, throat, skin, and lungs; nausea; dizziness Styrene Source: Carpets, plastic products Threat: Kidney and liver damage Benzo-α-pyrene Source: Tobacco smoke, woodstoves Threat: Lung cancer Radon-222 Source: Radioactive soil and rock surrounding foundation, water supply Threat: Lung cancer Fig. 15-8, p. 377

47 Air Pollution and the Human Respiratory System Natural protective system; hairs in nose filter out large particles, mucus captures particles, cilia (tiny mucus coated, hair-like structures) transport pollutants they trap Lung cancer, chronic bronchitis, emphysema, asthma Premature deaths Air pollution kills 2.4 million people prematurely every year worldwide

48 Major components of respiratory system Nasal cavity Oral cavity Pharynx (throat) Trachea (windpipe) Bronchus Epithelial cell Cilia Goblet cell (secreting mucus) Mucus Bronchioles Alveolar duct Right lung Bronchioles Alveolar sac (sectioned) Alveoli Fig. 15-9, p. 378

49 Premature deaths from air pollution in US Deaths per 100,000 adults per year < Fig , p. 378

50 15-3 How Should We Deal with Air Pollution? Concept 15-3 Legal, economic, and technological tools can help clean up air pollution, but the best solution is to prevent it.

51 U.S. Outdoor Air Pollution Control Laws Clean Air Acts 1970, 1977, 1990 Air-quality standards for 6 major outdoor pollutants Carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), SPM, ozone (O3), and lead Levels of these 6 pollutants have fallen dramatically between 1980 and 2008

52 *Improving Air Pollution Laws (1) Emphasize pollution prevention Increase fuel economy standards Regulate emissions from two-cycle engines Regulate ultra-fine particles

53 *Improving Air Pollution Laws (2) Increase regulations at airports Decrease urban ozone Increase regulations for indoor air pollution Better enforcement of Clean Air Act

54 *Using the Marketplace to Reduce Air Pollution Clean Air Act of 1990 authorized emissions trading (cap and trade) program Enables 110 most polluting coal burning power plants in 21 states to buy and sell SO2 pollution rights Proponents cheaper and more efficient Critics companies buy their way out Success depends on cap being gradually lowered

55 Prevention Burn low-sulfur coal Stationary Source Air Pollution Remove sulfur from coal Solutions Dispersion or Cleanup Disperse emissions above thermal inversion layer with tall smokestacks Convert coal to a liquid or gaseous fuel Remove pollutants after combustion Shift to less polluting energy sources Tax each unit of pollution produced Fig , p. 380

56 Solutions Motor Vehicle Air Pollution Prevention Use mass transit Walk or bike Cleanup Require emission control devices Use less polluting fuels Improve fuel efficiency Get older, polluting cars off the road Give large tax write-offs or rebates for buying lowpolluting, energy efficient vehicles Inspect car exhaust systems twice a year Set strict emission standards Fig , p. 381

57 Prevention Clean ceiling tiles and line AC ducts to prevent release of mineral fibers Ban smoking or limit it to well-ventilated areas Set stricter formaldehyde emissions standards for carpet, furniture, and building materials Prevent radon infiltration Use office machines in wellventilated areas Use less polluting substitutes for harmful cleaning agents, paints, and other products Solutions Indoor Air Pollution Cleanup or Dilution Use adjustable fresh air vents for work spaces Increase intake of outside air Change air more frequently Circulate a building s air through rooftop greenhouses Use efficient venting systems for woodburning stoves Use exhaust hoods for stoves and appliances burning natural gas Fig , p. 381

58 Fig , p. 381

59 Solutions Air Pollution Outdoor Improve energy efficiency to reduce fossil fuel use Rely more on lower-polluting natural gas Rely more on renewable energy (especially solar cells, wind, geothermal and solar-produced hydrogen) Transfer energy efficiency, renewable energy, and pollution prevention technologies to developing countries Indoor Reduce poverty Distribute cheap and efficient cookstoves or solar cookers to poor families in developing countries Reduce or ban indoor smoking Develop simple and cheap tests for indoor pollutants such as particulates, radon, and formaldehyde Fig , p. 382

60 15-4 How Might the Earth s Climate Change in the Future? Concept 15-4 Considerable scientific evidence indicates that emissions of greenhouse gases into the earth s atmosphere from human activities will lead to significant climate change during this century.

61 Climate Change AbATJCugs

62 Past Climate Changes Glacial and interglacial periods over past 900,000 yrs Global cooling and global warming Measurement of past temperature changes Radioisotopes in rocks and fossils Tiny bubbles of ancient air found in ice cores from glaciers Tree rings Historical measurements since 1861

63 AVERAGE TEMPERATURE (over past 900,000 years AVERAGE TEMPERATURE (over past 130 years TEMPERATURE CHANGE (over past 22,000 years TEMPERATURE CHANGE (over past 1,000 years Stepped Art Fig , p. 383

64 Ice cores are extracted by drilling deep holes into ancient glaciers at various sites like this one in Antarctica.. Fig , p. 383

65 The Greenhouse Effect Life on Earth is totally dependent on natural greenhouse effect Without this greenhouse effect, the world would be too cold to support the forms of life we find today Natural greenhouse gases Water vapor (H 2 O) Carbon dioxide (CO 2 ) Methane (CH 4 ) Nitrous Oxide (N 2 O)

66 List the 4 natural greenhouse gasses. What is the importance of the greenhouse effect?

67 diagrams/greenhouse/

68 Evidence to Support Global Warming (1) Intergovernmental Panel on Climate Change 2007 IPCC report Rise in average global surface temperature 10 warmest years on record since 1970

69 Evidence to Support Global Warming (2) Annual greenhouse gas emissions up 70% between 1970 and 2008 Changes in glaciers, rainfall patterns, hurricanes Sea level rise in this century 4 8 inches

70 Melting of Alaska s Muir Glacier in Glacier Bay National Park and Preserve between 1948 and Mountain glaciers are now melting everywhere in the world.

71 The big melt. Each summer, some of the floating sea ice in the Arctic Sea melts and Then refreezes during winter. But in recent years, rising atmospheric and ocean temps have caused more and more ice to melt. Satellite data show a 39% drop in the average Cover of summer Arctic ice between 1979 and Such summer ice may be gone by 2037, and perhaps earlier. Sept Sept Russia Russia * North pole Greenland * North pole Greenland Alaska (U.S.) Alaska (U.S.) Canada Canada Fig , p. 385

72 CO 2 Emissions Are the Major Culprit 1850: 285 ppm (Start of the Industrial Revolution) 2009: 388 ppm Over 450 ppm is tipping point (could set into motion large-scale climate changes for hundreds to thousands of years) 350 ppm as intermediate goal

73 Science Focus: Scientific Consensus about Future Global Temperature Changes? Temperature as a function of greenhouse gases Mathematical models Model data and assumptions Predictions and model reliability Recent warming due to human activities

74 Simplified model of some major processes that interact to determine the average temperature and greenhouse gas content of the lower atmosphere and thus the Earth s climate. Red arrows show processes resulting in warming; blue cooling. Troposphere Aerosols Greenhouse gases Warming from decrease Cooling from increase CO 2 removal by plants and soil organisms CO 2 emissions from land clearing, fires, and decay Heat and CO 2 removal Heat and CO 2 emissions Ice and snow cover Shallow ocean Natural and human emissions Land and soil biota Long-term storage Deep ocean Fig. 15-A, p. 386

75 Fig. 15-B, p. 387

76 What Role for Oceans in Climate Change? Oceans help to moderate earth s avg surface temp and thus climate by removing about 25-30% of CO2 pumped into lower atmosphere by human activities Absorb heat from lower atmoshere and slowly transfer some CO2 to deep ocean CO 2 solubility decreases with increasing temperature Upper ocean getting warmer Acidity of ocean increasing

77 15-5 What Are Some Possible Effects of a Projected Climate Change? Concept 15-5 The projected change in the earth s climate during this century could have severe and longlasting consequences, including increased drought and flooding, rising sea levels, and shifts in locations of agriculture and wildlife habitats.

78 Potential Severe Consequences Rapid projected temperature increase 2 Cº inevitable 4 Cº possible Effects will last for at least 1,000 years

79 Fig , p. 389

80 Harmful Effects of Global Warming (1) Excessive heat Drought Ice and snow melt Rising sea levels Extreme weather

81 Harmful Effects of Global Warming (2) Threat to biodiversity Food production may decline Change location of agricultural crops Threats to human health

82 Glaciers covering about 80% of Greenland, the world s largest island, contain about 10% of the world s freshwater. This is enough water to raise global sea level by 23 ft if they all melt. Complete melting unlikely, but partial summer melting of some of its glacial ice increased dramatically between 1982 and Fig , p. 390

83 Areas of Florida that will be flooded (red) if the average sea level rises by 1 meter (3.3 ft). Fig , p. 391

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85 15-6 What Can We Do to Slow Projected Climate Change? Concept 15-6 To slow the rate of projected climate change, we can increase energy efficiency, sharply reduce greenhouse gas emissions, rely more on renewable energy resources, and slow population growth.

86 Options to Deal with Climate Change Two approaches: 1. Drastically reduce greenhouse gas emissions 2. Develop strategies to reduce its harmful effects Mix both approaches Governments beginning to act

87 Solutions Prevention Cut fossil fuel use (especially coal) Shift from coal to natural gas Improve energy efficiency Shift to renewable energy resources Transfer energy efficiency and renewable energy technologies to developing countries Reduce deforestation Use more sustainable agriculture and forestry Limit urban sprawl Reduce poverty Slow population growth Slowing Climate Change Cleanup Remove CO 2 from smokestack and vehicle emissions Store (sequester) CO 2 by planting trees Sequester CO 2 in soil by using notill cultivation and taking cropland out of production Sequester CO 2 deep underground (with no leaks allowed) Sequester CO 2 in the deep ocean (with no leaks allowed) Repair leaky natural gas pipelines and facilities Use animal feeds that reduce CH 4 emissions from cows (belching) Fig , p. 393

88 Reducing the Threat of Climate Change (1) Improve energy efficiency to reduce fossil fuel use Shift from coal to natural gas Improve energy efficiency Shift to renewable energy sources

89 Reducing the Threat of Climate Change (2) Transfer appropriate technology to developing countries Reduce deforestation Sustainable agriculture and forestry Reduce poverty Slow population growth

90 Reducing the Threat of Climate Change (3) Decrease CO 2 emissions Sequester CO 2 Plant trees Agriculture Underground Deep ocean Repair leaking natural gas lines Reduce methane emissions from animals

91 Science Focus: Is Capturing and Storing CO 2 the Answer? (1) Global tree planting Restore wetlands Plant fast-growing perennials

92 Science Focus: Is Capturing and Storing CO 2 the Answer? (2) Preserve natural forests Seed oceans with iron to promote growth of phytoplankton Sequester carbon dioxide underground and under the ocean floor

93 Oil rig Tanker delivers CO 2 from plant to rig Coal power plant Tree plantation CO 2 is pumped down from rig for disposal in deep ocean or under seafloor sediments Abandoned oil field Switchgrass CO 2 is pumped underground Crop field Spent oil or natural gas reservoir Spent coal bed cavern Deep, saltwater-filled cavern = CO 2 pumping = CO 2 deposit Fig. 15-C, p. 394

94 What are the limitations to carbon capture and storage?

95 Government Roles in Reducing the Threat of Climate Change (1) Regulate carbon dioxide and methane as pollutants Carbon taxes Cap total CO 2 emissions Subsidize energy-efficient technologies Technology transfers

96 Government Roles in Reducing the Threat of Climate Change (2) International climate negotiations Kyoto Protocol (US withdrew in 2001) Act locally Costa Rica, aims to be first country to be carbon neutral U.S. states; 30 US states had greenhouse gas reduction programs by 2009 Large corporations such as Alcoa, DuPont, IBM, Toyota, General Electric have set goals for reducing greenhouse gas emissions Colleges and universities; such as Oberlin College

97 Fig , p. 396

98 Ways to prepare for possible long term harmful effects of climate change. Develop crops that need less water Waste less water Connect wildlife reserves with corridors Move people away from low-lying coastal areas Move hazardous material storage tanks away from coast Stockpile 1- to 5-year supply of key foods Prohibit new construction on low-lying coastal areas or build houses on stilts Expand existing wildlife reserves toward poles Fig , p. 396

99 15-7 How Have We Depleted Ozone in the Stratosphere and What Can We Do about It? Concept 15-7A Widespread use of certain chemicals has reduced ozone levels in the stratosphere and allowed more harmful ultraviolet radiation to reach the earth s surface. Concept 15-7B To reverse ozone depletion, we need to stop producing ozone-depleting chemicals and adhere to the international treaties that ban such chemicals.

100 Human Impact on the Ozone Layer Location and purpose of the ozone layer Blocks UV-A and UV-B radiation Seasonal and long-term depletion of ozone Threat to humans, animals, plants Causes chlorofluorocarbons (CFCs)

101 Individuals Matter: Banning of Chlorofluorocarbons (CFCs) Chemists Rowland and Molina Nobel Prize in 1995 Called for ban Remain in atmosphere Rise into stratosphere Break down into atoms that accelerate ozone depletion Stay in stratosphere for long periods Defended research against big industry

102 Former Uses of CFCs Coolants in air conditioners and refrigerators Propellants in aerosol cans Cleaning solutions for electronic parts Fumigants Bubbles in plastic packing foam

103 Fig , p. 398

104 Fig , p. 398

105 Reversing Ozone Depletion Stop producing ozone-depleting chemicals Slow recovery Montreal Protocol Copenhagen Protocol International cooperation

106 Three Big Ideas from This Chapter - #1 All countries need to step up efforts to control and prevent outdoor and indoor air pollution.

107 Three Big Ideas from This Chapter - #2 Reducing the possible harmful effects of projected rapid climate change during this century requires emergency action to cut energy waste, sharply reduce greenhouse gas emissions, rely more on renewable energy resources, and slow population growth.

108 Three Big Ideas from This Chapter - #3 We need to continue phasing out the use of chemicals that have reduced ozone levels in the stratosphere and allowed more harmful ultraviolet radiation to reach the earth s surface.

109 Teacher s Guide to Climate Change e/teachersguide.htm tml