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Chapter 19

Chapter 19. Air Pollution. Air: The Endangered Global Commons. Mixture of gases: 78% Nitrogen, 21% Oxygen, 0.04% Carbon Dioxide, and others Contains water vapor and various pollutants A renewable resource cleansed by natural processes and regenerated by living things

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Chapter 19

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  1. Chapter 19 Air Pollution

  2. Air: The Endangered Global Commons • Mixture of gases: 78% Nitrogen, 21% Oxygen, 0.04% Carbon Dioxide, and others • Contains water vapor and various pollutants • A renewable resource cleansed by natural processes and regenerated by living things • Used by many and protected by few – it suffers from the tragedy that befalls many commons

  3. Natural Air Pollutants

  4. Anthropogenic Pollutants • Generally create long-term threat • Power plants, automobiles, factories, and other human sources emit large quantities in restricted areas • Higher concern because it is produced in localized regions so that concentrations reach potentially dangerous levels

  5. STRUCTURE AND SCIENCE OF THE ATMOSPHERE • The atmosphere consists of several layers with different temperatures, pressures, and compositions. Figure 19-2

  6. Atmospheric pressure (millibars) Temperature Pressure Thermosphere Mesopause Heating via ozone Mesosphere Altitude (kilometers) Altitude (miles) Stratopause Stratosphere Tropopause Ozone “layer” Heating from the earth Troposphere Pressure = 1,000 millibars at ground level (Sea level) Temperature (˚C) Fig. 19-2, p. 440

  7. STRUCTURE AND SCIENCE OF THE ATMOSPHERE • The atmosphere’s innermost layer (troposphere) is made up mostly of nitrogen and oxygen, with smaller amounts of water vapor and CO2. • Ozone in the atmosphere’s second layer (stratosphere) filters out most of the sun’s UV radiation that is harmful to us and most other species.

  8. AIR POLLUTION • Some primary air pollutants may react with one another or with other chemicals in the air to form secondary air pollutants. Figure 19-3

  9. Major Air Pollutants • Carbon oxides: • Carbon monoxide (CO) is a highly toxic gas that forms during the incomplete combustion of carbon-containing materials. • 93% of carbon dioxide (CO2) in the troposphere occurs as a result of the carbon cycle. • 7% of CO2 in the troposphere occurs as a result of human activities (mostly burning fossil fuels). • It is not regulated as a pollutant under the U.S. Clean Air Act.

  10. Major Air Pollutants • Nitrogen oxides and nitric acid: • Nitrogen oxide (NO) forms when nitrogen and oxygen gas in air react at the high-combustion temperatures in automobile engines and coal-burning plants. NO can also form from lightening and certain soil bacteria. • NO reacts with air to form NO2. • NO2 reacts with water vapor in the air to form nitric acid (HNO3) and nitrate salts (NO3-) which are components of acid deposition.

  11. Major Air Pollutants • Sulfur dioxide (SO2)andsulfuric acid: • About one-third of SO2 in the troposphere occurs naturally through the sulfur cycle. • Two-thirds come from human sources, mostly combustion (S+ O2 SO2) of sulfur-containing coal and from oil refining and smelting of sulfide ores. • SO2 in the atmosphere can be converted to sulfuric acid (H2SO4) and sulfate salts (SO42-) that return to earth as a component of acid deposition.

  12. Major Air Pollutants • Suspended particulate matter (SPM): • Consists of a variety of solid particles and liquid droplets small and light enough to remain suspended in the air. • The most harmful forms of SPM are fine particles (PM-10, with an average diameter < 10 micrometers) and ultrafine particles (PM-2.5). • According to the EPA, SPM is responsible for about 60,000 premature deaths a year in the U.S.

  13. Major Air Pollutants • Ozone (O3): • Is a highly reactive gas that is a major component of photochemical smog. • It can • Cause and aggravate respiratory illness. • Can aggravate heart disease. • Damage plants, rubber in tires, fabrics, and paints.

  14. Major Air Pollutants • Volatile organic compounds (VOCs): • Most are hydorcarbons emitted by the leaves of many plants and methane. • About two thirds of global methane emissions comes from human sources. • Other VOCs include industrial solvents such as trichlorethylene (TCE), benzene, and vinyl chloride. • Long-term exposure to benzene can cause cancer, blood disorders, and immune system damage.

  15. Major Air Pollutants • Radon (Rn): • Is a naturally occurring radioactive gas found in some types of soil and rock. • It can seep into homes and buildings sitting above such deposits.

  16. Major Air Pollutants

  17. URBAN OUTDOOR AIR POLLUTION • Industrial smog is a mixture of sulfur dioxide, droplets of sulfuric acid, and a variety of suspended solid particles emitted mostly by burning coal. • In most developed countries where coal and heavy oil is burned, industrial smog is not a problem due to reasonably good pollution control or with tall smokestacks that transfer the pollutant to rural areas.

  18. Sunlight plus Cars Equals Photochemical Smog • Photochemical smog is a mixture of air pollutants formed by the reaction of nitrogen oxides and volatile organic hydrocarbons under the influence of sunlight.

  19. Sunlight plus Cars Equals Photochemical Smog • Mexico City is one of the many cities in sunny, warm, dry climates with many motor vehicles that suffer from photochemical smog. Figure 19-4

  20. Factors Reducing Levels of Outdoor Air Pollution • Settling out – heavier particles settle • Rain and snow – cleanse the air pollutant • Salty sea spray – wash out particulates and water-soluble pollutants • Winds – sweep away and dilute with cleaner air • Chemical reactions – formation of acid rain – chemical falls to Earth The pollutants do not disappear; they are merely shifted elsewhere or deposited onto other medium

  21. Factors Increasing Levels of Outdoor Air Pollution • Urban buildings – slow wind speed • Hills and mountains – reduce flow of air in valleys • Higher temperatures – promote chemical reactions • VOC emissions from certain trees and plants • Grasshopper effect – volatile air pollutants transported from tropics and temperate forests toward the poles during the winter • Temperature inversions – cause buildup

  22. Temperature Inversions • Cold, cloudy weather in a valley surrounded by mountains can trap air pollutants (left). • Areas with sunny climate, light winds, mountains on three sides and an ocean on the other (right) are susceptible to inversions. Figure 19-5

  23. During normal conditions, air temperature decreases with altitude, thus pollutants ascend and mix with atmospheric gases In a temperature inversion, however, warm air forms a lid over cooler air, thus trapping air pollution

  24. San Diego, CA Inversion layer Inversion layer Fig. 19-5, p. 447

  25. City with several million people and motor vehicles in an area with a sunny climate, light winds, mountains on three sides, and the ocean on the other side – conditions ideal for photochemical smog worsened by frequent thermal inversions – example: Los Angeles, CA (Brown-air smog)

  26. Brown-air cities • Early morning traffic provides the ingredients for photochemical smog • Reaches highest levels in early afternoon • Suburbs and surrounding rural areas usually have higher levels of photochemical smog than the cities themselves • Major episodes usually occur during summer

  27. Although anthropogenic pollutants are the most significant sources of air pollution, researchers have found some instances in which naturally occurring pollutants noticeably affect air quality. In Atlanta, the trees emit a number of highly reactive hydrocarbons. These chemicals react with nitrogen dioxide from automobiles and other combustion sources to produce ozone. New research shows that hydrocarbons from trees are 50 to 100 times more reactive than hydrocarbons from human sources.

  28. ACID DEPOSITION • Sulfur dioxides, nitrogen oxides, and particulates can react in the atmosphere to produce acidic chemicals that can travel long distances before returning to the earth’s surface. • Tall smokestacks reduce local air pollution but can increase regional air pollution.

  29. ACID DEPOSITION • Acid deposition consists of rain, snow, dust, or gas with a pH lower than 5.6. Figure 19-6

  30. Wind Transformation to sulfuric acid (H2SO4) and nitric acid (HNO3) Windborne ammonia gas and particles of cultivated soil partially neutralize acids and form dry sulfate and nitrate salts Wet acid depostion (droplets of H2SO4 and HNO3 dissolved in rain and snow) Nitric oxide (NO) Sulfur dioxide (SO2) and NO Dry acid deposition (sulfur dioxide gas and particles of sulfate and nitrate salts) Acid fog Farm Lakes in shallow soil low in limestone become acidic Ocean Lakes in deep soil high in limestone are buffered Fig. 19-6, p. 448

  31. Harmful Effects of Acid Rain • Cause or worsen respiratory disease • Attack metallic and stone objects • Decrease atmosphere visibility • Kill fish • Deplete soils of vital plant nutrients • Harm crops and plants

  32. ACID DEPOSITION • Acid deposition contributes to chronic respiratory disease and can leach toxic metals (such as lead and mercury) from soils and rocks into acidic lakes used as sources for drinking water.

  33. ACID DEPOSITION • Air pollution is one of several interacting stresses that can damage, weaken, or kill trees and pollute surface and groundwater. Figure 19-9

  34. Acid deposition effect on aquatic ecosystems • Fish die if pH drops below 4.5 • Aluminum ions are released from soil, carried into lakes, can clog fish gills • Mercury buildup in fish can affect humans (kidneys, brain) Note: acid rain can be buffered by limestone, which reduces acidity

  35. Factors which determine how severe the health effects are from mercury exposure • The chemical form of mercury • The dose • The age of person exposed (fetus most susceptible) • The duration of exposure • The route of exposure – inhalation, ingestion, dermal contact, etc. • The health of the person exposed

  36. Methylmercury effects on humans • Impaired neurological development (fetuses, infants, children) • Impacts on cognitive thinking, memory, attention • Impaired peripheral vision • Disturbances in sensations (“pins and needles” feelings) • Impairment of speech, hearing, walking

  37. Acid deposition effect on plants • Tree leaves, needles damaged • Important nutrients (Ca, Mg) leached, reducing plant productivity • Aluminum ions are mobilized, reduce plant productivity • Lead, cadmium, mercury are mobilized, reduce plant productivity • Plants weakened and become susceptible to other disease

  38. Forest destroyed due to acid rain

  39. Solutions Acid Deposition Prevention Cleanup Reduce air pollution by improving energy efficiency Add lime to neutralize acidified lakes Reduce coal use Add phosphate fertilizer to neutralize acidified lakes Increase natural gas use Increase use of renewable energy resources Burn low-sulfur coal Remove SO2 particulates & NOx from smokestack gases Remove NOx from motor vehicular exhaust Tax emissions of SO2 Fig. 19-10, p. 452

  40. INDOOR AIR POLLUTION • Indoor air pollution usually is a greater threat to human health than outdoor air pollution. • According to the EPA, the four most dangerous indoor air pollutants in developed countries are: • Tobacco smoke. • Formaldehyde. • Radioactive radon-222 gas. • Very small fine and ultrafine particles.

  41. Sick-building Syndrome • Almost one in five commercial building in the U.S. considered “sick” • Symptoms: • Dizziness • Headaches • Sore throats • Chronic fatigue • Respiratory infections • Depression

  42. Para-dichlorobenzene Chloroform Tetrachloroethylene Formaldehyde 1, 1, 1- Trichloroethane Styrene Nitrogen Oxides Benzo-a-pyrene Particulates Tobacco Smoke Radon-222 Asbestos Carbon Monoxide Methylene Chloride Fig. 19-11, p. 453

  43. INDOOR AIR POLLUTION • Household dust mites that feed on human skin and dust, live in materials such as bedding and furniture fabrics. • Can cause asthma attacks and allergic reactions in some people. Figure 19-12

  44. Case Study: Radioactive Radon • Radon-222, a radioactive gas found in some soils and rocks, can seep into some houses and increase the risk of lung cancer. Sources and paths of entry for indoor radon-222 gas. Figure 19-13

  45. How does your respiratory system help protect you from air pollution? • Hairs in your nose • Sticky mucus in the lining of your upper respiratory tract • Sneezing • Coughing • Cilia in your upper respiratory tract

  46. Acute effects vs. chronic effects

  47. Air Pollution is a Big Killer • Each year, air pollution prematurely kills about 3 million people, mostly from indoor air pollution in developing countries. • In the U.S., the EPA estimates that annual deaths related to indoor and outdoor air pollution range from 150,000 to 350,000. • According to the EPA, each year more than 125,000 Americans get cancer from breathing diesel fumes.

  48. PREVENTING AND REDUCING AIR POLLUTION – Clean Air Act • Emission standards for cars • Emissions standards for new industries • Ambient air quality standards for urban areas – established by the EPA covers six criteria air pollutants • Carbon monoxide • Nitrogen oxides • Sulfur dioxides • Suspended particulate matter (less than PM-10) • Volatile organic compounds • Ozone • Lead

  49. Solutions: Reducing Outdoor Air Pollution • There are a of ways to prevent and control air pollution from coal-burning facilities. • Electrostatic precipitator: are used to attract negatively charged particles in a smokestack into a collector. • Wet scrubber: fine mists of water vapor trap particulates and convert them to a sludge that is collected and disposed of usually in a landfill.

  50. Electrostatic Precipitator • Can remove 99% of particulate matter • Does not remove hazardous ultrafine particles. • Produces toxic dust that must be safely disposed of. • Uses large amounts of electricity Figure 19-18

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