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CHAPTER 19

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CHAPTER 19

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  1. CHAPTER 19 Atmospheric Pollution

  2. An introduction to air pollution: Donora Smog • On October 26, 1948, people in Donora, Pennsylvania woke up to a dense fog that lasted 5 days • The town has a large steel mill that used high-sulfur coal and a plant that roasted sulfur-containing ores • People complained of difficulty breathing, stomach pain, headaches, nausea, and choking • Within 1 month, 70 people died and 6,000 got sick • Mill owners did not think their mills were responsible • State and national laws now control air pollution • Culminating in the Clean Air Act (1970)

  3. Donora, Pennsylvania

  4. Air pollution essentials • The atmosphere contains many gases • N2, O2, Ar, CO2, water vapor • 40 trace gases: ozone, helium, hydrogen, nitrogen oxides • Aerosols: microscopic liquid or solid particles (dust, pollen, sea salts, etc.) from land and water • The Industrial Revolution changed the mixture of atmospheric gases and particles • Air pollutants: substances in the atmosphere (gases and aerosols) that have harmful effects

  5. Pollutants • Three factors determine the level of air pollution • The amount of pollutants entering the air • The amount of space into which the pollution is added • Mechanisms that remove pollutants from the air • Troposphere: the lower atmosphere • The site and source of weather, water vapor, clouds • Pollutants are removed within hours or days • Pollutants in the upper troposphere can persist for days • Pollutants in the stratosphere are resistant to cleansing • Ozone-depleting chemicals (chlorine, bromine)

  6. Layers of the atmosphere

  7. Atmospheric cleansing • Natural air pollutants: volcanoes, fires, dust storms • Plants emit volatile organic compounds • Mechanisms in the biosphere remove, assimilate, and recycle natural pollutants • Hydroxyl radical (OH): a naturally occurring compound • Oxidizes many gaseous pollutants to harmless products brought to land or water by precipitation • Sea salts: a cleansing agent that helps form raindrops • Picked up by wind flowing over oceans • Sunlight: breaks down organic molecules

  8. Hydroxyl radicals • They also remove anthropogenic pollutants from the air • Highly reactive hydrocarbons are rapidly oxidized • Nitrogen oxides are oxidized within a day • Less reactive substances (e.g., CO) take months • Atmospheric levels of hydroxyl are determined by levels of anthropogenic air pollutants • Hydroxyl’s cleansing power is used up • Pollutants are able to build up • Photochemical breakdown of ozone is a major source of hydroxyl radical

  9. The hydroxyl radical

  10. Smogs and brown clouds • Industrial smog: smoke + fog • An irritating, grayish mix of soot, sulfur compounds, and water vapor • In industrialized, cool areas that use coal • China, India, Korea, eastern European countries • Photochemical smog: in cities with huge freeway systems • A brownish, irritating haze in warm, sunny areas • Arises during the morning traffic • Pollutants from vehicle exhaust are acted on by sunlight • Nitrogen oxides, volatile organic compounds

  11. Industrial and photochemical smog

  12. Los Angeles air

  13. Inversions • Weather conditions can intensify smog • Daytime air temperature is usually highest near the ground • Warm air rises and carries air pollution up and away • Temperature inversion: sometimes, warm air overlays cooler air • Often occurs at night and is usually short-lived • Sun heats the air and pollutants are carried away • Cloudy weather prevents heating air so pollutants stay • Mountains can further trap smog (e.g., Los Angeles)

  14. Inversions harm health • Long-term temperature inversions allow pollutants to build up to dangerous levels • People with breathing problems should stay inside • Smog causes headaches, nausea, eye/throat irritation • It aggravates asthma, emphysema • Air pollution disasters: air pollution reaches lethal levels • Under severe temperature inversions • In 1952, 4,000 people died in London

  15. Temperature inversion

  16. Atmospheric brown clouds • Atmospheric brown cloud (ABC): relatively new • 1–3 km blanket of pollution over south/central Asia • Similar to North Temperate Zone’s aerosol pollution • But persists year round and has a different make up • ABC: black carbon and soot • From burning biomass and fossil fuels (coal, diesel) • Impacts: dimming over large cities, less rainfall, heating of air, decreased reflection of snow and ice • Shrinking glaciers will reduce water sources • Weaker Indian monsoons, less crops, health effects

  17. Processes producing air pollution • Incomplete combustion of fossil fuels and refuse • Creating gaseous and particulate products • Evaporation: creates gaseous and particulate products • Strong winds: pick up dust and other particles • Primary pollutants: direct products of combustion and evaporation • Particulates, VOCs, CO, NOx, SO2, lead, air toxics • Secondary pollutants: reactions of primary pollutants in the air • Ozone, peroxyacetyl, nitrates, sulfuric and nitric acids

  18. Prime sources of anthropogenic pollutants

  19. Primary pollutants • Power plants: the major source of sulfur dioxide • Industrial plants: particulates • Transportation: carbon monoxide, nitrogen oxides • Burning fossil fuels and wastes: soot, smoke • Unburned fragments of fuel molecules: VOCs • Nitrogen oxides (NOx): nitrogen gas is oxidized to nitric oxide (NO) under high combustion temperatures • Nitric oxide and oxygen form nitrogen dioxide (NO2; photochemical smog) and nitrogen tetroxide (N2O4) • Coal also contains sulfur and heavy metals

  20. Industrial pollution

  21. Tracking pollution • Clearinghouse for Inventories and Emissions Factors • Operated by the EPA • Tracks trends in national emissions of primary pollutants from all sources • Ambient concentrations of pollutants in the air • Measured by the EPA • Thousands of monitoring stations in the U.S. • 2008 air pollution levels in the U.S.: 116 million tons • 1970: 301 million tons • Shows the success of the Clean Air Act regulations

  22. U.S. emissions of five primary air pollutants

  23. Clean Air Act impacts

  24. Comparison of growth vs. emissions

  25. Getting the lead out • Lead: the sixth type of primary pollutant • Far smaller emissions than the first five primary pollutants • Added to gasoline to reduce engine knock • Phased out by the EPA during the 1980s and 1990s • Emissions remained airborne and traveled great distances • U.S. air concentrations have dropped by 99% • Decreased emissions in the U.S. and other nations have had a global impact • Further reductions must come from industry and smelters

  26. Toxics and radon • Air concentrations of toxic chemicals and radon are small • Some toxic compounds (e.g., benzene) come from transportation • Most come from industry and small businesses • Radon: produced by spontaneous decay of fissionable material in rocks and soils • Escapes naturally • Seeps into buildings through foundation cracks and basement floors • May collect in structures

  27. Secondary pollutants • Photochemical oxidants: ozone and other reactive organic compounds formed by nitrogen oxides and VOCs • Sunlight provides the reaction’s energy • Ozone concentrations in preindustrial times: 10–15 ppb • Unpolluted, summer air in North America: 20–50 ppb • Polluted air: 150 ppb or more (very unhealthy) • Ambient U.S. ozone levels decreased 20% 1980–92 • But only a few percent in the 2000s • Ozone standards are leaders in nonattainment areas • 132 million live in areas not meeting ozone standards

  28. Ozone formation • Nitrogen dioxide absorbs light energy and splits • Forms nitric oxide and atomic oxygen • The oxygen combines with oxygen gas, forming ozone • Ozone and nitric oxide usually react to form NO2 and O2 • No accumulation of ozone • When VOCs are present, nitric oxide reacts with them • Creates highly reactive, damaging peroxyacetyl nitrates (PANs) • Oxidized PANs produce aldehydes and ketones • Ozone accumulates

  29. Formation of ozone and other photochemical oxidants

  30. Acid precipitation and deposition • Sulfuric acids and nitric acids • Products of sulfur dioxide and nitrogen oxides reacting with atmospheric moisture and oxidants (e.g., hydroxyl) • The acids in acid rain (acid deposition) • Acid precipitation: any precipitation (rain, fog, mist, snow) more acidic than usual • Acid deposition: acid precipitation plus dry-particle fallout • Affects broad areas of North America, Europe and other industrialized nations • Precipitation is 10–1,000 times more acidic than usual

  31. Acid deposition

  32. Acids and bases • An acid: any chemical that releases hydrogen ions (H+) when dissolved in water • Sour taste, corrosiveness • Ionizes (separates) to hydrogen ions + a negative ion • The more hydrogen ions, the more acidic the solution • A base: any chemical that releases hydroxide ions (OHˉ) when dissolved in water • Bitter taste and caustic properties • pH: the concentration of hydrogen ions • The pH scale ranges from 0 to 14

  33. The pH scale • The pH scale: 0 (highly acidic) – 7 (neutral) – 14 (highly basic) • From 0 to 7: the concentration of H+ decreases • From 7 to 14: the concentration of OHˉ increases • The numbers represent the negative logarithm (power of 10) of the H+ concentration in grams/liter (g/L) • A pH = 1: H+ concentration = 10-1 g/L • There is a tenfold difference between units • A pH of 5 is ten times as acidic as a pH of 6

  34. The pH scale

  35. Extent and potency of acid precipitation • Rainfall is normally slightly acidic (pH = 5.6) • Acid precipitation: any precipitation with a pH < 5.5 • Acid precipitation is now the norm over most of the industrialized world • Eastern North America: rain and snow pH = 4.6 • Polluted air from the Midwest and industrial Canada • Can be as low as pH = 3.0 • Mountain forests east of Los Angeles have a pH = 2.8 • 1,000 times more acidic than usual

  36. Acid deposition in eastern North America

  37. Natural sources of acid deposition • Sulfuric acid (H2SO4) and nitric acid (HNO3) • Occurs in a ratio of 2 to 1 • But west U.S. and Canada have more nitric acid • Burning fuels are oxidized by hydroxyl radicals in the troposphere • Forming sulfuric and nitric acid • Natural sources of sulfur dioxide: 50–70 million tons/year (volcanoes, sea spray, microbial processes) • Natural sources of nitrogen oxides: 30–40 million tons/year (lightning, biomass burning, microbial processes)

  38. Anthropogenic sources of acid deposition • Sulfur dioxide: 100–130 million tons/year • U.S. sources: fuel (coal) combustion • Nitrogen oxides: 60–70 million tons/year • Most from transportation • Anthropogenic sources: concentrated in industrialized areas • Emissions have increased 4x since 1900 • Old U.S. coal-burning power plants are reducing emissions • Deposition has decreased 33–35% in the past 15 years • Fossil-fuel-burning electric utility plants still emit SO2 and NOx

  39. Midwestern coal-burning power plant

  40. Impacts of air pollutants • We are exposed to a mixture of pollutants that varies over time and place • Plants may be so stressed from pollution that they become vulnerable to drought or insects • Human health: every one of the primary and secondary air pollutants is a threat to human health • Acute exposure can be life threatening • Chronic exposure: long-term exposure that causes gradual deterioration and premature mortality • Some pollutants contribute to lung cancer

  41. The respiratory system

  42. Long-term exposure and chronic effects • Sulfur dioxide: leads to bronchitis (inflammation of the bronchi) • Ozone: leads to inflammation and scarring of the lungs • Carbon monoxide: reduces the oxygen-carrying capacity of the blood and leads to heart disease • Nitrogen oxides: impair lung function and affect the immune system • Particulate matter: respiratory and cardiovascular pathologies • Other factors (diet, exercise, genetics) influence effects

  43. COPD • Chronic obstructive pulmonary disease (COPD) • A slowly progressive lung disease that makes it hard to breathe • The 4th leading cause of death: affects 18 million in the U.S. • Affects 10% of adults over 40 worldwide • From smoking and burning wood or dung for fuel • Involves three diseases: emphysema (destruction of the lung alveoli), bronchitis, and asthma

  44. Asthma • Most sensitive to air pollution: small children, asthmatics, those with chronic pulmonary or heart disease, the elderly • Asthma: an immune disorder • Impaired breathing caused by constricted airways • Is triggered by allergens (dust, mites, mold, pet dander) • Is also triggered by pollution (ozone, particulates, SO2) • Causes 500,000 hospitalizations/year • 1.8 million visits to emergency departments • In the last decade, U.S. asthma has doubled (to 23 million)

  45. Strong evidence • Studies of thousands of adults show strong evidence of harm caused by fine particulates and sulfur pollution • Asthma, chronic bronchitis, cardiovascular problems, etc. • Higher concentrations of fine particles correlate with increased mortality from cardiopulmonary disease and lung cancer • The EPA used these studies to regulate fine particles • Fine particles and ozone exceeded California standards • Meeting standards would save $28 billion/year in avoided health costs, missed work, premature deaths, etc.

  46. Lead again • Lead poisoning causes mental retardation • In the 1980s, elevated levels were present in adults and children • Children: learning disabilities • Adults: high blood pressure • The major source of lead: leaded gasoline • Inhaled, settled on food or other items put in the mouth • The EPA mandated elimination of leaded gasoline by 1996 • Dramatically reduced lead in the environment

  47. Acute and carcinogenic effects • Air pollution can kill people already suffering from heart or respiratory diseases • Lethal doses also occur in accidental poisoning • Moderate air pollution can change cardiac rhythms in people with heart disease • Triggering fatal heart attacks • Diesel: a likely human carcinogen • Benzene: clearly correlated with cancer • In motor fuels, solvents, explosives, smoke, medicines • Linked to leukemia, blood disorders, damaged immunity

  48. Diesel truck exhaust

  49. The environment • Plants are more sensitive than humans to air pollution • Sulfur dioxide from smelters and power plants killed large areas of vegetation • Ozone damages crops, orchards, and forests • Ozone enters plants through stomata (pores) • Symptoms of damage: black flecks, yellow leaves • Crops vary in their susceptibility to ozone • Soybeans, corn, wheat are damaged at ambient ozone levels • Countries lose billions of dollars/year in lower yields

  50. Ambient ozone injury