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Air Pollution
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  1. Air Pollution G. Tyler Miller’s Living in the Environment 13th Edition Chapter 17

  2. Key Topics Key Topics Structure and composition of the atmosphere Types and sources of outdoor air pollution Types, formation, and effects of smog Sources and effects of acid deposition Effects of air pollution Prevention and control of air pollution

  3. Structure and Science of the Atmosphere • The atmosphere consists of several layers with different temperatures, pressures, and composition • The atmosphere is a thin layer of gases divided into several spherical sublayers. • Density and atmospheric pressure vary throughout the atmosphere due to gravitational forces that pull the gas molecules toward the earth’s surface. • Air at sea level has a higher density than air at the top of a mountain. • Atmospheric pressure is a measure of the mass per unit of air. It decreases with altitude.

  4. Atmosphere About 75–80% of the earth’s air mass is found in the troposphere, the atmospheric layer closest to the earth’s surface. This layer extends about 11 miles above sea level at the equator and about 5 miles above the poles. About 99% of the volume of air is made up of nitrogen (78%) and oxygen (21%) with the rest consisting of water vapor, argon, carbon dioxide, and traces of several other gases. This layer is also responsible for short-term weather and long-term climate.

  5. Stratosphere • The stratosphere is the second layer of the atmosphere and extends from 11–30 miles above the earth’s surface. • Ozone is produced when oxygen molecules interact with ultraviolet radiation (3 O2 + UV  2 O3). This “global sunscreen” keeps about 95% of the sun’s harmful UV radiation from reaching the earth’s surface. • This ozone layer protects us from sunburn, cataracts, cancer of skin and eye, and damage to our immune system.

  6. Outdoor Air Pollution • Air pollution: presence of one or more chemicals in atmosphere to (1)cause harm to us, other life and materials(2)alter climate. • Comes mostly from natural sources and burning fossil fuels. • Chemicals in the atmosphere in concentrations high enough to affect climate, materials, and health are what constitute air pollution. • Natural sources of air pollution such as dust particles, organic chemicals released by plant decay, forest fires, etc. rarely reach harmful levels. • Increased use of fossil fuels has greatly increased the amount of pollution in our air.

  7. Table 17-1 Major Classes of Air Pollutants in outdoor air(ambient air) Class Carbon oxides Sulfur oxides Nitrogen oxides Volatile organic compounds (VOCs) Suspended particulate matter (SPM) Photochemical oxidants Radioactive substances Hazardous air pollutants (HAPs), which cause health effects such as cancer, birth defects, and nervous system problems Examples Carbon monoxide (CO) and carbon dioxide (CO2) Sulfur dioxide (SO2) and sulfur trioxide (SO3) Nitric oxide (NO), nitrogen dioxide (NO2), nitrous oxide (N2O) (NO and NO2 often are lumped together and labeled NOx) Methane (CH4), propane (C3H8), chlorofluorocarbons (CFCs) Solid particles (dust, soot, asbestos, lead, nitrate, and sulfate salts), liquid droplets (sulfuric acid, PCBs, dioxins, and pesticides) Ozone (O3), peroxyacyl nitrates (PANs), hydrogen peroxide (H2O2), aldehydes Radon-222, iodine-131, strontium-90, plutonium-239 (Table 3-1, p. 49) Carbon tetrachloride (CCl4), methyl chloride (CH3Cl), chloroform (CHCl3), benzene (C6H6), ethylene dibromide (C2H2Br2), formaldehyde (CH2O(CH2O2) Table 20-1Page 436

  8. Outdoor air pollutants • Two categories: • primary pollutants that enter directly into the troposphere (soot, carbon monoxide) and • secondary pollutants that may form when primary pollutants interact with one another or with the air to form new pollutants. • Cities generally have higher pollution levels. Winds can carry these pollutants away from their source. • Indoor air pollutants come from infiltration of outside air or produced inside buildings. • Air pollution is classified as a high-risk human health problem. US and most developed countries have set gov’t max. allowable atmospheric concentration for six criteria air pollutants (Table 17-2) • Most people exposed to poor air live in developing countries.

  9. Sources and types of air pollution

  10. Major Sources of Primary Pollutants Stationary Sources • Combustion of fuels for power and heat – Power Plants • Other burning such as Wood & crop burning or forest fires • Industrial/ commercial processes • Solvents and aerosols Mobile Sources • Highway: cars, trucks, buses and motorcycles • Off-highway: aircraft, boats, locomotives, farm equipment, RVs, construction machinery, and lawn mowers

  11. Photochemical and Industrial Smog • Photochemical smog is formed by the reaction of nitrogen oxides and volatile hydrocarbons under the influence of sunlight. • A photochemical reaction is any chemical reaction activated by light. • Photochemical smog contains more than 100 primary and secondary pollutants. • Some NO2 reacts with hydrocarbons to produce a mixture of ozone, nitric acid, aldehydes, peroxyacyl nitrates (PANs), and other pollutants. Highly reactive • These substances are photochemical oxidants and can irritate the respiratory tract and damage crops and trees. • Photochemical smog is more common in cities in warm, dry, sunny areas.

  12. Solar radiation Ultraviolet radiation NO Nitric oxide O2 Molecular oxygen NO2 Nitrogen dioxide H2O Water O Atomic oxygen Hydrocarbons PANs Peroxyacyl nitrates HNO3 Nitric acid O3 Ozone Aldehydes (e.g., formaldehyde) Photochemical smog

  13. Industrial smog • Industrial smog is a mixture of sulfur dioxide, droplets of sulfuric acid, and a variety of suspended solid particles emitted by burning coal and oil. • When coal is burned, it is converted to carbon dioxide, carbon monoxide, and unburned carbon particles (soot). • Coal and oil also contain sulfur that is then converted to sulfur dioxide. • Sulfur dioxide + water = Sulfuric acid + ammonia in air • = Ammonium Sulfate. • These various components give the air a gray color. • China has a serious gray-smog problem in many areas, and many people die prematurely from this.

  14. Outdoor air pollution • Outdoor air pollution can be reduced and increased. Frequency and severity of smog depends on climate, pop. density, amt. of industry, fuels used in heating, industry, transportation. • Three natural factors help reduce outdoor air pollution: • rain and snow, and winds. • Each of these factors helps remove pollutants, but they are then deposited elsewhere. • Four factors can increase outdoor air pollution: • urban buildings, • hills and mountains, • high temperature • Air pollution can reduce the rain and snowfall the help cleanse the air of pollutants.

  15. Temperature Inversions • During daylight, turbulence, caused by the mixing of warm and cold air, disperses air pollutants. • However, a temperature inversion, where a layer of warm air sits over a layer of cold air, prevents the mixing, and dense, colder air becomes stagnant and accumulates more pollutants. • Two areasparticularly susceptible to inversions: • 1.a city located in a valley surrounded by mountains that experiences cloudy, cold weather part of the year and • 2.a sunny climate with light winds and mountains on three sides and several million people and vehicles (Los Angeles basin).

  16. Temperature Inversion

  17. Air Pollution from Acid Deposition • Acidic particles (SO2 and NO)remain in the atmosphere for 2–14 days, depending on the prevailing winds, precipitation, and other weather patterns. They form secondary pollutants(nitric acid vapor, H2SO4) • The acidic substances return to the earth in one of two forms: • wet deposition as acidic rain, snow, fog, and cold vapor with a pH less than 5.6 and • dry deposition as acidic particles. • Acid deposition is a problem in areas downwind from coal-burning facilities and urban areas. • Some areas have basic compounds in the soil that act to buffer or neutralize some acidic deposits. • Many acid-producing chemicals generated in one country end up in other countries due to prevailing winds.

  18. 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 deposition (droplets of H2SO4 and HNO3 dissolved in rain and snow) Nitric oxide (NO) Dry acid deposition (sulfur dioxide gas and particles of sulfate and nitrate salts) Sulfur dioxide (SO2) and NO Acid fog Farm Lakes in shallow soil low in limestone become acidic Ocean Lakes in deep soil high in limestone are buffered Acid Rain Chemistry • See Miller for geography of power plants and sensitive soils, p. 429, figure 17-11

  19. Acid deposition can deplete some soil nutrients, release toxic ions into soil, and weaken plants that become susceptible to other stresses. • There may be an initial growth stimulus from added nitrogen and sulfur, but continued deposition leaches essential magnesium and calcium salts from the soil and lowers plant productivity. • Acid can also dissolve aluminum, cadmium, and mercury ions from the soil. These ions are toxic to plants and animals. • The mountaintop trees are those that are most harmed by acidic rain because they are also growing in thin soils.

  20. Acid Rain Effects What are the effects? In Soils: H+ displaces cations in clay and humus, resulting in nutrient depletion

  21. Effects of Acid deposition • Acid deposition can cause or worsen respiratory disease, attack metallic and stone objects, decrease atmospheric visibility, and kill fish. • Large amounts of money are spent each year to clean and repair monuments and statues damaged by acid deposition. • Acid deposition also decreases atmospheric visibility. • Many lakes in northern Europe and the eastern U.S. have few, if any, fish due to decreased pH.

  22. Emission Acid deposition SO2 H2O2 PANs NOX O3 Others Increased Susceptibility to drought, extreme cold, insects, mosses, and disease organisms Reduced photosynthesis and growth Direct damage to leaves and bark Soil acidification Tree death Reduced nutrient and water uptake Leaching of Soil nutrients Root damage Release of toxic metal icons Acid Groundwater

  23. Prevention and control of acid deposition • A number of methods but politically difficult to implement. • The best approaches are those that reduce or eliminate emissions of SO2, NOx, and particulates. • Use of low sulfur coal is both good and bad. More need to be burned for the same amount of electricity. And it emits more mercury, CO2, and radioactive particles. • Inclusion of environmental and health costs to the current costs of coal would give a more realistic picture. • Approaches to neutralize acid lakes include adding limestone or lime to the water or soil or adding a small amount of phosphate fertilizer; this approach is being evaluated.

  24. Indoor Air Pollution

  25. Why is indoor air quality important? • 70 to 90% of time spent indoors, mostly at home • Many significant pollution sources in the home (e.g. gas cookers, paints and glues) • Personal exposure to many common pollutants is driven by indoor exposure • Especially important for susceptible groups – e.g. the sick, old and very young

  26. Indoor air pollution • Indoor air pollution a much greater threat to than outdoor air pollution. • EPA studies have shown that: • levels of 11 common pollutants are 2–5 times greater inside homes and commercial buildings than outside. • inside cars in traffic-clogged areas, the pollution may be 18 times higher than outside. • health risks are magnified because people usually spend 70–98% of their time indoors or in vehicles. • The EPA lists the four most dangerous indoor air pollutants in developed countries as cigarette smoke, formaldehyde, radioactive radon-222 gas, and very small fine and ultrafine particles. • In developing countries, as many as 2.8 million people die prematurely each year from breathing elevated levels of indoor smoke and particulates.

  27. Formaldehyde the difficult chemical in common household materials. • Radon-222 gas is found in some soils and rocks and can seep into some homes and increase the risk of lung cancer. • Radon <=radioactive decay of uranium-238. • Radon is thought to be the second leading cause of lung cancer deaths each year in the U.S. • It is recommended that everyone living in a detached home, a townhouse, or the first three levels of an apartment building test for radon. • Remedies include sealing cracks in foundation and walls, increasing ventilation, and using a fan for cross ventilation.

  28. Effects of Air Pollution on Living Organisms • Prolonged or acute exposure to air pollutants can overload or break down the body defenses. • Several respiratory diseases can develop such as asthma, lung cancer, chronic bronchitis, and emphysema. • People with respiratory diseases, older adults, infants, pregnant women, and people with heart disease are especially vulnerable to air pollution • Each year, air pollution kills about 3 million people, mostly from indoor air pollution in developing countries. • Air pollution deaths in the U.S. range from 150,000 to 350,000 people per year. Millions more become ill. Costs about 150 billion in health care in US alone.

  29. Occupational Exposures

  30. Solutions: Preventing and Reducing Air Pollution • Clean Air Acts in the USA have reduced outdoor air pollution. • The U.S. Congress passed Clean Air Acts in 1970, 1977, and 1990. • National air quality standards (NAAQS) were established for six outdoor criteria pollutants. • Two limits were established: a primary standard is set to protect human health and a secondary standard is set to prevent environmental and property damage. • Allowing producers of air pollutants to buy and sell government air pollution allotments in the marketplace can help reduce emissions. Cap and Trade

  31. Emission Reduction

  32. Important Indoor Air pollutants • Nitrogen dioxide • Carbon monoxide • Formaldehyde • Volatile Organic Compounds (VOCs) • House dust mites (and other allergens, e.g. from pets) • Environmental tobacco smoke • Fine particles • Chlorinated organic compounds (e.g. pesticides) • Asbestos and man-made mineral fibres • Radon

  33. Indoor Air Pollution

  34. TheCleanAirAct Congress found: • Most people now live in urban areas • Growth results in air pollution • Air pollution endangers living things It decided: • Prevention and control at the source was appropriate • Such efforts are the responsibility of states and local authorities • Federal funds and leadership are essential for the development of effective programs

  35. Clean Air Act • Originally signed 1963 • States controlled standards • 1970 – Uniform Standards by Federal Govt. • Criteria Pollutants • Primary – Human health risk • Secondary – Protect materials, crops, climate, visibility, personal comfort

  36. Why is indoor air quality important? • 70 to 90% of time spent indoors, mostly at home • Many significant pollution sources in the home (e.g. gas cookers, paints and glues) • Personal exposure to many common pollutants is driven by indoor exposure • Especially important for susceptible groups – e.g. the sick, old and very young

  37. Clean Air Act • 1990 version • Acid rain, urban smog, toxic air pollutants, ozone depletion, marketing pollution rights, VOC’s • 1997 version • Reduced ambient ozone levels • Cost $15 billion/year -> save 15,000 lives • Reduce bronchitis cases by 60,000 per year • Reduce hospital respiratory admission 9000/year

  38. Clean Air Act President George W. Bush signed rules amending Clean Air Act that allowed power plants and other industries to increase pollution significantly without adopting control measures

  39. Clean Air Act • EPA to develop NAAQS for 7 major outdoor pollutants • Non-attainment areas • EPA set emission standards for 300 compounds • Congress to set timetable for achieving them