Air Pollution


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Air Pollution

  1. 1. Air Pollution Presented by Dr. B. Victor
  2. 2. About the presenter <ul><li>Dr.B.Victor is a highly experienced postgraduate biology teacher, recently retired from the reputed educational institution St. Xavier’ s College, Palayamkottai, India-627001. </li></ul><ul><li>He was the dean of sciences and assistant controller of examinations. </li></ul><ul><li>He has more than 32 years of teaching and research experience </li></ul><ul><li>He has taught a diversity of courses ranging from Send your comments to : pre- university to post graduate classes. </li></ul><ul><li>[email_address] </li></ul>
  3. 3. Presentation outline <ul><li>What is pollution? </li></ul><ul><li>Kinds of pollution sources </li></ul><ul><li>Sources of air pollutants </li></ul><ul><li>Kinds of air pollutants </li></ul><ul><li>Effects of air pollutants </li></ul><ul><li>Green house effect and global warming </li></ul><ul><li>Acid rain </li></ul><ul><li>Indoor air pollution </li></ul><ul><li>Control measures </li></ul>
  4. 4. Gaia hypothesis <ul><li>The Earth is like a living organism, which itself engaged in a self regulation to support its own &quot;survival&quot; </li></ul><ul><li>&quot;The chemical and physical condition of the surface of the Earth, of the atmosphere, and of the oceans has been made fit and is actively made fit and comfortable by the presence of life itself.&quot; </li></ul>
  5. 5. This is what earth looks like
  6. 6. Pollution - Definition: <ul><li>   Any addition to air, water, soil etc that threatens the health, survival of humans or other living organisms </li></ul><ul><li>1. Natural - volcanic eruption </li></ul><ul><li>2. Anthropogenic - burning coal </li></ul>
  7. 7. Types of Sources: <ul><li>Point source - single, identifiable source e.g. smokestack, drainpipe etc </li></ul><ul><li>Non-point source - dispersed source, e.g. runoff from pesticides, fertilizers </li></ul>
  8. 8. Non-point sources
  9. 9. Point source
  10. 10. What are the key environmental problems <ul><li>    A. Population growth  B. Resource use without preventing pollution and reducing waste  C. Degrading habitats and reduction of biodiversity  D. Poverty  E. Failure of govt to encourage earth sustaining economic development </li></ul>
  11. 11. The Paul Ehrlich Equation <ul><li>I = P * A * T = Eye PAT </li></ul><ul><li>I mpact =  P opulation x  A ffluence x T echnology. where: I is the impact on the environment resulting from consumption P is the population number A is the consumption per capita (affluence) T is the technology factor </li></ul>
  12. 12. The Atmosphere <ul><li>Gases that envelop the Earth and are held here by gravity regulates temperature. </li></ul><ul><li>Major gases: </li></ul><ul><li>78.08% nitrogen </li></ul><ul><li>20.95% oxygen </li></ul><ul><li>0.93% argon </li></ul><ul><li>0.03% carbon dioxide </li></ul><ul><li>trace amounts of water vapor (close to surface) 0.01% by volume near poles to 5% near equator and many others hydrogen, neon, helium, krypton, ozone and methane </li></ul>
  13. 13. Composition of Air
  14. 14. Layers of the atmosphere
  15. 15. Layers of the atmosphere <ul><li>Troposphere : 75% of mass of air; 17 km thick A turbulent layer of rising and falling air currents. </li></ul><ul><li>Stratosphere : extends up to 50 km above the Earth's surface. Less dense, contains nearly 99% of remaining atm.; similar composition. Ozone has a higher volume here (1000 x troposphere), water vapor has a lower volume (1/1000). Calm air. Little vertical mixing. </li></ul><ul><li>Mesosphere : 50-90 km </li></ul><ul><li>Thermosphere : 90-110 km </li></ul>
  16. 16. Stratospheric ozone layer, O3 <ul><li>. </li></ul><ul><li>Formed by a natural process. </li></ul><ul><li>Produced by O2 interacting with lightning and UV radiation. </li></ul><ul><li>Absorbs most of the shorter wavelengths - UV radiation which is damaging to living things causing cancer, sunburn, cataracts etc. </li></ul><ul><li>allows life to live on earth </li></ul><ul><li>ozone depletion - a reduction of the ozone layer. </li></ul>
  17. 17. What are the major sources and types of air pollution?
  18. 18. Air pollution :Definition <ul><li>the presence of one or more chemicals in the atmosphere in sufficient quantities and duration to cause harm to humans etc. </li></ul>
  19. 19. Air Pollution <ul><li>Air pollution results from human activities such as burning fossil fuels (oil, coal, and gasoline) to create electricity and power automobiles, and manufacture industrial products such as chemicals and plastic. </li></ul><ul><li>The air Pollutants are particulates, HC, CO2, CO, NO, NO2, SO3 -- source may be industrial, autos, etc. </li></ul>
  20. 20. Air pollution <ul><li>The increased carbon dioxide in the atmosphere contributes to the warming of the global climate, the so-called &quot;greenhouse effect.&quot; </li></ul><ul><li>The increased Chlorofluoro-carbons in the atmosphere has been depleting stratospheric ozone. </li></ul>
  21. 21. Sources of Air pollution <ul><li>Natural: </li></ul><ul><li>volcanoes, fumaroles and hot springs </li></ul><ul><li>decay from marshes, bogs </li></ul><ul><li>increase ozone due to thunderstorms, fires. </li></ul>
  22. 22. Man made (most severe for human health): <ul><li>Stationary sources - those that are fixed in location. </li></ul><ul><li>point sources e.g. smoke stacks, 14% air pollution from plants generating electricity; </li></ul><ul><li>fugitive sources e.g. construction sites, exposed areas; </li></ul><ul><li>area sources e.g. dense urban community or agricultural area </li></ul><ul><li>Mobile sources - those that move while polluting, e.g. trucks, cars, busses etc. 60% of air pollution from motor vehicles. 80-88% in major cities! </li></ul>
  23. 24. What are the main categories of air pollutants?
  24. 25. The main categories of air pollutants <ul><li>Primary: those emitted directly into the air; e.g. sulfur dioxide (SO2), carbon monoxide (CO), nitric oxide (NO), nitrogen dioxide (NO2) </li></ul><ul><li>Secondary : those that form as a result of a chemical reaction of the primary pollutant with a natural component of the environment.; e.g. some ozone, sulfuric and nitric acids. </li></ul>
  25. 26. Types of pollutants <ul><li>Primary pollutants </li></ul><ul><li>Pollutants that are emitted directly from identifiable sources –produced by both natural events or human activities </li></ul><ul><li>Eg. Dust storms, emission from vehicles </li></ul><ul><li>Secondary pollutants </li></ul><ul><li>When certain chemical reactions take place among the primary pollutants </li></ul><ul><li>Eg. Sulphuric acid </li></ul>
  26. 27. Primary pollutants <ul><li>Carbon oxides (CO2 and CO) </li></ul><ul><li>Nitrogen oxides </li></ul><ul><li>Sulphur oxides </li></ul><ul><li>Volatile organic compounds – hydro carbons </li></ul><ul><li>Suspended particulate matter </li></ul>
  27. 28. Primary air pollutants- Auto exhaust <ul><li>hydrocarbons, methane, butane, propane others. </li></ul><ul><li>hydrogen sulfide, H2S, gas. Toxic. </li></ul><ul><li>particulates, visible - dust, smoke, soot, very fine <2.5 µm. </li></ul><ul><li>lead, batteries, additive to gasoline (phased out). Becomes airborne, spread to land </li></ul>
  28. 29. Primary air pollutants <ul><li>Sulfur dioxide, SO2 , colorless, odorless gas. particulates of SO4 which combines with water to form acid rain. Toxic to plants and animals; paint damage. </li></ul><ul><li>Carbon monoxide CO colorless, odorless gas, readily combines with hemoglobin in blood. Toxic. </li></ul><ul><li>Nitrogen oxides, NO, nitric oxide and nitrogen dioxide NO2 . NO2 yellow brown to reddish gas. (NOx) Converted to nitrates in atmosphere causing acid rain. </li></ul><ul><li>Photochemical smog , brown air smog. Smog is smoke + fog. </li></ul>
  29. 30. Photochemical Smog <ul><li>Smog is a kind of air pollution, originally named for the mixture of smoke and fog in the air. </li></ul><ul><li>HC and NO react in presence of sunlight to produce ozone and PAN (peroxy acetyl nitrate) </li></ul><ul><li>Nitrogen oxides + hydrocarbons + Ultraviolet radiation -----> Peroxyacetyl nitrate PAN + O3 ozone. </li></ul>
  30. 31. Photochemical smog- Effects <ul><li>breathing ozone results in respiratory distress, headaches. </li></ul><ul><li>PAN damages plants </li></ul><ul><li>PAH's polynuclear aromatic hydrocarbons, carcinogenic. </li></ul>
  31. 32. Photochemical Smog
  32. 33. What are the effects of air pollution?
  33. 34. The effects of air pollution <ul><li>reduces visual range and atmospheric clarity, less contrast, less visibility </li></ul><ul><li>damage to vegetation, including leaves, needles, fruit, growth rate, reproduction, hardiness. </li></ul><ul><li>Decline in net primary productivity NPP. </li></ul><ul><li>Crop losses 1.9-5.4 b/yr. </li></ul>
  34. 35. The effects of air pollution <ul><li>degradation of human health, from mild problems e.g. eye irritation, to severe e.g. respiratory disease asthma, bronchitis, emphysema, cancer. </li></ul><ul><li>CO, carbon monoxide , 90% natural, 10% from incomplete combustion, cigarettes, combines with hemoglobin and reduces bloods ability to carry oxygen. 150,000-350,000 deaths/yr. </li></ul>
  35. 36. The effects of air pollution <ul><li>degradation of vertebrate health, aquatic life, with impacts on respiration, bones, teeth, reproduction; increase lake acidity, decline in NPP </li></ul><ul><li>degradation of soil and water, when air pollutants settle, toxic metals in soil, soils leached </li></ul><ul><li>deterioration of man-made structures, break down car paint, roofing; acid rain chemically dissolves marble statues and other building materials </li></ul>
  36. 37. Effects of air pollution <ul><li>Air pollutants can overload or break down the natural defenses such as hair in our nose, sticky mucus in the lining of the upper respiratory tract causing diseases like lung cancer, asthma, chronic bronchitis etc., </li></ul>
  37. 38. Effects of air pollution <ul><li>Cigarette smoking is responsible for the greatest exposure to carbon monoxide.Exposure to air containing even 0.001% of carbon monoxide for several hours can cause collapse, coma and even death. </li></ul><ul><li>CO is attached to blood hemoglobin reduces the oxygen carrying capacity of blood. This impairs perception and thinking, slows reflexes and causes headaches, drowsiness, dizziness and nausea and blurred vision. </li></ul>
  38. 39. <ul><li>Nitrogen oxides and suspended particles both can irritate lungs, aggravate asthma or chronic bronchitis and increase respiratory infections. </li></ul><ul><li>Many volatile organic compounds such as benzene and formaldehyde and toxic particulates such as lead and cadmium can cause mutations, reproductive problems and cancer, breathlessness and irritation of the eye, nose and throat. </li></ul>Effects of air pollution
  39. 40. <ul><li>Sulphur dioxide irritates respiratory tissues and chronic exposure causes bronchitis. </li></ul><ul><li>Sulphur dioxide also reacts with water, oxygen and other materials to form sulphur containing acids – The acids can become attached to particles which when inhaled are very corrosive to the lung. </li></ul>Effects of air pollution
  40. 41. Effects of air pollution <ul><li>Chronic exposure of the leaves to air pollutants can break down the waxy coating that helps prevent excessive water loss and leads to damage from diseases, pests, drought and frost. </li></ul><ul><li>It also affects photosynthesis, respiration and other metabolisms. </li></ul>
  41. 42. Doubling carbon dioxide
  42. 43. Doubling of carbon dioxide <ul><li>In 1850, atmospheric carbon dioxide was about 280 parts per million (ppm). </li></ul><ul><li>Today, it is about 350 ppm. </li></ul><ul><li>This increase is due largely to burning of fossil fuels and clearing of forests. </li></ul><ul><li>Oceans (and photosynthetic organisms) currently absorb half of the carbon dioxide emitted. </li></ul>
  43. 44. Carbon dioxide concentration
  44. 45. Increase in carbon dioxide levels between 1960 and 1990.
  45. 46. Increase in the emissions of carbon during the interval from 1860-1995
  46. 47. Concentration of carbon dioxide
  47. 48. Cycle of carbon dioxide
  48. 49. Impact of increasing CO2 levels in the atmosphere <ul><li>Increased photosynthesis and productivity by the earth’s vegetation . </li></ul><ul><li>Increased plant production also means increased respiration . </li></ul><ul><li>Elevated atmospheric CO2 is global warming </li></ul><ul><li>Elevated CO2 means an increase in global temperature - the greenhouse effect . </li></ul><ul><li>Global temperatures may increase by 3oC-4oC by the end of the next century . </li></ul>
  49. 50. Green house effect
  50. 51. Greenhouse gases (GHGs) <ul><li>Some greenhouse gases occur naturally in the atmosphere, while others result from human activities. </li></ul><ul><li>Naturally occuring greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, and ozone. </li></ul>
  51. 52. Greenhouse gases (GHGs) <ul><li>Carbon dioxide is a product of burning fossil fuel and wood. </li></ul><ul><li>Nitrous oxide (NO2), produced by fertilizer use and released from decomposition of animal wastes. </li></ul><ul><li>Methane (CH4) is produced by bacteria from sediments, swamps, and in flooded rice paddies. </li></ul><ul><li>Chlorofluorocarbons (CFCs), Freon (a refrigerant) deplete the ozone layer in the upper atmosphere. </li></ul><ul><li>Halons, such as halocarbons), are released from fire extinguishers. </li></ul><ul><li>Water vapor in clouds reradiate heat back to Earth. </li></ul>
  52. 53. Green house gas emissions
  53. 54. Greenhouse gases
  54. 55. Green house effect <ul><li>Carbon dioxide and other gases allow light to pass, but trap heat in the atmosphere much like glass in a greenhouse traps heat. </li></ul><ul><li>This greenhouse effect is thought to be responsible for global warming. </li></ul><ul><li>Carbon dioxide contributes to only 56% of greenhouse heating. </li></ul><ul><li>The average surface temperature of Earth is about 15°C (59°F). </li></ul><ul><li>Global Warming is increase in the average temperature of the atmosphere, oceans, and landmasses of Earth. </li></ul><ul><li>A A </li></ul>
  55. 56. Greenhouse effect
  56. 57. Greenhouse effect
  57. 58. Impact of Global warming <ul><li>Temperature extremes  </li></ul><ul><li>  Rise in sea level, and change in precipitation </li></ul><ul><li>Injuries from storms, coastal flooding  </li></ul><ul><li>Interruption of power supply, contamination of drinking water  </li></ul><ul><li>Drought  </li></ul><ul><li>Food shortages due to shift in agricultural food production  </li></ul><ul><li>Air pollution ( made worse by warming)  </li></ul><ul><li>Asthma, bronchitis, emphysema complications  </li></ul><ul><li>Strain on public health systems  </li></ul><ul><li>Increased need due to population migrations  </li></ul><ul><li>Unable to contain spread of infectious diseases  </li></ul>
  58. 60. Conserve Energy <ul><li>Be energy-wise </li></ul><ul><li>Explore alternatives </li></ul><ul><li>Recycle as much as is possible. </li></ul><ul><li>Take showers instead of baths. </li></ul><ul><li>Check your taps. </li></ul><ul><li>Check the lights </li></ul><ul><li>Check your stove. </li></ul><ul><li>Use less cooking water. </li></ul><ul><li>Check the refrigerator. </li></ul>
  59. 61. Ozone depletion
  60. 62. Ground level Ozone <ul><li>Ozone (O3) is a key constituent of the troposphere. </li></ul><ul><li>Ozone (Greek ozein, “to smell”), pale blue, highly poisonous gas with a strong odor. </li></ul><ul><li>Ozone is considered a pollutant at ground level. </li></ul><ul><li>Breathing O3 affects both the respiratory and nervous systems, resulting in respiratory distress, headache, and exhaustion. </li></ul><ul><li>Ozone is damaging to plants, resulting in leaf mottling and reduced growth. </li></ul>
  61. 63. The Ozone Layer <ul><li>Earth's atmosphere consists of a number of different layers. </li></ul><ul><li>The troposphere is the lower atmospheric layer. </li></ul><ul><li>The stratosphere is often referred to as the upper atmosphere. </li></ul><ul><li>The stratosphere contains the ozone shield, a layer of ozone (O3) in the stratosphere, 50 km above the ground. </li></ul>
  62. 64. The Ozone Layer
  63. 65. Hazards of UV radiation <ul><li>Hazards of UV radiation include increased mutation rate, which can lead to skin cancer and cataracts, depression of the immune system, impaired crop and tree growth, and the death of plankton. </li></ul>
  64. 66. Health effects of Ozone depletion <ul><li>Each 1% drop in ozone is thought to increase human skin cancer rates by 4-6%. </li></ul><ul><li>The United Nations Environment Program predicts a 26 percent rise in cataracts and non-melanoma skin cancers for every 10% drop in ozone. </li></ul><ul><li>This translates to 1.75 million cases of cataracts and 300,000 more cases of skin cancer every year. </li></ul>
  65. 67. Ozone Hole above Antarctica <ul><li>During the 1980s scientists discovered a &quot;hole&quot; in the ozone over Antarctica. </li></ul><ul><li>By the 1990s atmospheric scientists had detected an annual loss of 40-50% of the ozone above Antarctica, which produced an ozone hole every spring. </li></ul><ul><li>One CFC molecule can destroy 100,000 ozone molecules. </li></ul>
  66. 68. The largest Antarctic ozone hole ever recorded (September 2006). <ul><li>The Antarctic ozone hole is an area of the Antarctic stratosphere in which the recent ozone levels have dropped to as low as 33% of their pre-1975 values. </li></ul>
  67. 69. What is acid rain; what are its causes and effects?
  68. 70. Environmental Impact of Acid deposition <ul><li>Sterilization of lakes and forests. </li></ul><ul><li>Reducing the populations of small invertebrates and decomposers. </li></ul><ul><li>Reducing agricultural yields. </li></ul><ul><li>Causing extensive structural damage by corroding marble, metal, and stonework. </li></ul><ul><li>Degrading water supplies by leaching heavy metals from the soil into drinking-water supplies. </li></ul><ul><li>Increases in lung cancer and colon cancer. </li></ul>
  69. 71. Wet and dry acid deposition <ul><li>Caused by SO2 and NO2. Alone cause dry acid deposition, with all forms of water vapor, these form sulfuric and nitric acid - acid rain downwind of sites of emission. </li></ul><ul><li>Logarithmic scale. pH of 4 is 10 x more acidic than pH of 5. Normal rain water pH 5.0-5.6 approx. Acid rain < 5.0 Affects industrialized areas worldwide. Scandinavia, Eastern Europe, N.E. U. S. Developing countries have more pollution, fewer controls than developed countries. </li></ul>
  70. 72. Acid Precipitation
  71. 73. Acid rain <ul><li>The term &quot;acid rain&quot; is commonly used to mean the deposition of acidic components in rain, snow, fog, dew, or dry particles. </li></ul><ul><li>The more accurate term is &quot;acid precipitation.“ </li></ul><ul><li>&quot;Clean&quot; or unpolluted rain is slightly acidic, its pH being about 5.6, because carbon dioxide and water in the air react together to form carbonic acid, a weak acid. </li></ul><ul><ul><li>H 2 O + CO 2 -> H 2 CO 3 (aq) </li></ul></ul><ul><li>The extra acidity in rain comes from the reaction of primary air pollutants, primarily sulfur oxides and nitrogen oxides, with water in the air to form strong acids (like sulfuric and nitric acid). </li></ul><ul><li>The main sources of these pollutants are vehicles and industrial and power-generating plants. </li></ul>
  72. 74. Acid Rain <ul><li>Nitric oxide & sulfur dioxide released primarily from electric power plants & motor vehicles </li></ul><ul><li>SO 2 + water vapor + ozone ---> H 2 SO 4 </li></ul><ul><li>NO + sunlight + O 2 ---> NO 2 + various atmospheric gases ---> HNO 3 </li></ul>
  73. 75. Effects of Acid Rain <ul><li>Acidify lakes and disrupt the normal cycling of nutrients, </li></ul><ul><li>leaches metals out of rocks and soil, </li></ul><ul><li>kill fish, plants; stress and defoliate trees due to moss growth, insect attack, and loss of nutrients. </li></ul>
  74. 76. Acid rain - causes <ul><li>The principal cause of acid rain is sulfur - and nitrogen compounds from human sources, such as electricity generation , factories and motor vehicles . Coal power plants are one of the most polluting. </li></ul>
  75. 77. What are the sources of indoor air pollution?
  76. 78. Sources of indoor air pollutants <ul><li>building materials, </li></ul><ul><li>cigarette smoking, </li></ul><ul><li>pesticides, </li></ul><ul><li>volatile organics from paints, furniture, rugs, insulation etc. </li></ul>
  77. 79. Sources of indoor air pollution <ul><li>11 common pollutants 2-5 times higher indoors than out </li></ul><ul><li>air inside car 18 times more polluted than air outside </li></ul><ul><li>17% of commercial buildings have serious indoor air pollution problems - sick building syndrome </li></ul>
  78. 80. Are there any natural indoor air pollutants? <ul><li>Radon gas accumulates in homes located in areas built on granites, phosphates, shales. </li></ul><ul><li>Synergistic effect with tobacco smoke; second leading cause of lung cancer </li></ul><ul><li>Sources: soils, groundwater, building materials. </li></ul><ul><li>Cannot be filtered out. Must be vented out. </li></ul>
  79. 81. Most dangerous indoor air pollutants <ul><li>Cigarette smoke </li></ul><ul><li>formaldehyde </li></ul><ul><li>radioactive radon 222 gas </li></ul><ul><li>asbestos </li></ul><ul><li>Others include: bacteria, fungi, dusts and other particulates, pollen, CO2, CO, O3, NOx, SO2, building materials such as fiberglass, etc. </li></ul>
  80. 82. Suggestions for the future: <ul><li>pollution prevention </li></ul><ul><li>full cost pricing i.e. shift costs to the production of air pollutants </li></ul><ul><li>improve energy efficiency </li></ul><ul><li>reduce use of fossil fuels </li></ul><ul><li>slow population growth </li></ul>
  81. 83. How serious is the problem of indoor air pollution? <ul><li>People with respiratory ailments are most affected Asbestos inhalation may cause: asbestosis, lung cancer, mesothelioma. </li></ul><ul><li>Asbestos workers, insulators pipe fitters, shipyard employees. </li></ul>
  82. 84. What are some of the symptoms of indoor air pollution? <ul><li>Irritation of mucous membranes, </li></ul><ul><li>coughing, </li></ul><ul><li>dizziness, </li></ul><ul><li>nausea, </li></ul><ul><li>death. </li></ul>
  83. 85. General solutions: <ul><li>switch from coal to cleaner fuels - use natural gas </li></ul><ul><li>reduce energy use, improve energy efficiency </li></ul><ul><li>burn less coal, use lower sulfur coals. Coal gasification </li></ul><ul><li>After burning the SO2 can be cleaned out by scrubbing </li></ul><ul><li>taxing emissions </li></ul>
  84. 86. General solutions to indoor air pollution: <ul><li>Ventilation: fans </li></ul><ul><li>source removal: no smoking </li></ul><ul><li>source modification: more efficient stove design. </li></ul><ul><li>pollutant removal: filters </li></ul><ul><li>education </li></ul>
  85. 87. What are the special problems associated with urban areas?
  86. 88. Urban trends: <ul><li>discourage auto use, reduce number of cars </li></ul><ul><li>stricter emission controls </li></ul><ul><li>require electric cars </li></ul><ul><li>improve public transport </li></ul><ul><li>mandatory carpools </li></ul><ul><li>industrial & household controls </li></ul><ul><li>reduce emissions- burn less fuel, be energy efficient </li></ul><ul><li>control NOx by recirculating exhaust </li></ul><ul><li>catalytic converters removes CO and hydrocarbons by converting to CO2 and water </li></ul><ul><li>effluent fees and emissions tests to assure catalytic converters are maintained </li></ul>
  87. 89. Special problems associated with urban areas <ul><li>Meteorological conditions along with topography can affect air pollution. </li></ul><ul><li>Natural ventilation occurs when winds are strong and turbulent, mixing is good, large mixing volume. </li></ul><ul><li>atmospheric inversion- temperature inversion, warmer air above cooler air, prevents dissipation of pollutants. pollutants collect, no wind. </li></ul>
  88. 90. Urban air pollution <ul><li>Urban air pollution determined by: </li></ul><ul><li>rate of emission per unit area </li></ul><ul><li>distance downwind that a mass of air can move </li></ul><ul><li>wind speed </li></ul><ul><li>height of mixing </li></ul>
  89. 91. Thank you