Sources Of Air Pollutants


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Sources Of Air Pollutants

  1. 1. O p tion E Environmental Chemistry Describe the main sources of carbon monoxide (CO), oxides of nitrogen (NO x ), oxides of sulfur (SO x ), particulates and volatile organic compounds (VOCs) in the atmosphere
  2. 2. Methane produced animals as a digestive gas (e.g. cows) Bacterial decomposition of organic matter in marshes and tropical regions (e.g. rice fields, rivers, lakes) Natural Sources of Carbon Monoxide
  3. 3. Oxidation of methane <ul><li>Methane oxidises to produce the primary pollutant CO and H 2 O </li></ul><ul><li>2CH 4 (g) + 3O 2 (g)  2CO (g) + 4H 2 O (l) </li></ul>
  4. 4. Man-made sources of Carbon Monoxide Factory combustion Power plants Combustion of Fossil fuels Vehicular exhausts
  5. 5. Combustion of fossil fuels <ul><li>Under the presence of oxygen, combustion of fossil fuels will produce carbon dioxide and water. </li></ul><ul><li>CH 4 + 2O 2  CO 2 + 2H 2 O </li></ul><ul><li>Lack of oxygen will result in incomplete combustion to produce carbon monoxide instead of carbon dioxide. </li></ul><ul><li>C 7 H 16 + 7 ½O 2  7CO + 8H 2 O </li></ul>
  6. 6. Oxides of Nitrogen (NO x ) <ul><li>Nitrogen gas exists as N 2 molecules in the air </li></ul><ul><li>N 2 is inert in room temperature and does not produce Oxides of Nitrogen as atoms are share a triple bond </li></ul><ul><li>Reaction occurs at high temperatures </li></ul><ul><ul><li>N2 (g) + O2 (g)  2NO (g) </li></ul></ul><ul><ul><li>N2 (g) + 2O2 (g)  2NO2 (g) </li></ul></ul>
  7. 7. Natural sources of Nitrogen Oxides <ul><li>B acterial decomposition of nitrogen containing compounds </li></ul><ul><li>High energy of lightning will produce N 2 O and NO </li></ul>
  8. 8. Man-made sources of Nitrogen Oxides E xhaust gases from internal combustion engines Wood and fuels Airplanes
  9. 9. Oxides of Sulfur (S O x ) <ul><li>Sulphur Dioxide (SO 2 ) is the most abundant in the atmosphere whilst sulphur trioxide (SO3) is only produced in very small amounts </li></ul><ul><li>Atmospheric Sulphur dioxide tend to oxidise into sulphur trioxide over time </li></ul><ul><li>Reaction is speeded up by the presence of heavy metal pollutants and finely divided particulates of ash </li></ul><ul><li>2SO 2 (g) + O 2 (g)  2SO 3 (g) </li></ul>
  10. 10. Sources of S O x : Coal <ul><li>Combustion of coal can produce SO x </li></ul><ul><li>Poor quality coal can contain up to 7% sulphur; although most contain 1 to 5% </li></ul><ul><li>Sulfur present in coal are in the form of elemental sulfur, iron pyrite and organic sulfur compounds </li></ul><ul><li>S (s) + O2 (g)  SO2 (g) </li></ul><ul><li>4FeS2 (g) + 11O2 (g)  2Fe2O3 (s) + 8SO2 (g) </li></ul>
  11. 11. Other sources of SO x <ul><li>Smelting plants oxidise sulfide ores to produce metal oxides; thus producing SO 2 </li></ul><ul><li>Cu 2 S (s) + 2O 2 (g)  2CuO (s) + SO 2 (g) </li></ul><ul><li>Production of Sulfuric acid </li></ul><ul><li>Sulfur dioxide is produced due to lack of oxygen </li></ul>
  12. 12. Natural Sources of SO x <ul><li>No major natural primary sources of sulphur dioxide </li></ul><ul><li>Small amounts produced from volcanic and bacterial activity </li></ul><ul><li>Sulphur dioxide is produced in the atmosphere from oxidation of H 2 S </li></ul><ul><li>2H 2 S (g) + 3O 2 (g)  2SO 2 (g) + 2H 2 O (l) </li></ul>
  13. 13. Particulates <ul><li>These substances are solid particles suspended and carried within the air. They are generally large enough to be seen. </li></ul>
  14. 14. Sources of Particulates <ul><li>Naturally produced by sandstorms, volcanic activity and forest fires started by lightning </li></ul><ul><li>Man-made sources include the combustion of fossil fuels used by the industry, vehicular exhaust from transportation, industrial plants which produce smoke, soot, ash and dust. </li></ul>
  15. 15. Volatile Organic Compounds (VOCs) <ul><li>These substances are primary pollutants directly introduced into the environment. Examples include hydrocarbon gases and volatile organic liquids that can easily convert into gases and escape into the air. </li></ul>
  16. 16. Sources of VOCs <ul><li>Methane (CH4) is produced by anaerobic bacterial decomposition of organic matter in bodies of water including swamps and oceans </li></ul><ul><li>Methane is also produce as a digestive gas in many animals (e.g. cows) </li></ul><ul><li>Vegetation produced VOCs called terpenes </li></ul><ul><li>Man-made sources include extracting, refining, transporting petroleum as well as using petroleum products can result in air pollution </li></ul>