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Mobile Air Pollution


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Mobile Air Pollution

  1. 1. Air Pollution Mobile Sources
  2. 2. The Thin Shell Called the Atmosphere <ul><li>Earth’s atmosphere is a thin layer of gas held around the surface by gravity. </li></ul><ul><li>90% of the atmosphere’s mass is within 15 km of the earth’s surface </li></ul><ul><ul><li>Earth's radius is about 6400 km </li></ul></ul><ul><ul><li>The atmosphere is like a layer of paint on a basketball </li></ul></ul>
  3. 3. Composition of the Atmosphere
  4. 4. Origin of the Atmosphere <ul><li>Earth’s primitive atmosphere consisted mainly of CO 2 released by volcanic eruptions </li></ul><ul><li>About 3.5 billion years ago, photosynthesizing algae (stromatolites) began to release oxygen which steadily increased over time. </li></ul><ul><li>This was the first global air pollution crisis because oxygen was poisonous to life forms that existed before photosynthesis. </li></ul><ul><li>Lead to major extinction event 2.2 billion years ago ( Great Oxygen Crises ). </li></ul>
  5. 5. Origin of the Atmosphere <ul><li>Volcanic eruptions also release trace amounts NH 3 (ammonia). </li></ul><ul><li>N 2 is formed from the reaction between NH 3 and oxygen in the atmosphere. </li></ul><ul><li>The high percentage of nitrogen in today’s atmosphere is because N 2 is not chemically active with other molecules in the atmosphere. </li></ul><ul><li>Conversely, the amount of O 2 in the atmosphere is limited because it is very reactive with other molecules in Combustion, Decomposition, and Respiration </li></ul>
  6. 6. What is an Air Pollutant? <ul><li>An air pollutant is anything in the atmosphere that is hazardous to life or the environment </li></ul><ul><li>Primary pollutant – one that is emitted directly into the atmosphere by the source </li></ul><ul><li>Secondary pollutant – one that not emitted directly, but is generated through chemical reactions over time from material emitted by the source </li></ul>
  7. 7. Air Pollutants Sources Primary Pollutants Secondary Pollutants Sources Natural Stationary CO CO 2 SO 2 NO NO 2 VOCs Particles SO 3 HNO 3 H 2 SO 4 O 3 PANs Mobile NO 2
  8. 8. Air Pollution <ul><li>Natural sources of air pollution are sources not caused by people or their activities. </li></ul><ul><ul><li>An erupting volcano emits particulate matter and gases </li></ul></ul><ul><ul><li>Forest and prairie fires can emit large quantities of pollutants </li></ul></ul><ul><ul><li>Plants and trees emit hydrocarbons </li></ul></ul><ul><ul><li>Dust storms can create large amounts of particulate matter. </li></ul></ul>
  9. 9. Human Air Pollution <ul><li>A mobile source of air pollution refers to a source that is capable of moving under its own power. </li></ul><ul><li>A stationary source of air pollution refers to an emission source that does not move (i.e., power plants, chemical and manufacturing industries). </li></ul>
  10. 10. Air Pollution Standards <ul><li>The Clean Air Act (1970), which was last amended in 1990, requires EPA to set National Ambient Air Quality Standards (NAAQS) for wide-spread pollutants from numerous and diverse sources considered harmful to public health and the environment. </li></ul><ul><li>EPA has set NAAQS for six principal pollutants, which are called &quot;criteria&quot; pollutants (see next slide). </li></ul><ul><ul><li>Units of measure for the standards are parts per million (ppm) by volume, milligrams per cubic meter of air (mg/m3), and micrograms per cubic meter of air (µg/m3). </li></ul></ul>
  11. 11. Table 8-5, p. 268
  12. 12. Air Pollution Standards <ul><li>The Clean Air Act established two types of national air quality standards. </li></ul><ul><li>Primary Standards set limits to protect public health, including the health of &quot;sensitive&quot; populations such as asthmatics, children, and the elderly. </li></ul><ul><li>Secondary Standards set limits to protect public welfare, including protection against visibility impairment, damage to animals, crops, vegetation, and buildings. </li></ul>
  13. 13. The Good News <ul><li>National air quality levels measured at thousands of monitoring stations across the country have shown improvements over the past 20 years for all six principal pollutants. </li></ul><ul><li>Since 1970, aggregate emissions of the six principal pollutants have been cut 48 percent. </li></ul>
  14. 14. The Good News
  15. 15. The Not So Good News <ul><li>Despite this progress, about 160 million tons of pollution are emitted into the air each year in the United States. </li></ul><ul><li>Approximately 146 million people live in counties where monitored air in 2002 was unhealthy at times because of high levels of at least one of the six principal air pollutants. </li></ul><ul><li>The vast majority of areas that experienced unhealthy air did so because of one or both of two pollutants—ozone and particulate matter (PM). </li></ul>
  16. 16. Vehicle Sources of Pollution <ul><li>Main problem: Gasoline and diesel fuels are mixtures of hydrocarbon compounds which contain hydrogen and carbon atoms. These atoms combine with oxygen during combustion. </li></ul><ul><li>Also contain additives such as lead. </li></ul><ul><li>Nitrogen atoms are also present and are combined with oxygen to produce gases. </li></ul>
  17. 17. Mobile Sources of Pollution <ul><li>Primary Pollutants from Engine Combustion </li></ul><ul><ul><li>Carbon Monoxide (CO) </li></ul></ul><ul><ul><li>Lead (Pb) </li></ul></ul><ul><ul><li>Hydrocarbons (VOCs) </li></ul></ul><ul><ul><li>Nitrogen Oxides (NOX) </li></ul></ul><ul><li>Secondary Pollutants from Engine Combustion </li></ul><ul><ul><li>Nitrogen Dioxide (NO 2 ) </li></ul></ul><ul><ul><li>Ozone (O 3 ) </li></ul></ul>
  18. 18. Carbon Monoxide (CO) <ul><li>Colorless and odorless gas </li></ul><ul><li>Most abundant air pollutant </li></ul><ul><li>Major source (~ 77%) is motor vehicle exhaust </li></ul><ul><li>Poorly running automobiles emit large amounts by incomplete combustion (low temperatures an/or not enough O 2 in engine). </li></ul>
  19. 19. Carbon Monoxide (CO) <ul><li>Extremely toxic – causes heart disease long-term, or death within an hour if concentration is 1600 ppm or more </li></ul><ul><li>Hemoglobin in the blood is 200 times more attracted to carbon monoxide than oxygen (leading to oxygen starvation of the body) </li></ul><ul><li>Most hazardous to human health of all criteria pollutants </li></ul>
  20. 20. Lead <ul><li>Lead is a metal found naturally in the environment as well as in manufactured products.  </li></ul><ul><li>The major sources of lead emissions have historically been motor vehicles (such as cars and trucks) and industrial sources.  </li></ul><ul><li>Due to the phase out of leaded gasoline, metals processing is the major source of lead emissions to the air today. </li></ul><ul><li>Exposure results in brain damage and memory loss, as well as low IQ in children </li></ul>
  21. 21. Volatile Organic Compounds (VOCs) <ul><li>The term VOC stands for volatile organic compounds. </li></ul><ul><li>Also called hydrocarbons, entirely made of carbon and hydrogen atoms </li></ul><ul><li>VOCs are carbon-containing chemicals that evaporate easily at room temperature. </li></ul><ul><li>Usually gasoline vapors and uncombusted fuel. </li></ul><ul><li>No direct adverse health effects, but they react with other substances to form smog </li></ul>
  22. 22. Nitrogen Oxides (NO x ) <ul><li>Nitrogen oxides, or NOx, is the generic term for a group of highly reactive gases, all of which contain nitrogen and oxygen in varying amounts. </li></ul><ul><li>The primary manmade sources of NOx are motor vehicles. </li></ul><ul><li>Due to the high temperatures and oxygen in a vehicle engine, N separates from N 2 and combines with O 2 to form NOx </li></ul>
  23. 23. Nitrogen Dioxide (NO 2 ) <ul><li>Can be emitted directly as a primary pollutant, but most is created by the oxidation of Nitric Oxide (NO) </li></ul><ul><li>Toxic gas that has a pungent odor and gives the air a yellow to reddish-brown color </li></ul><ul><li>Corrosive and can react with other substances to produce other secondary pollutants </li></ul><ul><li>Irritates the lungs and can reduce immunity to infection at high levels </li></ul><ul><li>Breaks down readily, so at its highest levels when traffic levels are the highest </li></ul>
  24. 24. Ozone <ul><li>At the surface, ozone (O 3 ) is a pollutant - it irritates the respiratory system and damages plants </li></ul><ul><li>Component of Photochemical Smog </li></ul><ul><li>Created differently than it is produced in the stratosphere </li></ul><ul><li>VOC + NOx + Heat + Sunlight = Ozone </li></ul><ul><li>Motor vehicle exhaust and industrial emissions, gasoline vapors, and chemical solvents are some of the major sources of NOx and VOC that help to form ozone.   </li></ul>
  25. 25. Smog <ul><li>A combination of the words “smoke” and “fog” </li></ul><ul><li>Two different types of smog occur </li></ul><ul><li>Photochemical smog ; dry air smog with ozone, peroxyacyl nitrate (PAN) and formaldehyde (see previous lecture) </li></ul><ul><li>Classic (London) Smog : original meaning of smog; mixture of smoke, sulfurous particles and soot with a fog </li></ul>
  26. 26. Photochemical Smog <ul><li>Occurs on sunny days due to intense traffic. </li></ul><ul><li>Oxides of nitrogen and hydrocarbons react in the presence of sunlight to produce a mixture of aerosols and gases. </li></ul><ul><li>Photochemical smog contains ozone, ketones, formaldehyde, and PAN (peroxyacetyl nitrates). </li></ul><ul><li>The next slides illustrates the chemical reactions </li></ul>
  27. 28. Photochemical Smog Peak Smog Hours
  28. 29. The Summertime Pollutant <ul><li>Peak ozone levels typically occur during hot, dry, stagnant summertime conditions.  </li></ul><ul><li>The length of the ozone season varies from one area of the United States to another.  </li></ul><ul><li>Southern and Southwestern states may have an ozone season that lasts nearly the entire year. </li></ul>
  29. 30. Photochemical Smog: Health Effects <ul><li>Increased incidents of respiratory distress. </li></ul><ul><li>Repeated exposures to ozone: </li></ul><ul><ul><li>Increased susceptibility to respiratory infection </li></ul></ul><ul><ul><li>Lung inflammation </li></ul></ul><ul><ul><li>Aggravation of pre-existing respiratory diseases such as asthma. </li></ul></ul><ul><ul><li>Decreases in lung function and increased respiratory symptoms such as chest pain and cough. </li></ul></ul>
  30. 31. Automobile Emission Control Strategies
  31. 32. Automobile Emission Control Strategies <ul><li>CO Reduction </li></ul><ul><ul><li>Increase O2 to the combustion chamber from the carburetor. </li></ul></ul><ul><ul><li>Higher air-to-fuel ratio </li></ul></ul><ul><ul><li>CO 2 instead of CO from exhaust. </li></ul></ul><ul><li>VOC Reduction </li></ul><ul><ul><li>Capture unburned vapors from fuel tank and carburetor using Charcoal Filters </li></ul></ul><ul><ul><li>Recycle VOC back into the combustion chamber via the ERG valve. </li></ul></ul><ul><ul><li>Increase combustion temperatures </li></ul></ul>
  32. 33. Automobile Emission Control Strategies <ul><li>Problem: Higher air to fuel ratios (CO reduction) and and higher temperatures (VOC reduction) increase the amount of NOx emitted via engine exhaust. </li></ul><ul><li>Solution: catalytic converter </li></ul>
  33. 34. What is a catalytic converter (CC)? <ul><li>A device that promotes ( catalyzes) reactions in order to convert HC, CO, and NO x into less harmful compounds before they exit the vehicle. </li></ul><ul><ul><li>HC + O 2  CO 2 + H 2 O (oxidation) </li></ul></ul><ul><ul><li>2CO + O 2  2CO 2 (oxidation) </li></ul></ul><ul><ul><li>2NO  N 2 + O 2 or 2NO 2  N 2 + 2O 2 (reduction) </li></ul></ul><ul><li>The catalyst in most CCs is Platinum which is why CCs are so expensive. </li></ul>
  34. 35. Are Catalytic Converters the Answer? <ul><li>Until recently, it was thought that catalytic converters offered the greatest potential for decreasing mobile source pollution. </li></ul><ul><li>The newest-model cars can remove up to 95% of the emissions. </li></ul><ul><li>However, mobile source pollution still a problem because of the ever increasing number of vehicles. </li></ul><ul><li>Real improvements in vehicle emissions will come from a switch from gasoline as a fuel and from reductions in the number of vehicles and miles driven. </li></ul>