Chapter 12: Air Pollution

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Chapter 12: Air Pollution. A brief history of air pollution Types and sources of air pollutants Factors that affect air pollution Air pollution and the urban environment Acid deposition. A Brief History of Air Pollution. disastrous London smog event of 1952 smog: smoke and fog; - PowerPoint PPT Presentation

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<ul><li><p>Chapter 12: Air PollutionA brief history of air pollutionTypes and sources of air pollutantsFactors that affect air pollutionAir pollution and the urban environmentAcid deposition</p></li><li><p>A Brief History of Air Pollutiondisastrous London smog event of 1952 smog: smoke and fog; 5 days, nearly 4000 deaths; Clean Air Act in 1956Los Angeles: photochemical smog forms in sunny weather and irritates the eyesU.S. Clean Air Act, 1970, 1990 set federal emission standards for states to implement and enforce</p></li><li><p>Types and Sources of Air PollutantsAir pollutants are airborne substances (either solids, liquids, or gases) that occur in concentrations high enough to threaten the health of people and animals,to harm vegetation and structures, or to toxify a givenenvironment.</p><p>They come from natural sources and human activities:Natural: dust, volcano, forest fire, ocean waves, Human: fixed sources (power plants, homes, ) mobile sources (cars, ships, )</p></li><li>Principal Air Pollutantsprimary and secondary pollutantsparticulate matter: a group of solid particles and liquid droplets that are small enough to remain suspended in the airPM10, PM2.5: </li><li><p>Over U.S.</p></li><li><p>Principal Air PollutantsVolatile organic compounds (VOCs): represent a class of organic compounds that are mainly hydrocarbons individual organic compounds composed of hydrogen and carbonnitrogen oxides: nitrogen dioxide (NO2) and nitric oxide (NO), together called NOxAlong with ozone, VOCs and NOx are major components of photochemical smog. Photochemical smog is a problem on most major cities of the world.</p></li><li><p>Ozone in the TropospherePhotochemical smog: in the presence of sunlightOzone: unpleasant odor, irritates eyes and hurt human health, reduce crop yield</p></li><li><p>Ozone in the Stratosphererelationship to ultraviolet radiationchlorine compounds chlorofluorocarbons (CFCs); a single chlorine removes as many as 100,000 ozone moleculesMontreal ProtocolWhen scientists first measured extremely low ozone values in the Antarctic stratosphere, they thought the instruments were malfunctioning.</p></li><li><p>Figure 1, p. 337Ozone hole in 2006;mainly due to changes inpolar stratospheric temperatures</p></li><li><p>Air Pollution: Trends and PatternsAir Quality Index (AQI): includes the pollutants CO, SO2, NO2, particulate matter, and O3Secondary air pollutants (e.g., O3) are particularly difficult to control, because they are not emitted directly into the atmosphere.</p></li><li><p>Fig. 12-11, p. 338</p></li><li><p>Factors affecting air pollutiondilutionturbulencemixingDilution is the solution to pollution - in the 1950s this motto led to the construction of tall smokestacks for large factories. Pollution was released higher in the atmosphere where winds were stronger. Air quality improved locally but suffered downwind.The role of the wind</p></li><li><p>The Role of Stability and Inversionstemperature lapse ratesinversionsmixing depthThe mixing layer can often be easily seen from an airplane.</p></li><li><p>The Role of Topographycold air drainageair blockage by mountain ranges</p></li><li><p>Severe Air Pollution PotentialSources (clustered close together)high pressure (for inversion and weak wind)Inversions Stagnation (unable to disperse pollutants) A valley (for accumulation of pollutants)Some locations, like Los Angeles and Mexico City, have an unfortunate combination of surrounding topography, frequent inversions, abundant emissions and plentiful sunlight - perfect conditions for photochemical smog.</p></li><li><p>Air Pollution and the Urban Environmenturban heat islandcountry breeze</p></li><li><p>Acid DepositionpHwet depositiondry depositionacid fog: SO2 and NOxacid rain effectsPrecipitation pH values</p><p>Figure 1: Ozone distribution over the South Pole on September 29, 2006, as measured by ozone monitoring equipment on NASAs Aura Satellite. Notice that the lowest ozone concentration or ozone hole (purple shades) covers most of Antarctica.Figure 12.11: The number of unhealthful days (by county) across the United States for any one of the five pollutants (CO, SO2, NO2, O3, and particulate matter) during 2003. (Data courtesy of United States Environmental Protection Agency.)</p></li></ul>