Unformatted text preview: 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 smog: smoke and fog; 5 days, nearly 4000 deaths; Clean Air Act in 1956 disastrous London smog event of 1952 Los Angeles: photochemical smog forms in sunny weather and irritates the eyes U.S. Clean Air Act, 1970, 1990 set federal emission standards for states to implement and enforce Types and Sources of Air Pollutants
Air 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 given environment. 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, ...) Principal Air Pollutants primary and secondary pollutants particulate matter: a group of solid particles and liquid droplets that are small enough to remain suspended in the air PM10, PM2.5: <10 or 2.5 micrometer in diameter Carbon monoxide: colorless, odorless, poisonous Globally, a large percentage of air pollution sources are natural. Within localized areas, however, humancaused sources are often the largest contributors. Over U.S. Principal Air Pollutants Volatile organic compounds (VOCs): represent a class of organic compounds that are mainly hydrocarbons individual organic compounds composed of hydrogen and carbon nitrogen oxides: nitrogen dioxide (NO2) and nitric oxide (NO), together called NOx Along with ozone, VOCs and NOx are major components of photochemical smog. Photochemical smog is a problem on most major cities of the world. Ozone in the Troposphere Photochemical smog: in the presence of sunlight Ozone: unpleasant odor, irritates eyes and hurt human health, reduce crop yield Ozone in the Stratosphere chlorofluorocarbons (CFCs); a single relationship to ultraviolet radiation chlorine compounds chlorine removes as many as 100,000 ozone molecules Montreal Protocol When scientists first measured extremely low ozone values in the Antarctic stratosphere, they thought the instruments were malfunctioning. Ozone hole in 2006; mainly due to changes in polar stratospheric temperatures
Figure 1, p. 337 Air Quality Index (AQI): Air Pollution: Trends and Patterns includes the pollutants CO, SO2, NO2, particulate matter, and O3 Secondary air pollutants (e.g., O3) are particularly difficult to control, because they are not emitted directly into the atmosphere. Fig. 12-11, p. 338 Factors affecting air pollution
The role of the wind dilution turbulence mixing "Dilution 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. temperature lapse rates inversions mixing depth The Role of Stability and Inversions The mixing layer can often be easily seen from an airplane. The Role of Topography cold air drainage air blockage by mountain ranges Severe Air Pollution Potential Sources (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. urban heat island country breeze Air Pollution and the Urban Environment pH wet deposition dry deposition acid fog: SO2 and NOx acid rain effects Acid Deposition Precipitation pH values ...
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- Fall '07