Chapter 13
AIR POLLUTION
Learning Objectives
After reading, studying, and discussing this chapter, students should be able to do the following:
1. Discuss how weather and air pollution are linked.
2. Distinguish between primary and secondary pollutants.
3. List five major primary pollutants.
4. Name the source category responsible for the greatest amount of air pollution (by weight).
5. Describe the role of strong sunlight in photochemical reactions including the formation of photochemical smog.
6. Give two examples of secondary pollutants.
7. Discuss the necessity for the Clean Air Act and its amendments.
8. Identify the strength of the wind and the stability of the air as the two most important
atmospheric conditions affecting the dispersion of pollutants.
9. Define the mixing depth and temperature inversions.
10. Discuss the impact of temperature inversions on air quality.
11. Contrast the factors that lead to the development of a surface inversion with those that cause an inversion aloft.
12. Explain how acid precipitation forms and discuss consequences of it.
13. Define the terms in the vocabulary review.
Chapter Outline
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I. Historical Perspective
A. Not a new problem
B. Some historic episodes
1. Belgium, 1930
2. Donora, PA, 1948
3. London, 1952
II. Sources and Types of Air Pollution
A. Primary pollutants
1. Particulate matter
2. Sulfur dioxide
3. Nitrogen oxides
4. Volatile organic compounds
5. Carbon monoxide
6. Lead
B. Secondary pollutants
1. Smog
a. London, “Classical”
b. Los Angeles “Photochemical”
III. Trends in Air Quality
IV. Meteorological Factors Affecting
Air Pollution
A. Wind
B. Atmospheric stability
1. Mixing depth
2. Temperature inversion
a. Surface temperature
inversions
b. Inversions aloft
V. Acid Precipitation
A. Extent and potency of acid
precipitation
B. Effects of acid precipitation
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Answers to the Chapter Review
1. Weather conditions influence the dilution and dispersal of pollutants. Air pollutants can affect weather and climate.
2. Primary pollutants are emitted directly from identifiable sources, whereas secondary pollutants are created in the atmosphere when certain chemical reactions take place among primary pollutants and normal atmospheric components.
3. a) volatile organics, b) sulfur dioxide, c) carbon monoxide, and d) nitrogen dioxide
4. a) transportation and b) carbon monoxide
5. Originally "smog" referred to the combination of smoke and fog that was London's
6. principal air pollution problem. Today, the term smog is used as a synonym for general air pollution.
6. Bright sunlight triggers photochemical reactions.
7. Ozone
8. Peaks occur in the afternoon. Although ozone season varies somewhat from place to place, it coincides with the warmer months when the Sun is sufficiently strong to trigger photochemical reactions.
9. There is “good” and “bad” ozone. Stratospheric ozone is good and necessary because it shields us from getting too much ultraviolet radiation from the Sun. However, on the ground, ozone is a major component in photochemical smog, which can cause respiratory problems and damage of crops, reducing agricultural yields.
10. Ozone is not a primary pollutant and therefore not emitted. It is a secondary pollutant created during photochemical reactions.
11. People now drive more total miles per year than they did 25 to 30 years ago
12. Strong winds allow the pollutants to be mixed with greater quantities of air. Further, strong winds are more turbulent and hence mix the pollutants more rapidly with the surrounding air. This is not the case with light winds
13. When an inversion exists, warm air overlying cooler air acts as a lid and prevents the upward movement of air currents and hence inhibits the dispersion of pollutants.
14. Surface inversions form when radiation from the ground to a clear night sky causes more rapid cooling of the surface than the air above. A relatively thin layer of air in contact with chilled ground is thus cooled more than the air above. Inversions aloft often form in association with sinking air. As the air subsides, it warms by compression. Since air near the ground is not usually involved in the subsidence, inversion develops between the lower zone and the subsiding warmer air above.
15. Los Angeles is an excellent example of how the geographic setting of a place can significantly contribute to air-quality problems. Air pollution episodes in Los Angeles are frequently related to inversions associated with the subsiding eastern portion of the subtropical high in the North Pacific. The cool waters of the Pacific Ocean and the mountains surrounding the city compound the problem. When winds move cool air from the Pacific into Los Angeles, the warmer air that is pushed aloft creates or strengthens an inversion aloft that acts as an effective lid. Because the surrounding mountains keep the smog from moving further inland, air pollution is trapped in the basin until a change in weather brings relief.
16. 100 times more acidic
17. Tall stacks release pollutants into the stronger and more persistent winds that exist at greater heights. Although this enhances dispersion, it also promotes long-distance transport.
18. The most publicized environmental effect has been the loss of fish populations in acidified lakes. Acid rain also accelerates the chemical weathering of stone structures and the corrosion of metals, and may impair the productivity of forests.
Suggested Activities
1. As an alternative to lecturing on pollutants and their effects, break the class up into several groups and have them use the Internet to research and then report to the rest of the class on topics such as, ozone depletion, global warming, acid precipitation, and smog.
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