108 CHAPTER 16 AIR POLLUTION Chapter Objectives
Describe the air around us. Identify natural sources of air pollution. Discuss human-caused air pollution. Explain how climate topography and atmospheric processes affect air quality. Compare the effects of air pollution. Evaluate air pollution control. Summarize current conditions and future prospects.
Key Terms Anaerobic Anthropogenic Electrostatic precipitator Epidemiologist Heat island
Innocuous Oxidation PCBs Reduction Respiration
Concept Review 16.1
The Air Around Us
Air pollution is the most widespread form of global pollution. Air quality has improved over the last 20 years due to technological developments to burn cleaner fuels more efficiently.
Natural Sources of Air Pollution
Air pollution occurs naturally as plants decompose, volcanoes erupt, forest fires burn, and storms blow across loose soils.
Human-Caused Air Pollution
Primary pollutants are harmful molecules sent into the atmosphere. o Fugitive emissions enter the air from soil erosion, strip mining, and construction. o Sulfur compounds enter as sea spray and volcanic emissions. Secondary pollutants become hazardous as they react with other chemicals in the air. o Sulfur dioxide (SO2) from industry and combustion oxidize into SO3 to form acid precipitation (H2SO4). o Nitrogen oxides combine with H2O to form nitric acid (HNO3). o CO2 from fossil fuel combustion is a leading cause of global warming. o Carbon monoxide (CO), also produced by fuel combustion, forms ozone (O3) in chemical reactions. Particulates affect human health, as well as reducing visibility and sunlight penetration. Heavy metals are metabolic poisons that affect water quality and living things. Volatile Organic Compounds (VOCs) form photochemical smog and combine with the atmospheric oxygen to form ozone, which is a strong oxidizer, damaging materials and plants. Other Hazardous Air Pollutants (HAPs) are chemicals that pose a risk by bioaccumulation and/or persistence. Aesthetic degradation includes those things, such as noise and odors, that reduce the quality of life but are not necessarily life threatening. As building construction becomes more efficient in preventing heat loss to the outdoors, indoor air pollution has become more concentrated and dangerous. Smoking is the most important air pollutant in its effects on human health.
Climate, Topography, and Atmospheric Processes
Temperature inversions trap pollutants near the earth’s surface as warmer air overlays cooler air. Air pollutants are heated by sunlight and other pollutants are added, concentrating and increasing contaminant levels. Concentrations of buildings and roads in urban areas create heat islands by blocking winds, preventing runoff, and decreasing vegetation. Changing wind patterns move pollutants globally from warm areas to cooler ones, where they precipitate out as temperature changes. Stratospheric ozone levels are depleted as CFCs and other industrial gases are dispersed. The Montreal Protocol of 1987 was instrumental in phasing out CFC production by the year 2000.
Effects of Air Pollution
Air Pollution Control
An estimated 5–6 million people die each year due to air pollution. Bronchitis, asthma, and chronic respiratory diseases are caused by pollutants obstructing or breaking down lung tissues. Plants are also affected as cells are damaged with exposure or as environmental factors combine (synergistic effect), causing damage. Acid precipitation affects aquatic ecosystems, forests, and buildings.
While minimizing the production of air pollutants would be the best approach to reducing pollution levels, technology can be used to o remove particulates by filtering o switch to cleaner-burning fuels The Clean Air Act was updated in 1990 to change the regulation of pollution controls in industries and power plants, limiting levels of sulfur dioxides, nitrogen oxides, and particulates.
Current Conditions and Future Prospects
Air quality has improved since the 1970s. Automobile traffic still contributes significantly to air pollution levels. Further changes in lifestyle and technology will improve air quality in the future.
Class Time: Allow 3–5 days to discuss the effects of air pollution on materials and living things, in addition to the time spent on the previous chapter.
Approach and Tips The discussion of air quality continues from the previous chapter. As mentioned previously, students need to know how secondary pollutants are created in specific terms. Use the information presented in the table as the basis for your discussion.
111 Table 16.1
Review the information students learned in the toxicology chapter and relate the information to toxins in the air. You can demonstrate thermal inversion using a small fish tank and water. Cool half of the water so that it is ice cold. Add blue food color so it is easier to see. Warm the other half of the water and add red food color. Place a partition in the fish tank and pour the two different temperatures on separate sides. When you remove the partition, the cold water will sink and the warm water will layer on top due to the difference in density. To assure success in this demonstration, you may want to add salt to the cold water to increase its density. Students should be able to discuss the goals of the Montreal Protocol and the Clean Air Act and predict the effects amending the act would have on global air quality. Acid rain experiments with seeds and plants are commonly used to illustrate the damaging effects acid precipitation has on forested and other areas. Another way to illustrate the harmful effects atmospheric acids have on buildings is to have students carve a piece of chalk with their name or a design of some sort. Then have them mist the chalk with dilute solutions of vinegar and observe the reaction that takes place.
112 Students should be able to explain the process of scrubbing or precipitators for effluent gas emissions. You may want to wait until studying the energy chapters for students to cover this information, however.
Applications Temperature Inversion The Texas Commission on Environmental Quality provides this demonstration to show what happens when a temperature inversion occurs. The demonstration also teaches students how temperature inversion can trap air pollutants near the surface of the earth. Follow the link below to access this demonstration. http://www.reachoutmichigan.org/funexperiments/agesubject/lessons/tnrcc/templ esson.html.
Common Mistakes and Misconceptions There are many common misconceptions that students have regarding this chapter. One is that pollutants will disperse around the globe and are therefore not that big of a problem. The truth is that indoor air pollution, like from a parent that smokes, is more dangerous for most than outdoor air pollution, and air pollution tends to be worse in areas with mountains around them, etc. In other words, they forget about the conservation of matter (that matter cannot be created or destroyed). They believe that pollution made in Europe cannot affect them, but remind them that air is a commons and spreads and can become a problem elsewhere. Another misconception is the urban heat effect. Students have a hard time understanding how cities will be warmer than the surrounding countryside and affect the weather patterns as well. Many students have also told me that they thought the “hole in the ozone” meant that we were covered with an ozone shield that actually has a hole in it (as if it is a plastic dome). This sounded crazy to me at the time; however, I have asked many classes of students, and this is a common misconception by many of them.
Suggested Website A good website for seeing images of the hole in the ozone is found at NASA. It is at http://www.nasa.gov/vision/earth/environment/ozone_resource_page.html. You can even see the daily ozone watch. The students can learn by looking back at ozone images from years ago to today and find how the hole is getting smaller, which is a huge environmental accomplishment.
113 Questions 1. Explain how secondary pollutants are formed from chemical reactions with primary pollutants. Give specific examples. 2. List the natural sources of air quality degradation and compare these to anthropogenic sources. 3. Differentiate between stratospheric ozone and tropospheric ozone and explain the origin of each. 4. Explain why indoor air pollution is more dangerous than outdoor air pollution. Give an example of one such pollutant in your house and what you could do to eliminate this pollutant from your indoor air.