The Big Picture

Until the second half of the twentieth century, air pollution and air quality were not considered a global concern. Although, locally and regionally, many heavily industrialized areas experienced poor air quality and human health was at risk. Now, however, air pollution and air quality is a global concern, as well as local and regional. The effects of air pollution are manifest far downwind from the sources of pollution and the cumulative effects of pollutant discharges have begun to affect global climate. Many of the air pollution problems we are experiencing today are historically linked to our dependence on the combustion of fossil fuels to satisfy domestic, industrial, and automotive energy demands. In the developed nations, improved and costly technologies and pollution regulations have decreased the units of air pollution generated per person, but problems still exist because populations are large. Urban dwellers who are exposed to high concentrations of pollutants experience higher mortality rates than people living in less polluted areas. Burgeoning cities in developing nations typically do not have adequate pollution control regulations and cannot afford the expensive technologies to control air pollution. In the developed and developing nations, air pollution problems extend far beyond the urban and industrial areas. Acid rain, ozone depletion, and global warming are international air pollution issues.

Frequently Asked Questions

When did air pollution become an environmental issue?

• Air pollution has been a localized problem since humans began using fire. Poor air quality in confined areas most certainly contributed to lung and respiratory diseases.
• Air pollution became a more regional problem in cities of the eighteenth century industrial revolution.
• Air pollution events in Donora, Pennsylvania (1948) and London, England (1952) caused numerous deaths and initiated the passage of regulations aimed at controlling and reducing air pollution. Though regulations have certainly attenuated air pollution, problems persist.
• Since the proliferation of automobiles, air pollution in cities such as Los Angeles, Mexico City, and Athens has become a severe environmental and human health problem. Beijing does not have as many automobiles but severe air pollution problems stem from its reliance on coal for heating and electrical production.
• Now air pollution is much more widespread. Not only are cities prone to air pollution problems but rural areas, especially those downwind from industrial centers, power plants, and concentrated livestock operations are experiencing health and environmental problems.

• Air pollution is aesthetically and economically undesirable because it reduces visibility, creates unpleasant odors, and damages statuary and other artificial structures.
• Air pollution damages plant leaves, interfering with photosynthesis, and pollutes the soil causing root damage. Consequently, crop yields can be reduced and natural plant communities are altered.
• Animals may experience many of the same respiratory problems that humans experience. The apparent decline in amphibians that are especially sensitive to environmental contaminants may be attributable to air pollution.
• The affects of air pollution on humans depend upon concentration and duration of exposure to pollutants and individual susceptibility. Some effects include toxic poisoning, cancer, birth defects, eye irritations, irritation of the respiratory system, increased susceptibility to viral infections (causing bronchitis and pneumonia) and heart disease, and aggravation of chronic asthma and emphysema (Figure 22.1).
• The combined effects of multiple contaminants may have synergistically adverse health consequences. Urban dwellers are especially susceptible to multiple exposures.
• An estimated 150 million people live in areas of the United States where air pollution is a health risk. Air pollution is a contributing factor to as many as 120,000 deaths per year and the annual health care costs stemming from exposure to air pollution is an estimated $50 billion.

• Air pollutants arise from natural sources and anthropogenic (man-made) sources (Table 22.1).
• Natural emissions include volcanic and geothermal eruptions, decaying matter in wetlands, atmospheric events, dust storms, and wildfires.
• For most forms of air pollution, natural sources contribute more emissions than anthropogenic sources (with the exception of sulfur oxides and nitrogen oxide).
• The global ecosystem is adapted to natural pollutant levels; additional inputs by humans may disrupt the ability of the ecosystem to maintain homeostasis.
• Anthropogenic sources are categorized as either stationary sources or mobile sources.
• Stationary sources may be point sources (such as power plants), fugitive sources (such as dirt roads and construction sites), or area sources (such as urban or agricultural areas that generate air pollutants). Mobile sources include automobiles, trains, aircraft, and ships.

• Air pollutants are either primary pollutants or secondary pollutants.
• Primary pollutants, such as particulates, sulfur dioxide, carbon monoxide, nitrogen oxides, and hydrocarbons, are emitted directly into the air.
• Secondary pollutants are pollutants that form when primary pollutants undergo chemical reactions in the atmosphere; these include tropospheric ozone and sulfuric acid in precipitation.
• Sulfur dioxide (SO₂) is a product of fossil fuel combustion (especially combustion of low-grade coal) and industrial processing. In the atmosphere SO₂ is converted to fine particulate sulfate (SO₄). SO₂ and SO₄ can damage plant and animal tissue. SO₂ and SO₄ are precursors of acid precipitation.
• Nitrogen oxides (primarily NO and NO₂) are products of fossil fuel combustion in automobiles and power plants. Nitrogen oxides are a major component of smog and are precursors to acid precipitation. Nitrogen oxides damage plant tissue and are respiratory tract irritants in animals.
• Carbon monoxide (CO) is a colorless, odorless gas that is readily absorbed by blood hemoglobin. If high concentrations of CO are present, oxygen uptake by aerobic animals may be impaired. CO poisoning is especially dangerous to fetuses and to persons with heart disease, anemia, or respiratory disease.
• Photochemical oxidants such as ozone and peroxyacyl nitrates (PANs) are formed when nitrogen dioxide interacts with sunlight. Nitrogen dioxide emissions are from automobiles, fossil fuel combustion, and industrial processing. Ozone in the stratosphere provides an import barrier to harmful ultraviolet radiation, however, high concentrations of ozone in the troposphere can damage plant leaf tissue and the respiratory tracts of animals. Ozone also damages man-made materials such as rubber, paint, and textiles.
• Hydrocarbons such as methane (CH₄), butane (C₄H₁₀), and propane (C₃H₈) are components of smog and in high concentration may cause respiratory problems and other serious complications in animals. Most hydrocarbons (>80%) originate from natural sources. Automobiles are the principal anthropogenic source.
• Hydrogen sulfide (H₂S) is a natural product of some marshes and swamps, but it is also generated during petroleum processing, refining, and metal smelting. In high concentrations, H₂S can be toxic to plants and animals.
• Hydrogen fluoride (HF) is highly toxic and is a product of aluminum processing, coal gasification, and coal combustion.
• Other gases such as chlorine gas, formalin, or vapors from industrial plants can create air pollution problems.
• Particulate matter consists of small particles of solid or liquids. Dust from farming and construction sites, smoke, and soot are common types of particulate matter. More toxic materials may form particulates such as heavy aerosol forms of heavy metals, asbestos, and very fine particulates such as sulfates and nitrates (Figure 22.3). The health consequences of particulate pollution are substantial. An estimated 2% to 9% of the deaths in U.S. cities can be associated with particulate pollution; in addition, cities with high levels of particulate contamination have a 15% to 20% higher mortality rate than cities with less severe particulate pollution.
• Asbestos is a naturally occurring mineral that is widely used in manufacturing, construction, and the automotive industry. Only within the last two decades have the health risks of asbestos exposure been understood. Asbestos is a potential carcinogen affecting lung tissue.
• Lead is now widely dispersed in the environment. Lead has been detected in samples of ice from Greenland's glaciers and fish tissue in remote Canadian lakes, far removed from lead sources. The main sources of lead contamination have been automobiles and leaded gasoline (now phased out in many developed nations). High concentrations of lead are found in soils along roadways and in urban dust. Birth defects and nervous system disorders have been attributed to lead poisoning; fetuses and children are especially susceptible.

• Urban and industrial areas typically have the most polluted air.
• Air pollution problems can be exacerbated by local topographic and meteorological conditions. Urban and industrial areas located in valleys or adjacent to mountain ranges are more likely to experience temperature inversions that trap cool, polluted air below relatively warmer air, thus preventing the dispersion of pollutants (Figures 22.4 and 22.5).
• The potential for air pollution depends upon the four factors that are depicted in Figure 22.6:
• the rate of pollutant emission per unit area,
• the distance downwind that an air mass encounters pollutant sources,
• wind speed,
• height of mixing.

• The word smog (smoke-fog) was probably first used in the early 1900's to describe poor air quality especially polluted air that reduces visibility in urban areas.
• There are two basic types of smog. Photochemical smog results from automobile emissions reacting with solar radiation to produce the brownish smog, characteristic of the smog of Los Angeles, California (Figure 22.7). Sulfurous smog is the gray smog generated in industrial areas such as London.
• Smog conditions change throughout the day as pollutants begin to accumulate and solar radiation intensifies (Figures 22.8 and 22.9).

• Optimistically, more is known about the causes and prevention of air pollution so pollution problems should abate. This is the apparent trend in the more developed nations, especially if measured as air pollution generated per capita. However, there are an increasing number of individuals.
• Pessimistically, increasing population and increasing economic pressures will intensify the problem of air pollution especially in developing nations. Developing nations are experiencing the most rapid increase in population and many of these individuals are moving to urban areas in the hope of economic improvement. Too often, the financial base to support pollution reduction programs is not sufficient. Mexico City is one of the prime examples of the unfortunate combination of insufficient pollution control, very high and increasing population, and climatic and topographic situations that exacerbate air pollution problems.

• Reduce automobile numbers and usage.
• Stricter automobile emissions standards and enforcement.
• Reduced or "non-polluting" cars (such as electric cars).
• Improved gasoline.
• Public transportation.
• Car pooling.
• Increased controls and enforcement on industry and household pollution.

• There are two types of acid rain: "wet" which includes rain, snow, and fog, and "dry" deposition of acidic particulates.
• "Pure" rain water is slightly acidic (average pH of 5.6) (Figure 22.11).
• The pH of acid rain may range from below pH 5.6 to extremely acidic pH 1.5. The pH scale is logarithmic so changes in pH values represent changes in pH by orders of magnitude.
• Acid rain was initially perceived as a problem confined to the highly industrialized regions of northern Europe and the northeastern United States. Now the problem is widespread.
• Acid rain does not respect international borders. Sources of acid rain may originate in one nation and the effects may be experienced in an adjacent country. Examples are the United States and Canada or Poland and Slovakia.

• Two types of emissions are responsible for most of the acid rain problems. Sulfur dioxide emissions (primarily from stationary sources such as power plants that combust coal) and emissions of nitrogen oxides (primarily from mobile sources such as automobile exhausts, as well as the combustion of other fossil fuels).
• In the atmosphere, these emissions combine with water or dust particles to form acidic precipitants.
• In the United States during the1980's the tonnage of SO₂ and NO_x emissions was approximately 20 million metric tons per year each (Figure 22.12).
• Eighty percent of the SO₂ and 65% of the NO_x emissions in the United States originate east of the Mississippi River.
• Industrial tall stacks were designed to disperse emissions and minimize local pollution problems but by releasing emissions higher in the atmosphere, pollutants are carried further downwind and their residence time in the atmosphere is increased.

• Acid rain can damage leaves and roots of plants and damage tissue of aquatic animals (Figure 22.15).
• The effects of acid rain depend, in part, upon the buffering capacity of the soil and water.
• Well-buffered soils, such as those formed from carbonate rock, or lakes with carbonate beds have a relatively high or neutral pH and are capable of counteracting some of the harmful effects of acid rain. However, pH may eventually be lowered with continual inputs of acid precipitants. Generally, soils of the arid portions of the western USA are well buffered.
• Poorly buffered soils and lakes, typically found in areas dominated by granitic rock, are most susceptible to acid rain problems. These conditions are most often associated with the humid, eastern USA. Acidic conditions in soils cause nutrients to be easily leached and certain metals to become toxic (e.g., Al, Pb, and Hg). In water, abnormally acidic conditions and aluminum toxicity are damaging to aquatic invertebrates, fish eggs, larvae, and gills and disrupt food chains by reducing nutrients available to photosynthetic algae.
• The addition of lime to lakes is a temporary, stopgap measure to prevent or remediate acidification.
• Toxic heavy metals that have been become mobilized due to lake acidification can be passed up food chains and present a risk to persons that consume fish.
• Acid rain can dissolve statuary, monuments, marble and limestone buildings, and corrode metal. The economic and cultural losses due to acid rain are extensive.

• The first priority should be reducing the volume of pollutants that are generated through conservation measures and improved efficiency of technologies that generate pollutants.
• Secondarily, pollutants should be collected, captured, or retained to prevent their dispersion into the environment, then the contaminants should be detoxified and the chemicals reused if possible.
• SO₂ emissions from coal-fueled power plants can be reduced by using low-sulfur coal, processing coal to reduce the sulfur content prior to combustion, coal gasification, and using post-combustion scrubbers.
• Emissions from automobiles can be reduced by installing and maintaining pollution control devices, such as catalytic converters, improving fuel efficiency, and restricting old vehicles or vehicles that emit a large volume of pollutants.

• The Clean air Act Amendment of 1990 was a set of comprehensive federal regulations that addressed a suite of air pollution problems (acid rain, toxic emissions, ozone depletion, and automobile exhaust).
• To reduce acid rain, the Act mandated that the nationwide total of SO₂ emissions will have to be reduced by 50% to 10 million metric tons by the year 2000. To help accomplish this goal, incentive programs have been developed to encourage industries to use clean air technologies.
• A controversial incentive program is the "pollution credits" program that allows producers of large volumes of pollutants to purchase pollution credits from industries that produce fewer units of pollution.
• A 90% reduction of highly toxic emissions is a goal of the Act. Pollution abatement of toxic emissions depends upon the implementation of clean air technologies.
• Reducing emissions of stratospheric ozone destroying chemicals has been implemented in phased programs.
• Stricter regulations governing automobile exhaust and improving efficiency were incorporated into the Act.

• Air quality standards (National Ambient Air Quality Standards) have been developed to limit the volumes of specific pollutants from industries, power plants, and automobiles.
• The effectiveness of relying on standards depends primarily upon developing standards that adequately reduce pollutant risks to human and environmental health and secondly upon the enforcement of those standards.
• Monitoring air quality standards provides a means of assessing the threat of air pollution to human health. Air quality monitoring of five pollutants is conducted (total suspended particulates, sulfur dioxide, carbon monoxide, ozone, and nitrogen dioxide) to obtain a Pollutant Standard Index. Cities can use this index to issue health advisories (Table 22.2).

• The cost of pollution abatement is complex.
• There are costs paid by polluters to develop, install, and maintain pollution control technologies. With stricter regulations, the cost of pollution control increases; this cost is often transferred to consumers. The cost of pollution control increases incrementally, it is relatively inexpensive to reduce large volumes of pollution initially, but subsequent reductions in pollution are much more costly to implement.
• Concurrently, as pollution levels are reduced, the cost of pollution damage to human and environmental health is reduced. Less pollution reduces the cost of health care, food production, and the maintenance of environmental quality.

Ecology In Your Backyard

• What air pollution problems exist in your region? What are the sources of the problems and how are the problems manifested in terms of human health and environmental quality? What pollutants are the most problematic?
• Many local or regional newspapers, television weather stations, and Internet resources can provide you with daily air quality information and health advisories.
• Via the Internet you can learn more about air pollution or contact your state or local agencies that address air pollution issues.
• At this web site: http://science.cc.uwf.edu/sh/curr/air.pollution/air.htm see the section entitled: "Determining Air Pollution In Your Local Area" for a simple exercise in particulate measurement.
• Please respond to these questions or send your thoughtful examples and comments to:

Hardcopy Links In The Library

• Hamill, P. 1993. Where the air was clear. Audubon, January/February 1993. pp. 38-49. An article about Mexico City's Air Pollution Problem.
• Hayes, R.D. 1993. Ravaged republics. Discover Magazine, March 1993. pp. 66-75. - An article about the Czech and Slovak Republics' air and water pollution problems.
• Malaspina, M., K. Schaefer, and R.Wiles. 1992. Air pollution solutions: What works. Report Number 1. The Environment Exchange, Washington, DC May 1992.

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Ecolinks On The Web

• http://earth1.epa.gov/oar/oaqps/peg_caa/pegcaa03.html - EPA Clean Air Act web site that explains air pollution and the Clean Air Act in "plain English."

• http://www.epa.gov/appd.html - EPA Air Pollution web site highlights air pollution reduction programs.

• http://h2o.usgs.gov/nwc/NWC/pH/html/ph.html - USGS Acid Rain web site provides recent measurements of precipitation pH. Also see the acid rain fact sheet at http://btdqs.usgs.gov/jgordon/arfs.html

• http://www.epa.gov/region4/air/asbestos/inform.htm - EPA Asbestos web site that provides basic information about asbestos, its uses, the potential health risks associated with exposure to asbestos fibers, and asbestos regulations. For additional information on asbestos see: http://www.epa.gov/docs/region04/air/asbestos/index.htm

• http://www.asbestos-institute.ca/reviews/oxford.html#0 - World Health Organization Asbestos. This is the executive summary of a report prepared by the World Health Organization on the human health risks of exposure to asbestos fibers.

• http://www.epa.gov/region09/air/breath96/exec.html - EPA Region 9 Air Quality. Read about air quality trends in EPA Region 9 (AZ, CA, HW, NV). Air quality programs are also discussed at: http://www.epa.gov/region09/air/

• http://www.colby.edu/personal/thtieten/air-mex.html - Mexico City Air Pollution. This is a discussion of automobile usage in Mexico City.

• http://www.ns.doe.ca/soe/cha4.html - Environment Canada Air Pollution - Atlantic Region. This web site provides a summary of air pollutant information for the Canada's Atlantic Region.

• http://www.aqmd.gov/otherlnk.html - Air Pollution. Several air pollution web sites are linked.

• http://www.epa.gov/docs/orcdizux/quiz/index.html Air Pollution Quiz. This EPA web site is an environmental quiz on air pollution issues.

• Note: If any of these links are not working, please see if alternative links are available at the Ecolinks Update Site.

Ecotest Online

1. The source of most particulate, carbon monoxide, and hydrocarbon air pollutants is ____.

a. industrial tall stacks

b. uncontrolled emissions from power plants

c. natural sources

d. automobiles

2. What are secondary air pollutants?

a. nontoxic emissions that present minor health risks

b. any pollutant comprising less than 5% of the total pollutant load

c. pollutants that form from primary pollutants upon discharge to the atmosphere

d. pollutants that bioaccumulate and biomagnify in food chains

3. Which of the following gases is colorless, odorless, and has a high affinity for blood hemoglobin?

a. CH4

b. CFC

c. NO2

d. CO

4. The potential for air pollution problems to develop depends upon all of the following factors except:

a. the wind speed

b. the distance downwind that an air mass encounters pollutant sources

c. the rate of pollutant emission per unit area

d. the buffering capacity of the regional climate

5. The brown smog that is typical of Los Angeles, California is primarily _____ smog.

a. photochemical

b. sulfurous

c. polygenic

d. methanogenic

6. During the 1980s, what was the approximate tonnage of both SO₂ and NO_x discharged to the atmosphere in the United States each year?

a. 20 million metric tons

b. 10 million metric tons

c. 5 million metric tons

d. 3 million metric tons

7. What region of the United States is the most susceptible to acid rain problems?

a. the arid region of southern California

b. the eastern region underlain by or soils derived from granitic rock

c. the mid-western region underlain by carbonate rock

d. the southwest near the Mexican border

8. A temperature inversion occurs when ____; polluted air may accumulate during inversions.

a. continental air masses override maritime air masses

b. relatively cool air is trapped below relatively warm air

c. fossil fuel combustion causes as rise in ambient air temperature

d. relatively warm air displaces relatively cool air

9. A Pollutant Standard Index is used to assess human health risks during air pollution episodes; this Index is based on pollutant levels for total suspended particulates, sulfur dioxide, carbon monoxide, ozone, and ______.

a. carbon dioxide

b. methane

c. chloroflurocarbons

d. nitrogen dioxide

10. Which of the following statements about the cost of air pollution control is false?

a. The cost of pollution control decreases incrementally, it is expensive to reduce large volumes of pollution initially, but subsequent reductions in pollution are much cheaper to implement.

b. As pollution levels are reduced, the cost of pollution damage to human and environmental health is reduced.

c. With stricter regulations, the cost of pollution control increases; polluters often transfer this cost to consumers.

d. Less pollution reduces the cost of health care, food production, and the maintenance of environmental quality.

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