CHAPTER 17 - Atmospheric Science and Air Pollution


I. Central Case: The 1952 A Killer Smog@ of London

A. Thick smog first settled over the city on December 5, 1952, when many residents stoked their coal stoves because of unusually cold temperatures.

B. A wind finally relieved Londoners of the smog on Tuesday, December 9, but by that time thousands of people had died from lung ailments.

C. Many similar events have taken place in Pennsylvania, New York, Mexico, and Malaysia.

D. We have improved, however, as declines in air pollution represent some of the biggest success of environmental policy.

E. Much remains to be done because there are hundreds of people who die prematurely each year due to vehicle emissions.

II. Atmospheric Science

A. The atmosphere is a thin layer of gases that surrounds Earth.

B. The atmosphere consists of several layers.

1. The bottommost layer is the troposphere, where temperature decreases with altitude.

2. The stratosphere extends from 11 km to 50 km above sea level, with its temperature rising gradually with altitude.

3. A portion of the stratosphere between 17 and 30 km above sea level contains most of the atmosphere= s ozone and is called the ozone layer; this layer greatly reduces the amount of UV radiation that reaches Earth= s surface. The protection of the ozone layer is vital for life on Earth.

4. Above the stratosphere lies the mesosphere, which extends from 50 to 90 km above sea level.

5. From the outer mesosphere, the thermosphere extends upward to an altitude of 500 km, where solar rays produce temperatures over 1,700 degrees Celsius.

C. Atmosphere properties include temperature, pressure, and humidity.

1. Atmospheric pressure measures the weight per unit area produced by a column of air and decreases with altitude.

2. Relative humidity is the amount of water vapor a given volume of air holds relative to the maximum amount it could contain for a given temperature.

3. The temperature of air varies with location and time, and these temperature differences affect air circulation.

D. Solar energy heats the atmosphere, helps create seasons, and causes air to circulate.

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1. Energy from the sun plays a major role in our atmosphere by driving most of its air movements.

2. The spatial relationship between Earth and the sun determines the amount of solar radiation that strikes each point of Earth= s surface.

3. Because Earth is tilted on its axis by about 23.5 degrees, the Northern and Southern Hemispheres each face the sun for one-half of the year.

4. Land and surface waters absorb solar energy, reradiating some heat and causing some water to evaporate.

5. The difference in air temperatures at different altitudes sets into motion convective circulation, as warm air rises, cools and expands, and then descends past other warm air that is rising.

E. The atmosphere drives weather and climate.

1. Weather consists of the local physical properties over short time periods in relatively small geographic areas.

2. Climate describes the pattern of atmospheric conditions found across a relatively large geographic region over a long period.

F. Weather is produced by interacting air masses.

1. The boundary between two air masses that differ in temperature and density is called a front.

a. A mass of warmer, moister air replacing a mass of colder, drier air is a warm front.

b. A mass of colder, drier air displacing a warmer, moister air mass is a cold front.

2. Opposing air masses may also differ in atmospheric pressure.

a. Air moving outward away from a center of high pressure as it descends is a high-pressure system.

b. Air moving toward a low atmosphere pressure at the center of a rising system is a low-pressure system.

3. One type of weather event has implications for environmental health.

a. If a layer of cool air occurs beneath a layer of warmer air, this is known as a temperature inversion, or thermal inversion.

b. The band of air in which temperature rises with altitude is called an inversion layer.

G. Global climate patterns result from large-scale circulation systems.

1. Sunlight near the equator produces pairs of convection cells called Hadley cells.

2. Two pairs of similar but less intense convective cells, Ferrel cells and polar cells, lift air an create precipitation around 60 degrees latitude north and south and cause air to descend at around 30 degrees latitude and in the polar regions.

3. These three pairs of cells account for the latitudinal distribution of moisture across Earth= s surface.

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4. As Earth rotates on its axis, north-south air currents of convective cells appear to be deflected from a straight path; this is called the Coriolis effect.

III. Outdoor Air Pollution

A. Air pollutants are gases and particulate material added to the atmosphere that can affect climate and/or harm organisms, including ourselves.

B. Much outdoor air pollution comes from natural sources.

1. Winds sweeping over arid terrain can send huge amounts of dust aloft.

2. Volcanic eruptions release large quantities of particulate matter, as well as sulfur dioxide and other gases, into the troposphere.

3. The burning of vegetation pollutes the atmosphere with smoke and soot.

C. Human activities create various types of outdoor air pollution.

1. Outdoor air pollution from human activity can originate from stationary or mobile sources.

2. Once in the air, a pollutant may do harm directly or may induce chemical reactions that produce harmful compounds.

a. Primary pollutants, such as soot and carbon monoxide, are pollutants emitted into the troposphere in a form that can be directly harmful or that can react to form harmful substances.

b. Secondary pollutants are harmful substances produced when primary pollutants interact or react with constituents of the atmosphere.

D. Legislation called the Clean Air Acts has addressed pollution in the United States.

1. Congress has passed a number of laws dealing with pollution.

a. The Clean Air Act of 1970 set strict standards for air quality, imposed limits on emissions, provided funds for research, and allowed citizens to sue parties violating the standards.

b. The Clean Air Act of 1990 sought to strengthen regulations pertaining to air quality standards, auto emissions, toxic air pollution, acidic deposition, and ozone depletion, while introducing market-based incentives.

E. The EPA sets standards for A criteria pollutants.@

1. The EPA gives special attention to several pollutants judged to pose especially great threats to human health and welfare.

2. For six criteria pollutants, the EPA has established maximum allowable concentrations.

a. Carbon monoxide is a colorless, odorless gas produced primarily by the incomplete combustion of fuels.

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b. Sulfur dioxide is a colorless gas released when coal is burned that contributes to acid rain.

c. Nitrogen dioxide is a highly reactive, foul-smelling reddish gas that contributes to smog and acid rain.

d. Tropospheric ozone results from the interaction of sunlight, heat, nitrogen oxides, and volatile organic compounds.

e. Particulate matter is any solid or liquid particle small enough to be carried aloft; it may cause damage to respiratory tissues when inhaled.

f. Lead is a metal that enters the atmosphere as a particulate pollutant released by industrial processes and fuel combustion.

F. Agencies monitor pollutants that affect air quality.

1. Volatile organic compounds (VOCs) are a large group of potentially harmful organic chemicals used in industrial processes such as dry cleaning and manufacturing.

2. Human activity accounts for about half of U.S. VOC emissions, but many tons of VOCs are released from natural sources (plants and animals) each year.

G. Air pollution has decreased markedly since 1970.

H. Toxic substances are also major pollutants.

1. Other chemicals known to cause serious health or environmental problems are classified as toxic air pollutants.

I. Burning fossil fuels produces industrial smog.

J. Photochemical smog is produced by a complex series of atmospheric reactions.

K. Synthetic chemicals deplete stratospheric ozone.

1. Ozone molecules are considered a pollutant at low altitudes, but at altitudes of 25 km (15 mi) they are highly effective at absorbing incoming ultraviolet radiation from the sun, thus protecting life on Earth= s surface.

2. Starting in the 1960s, atmospheric scientists began wondering why their measurements of ozone were lower than theoretical models predicted.

3. In 1974, Sherwood Rowland and Mario Molina broke the news that chlorofluorocarbons (CFCs) depleted stratospheric ozone by splitting ozone molecules and creating O2 molecules from them.

4. In 1985, scientists from the British Antarctic Survey announced that stratospheric ozone levels over Antarctica had declined 40 to 60% in the previous decade, leaving behind a thinned ozone concentration that was soon dubbed the A ozone hole.@

L. The Montreal Protocol addressed ozone depletion.

1. The world community came together in 1987 to design the Montreal Protocol, which has been signed by 180 nations.

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2. The production and use of ozone-depleting compounds has fallen 95% since the late 1980s.

3. Environmental scientists have attributed the success of the Montreal Protocol to two factors.

a. Policymakers engaged industry in helping to solve the problem.

b. The process after 1987 successfully followed an adaptive management approach, which allows for altering strategies midstream in response to new scientific data, technological advances, or economic figures.

M. Acidic deposition represents another transboundary pollution problem.

1. Acidic deposition refers to the deposition of acidic or acid-forming pollutants from the atmosphere onto Earth= s surface.

2. Acidic deposition is one type of atmospheric deposition, which is the wet or dry deposition on land of a wide variety of pollutants.

3. Because the pollutants leading to acid rain may travel long distances, their effects can be felt from their point sources.

N. Acid deposition has not been reduced as much as scientists had hoped.

IV. Indoor Air Pollution

A. Indoor air generally contains higher concentrations of pollutants than do outdoor spaces.

B. The average U.S. citizen spends at least 90% of his or her time indoors.

C. Some attempts to be environmentally prudent during the A energy crisis@ of 1973-1974 resulted in worsening the environmental problem of indoor air pollution in developed countries by limiting ventilation and constructing windows that do not open.

D. Indoor air pollution in the developing world arises from fuelwood burning.

E. Recognizing indoor air pollution as a problem is still fairly novel.

1. The 1970 U.S. Clean Air Act did not even mention indoor air pollution; rather, indoor spaces were assumed to be safe havens from outdoor pollution.

2. Today we know far less about indoor air pollution than we do about outdoor air pollution.

F. Tobacco smoke and radon are the most deadly indoor pollutants in the developed world.

1. Secondhand smoke has been found to cause many of the same problems as directly inhaled cigarette smoke.

2. After cigarette smoke, radon gas is the second-leading cause of lung cancer for Americans.

G. Many volatile organic compounds pollute indoor air.

1. Products that emit VOCs surround us; VOCs are emitted in very small amounts.


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2. The implications for human health of chronic exposure to VOCs are far from clear. There are so many, at such low levels, that it is difficult to study their effects.

H. Living organisms can pollute indoor spaces.

1. Dust mites, animal dander, fungi, mold, mildew, and bacteria can all cause health problems.

2. These organisms may be the most widespread source of indoor air pollution in the developed world.

3. Microbes that induce allergic responses are thought to be one frequent cause of building-related illness.

I. We can reduce indoor air pollution.

1. The use of low-toxicity materials and adequate ventilation are the keys to alleviating indoor air pollution in almost any situation.

2. Remedies for fuelwood pollution in the developing world include drying wood before burning, cooking outside, shifting to less-polluting fuels, and replacing inefficient fires with cleaner-burning stoves.

V. Conclusion

A. Indoor air pollution is a potentially serious health threat but one that we can do a great deal to minimize for ourselves and our families.

B. Outdoor air pollution has been addressed more effectively by government legislation and regulation.

C. Much room for improvement remains, particularly in reducing acidic deposition and photochemical smog.




















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