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260 Copyright © 2011 Pearson Education, Inc

17 Atmospheric Science and Air Pollution

Chapter Objectives This chapter will help students:

Describe the composition, structure, and function of Earth’s atmosphere

Relate weather and climate to atmospheric conditions

Identify major pollutants, outline the scope of outdoor air pollution, and assess

potential solutions

Explain stratospheric ozone depletion and identify steps taken to address it

Define acidic deposition and illustrate its consequences

Characterize the scope of indoor air pollution and assess potential solutions

Lecture Outline I. Central Case: L.A. and its Sister Cities Struggle for A Breath of Clean Air

A. Today, L.A. still suffers the nation’s worst smog, but its skies are clearer than

in some of its ―sister cities‖ elsewhere in the world.

B. One of L.A.’s sister cities is Tehran, the capital of Iran. Both cities have a lot

of smog.

C. Health authorities blame several thousand premature deaths per year in Tehran

on lung and respiratory diseases resulting from air pollution. In 2006, fully

3,600 people succumbed in just a month.

D. As in Los Angeles, traffic generates most of the pollution in Tehran.

E. As with Los Angeles, topography worsens the problem.

F. And as with Los Angeles in recent decades, people are streaming Tehran from

elsewhere. As a result, the government’s efforts to rein in pollution are being

overwhelmed by population growth.


G. Cities like Tehran are taking steps to improve their air quality, just as

American cities like Los Angeles have done before them.

II. The Atmosphere

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

2. Earth’s atmosphere consists of 78% nitrogen (N2) and 21% oxygen (O2).

The remaining 1% is composed of argon (Ar) and minute concentrations

of several other gases.

3. Over our planet’s long history, the atmosphere’s composition has changed.

A. The atmosphere is layered.

1. The bottommost layer is the troposphere, which blanket’s Earth surface

and gives us the air we need to live.

2. The stratosphere extends from 11-50 km above sea level, its temperature

rising gradually with altitude.

3. A portion of the stratosphere between 17 km 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 50-80 km

above sea level.

5. From the outer mesosphere, the thermosphere extends upward to an

altitude of 500 km.

B. Atmospheric properties include temperature, pressure, and humidity.

1. Atmospheric pressure measures the force per unit area produced by a

column of air, and decreases with altitude.

2. Relative humidity is the ratio of water vapor a given volume of air

contains to the maximum amount it could contain at a given temperature.

3. The temperature of air varies with location and time.

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

circulate.

1. Energy from the sun heats air in the atmosphere, drives air movement,

helps create seasons, and influences weather and climate.

2. The spatial relationship between Earth and the sun determines how much

solar radiation strikes each point on Earth’s surface.

3. Because Earth is tilted on its axis (an imaginary line connecting the poles,

running perpendicular to the equator) by about 23.5°, the Northern and

Southern Hemispheres each tilt toward the sun for half the year, resulting

in the seasons.


4. Land and surface water absorb solar energy and then radiate heat, causing

some water to evaporate.

5. The difference in air temperatures at different altitudes sets into motion

convective circulation as warm air rises, cools, expands, and descends

past other warm air that is rising.

D. The atmosphere drives weather and climate.

1. Weather specifies atmospheric conditions over short time periods,

typically hours or days, and within relatively small geographic areas.

2. Climate, in contrast, describes the pattern of atmospheric conditions found

across large geographic regions over long periods of time, typically

seasons, years, or millennia.

E. Air masses interact to produce weather.

1. The boundary between air masses that differ in temperature and moisture

(and therefore 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. Adjacent air masses may also differ in atmospheric pressure.

a. A high-pressure system contains air that descends because it is cool

and then spreads outward as it nears the ground. High-pressure systems

typically bring fair weather.

b. In a low-pressure system, warmer air rises, drawing air inward toward

the center of low atmospheric pressure. The rising air expands and

cools, and clouds and precipitation often result.

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.

F. Large-scale circulation systems produce global climate patterns.

1. Near the equator, solar radiation sets in motion a pair of convective cells

known as Hadley cells.

2. Two pairs of similar but less intense convective cells, called Ferrel cells

and polar cells, lift air and create precipitation around 60° latitude north

and south and cause air to descend at around 30° latitude and in the polar

regions.

3. These three pairs of cells account for the latitudinal distribution of

moisture across Earth’s surface.


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.

G. Storms pose hazards.

1. Hurricanes form when winds rush into areas of low pressure where warm

moisture-laden air over tropical oceans is rising.

2. Tornadoes form when a mass of warm air meets a mass of cold air and

the warm air rises quickly, setting a powerful convective current in

motion.

III. Outdoor Air Pollution

1. Whether from primitive wood fires or modern coal-burning power plants,

people have generated air pollutants, gases and particulate material added

to the atmosphere that can affect climate or harm people or other

organisms.

2. Air pollution refers to the release of air pollutants.

3. In recent decades, government policy and improved technologies have

helped us reduce most types of outdoor air pollution (often called

ambient air pollution) in industrialized nations.

A. Natural sources can pollute.

1. Natural processes produce a great deal of air pollution. Some of these

natural impacts are made worse by human activity and land-use policies.

2. Volcanic eruptions release large quantities of particulate matter, as well as

sulfur dioxide and other gases, into the troposphere.

3. Sulfur dioxide reacts with water and oxygen and condenses into fine

particles called aerosols.

4. Fires from burning vegetation also pollute the atmosphere with soot and

gases.

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

B. We create outdoor air pollution.

1. Since the onset of industrialization, human activity has introduced a

variety of sources of air pollution. Air pollution can emanate from mobile

or stationary sources, and from point sources or non-point 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.

3. Pollutants differ in the amount of time they spend in the atmosphere—

called their residence time—because substances differ in how readily they

react in air and in how quickly they settle to the ground.

C. Clean Air Act legislation addresses 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 an emissions

trading program.

c. In 1995, businesses and industry were allocated permits to release

sulfur dioxide that they could buy, sell, or trade among one another.

This market-based incentive program reduced sulfur dioxide levels.

D. The EPA sets standards for ―criteria pollutants.‖

1. The EPA and the states focus on six criteria pollutants, pollutants judged

to pose especially great threats to human health.

a. Carbon monoxide is a colorless, odorless gas produced primarily by

the incomplete combustion of fuels.

b. Sulfur dioxide is a colorless gas with a pungent odor that is released

when coal is burned. It contributes to acid deposition.

c. Nitrogen dioxide is a highly reactive, foul-smelling reddish gas that

contributes to smog and acid deposition.

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.

E. Agencies monitor emissions.

1. Volatile organic compounds (VOCs) are carbon-containing chemicals

used in and emitted by vehicle engines and a wide variety of solvents and

industrial processes, as well as by many household chemicals and

consumer items.

2. In the United States in 2008, human activity polluted the air with 123

million tons of the six monitored pollutants.


F. We have reduced U.S. air pollution.

1. Reduction in air pollutants have occurred despite population increases.

2. New technologies such as catalytic converters, electrostatic precipitators,

and scrubbers helped to reduce pollutants.

G. Toxic pollutants pose health risks.

1. Toxic air pollutants are substances known to cause cancer, reproductive

defects, or neurological, developmental, immune system, and respiratory

problems in people and other organisms.

H. Industrializing nations are suffering increasing air pollution.

1. Chinese cities suffer the worst air pollution as they industrialize rapidly.

I. Air quality is a rural issue, too.

J. Smog is our most common air quality problem.

1. Since the onset of the industrial revolution, cities have suffered a type of

smog we call industrial smog, or gray-air smog.

K. Photochemical smog results from a series of reactions.

1. Photochemical smog, or brown-air smog, is formed when sunlight drives

chemical reactions between primary pollutants and normal atmospheric

compounds, producing a mix of over 100 different chemicals, tropospheric

ozone often being the most abundant.

L. We can take steps to reduce smog.

M. 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. Years of dynamic research by hundreds of scientists revealed that certain

airborne chemicals can destroy ozone by splitting its molecules apart, and

that most of these ozone-depleting substances are human-made.

3. In particular, researchers pinpointed halocarbons—human-made

compounds derived from simple hydrocarbons such as ethane and methane

in which hydrogen atoms are replaced by halogen atoms such as chlorine,

bromine, or fluorine.

a. Industry was mass-producing one class of halocarbon,

chlorofluorocarbons (CFCs), at a rate of a million tons per year in

the early 1970s, and this rate was growing by 20% a year.

4. CFCs reach the stratosphere unchanged and can linger there for a century

or more.

N. The Antarctic ozone hole appears each spring.


1. In 1985, researchers shocked the world by announcing that stratospheric

ozone levels over Antarctica in springtime had declined by half in just the

previous decade, leaving a thinned ozone concentration that was soon

dubbed the ozone hole.

2. In the Antarctic spring (starting in September), sunshine returns and UV

radiation dissipates the clouds, releasing chlorine atoms, which begin

destroying ozone.

3. The ozone hole vanishes until the following spring, and the globe as a

whole loses a bit more of its ozone layer.

O. The Montreal Protocol addressed ozone depletion.

1. The world community came together in 1987 to design the Montreal

Protocol, which has been signed by 196 nations.

2. As a result, we have evidently stopped the Antarctic ozone hole from

growing worse. However, the ozone layer is not expected to recover

completely until 2060–2075.

3. Environmental scientists have attributed the success of the Montreal

Protocol to several factors.

a. Informative scientific research developed rapidly, facilitated by new

and evolving technologies.

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

Industry became willing to develop replacement chemicals in part

because patents on CFCs were running out and firms wanted to

position themselves to profit from next-generation chemicals.

c. Implementation of the Montreal Protocol after 1987 followed an

adaptive management approach, adjusting strategies midstream in

response to new scientific data, technological advances, or economic

figures.

P. Acidic deposition is 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.

Q. Acidic deposition has many impacts.

1. Acid deposition can also mobilize toxic metal ions from the soil and

convert them from insoluble to soluble molecules where they hinder

nutrient uptake by plants.

2. Acid water running off the land is toxic to many aquatic and terrestrial life

forms and has led to the death of ecosystems.

3. Other than altering natural ecosystems, acid precipitation also damages

crops.


4. Because the pollutants leading to acid rain may travel long distances, their

effects can be felt far from their points of origin.

R. We have begun to address acid deposition.

IV. Indoor Air Pollution

1. Indoor air generally contains higher concentrations of pollutants than does

outdoor air. As a result, the health effects from indoor air pollution in

workplaces, schools, and homes outweigh those from outdoor air

pollution.

A. Indoor air pollution in the developing world arises from burning wood.

B. Tobacco smoke and radon are the most dangerous indoor pollutants in

developed nations.

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.

C. Many VOCs pollute indoor air.

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

amounts.

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.

D. Living organisms can pollute.

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

health problems.

2. Microbes that induce allergic responses are thought to be one frequent

cause of building-related illness.

3. When the cause of such an illness is a mystery, and when symptoms are

general and nonspecific, the illness is often called sick-building

syndrome.

E. We can reduce indoor air pollution.

1. Using low-toxicity materials, monitoring air quality, keeping rooms clean,

and providing adequate ventilation are the keys to alleviating indoor air

pollution in most situations.

2. In the developed world, we can try to limit our use of plastics and treated

wood when possible and to limit our exposure to pesticides, cleaning

fluids, and other known toxicants by keeping them in a garage or outdoor

shed.


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.

Key Terms

acidic deposition

acid rain

aerosols

air pollutant

air pollution

ambient air pollution

atmosphere

atmospheric deposition

atmospheric pressure

carbon monoxide

chlorofluorocarbons (CFCs)

Clean Air Act of 1970

Clean Air Act of 1990

climate

cold front

convective circulation

Coriolis effect

criteria pollutant

Ferrel cell

front

ground-level ozone

Hadley cell

halocarbons

high-pressure system

hurricanes

indoor air pollution

industrial smog

inversion layer

lead

low-pressure system

Montreal Protocol

nitrogen dioxide

nitrogen oxides

outdoor air pollution

ozone-depleting substances

ozone hole

ozone layer

particulate matter

photochemical smog

polar cell

primary pollutant

relative humidity

residence time

scrubbers

secondary pollutant

sick-building syndrome

stratosphere

sulfur dioxide

temperature inversion

thermal inversion

tornadoes

toxic air pollutant

troposphere

tropospheric ozone

volatile organic compounds

(VOCs)

warm front

weather


Teaching Tips 1. The AirData website of the U.S. Environmental Protection Agency

(www.epa.gov/air/data/index.html) provides air pollution data for the entire

United States and produces reports and maps using criteria that you specify. Air

data are acquired from two EPA databases: Air Quality System (AQS) and

National Emission Inventory (NEI).

Present students with air data from your region or ask them to retrieve data

themselves. The database will generate tables showing the facilities within a

state or a county that emit various particulates, in the order of total amount of

emission.

2. Assign students to read papers about air pollution and environmental justice at

the University of Michigan’s website (www.umich.edu/~snre492/cases.html).

You can have groups of students each choose a paper from the website that

relates to air pollution. Have them read the paper and then do follow-up

research to find out the current status of the problem. The groups can write

reports, do poster projects, or do PowerPoint presentations to the class or an

invited assembly.

Ask students to consider the following questions:

What was the initial discovery?

What was the source of the problem?

What lawsuits have been filed? What were the outcomes?

What health effects have been documented?

What do you think can be done to prevent similar problems?

3. As a classroom demonstration or student assignment, go to Smog City at

www.smogcity.com, developed by the Sacramento Metropolitan Air Quality

Management District. Smog City is an interactive air pollution simulator that

shows how population, environmental factors, and land use contribute to air

pollution. Smog City allows the user to adjust these factors to see the effect on

ground-level ozone formation. Ask students to consider the following

questions:

Does one factor seem to affect smog formation more than others?

How do weather variables affect smog formation?

How does population affect smog formation?

What can you do as an individual to reduce smog?

4. To find out about pollution in your community, go to Scorecard: The Pollution

Information Site (www.scorecard.org/). Have students enter their ZIP codes to

learn about toxic chemicals released into the air by local sources.


5. A poster project can be an exercise in learning good communication skills.

Students must summarize a great deal of information, use principles of color

and design, and have both graphic impact and a presentation style that draws

and holds interest. A short presentation to use in class, or to have students

access on their own, can be found at dv.pima.edu/~jduek. Click on ―Education

Power Points‖ and from that page choose ―Poster Projects.‖ It includes an

outline for students to follow and for instructors to use in grading projects:

20% content: written material and visual material

20% accuracy: content, grammar, and spelling

20% neatness: lettering, visuals, and use of color/design/layout

20% layout: tips are given about colors, lettering, placement, shape, and

decoration

20% creativity: written, visual, layout, humor, and other creative directions

6. Provide white or light-colored cotton squares to students for an outdoor activity

that will answer this question: ―Is there particulate matter in the atmosphere

around campus that I am unable to see?‖ Be sure that all swatches are the same

size. Ask students if they can predict where there might be higher levels of air

quality impact. If in urban areas, regions near the ground that are subject to

diesel fumes provide interesting collecting sites. If possible, leave the swatches

outdoors secured to trees, posts, or even the building. Retrieve the material after

24 hours and examine the swatches against a control swatch kept inside the

classroom in an airtight container. Ask students if any of their predictions match

the visual results.

Additional Resources Websites

1. AIRNow, U.S. Environmental Protection Agency (airnow.gov)

This interagency and international website provides air quality forecasts,

information, and reports on air quality to the general public.

2. Air and Radiation: Where You Live, U.S. Environmental Protection Agency

(www.epa.gov/air/where.html)

This resource has general information about air quality and regulation,

including criteria on air pollutants, air quality trends, and toxic air pollution.

3. Encyclopedia of the Atmospheric Environment, Manchester Metropolitan

University (www.ace.mmu.ac.uk/eae/english.html)

Published by the Atmosphere, Climate, and Environment Information

Programme, this website is supported by the United Kingdom Department for

Environment, Food, and Rural Affairs. It is a source of information on air

quality, ozone depletion, acid rain, and global warming.


4. The Hubbard Brook Ecosystem Study, Hubbard Brook Research Station

(www.hubbardbrook.org)

The home page of the Hubbard Brook Ecosystem Study (HBES) provides

access to its three main resources: Research and Data, Hubbard Brook Research

Foundation, and Educational Resources.

Audiovisual Materials

1. Ozone: Cancer of the Sky, 1994, produced by Television New Zealand Natural

History, distributed by The Video Project (www.videoproject.com)

This video presents general information about the ozone layer. The program

follows scientists as they convene in Antarctica to study the ozone hole that

forms there each spring.

2. Atmospheric Hole: The History of the Ozone Layer, distributed by Films for the

Humanities and Sciences (www.films.com)

This program shows how the ozone layer is depleted and how its depletion is

stunting, mutating, and destroying life.

3. What’s Up with the Weather? NOVA video, distributed by WGBH

(shop.wgbh.org)

This video examines today’s extreme weather patterns, such as flooding,

hurricanes, and high temperatures. It explores whether these are natural

phenomena or whether they are indicators of global warming.

4. The Air We Breathe, 1997, produced by Hamm Productions and the National

Film Board of Canada, distributed by Bullfrog Films (www.bullfrogfilms.com)

In two videos, this program shows the connection between suburban sprawl, air

pollution, and increases in asthma and other respiratory diseases.

5. What’s in Our Air, 1999, produced and distributed by Rainbow Video and Film

Productions (www.rainbowvideoandfilm.net)

This 25-minute video documents community members in Oregon, Washington,

and California using low-tech bucket monitors to sample the air for 43

hazardous air pollutants.

Weighing the Issues: Facts to Consider Your Region’s Air Quality

Facts to consider: To determine local air quality, you could suggest websites for

county departments of environmental quality or some equivalent state agency that

monitors air quality. For national comparisons, you may recommend the first

website in the Additional Resources section of this manual, AIRNow

(www.airnow.gov), as a source of comparative information. The Internet has


numerous websites that offer international and local ideas for pollution reduction.

Ideas and opinions about the causes of local air pollution and solutions for reducing

it will vary, depending on the social, economic, and industrial context of the county

being investigated and the experience, knowledge, and priorities of the student.

Smog-busting Solutions

Facts to consider: This question most definitely requires a personal response, as

each student’s local air quality is affected by some form of air pollution, no matter

how minute. First, the student should address the issue from a personal perspective

— has the student ever gotten an emissions test? Do they know where to get one?

Could the student consume less fuel? If not, could subsidies help in this regard?

Would the student consider a new, more environmentally responsible vehicle?

Second, pursue the city’s approach to tackling air pollution. Start first with public

transportation—is it available? Like Tehran, are there restricted fuel types? How

does one become aware of the city’s pollution level—is this publicized, how?

Then, the student can address recommendations, and the benefits and drawbacks to

those recommendations.

How Safe Is Your Indoor Environment?

Facts to consider: This question requires an individual response, but responses

should consider a wide range of potential sources of air pollution, as designated by

the EPA. These sources include: asbestos; biological pollutants such as mold,

mildew, or pollen; carbon monoxide from gas appliances or woodstoves;

formaldehyde used in building materials; organic chemicals used in cleaning

products, dry cleaning, or hobbies; lead from old paint; nitrogen dioxide from gas

or kerosene heaters; pesticides to control indoor insects or microorganisms;

naturally occurring radon gas; combustion products from fireplaces or woodstoves;

and secondhand smoke. General ways to make indoor spaces safer from pollution

include limiting use of plastics and treated wood where possible, increasing

ventilation, having the space tested for radon gas, and storing cleansers and other

household products in a garage or shed.

The Science behind the Stories: Thinking Like a Scientist Discovering Ozone Depletion and the Substances Behind It

Observation: By the 1970s, industrial chemicals known as chlorofluorocarbons

(CFCs) were being produced in vast quantities.In 1974, F. Sherwood Rowland and

Mario Molina published a paper whose main point was that the inertness of CFCs

could have disastrous consequences for the ozone layer.


Hypothesis: CFCs were causing significant decreases in global stratospheric ozone.

Rowland and Molina hypothesized that CFCs would not be broken down in the

lower atmosphere and would reach the stratosphere undamaged. Intense ultraviolet

light would break down CFCs into chlorine and carbon atoms. The chlorine atoms

would catalyze the destruction of ozone molecules.

Experiment: Several experiments were needed to provide data for this hypothesis.

Richard Stolarski and Ralph Cicerone showed that chlorine atoms acted as catalysts

for ozone molecule destruction. James Lovelock devised an instrument to measure

extremely low concentrations of atmospheric gases. James Farman and his

colleagues reported that Antarctic atmospheric ozone levels had been dramatically

falling since the 1970s. Paul Crutzen showed that the Antarctic ozone hole was the

result of a combination of Antarctic weather conditions and the presence of CFCs

in the stratosphere.

Results: By the mid-1980s, scientists had conclusive evidence that global ozone

levels were declining, particularly over Antarctica, and that those declines were due

primarily to CFCs and other human-made chemicals.

Acid Rain at Hubbard Brook Research Forest

Observation: Long-term studies of water flow and nutrient cycling are important to

understanding the interplay between abiotic and biotic portions of any ecosystem.

Study: The 7,800-acre Hubbard Research Forest was established in New

Hampshire in 1955 as a long-term hydrological study and was augmented in 1963

by Dartmouth University researchers to include the study of nutrient cycling.

Precipitation was collected in clean plastic bottles from funnels with a 30-cm

opening. These bottles were retrieved each week and measured for acidity and

electrical conductivity. Concentrations of specific compounds were also measured

by other labs.

Results: In the 1960s, Gene Likens, F. Herbert Bormann, and others found that the

pH of the Hubbard Brook precipitation was several hundred times more acidic than

natural rainwater. Other studies in the 1970s supported this finding, eventually

showing that the precipitation from Pennsylvania to Maine was averaging a pH of

4.0, with some precipitation measuring as low as 2.1.

The result of this study was the implementation of the National Atmospheric

Deposition Program to measure precipitation and dry deposition across the United

States. This program developed a nationwide pH map, which showed that the

northeast United States had the worst acid deposition problem. It was hypothesized

that the fossil-fuel burning plants of the Midwest provided the compounds that

increased the acidity of the soil in the northeast United States. The Clean Air Act of

1970 was amended in 1990 to restrict acidic compounds from these Midwest

factories and power plants. In 1996, researchers also found that acidic deposition

was leaching calcium and magnesium out of the soil while increasing the amount of

aluminum in the soil. These nutrient deficiencies and surpluses weakened trees and

slowed forest growth, making trees more vulnerable to drought and insect damage.


Answers to End-of-Chapter Questions Testing Your Comprehension

1. The Earth’s atmosphere is about 500 km (300 mi) thick, consisting of four

layers: 1. The bottommost layer, the troposphere, is only 11 km (7 mi) thick but

contains three-quarters of the atmosphere’s mass. 2. The stratosphere extends

from 11–50 km (7–31 mi) above sea level and contains most of the

atmosphere’s UV-absorbing ozone. 3. The mesosphere is a zone of declining

temperatures and extremely low pressures, extending 50–90 km (31–56 mi)

above sea level. 4. Finally, the thermosphere is the outermost layer of the

atmosphere, extending from 90–500 km (56–300 mi) above sea level. In this

layer, infrequent molecular collisions allow the atmosphere to become

chemically stratified, with lighter hydrogen and helium rising to the top of the

layer, and the heavier oxygen and nitrogen sinking toward the bottom.

2. The ozone layer is concentrated 17–30 km (10–19 mi) above sea level in the

stratosphere. Stratospheric ozone absorbs UV radiation, which is harmful to

life. Tropospheric ozone can contact living organisms, and react chemically

with their tissues, causing harmful oxidation to occur. This oxidation can

chemically alter a cell’s DNA, leading to mutations and the possibilities of cell

death or cancer.

3. Solar energy heats air, causing pressure gradients that drive Earth’s atmospheric

circulation. This circulation distributes heat and moisture over Earth’s surface

(i.e., determines the main factors of climate). Hadley, Ferrel, and polar cells are

convection patterns in the atmosphere, driven by the sun’s energy, that produce

predictable bands of precipitation and wind direction over the globe. These

factors in turn control the distribution of Earth’s biomes.

4. The London smog event of 1952 was caused by the exhaust of coal-burning

power plants and of home fireplaces/furnaces being trapped in a layer of colder,

denser air near the surface—a so-called thermal inversion.

5. A primary pollutant, such as soot, is emitted into the atmosphere in a form that

is directly harmful. A secondary pollutant is produced in the atmosphere by

means of a chemical reaction occurring there. For example, the nitric acid in

acid rain is produced by reaction of the primary pollutant NO2 and water vapor

in the air.

6. In certain areas, concentrations of these pollutants have risen, regularly reaching

unhealthy levels. Emissions of major pollutants have dropped, and due to their

ill effects, these are monitored closely, especially primary compounds that can

react to make secondary pollutants. One contaminant, carbon monoxide, poses

risk to humans and other animals because it can bind irreversibly to hemoglobin

in red blood cells, preventing the hemoglobin from binding with oxygen.

7. The word ―smog‖ is a combination of ―smoke‖ and ―fog.‖ It refers to unhealthy

mixes of air pollutants that often occur over urban areas, especially when the air

pollutants are trapped by a temperature inversion. Photochemical smog is


caused by secondary pollutants and other chemicals, often including ozone and

NO2. Industrial smog is caused by the by-products of industrial combustion,

especially soot, CO, CO2, SO2, and NO2, resulting in a characteristically gray,

acidic mixture.

8. CFCs split O3 to produce O2. Because CFCs persist in the atmosphere for years,

are mixed all over the world regardless of their source, and destroy UV-

protective stratospheric ozone, they are considered a long-term international

problem. Many nations have come together to create the Montreal Protocol,

which limited the production of CFCs and similar chemicals internationally.

9. Acidic deposition, an example of a secondary pollutant, can occur far from the

source of its precursor pollutants because of the long-range atmospheric

transport that happens while the atmospheric chemical reactions are taking

place. Acidic deposition can change soil chemistry, kill trees, acidify lakes,

harm aquatic organisms, eat away at buildings, and cause other impacts.

10. Common indoor air pollution sources include tobacco smoke, radon gas,

volatile organic compounds, living organisms from mites to bacteria, and

smoke from indoor fires. Exposure can be reduced for each (in the order of the

factors just mentioned) by not smoking indoors, ventilating confined spaces in

basements, choosing alternative products for floor coverings or cleaning

compounds, minimizing sources of standing water in HVAC systems, and

limiting wood fires to the outdoors, or at least providing a working chimney and

adequate ventilation.

Calculating Ecological Footprints

Total NOx emissions

(lb)

NOx emissions

due to light-duty

vehicles (lb)

You 107.20 62.48

Your Class Answers will vary Answers will vary

Your State Answers will vary Answers will vary

United States 32,599,520,000 19,000,168,000

1. The U.S. population increase from 2008 to 2020 is projected to be 9.9%. NOx

emissions have decreased slightly during the past decade, even as the

population has grown, largely the result of improved technology. Unless

unexpected technological breakthroughs occur, or unless fuel demand surges,

we may expect these trends to continue.

2. By cutting the miles you drive in half, 12.45 pounds of NOx emissions could be

avoided, which would be an 8.5% reduction in your total NOx emissions.


3. Answers will vary. Anything that would reduce your combustion of fossil fuels

would also reduce your amount of NOx emissions (e.g., setting your thermostat

lower in the winter and higher in the summer; turning off necessary lights;

taking cooler, shorter showers). Reducing the per capita share of vehicle miles

traveled is as easy as carpooling, combining several errands into one trip, or

walking/biking when possible.

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