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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.
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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.
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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.
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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.
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.
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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.
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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.
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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.
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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.
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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
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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.
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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.
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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
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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.
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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.
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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
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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 UVprotective 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)
You
Your Class
Your State
United States
107.20
Answers will vary
Answers will vary
32,599,520,000
NOx emissions
due to light-duty
vehicles (lb)
62.48
Answers will vary
Answers will vary
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.
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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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