17
Atmospheric Science and
Air Pollution
Chapter Objectives
This chapter will help students:
Describe the composition, structure, and function of Earth’s atmosphere
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: Charging toward Cleaner Air in London
A. Thick and blinding 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 successes 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. The Atmosphere
A. The atmosphere is a thin layer of gases that surrounds Earth.
B. The atmosphere consists of several layers.
C.
D.
E.
F.
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.
Atmospheric 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.
Solar energy heats the atmosphere, helps create seasons, and causes
air to circulate.
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 onehalf 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.
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.
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 and 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.
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. Natural sources can pollute.
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
and can even cause global cooling by a fraction of a degree.
3. Sulfur dioxide reacts with water and oxygen and condenses into
fine particles called aerosols.
4. The burning of vegetation pollutes the atmosphere with smoke
and soot.
C. We create various types of outdoor air pollution.
1. Since the onset of industrialization, 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. Clean Air Acts legislation 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.
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.
E. The EPA sets standards for “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.
b. Sulfur dioxide is a colorless gas with a pungent odor that is
released when coal is burned and 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 emitted by vehicle engines
and used in solvents and industrial processes such as dry
cleaning, household chemicals, 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.
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.
H. Toxic substances also pollute.
1. Other chemicals known to cause serious health or environmental
problems are classified as toxic air pollutants.
I. Recent policy proposals have been contentious.
J.
K.
L.
M.
N.
O.
P.
1. The George Bush administration has vigorously advocated
proposals that would overturn key provisions of the Clean Air
Act.
Burning fossil fuels produces industrial smog.
Photochemical smog is produced by a complex series of
atmospheric reactions.
Air quality is a rural issue too.
1. Pesticide drift contributes to poor air quality in rural areas.
2. Huge confined animal feeding operations with their associated
manure add methane, sulfur dioxide, hydrogen sulfide, and
ammonia to rural areas. These pollutants have harmful effects on
humans and animals.
Industrializing nations are suffering increasing air pollution.
1. Chinese cities suffer the worst air pollution as they industrialize
rapidly.
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 “ozone hole.”
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.
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.
4. Due to the lag time between policy implementation and desired
effect, scientists often advocate a proactive approach, following
the precautionary principle.
Acidic deposition represents another transboundary pollution
problem.
1. Acidic deposition refers to the deposition of acidic or acidforming 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 far from their point sources.
4. 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.
5. Acid water running off the land is toxic to many aquatic life
forms and has led to the death of ecosystems.
Q. Acid deposition has not been reduced as much as scientists had
hoped.
IV. Indoor Air Pollution
A. Indoor air pollution in the developing world arises from fuelwood
burning.
B. Tobacco and radon gas are the two most dangerous indoor air
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.
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 indoor air.
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.
E. We can reduce indoor air pollution.
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.
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.