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Environmental Science
A Study of Interrelationships
Twelfth Edition
Enger & Smith
Chapter 16
Air Quality Issues
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Air Quality Issues
Outline
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The Atmosphere
Pollution of the Atmosphere
Categories of Air Pollutants
Control of Air Pollution
Acid Deposition
Ozone Depletion
Global Warming and Climate Change
Addressing Climate Change
Indoor Air Pollution
The Atmosphere
 The atmosphere is composed of 78.1% N,
20.9% O, and about 1% of other gases such as
argon, carbon dioxide, methane, and water
vapor.
 Most of the atmosphere is held close to the
Earth by the pull of gravitational force, thus it
gets less dense with increasing distance from
the Earth.
Air Quality Issues
The Atmosphere
 The troposphere extends from the Earth’s surface
to about 10 km above the Earth.
 The stratosphere extends from the top of the
troposphere to about 50 km above the Earth.
• Most ozone is located in a band between 15 and 30 km.
 The mesosphere extends from 50-80 km above
the Earth.
 The thermosphere extends to about 300 km above
the Earth.
The Atmosphere
The Atmosphere
 As the air absorbs heat from the Earth, it
expands and rises.
• When heat is radiated into space, air cools, becomes
more dense, and flows toward the Earth.
 As the air circulates vertically, it also moves
horizontally as the Earth spins on its axis.
 The combination of all air movements creates
the wind and weather patterns characteristic of
different regions of the world.
Pollution of the Atmosphere
 Pollution is any addition of matter or energy that
degrades the environment for humans and other
organisms.
 Because human actions are the major cause of
pollution, we can do something to prevent it.
 Automobile emissions, chemical odors, factory
smoke, and similar materials are considered air
pollution.
Pollution of the Atmosphere
 Air pollution is directly related to the number of
people living in an area and the kinds of
activities in which they are involved.
 In urbanized, industrialized societies, there are
dense concentrations of people that use large
quantities of fossil fuels for manufacturing,
transportation, and domestic purposes.
 These activities release large quantities of
polluting byproducts into our environment.
Pollution of the Atmosphere
 In urbanized areas, pollution cannot be
sufficiently diluted before the air reaches another
city.
• Polluted air from Chicago is further polluted when it
reaches Gary, Indiana;
• is supplemented by wastes of Detroit and Cleveland;
• and finally moves over southeastern Canada and
New England to the ocean.
 Air pollution is not just an aesthetic problem; it
also causes health problems.
Pollution of the Atmosphere
Air pollution and population centers
Pollution of the Atmosphere
 Many of the megacities of the developing world
have extremely poor air quality.
 The causes of this pollution are open fires,
poorly maintained motor vehicles, and poorly
regulated industrial plants.
• Air pollution increases the death rate and lowers the
general health of the population.
– Chronic coughing and susceptibility to infections are
common.
Categories of Air Pollutants
 Five major types of materials are released directly
into the atmosphere in unmodified forms in
sufficient quantities to pose a health risk. These
are called primary air pollutants.
 They are:
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Carbon monoxide
Volatile organic compounds (hydrocarbons)
Particulate matter
Sulfur dioxide
Oxides of nitrogen
Categories of Air Pollutants
 Secondary air pollutants form under reaction of
primary pollutants and water or sunlight.
• Ozone
 Criteria air pollutants are those pollutants for
which specific air quality standards have been set.
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Nitrogen dioxide (NO2)
Ozone (O3)
Sulfur dioxide (SO2)
Particulate matter (PM)
Carbon monoxide (CO)
Lead (Pb)
Categories of Air Pollutants
 Carbon monoxide is produced when organic
materials are burned with insufficient oxygen.
• The single largest source is the automobile.
– 60% from vehicles driven on roads
– 20% from vehicles not used on roads
– Remainder from burning, i.e., power plants, leaves, etc.
• Carbon monoxide binds to hemoglobin in blood and
makes the hemoglobin less able to carry oxygen.
• It is most dangerous in enclosed spaces; several hours
of exposure to air containing only 0.001% CO can
cause death.
Categories of Air Pollutants
Carbon monoxide
Categories of Air Pollutants
 Cigarette smoking is an important source because
the person is inhaling CO directly.
 U.S. levels of CO have decreased by about 67%
between 1970 and 2007.
Categories of Air Pollutants
 Particulate matter consists of minute pieces of
solid materials (< 10 microns) and liquid droplets
dispersed into the atmosphere.
• The EPA has set standards for particles smaller than 10
microns (PM10) and 2.5 microns (PM 2.5).
• Larger than 2.5 microns are primary pollutants; smaller
than 2.5 are mostly secondary pollutants.
• Particulates can accumulate in lungs and interfere with
the ability of lungs to exchange gases.
Categories of Air Pollutants
 Amount of PM10 has decreased 28% between 1990
and 2007.
 U.S. EPA has been setting PM2.5 standards for a
shorter period of time.
• Amount decreased 11% between 2000 and 2007.
 Most communities now meet the standards set for
PM10 but exceed the standards set for PM25.
Categories of Air Pollutants
 Sulfur dioxide (SO2) is a compound of sulfur and
oxygen produced when sulfur-containing fossil
fuels are burned.
• Burning coal releases SO2.
• Today over 70% of SO2 released into the atmosphere is
from coal-burning power plants.
– U.S. levels of SO2 decreased 56% between 1990 and 2007.
 Nearly all communities meet the SO2 standards set
by the U.S. EPA.
Categories of Air Pollutants
 Oxides of nitrogen (NOx) are formed when fossil
fuels are burned.
 The nitrogen and oxygen molecules in the air
combine with one another when subjected to the
high temperatures of combustion.
• Nitrogen monoxide (NO) and nitrogen dioxide (NO2) are
the most common.
• Burning fossil fuels in internal combustion engines is the
primary source of nitrogen oxides.
– Automobiles produce 38%
– Non-road motorized equipment produces 21%
– Electrical generations produces 22%
Categories of Air Pollutants
 About 75% of the NO produced by an
automobile engine is converted back into N2 and
O2 by the catalytic converter.
• An increase in the number of cars and miles driven
offsets the gains attributable to catalytic converters.
 Although all communities meet the EPA
standards for nitrogen oxides, they remain a
problem because they contribute to the
development of photochemical smog.
Categories of Air Pollutants
 Lead (Pb) can enter the body through breathing
airborne particles or consuming lead deposited on
surfaces.
 Lead accumulates in the body and can cause
mental retardation and kidney damage.
 Leaded gasoline was primary source.
• Currently, over 80% of gasoline sold in the world is
unleaded. Those still using it plan to phase it out.
• In the U.S. lead emissions peaked at about 258,000 tons
per year. In 2007 they were about 1300 tons per year, a
reduction of 99.5%, meeting EPA standards in the U.S.
Categories of Air Pollutants
 Volatile organic compounds readily evaporate
and become pollutants in the air. They are also
known as hydrocarbons, a group of organic
compounds consisting of carbon and hydrogen.
 The use of internal combustion engines accounts
for 37% of VOCs released into the air.
• Solvents contribute about 22%
• Fires contribute about 15%
Categories of Air Pollutants
 VOCs aid the production of secondary air
pollutants found in smog.
 Some VOCs are toxic and are known as
hazardous air pollutants.
 The EPA does not publish VOC reduction data.
• VOC levels are reduced when ozone levels fall. VOC
levels have fallen substantially in recent years.
Categories of Air Pollutants
 Ozone (O3) is a molecule of three oxygen atoms
bonded to one another.
• It is an extremely reactive secondary pollutant that can:
– Cause permanent lung damage
– Irritate respiratory tissues
– Damage plants
– Reduce agricultural yields
• Zone levels fell by only about 9% from 1990 to 2007 and
are still a problem particularly in southern California and
the U.S. Northeast.
Categories of Air Pollutants
 Photochemical smog is a mixture of pollutants.
 It forms when nitrogen dioxide and VOCs interact in
primary pollutants interact under the influence of
sunlight.
• Two most destructive components:
– Ozone
– Peroxyacetyl nitrates
Categories of Air Pollutants
Daily changes in photochemical smog
Categories of Air Pollutants
 Cities with warm climates and lots of sunlight are
more prone to develop photochemical smog.
• Warm temperatures and sunlight are needed.
• Smog is more likely to be a problem in the summer
with higher temperatures and longer days.
• Cities adjacent to mountains or in valleys tend to have
trouble with photochemical smog because pollutants
are trapped by thermal inversions.
Categories of Air Pollutants
 Thermal inversions occur when warm air
becomes sandwiched between two layers of
cold air and acts like a lid on a valley.
 Warm air cannot rise, causing smog
accumulation.
• Ozone levels fell by about 9% from 1990 to 2007 and
are still a problem, particularly in southern California
and the U.S. Northeast.
• Since ozone is produced by VOCs and Nox it is
necessary to further reduce the levels of these two
components to decrease the production of ozone.
Categories of Air Pollutants
Thermal inversion
Categories of Air Pollutants
 Hazardous air pollutants (HAP), or air toxics, are
compounds that can harm human health or
damage the environment.
• Some released from consumer activities:
– Benzene escapes during automobile refueling.
– Some consumer products such as glues and cleaners
release toxic materials into the air.
• The majority are released from manufacturing:
– Perchloroethylene is released from dry cleaning processes.
Control of Air Pollution
 All of the air pollutants examined thus far are
produced by humans. Thus, their release into
the atmosphere can be controlled.
• In the U.S., implementation of the Clean Air Act has
been the primary means of controlling air pollution.
 Engineering changes in autos have reduced the
amount of VOCs that escape from the gas tank
and crankcase.
 Modifications to the pumps at gas stations and
filler pipes of cars has been beneficial.
Control of Pollution
 In the U.S., implementation of the requirements
of the Clean Air Act has been the primary means
of controlling air pollution.
• Under the Clean Air Act, a variety of pollution control
mechanisms have been employed and the quality of
air has improved significantly in the last 27 years.
• The EPA is responsible for developing and meeting
air quality standards.
• Industry must meet a series of detailed control
requirements with the goal of improving air quality.
Control of Air Pollution
 Motor vehicles are the primary source of several
important air pollutants: carbon monoxide, VOCs,
and nitrogen oxides.
• Catalytic converters reduce these emissions.
 Lead-free fuel has reduced the amount of lead in
the atmosphere.
 Ozone levels depend on VOC and NO2 levels, and
have fallen somewhat but still need improvement in
some areas of the country, particularly California
and the northeast U.S.
Control of Air Pollution
 Mining, farming, transfer of grain or coal, and
road dust are sources of particulate emissions.
 Forest fires, grass fires, leaf burning, fireplaces,
and woodstoves are a significant source of
particulate matter.
• Some municipalities ban wood burning stoves and
fireplaces, while high-efficiency wood stoves
significantly reduce particulate emissions.
 Burning of fossil fuels is another source of
particulate matter.
 Diesel engines are a source of particulate
matter.
Control of Air Pollution
Improvement in air quality
Control of Air Pollution
 Power plant emissions
 Particulates and sulfur dioxide are associated with
electric power plants.
• Filters and mechanical means control particulates.
• The control of sulfur dioxide requires changes to the
way electricity is produced. The EPA has set limits and
allow the electric utility to decide which options are best
for them.
Control of Air Pollution
 Low-sulfur coal reduces sulfur emissions by
66%.
 Switching to oil, natural gas, or nuclear fuels
further reduces sulfur emissions.
 40% of sulfur can be removed before the fuel is
used.
 Smokestack gases can be scrubbed before they
are emitted.
• The technology is available, but costly to install,
maintain, and operate.
Acid Deposition
 Acid deposition is the accumulation of potential
acid-forming particles on a surface.
 When dry particles are deposited, an acid does
not actually form until these materials mix with
water.
 All of these sources of acid-forming particles are
commonly referred to as acid rain.
Acid Deposition
 Acid deposition is the accumulation of potential
acid-forming particles on a surface.
 When dry particles are deposited, an acid does
not actually form until these materials mix with
water.
 All of these sources of acid-forming particles are
commonly referred to as acid rain.
SO2 + H2O  H2SO4 (Sulfuric Acid) Acid Rain
Limestone degradation:H2SO4 + CaCO3  CaSO4 (soluble
in water)
Limestone degradation
Forest Decline
Acid Deposition
Sources of acid deposition
Acid Drainage
Acid Deposition
 Acid rain is a worldwide problem.
 Acid rains can have concentrations of acid 1000
times higher than normal.
 Harmful effects of acid rain include:
• Property and structural damage
– Limestone degradation
• Damage to forests
– Acidic soil results in reduced nutrient absorption
• Lake acidification causes food chain disruption
Ozone Depletion
 In 1985, it was discovered that a significant
thinning of the ozone layer over the Antarctic
occurred during the Southern Hemisphere
spring.
 The stratosphere was being reduced, and this
area became known as the “ozone hole.”
 Ozone in the outer layers of the atmosphere
shields the Earth from the harmful effects of
ultraviolet light radiation.
Ozone Depletion
 Chlorofluorocarbons and similar compounds can
release chlorine atoms which can lead to the
destruction of ozone.
 It can take 10 to 20 years for chlorofluorocarbon
molecules to get into the stratosphere.
 They can then react with the ozone for up to 120
years.
Ozone Depletion
 Chlorofluorocarbons are strongly implicated in the ozone
reduction in the upper atmosphere.
 It can take 10 to 20 years for chlorofluorocarbon
molecules to get into the stratosphere.
 They can then react with the ozone for up to 120 years.
UV + O3  O2 + O
O2 + O ---> O3 Ozone formation
Ozone Depletion (causing ozone hole) global warming
Cl + O3  ClO + O2
ClO + O  Cl + O2
Ozone Depletion
 In 1987, several industrialized countries including
Canada, the United States, the United Kingdom,
Sweden, Norway, Netherlands, the Soviet Union,
and West Germany agreed to freeze
chlorofluorocarbon and halon (used in fire
extinguishers) production and reduce production
by 50% by 2000.
 This document, known as the Montreal Protocol,
was ratified by Congress in 1988.
 As a result, emissions dropped 87% from their
peak in 1988.
Ozone Depletion
 Size of ozone hole
Global Warming and Climate Change
 Climatic records indicate over the past 160,000
years a close correlation between greenhouse gas
concentration and global temperatures.
 UN established the Intergovernmental Panel on
Climate Change (IPCC)
Global Warming and Climate Change
 The Fourth Assessment Report, Climate Change
2007, concluded:
• The average temperature on Earth has increased 0.56 to
0.92°C (1.0-1.7° F) in the past 100 years. 1998 was the
hottest year on record; 2005 was the second warmest;
2002 was the third.
• Sea level is rising about 1.8 mm/yr or 18 cm in 100 years.
• A strong correlation exists between temperature increase
and amount of greenhouse gases in the atmosphere.
• Human activity greatly increases amounts of greenhouse
gases in atmosphere.
Global Warming and Climate Change
 Greenhouse effect:
• Greenhouse gases allow sunlight to penetrate the
atmosphere.
• Sunlight is absorbed by Earth’s surface.
• It is reradiated as infrared energy (heat).
• The heat is absorbed by gases in the atmosphere.
Global Warming and Climate Change
Greenhouse effect
Global Warming and Climate Change
 Carbon dioxide is the most abundant of the
greenhouse gases.
• Deforestation contributes to the amount of carbon
dioxide in the atmosphere.
 Methane comes from biological sources and
from some fossil-fuel burning activities.
 Nitrous oxide enters the atmosphere from fossil
fuels and fertilizers.
 Chlorofluorocarbons from refrigerants, cleaning
solvents, and propellants are also a component
of the greenhouse effect.
Global Warming and Climate Change
 Although a small increase in the average
temperature of the Earth may seem trivial, it
could set in motion changes that could
significantly alter the climate of major regions of
the world.
• Computer models suggest a cascade of
consequences that affect the hydrologic cycle, sea
level, human health, the survival and distribution of
organisms, and the use of natural resources by
people.
Global Warming and Climate Change
 Potential Consequences of Global Warming
• Rising sea level
– Beach and coastal wetland erosion
– Substantial loss of coastal area
– Land area of some island nations and countries like
Bangladesh would change dramatically as flooding
occurred.
Global Warming and Climate Change
 Potential Consequences of Global Warming
 Rising Sea Level
• Water expands when it is warmed.
• Melting glaciers add more water to the oceans.
– Beaches and coastal wetlands erode, inundating lowlying areas, and coastal areas become more vulnerable
to flooding from storm surges and intense rainfall.
– By 2100 sea level is expected to rise 15–90 cm or
6–35 inches.
– A 50 cm rise results in substantial land loss in North
America.
Global Warming and Climate Change
 Potential Consequences of Global Warming
• Health effects
– Most direct effect of climate change would be impacts of
hotter temperatures.
– Hot temperatures force cardiovascular system to work
harder to cool the body.
– Heat exhaustion and some respiratory problems increase.
– Aggravate air quality problems.
– Spread of tropical disease such as malaria, dengue fever,
yellow fever, and encephalitis to temperate parts of the
world.
Global Warming and Climate Change
 Potential Consequences of Global Warming
 Geographic distribution of organisms could be
altered.
• Equatorial organisms move toward the poles, and tundra
biomes are affected due to the thawing of permafrost.
• Coral reefs are affected by increased water temperature
and increased acidity of ocean water from dissolved CO2.
• Low lying islands and shorelines are impacted by rising
sea level. Mangrove forests and marshes will be
inundated and subjected to violent weather and storm
surges.
Global Warming and Climate Change
 Potential consequences of global warming
 Climate strongly affects crop yield.
 In regions with drought and heat stress, yields
will fall.
 Yields will increase in areas with warmer
temperatures and more rainfall.
 Episodes of severe weather will cause crop
damage that will affect yields.
Global Warming and Climate Change
Addressing Climate Change
 Approaches to dealing with climate change involve
technological change coupled with political will and
economic realities.
• Increase efficiency of energy utilization and reduce
carbon dioxide production.
– Carbon tax
A carbon tax is an environmental tax on emissions of
carbon dioxide (CO2).
• Increase the amount of carbon dioxide removed from
the atmosphere.
– Increased vegetation growth
– May be a short-term benefit
Addressing Climate Change
 Political and Economic Forces
• It will be more difficult to achieve global consensus to
reduce CO2 emissions, as CO2 is released as a result of
energy consumption which affects all sections of the
economy.
• Increases in energy efficiency and reductions in
greenhouse gas emissions are likely to have important
related benefits that could offset the costs.
– Improving fuel efficiency and reducing pollution can be
offset by lower health care costs and higher worker
productivity.
Addressing Climate Change
– Many candidates for longer-term technological
transition have been identified, and some have
already begun to penetrate the market.
– Wind energy systems competitive with coal-burning
power plants
– The U.S. DOE has concluded that relying on
already proven technology, the U.S. could reduce
its carbon emissions by 400 million metric tons in
2010.
– This would stabilize emissions in that year at 1990 levels.
– Savings from reduced energy costs would be roughly
equal to the added cost of investment.
Addressing Climate Change
– Resources and policies to increase investment
in renewable and other long-term technologies
will be needed.
Indoor Air Pollution
 Growing evidence indicates air within homes
and other buildings can be more seriously
polluted than outdoor air in the most
industrialized cities.
 These pollutants are thought to have adverse
effects on human health.
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Asbestos
Formaldehyde (in many consumer products)
Airborne pesticide residues
Chloroform
Perchloroethylene
Paradichlorobenzene
Indoor Air Pollution
 Smoking is the most important pollutant.
 Weatherizing to increase efficiency slows air
exchange and tends to trap pollutants.
 Movements to reduce indoor air pollution lag
behind regulations governing outdoor air
pollution.
 The EPA is conducting research to identify and
rank the human health risks that result from
exposure to individual indoor pollutants or
mixtures of multiple indoor pollutants.
Indoor Air Pollution
 Secondhand smoke is exposure to
environmental tobacco smoke as a result of
living and working in places where people
smoke.
 In July 1993, the EPA recommended several
actions to prevent people from being exposed to
secondhand indoor smoke:
• People not smoke in their homes or permit others to
do so.
• All organizations that deal with children have policies
that protect children from secondhand smoke.
Indoor Air Pollution
• Every company has a policy that protects employees
from secondhand smoke.
• Today only 16 states do not have some kind of a
statewide ban on smoking in public places.
• Even if a state does not have legislation, many cities
and other jurisdictions within those states do.
Indoor Air Pollution
 Radon is an inert radioactive gas with a half-life of
3.8 days.
 It is formed as a byproduct of uranium-238 decay.
 It may undergo radioactive decay in human lungs
when inhaled.
 Increased incidence of lung cancer is the only
known health effect associated with radon decay
products.
Indoor Air Pollution
 Radon usually diffuses up through rocks and soil
and escapes harmlessly into the atmosphere, but it
can diffuse into groundwater.
 It can enter a home through an open space in the
foundation, from gaps around pipes, or from wells.
 The EPA and the U.S. surgeon general
recommend that all Americans (with a few
exceptions) test their homes for radon.
 If radon is detected, simple and inexpensive
actions may be taken to lower the level in the
home.
Indoor Air Pollution
Generalized geologic radon potential of the United States
Indoor Air Pollution
 Noise is unwanted sound.
 Research has shown that exposure to noise can
cause physical as well as mental harm.
 The loudness of a sound is measured by decibels.
 The frequency or pitch of a sound is a factor in
determining its degree of harm.
 Noise pollution is linked to a variety of ailments;
research has shown it may also cause blood
vessels to constrict, it disturbs unborn children,
and sometimes causes seizures in epileptics.
Indoor Air Pollution
 The Noise Control Act of 1972 was the first
major attempt in the U.S. to protect the public
health and welfare from detrimental noise.
 Many European countries do more to control
noise than the U.S. does.
• Several European countries have developed quiet
construction equipment in conjunction with strongly
enforced noise ordinances.
Summary
 The atmosphere has a tremendous ability to
disperse pollutants.
 Carbon monoxide, hydrocarbons, particulate
matter, sulfur dioxide, and oxides of nitrogen are
the primary air pollutants.
 The U.S. EPA establishes standards for six
pollutants known as criteria air pollutants: carbon
monoxide, nitrogen dioxide, sulfur dioxide, volatile
organic compounds, ozone, and lead.
 Acid rain is caused by emissions of sulfur dioxide
and oxides of nitrogen in the upper atmosphere.
Summary
 These compounds form acids that are washed
from the air when it rains or snows or settle as
particles on surfaces.
 The control of acid rain requires the use of
scrubbers, precipitators, and filters, or the
removal of sulfur from fuels.
 Many are concerned about the damaging effects
of greenhouse gases: carbon dioxide, nitrous
oxide, methane, and chlorofluorocarbons.
Summary
 These greenhouse gases are likely to be
causing an increase in the average temperature
of the Earth and are leading to major changes in
the climate.
 Significant impacts on our health, the vitality of
forests and other natural areas, the distribution
of freshwater supplies, and the productivity of
agriculture are among the probable
consequences of climate change.
Summary
 Chlorofluorocarbons also lead to the destruction
of ozone in the upper atmosphere, which results
in increased amounts of ultraviolet light reaching
Earth.
 Many commonly used materials release gases
into closed spaces (indoor air pollution) where
they cause health problems.
 The most important of these health problems are
associated with tobacco smoking.