Air Pollution and
Air pollution and its effects are not a recent occurrence,
as evidenced by the following quote:
". . . whosoever shall be found guilty of
burning coal shall suffer the loss of his head."
King Edward II, circa 1300 a.d.
A Brief History
Air pollution has become a widespread problem during this
century. There have been several documented episodes of air
pollution in which loss of human life occurred:
In 1931, in the heavily industrialized area of
Manchester England, over 500 persons lost their lives due
to exposure to particulates and acids in the air. In
1948, in the steel mill town of Donora, Pennsylvania,
about twenty persons died and several thousand became ill
from the effects of airborne contaminants.
Today, an estimated 3000 cancer deaths yearly are
attributable to second hand tobacco smoke alone.
What is Air Pollution?
We earlier defined pollution as something that poses a
potential risk to human health or the environment.
Then, air pollution is the presence, in the outdoor
air or the air inside a structure, of substances which
pose a potential threat to human health and/or the
The presence of particles which decrease visibility
is also now considered to be a form of air pollution as
evidenced by the fact that the U.S. EPA has negotiated an
agreement with a major western power company to improve
the air quality in the Grand Canyon National Park area.
The U.S. EPA estimates that 50 percent of the U.S.
population is exposed to air pollutants exceeding current
Sources and Types of Air Pollution
Major Sources of Air Pollution
||Air Pollutants Created
|Energy production from fossil fuels
||Carbon dioxide, sulfur oxides,
||Increase in greenhouse gases, acidic
|Automobiles, other transportation
||Carbon dioxide, nitrogen and sulfur
oxides, products of incomplete combustion
||Increase in greenhouse gases, acidic
|Refrigeration devices including home,
commercial, and vehicles
||Destruction of the stratospheric
||Various depending on the industry and
process, including toxic materials
||Destruction of the stratospheric
ozone layer, toxic emissions
Types of Air Pollutants
Air pollutants can be classified by several different
methods, including gaseous and particulate; conventional and
toxic; conventional, acidic and toxic; or greenhouse, acidic,
toxic and particulate.
Some pollutants may fall into more than one category.
Others may not fit well within any of these categories.
Greenhouse gases include carbon dioxide [CO2],
nitrous oxide [N2O], chlorofluorocarbons, and some other
organic compounds. Acidic pollutants include sulfur
oxides [SOx], nitrous oxides [NOx], hydrochloric acid
[HCl], and other acids.
Toxic pollutants include carbon monoxide [CO], many
organic compounds such as benzene, PCBs, dioxins, and
furans, and inorganics such as lead, arsenic, beryllium,
mercury, and asbestos.
Particulate pollutants include materials formed from
combustion and mechanical processes.
Federal Regulations Relating to Air Quality and Control
Note: The first air pollution
regulations were passed in England to reduce the emissions from
the burning of coal. They were passed in 1273 a.d. That's right,
Air Pollution Control Act of 1955, PL 84-159
Established federal funding for air pollution
research, federal technical assistance and training
Air Pollution Control Act Amendments of 1960, PL 87-761
A continuance of the APCA of 1955, and a study of
human health effects caused by motor vehicle emissions
The Clean Air Act of 1963, PL 88-206
Matching grants to state and local government
(federal share of 66 to 75 percent), increased research
and training, efforts to control air pollution from
Motor Vehicle Air Pollution Control Act of 1965,
Required automobile exhaust emission standards to be
met in 1968
The Air Quality Act of 1967, PL 90-148
Time tables for establishment of air quality criteria
for different pollutants, state or federal enforcement of
air quality limits. Program was understaffed, under
funded and unsuccessful.
The Clean Air Act Amendments of 1970, PL 91-604
The establishment of national ambient air quality
standards for particulates, carbon monoxide, sulfur
oxides, hydrocarbons, and others.
National emission standards for existing and new
facilities, fines and criminal penalties for intentional
violation, new stricter automobile emission standards,
additional research funding
The Clean Air Amendments Act of 1977, PL 95-95
Continuance of the 1970 requirements, additional
restrictions for "non-attainment areas."
The Clean Air Act of 1990, PL
A complete revamping of the air pollution control
regulations, including compliance time tables (3 to 20
years) for major noncompliance areas.
Tighter emission standards for vehicles, reformulated
gasolines, air toxics requirements, acid rain controls,
new permitting program with stiffer civil and criminal
One Success Story
Twenty years ago, an important topic in the air pollution
field was lead in the air.
Tetraethyl lead was used for years as an octane
boosting additive in gasolines.
Lead is known to cause lower intelligence and
behavior problems in children and high blood pressure in
It has also been suspected of causing defects in
Today, little is heard about lead in the atmosphere. Why?
Because, atmospheric lead has been almost eliminated.
Beginning with the 1965 Motor Vehicle Air Pollution
Control Act, the U.S. began a gradual phase out of lead
as a gasoline additive.
Lead was completely phased out of gasoline in 1995.
Lead is a regulatory success story in the US.
Many other industrialized nations have also phased
out lead. However, most developing nations are still
using tetraethyl lead as a gasoline additive. In 1988
Mexico, a developing nation, began a program to reduce
lead additives in gasoline.
Almost certainly, in the future we will witness an
increased effort among developing and underdeveloped
nations to reduce their levels of pollution, including
||Concentration, % by volume
||3.3 x 10-2
||5 x 10-5
||1 x 10-6
||2 x 10-4
*The concentration of these gases has been significantly
modified by human activity over the last 100 years.
Acidic pollutants reduce the pH of natural precipitation or
consume alkalinity. Acid precipitation was recognized as early as
1852 by Robert Smith in Manchester, England, where coal was used
The acidity also increases the leaching of metals
bound in the soil.
Adding to the problem in some cases are toxic metals
present in the precipitation which originated at the
And, not all acidity reaches the surface in precipitation.
Acidic particles can contact surfaces and become dry
deposition. Up to 40 percent of the total acidity
reaching the surface can be deposited this way.
Thus acid deposition would be a better term than acid
rain or acid precipitation although the latter terms are
Effects of Acidic Precipitation
It consumes alkalinity in natural wasters, eventually
depressing the pH of the water. Most aquatic life are
very sensitive to pH changes. In some cases, the acid
precipitation causes the release of metals previously
bound in the soil. Aluminum is thought to be a major
factor in acid precipitation and aquatic toxicity.
Acid precipitation is corroding many structures
(bridges, buildings, etc.) at a rate several times
Acid precipitation is causing the destruction of
sculptures and paintings at an alarming rate
The Extent of the Problem
A significant portion of the soils and lakes in the
northeastern United States and southeastern Canada have
already been affected by acidic precipitation.
Acidic precipitation is primarily the result of
pollutant discharges from coal fired power plants such as
those in the Ohio Valley of the mid-west.
Emissions from motor vehicles exacerbates the
The mid-west power plant emissions are transported by
wind to the northeastern U.S. and southeastern Canada.
Other regions of the U.S. are in imminent danger from
These areas include the northern Minnesota area, as
well as the area surrounding several major metropolitan
A large portion of central and northern Europe have
already been damaged from acidic precipitation, including
much of the Scandinavian states, as well as portions of
Switzerland and Germany.
Depressed pH levels in precipitation are
recorded in central Europe from the 1870's.
In recent years, the pH of precipitation in
much of Europe has been 4.0 to 4.5.
Acid precipitation varies in strength across the
nation, and the world.
Due to long atmospheric residence times,
these pollutants are often deposited in locations
hundreds of miles from their emission sources.
The Ohio River valley is an industrialized
area that contributes significant amounts of
acidic precipitation to the northeastern U.S. and
southeastern Canada, literally hundreds of miles
from their source.
Controlling Acid Emissions
Convert from high sulfur coal to low sulfur coal
Use nuclear power
Recent changes in the regulatory process allow for
faster permitting of nuclear power plants
There is little chance that nuclear power
will supply a greater fraction of power in the
Liability risk, technical/operational
problems, and environmental opposition are strong
reasons not to build additional nuclear power
A caustic spray neutralizes the acidity
This produces a sludge which must be landfilled or
otherwise disposed of
Fluidized bed combustion
The coal is combusted in a bed of limestone
The limestone neutralizes the acidity as it is
Fine particle pollution is smaller than 1 micron
Most are created by condensation processes following
combustion. Examples include
coal power plant smoke
home fire places
This type of particulate is by far the most harmful
because the small particles penetrate into the alveoli of
the lungs before depositing
Large particle pollution is greater than 1 micron
Created by mechanical processes such as
industrial machining operations
sanding or other mechanical surface preparations for
Effects of particulate pollutants
Small particles pass through the nasal area into the
lungs. There is a much greater risk of deposition in the
lungs for these small particles
Removal of Particulate Pollutants
The bag house filter is common for removal of
Its operating principle is similar to a home
Small particles are statically charged
The electrically charged metal plates attract the
particles, removing them
Wet scrubber, discussed earlier
Green House Gases
Greenhouse gases are those gases which impede the exit of
reflected solar energy.
Greenhouse Gases Include:
Fraction of trapped
energy attributable to gas
increase in gas conc., percent
||Fossil fuel combustion
||Vehicle, residential and commercial
refrigeration systems, foams, aerosol propellants
||Cattle, rice paddies
Carbon dioxide is responsible for two-thirds of the
additional solar radiation trapped in the atmosphere.
And, the atmospheric concentration of carbon dioxide is
increasing at a rate of 0.5 percent per year.
Although the atmospheric life of CO2 is not well
established, it is probably on the order of 50 to 100
Where CFCs are only responsible for ten percent of
the excess solar energy trapped by the atmosphere, they
are increasing at a rate of four percent per year.
Even worse, CFCs have estimated atmospheric life
times of 50 to 400 years.
Thus, even if we stopped burning fossil fuels and
stopped producing CFCs today, we could expect those
already in the atmosphere to affect the earth's
temperature for at least the next one or two centuries.
Effects of CFCs
Estimates of how great these greenhouse gases will
affect the earth vary.
Temperature records are not of sufficient accuracy
and number prior to the late 1800's to assist in a global
However, since that period, there has been a gradual
warming of the earth. The global average temperature has
probably increased 0.3 to 0.6ºC since about 1860.
There are strong indications that the global
temperature will increase more rapidly in the 21st
The average global temperature is expected to
increase 2 to 4ºC (4 to 9ºF) during the next century.
This corresponds roughly to a doubling of the atmospheric
Human activity has already caused a 25 percent
increase in global atmospheric CO2. This increase in
global temperature will have far reaching effects on the
Although the exact effects of global warming are not
certain, experts believe that significant changes in the
earth's weather patterns are possible, in conjunction
with alterations in the ocean currents.
It has been predicted that increased CO2 levels will
also result in an increase in global precipitation.
The increased temperature will result in greater
evaporation rates over the oceans. However, some areas
may still have reduced rainfall amounts.
Atmospheric Ozone Destruction
The stratosphere is the layer of atmosphere above the
troposphere, from 12 to 70 km high.
In this region, and above, reactions involving
atmospheric chemicals, pollutants, and light occur.
The oxygen in the upper atmosphere, above
approximately 150 km, absorbs damaging short
wavehigh energy radiation protecting life on earth
In the upper atmosphere, sunlight provides energy
that breaks apart the molecular oxygen, O2, in the
atmosphere. The separate atomic oxygen, O, then combines
with molecular oxygen forming ozone, O3. This ozone
absorbs ultraviolet radiation emitted by the sun. It
Chlorofluorocarbons (CFCs) Destroy Ozone
These are the same chemicals implicated in global
warming. When emitted to the atmosphere CFCs migrate to
the upper layers.
The CFCs are eventually broken down, releasing their
The chlorine then reacts with ozone destroying it.
The world first used CFCs in the 1930s.
Global atmospheric CFC concentrations did not
increase substantially until the 1960s. Scientists became
concerned about their impact on the ozone layer in the
1970s. Then, in 1985 scientists detected a
"hole" in the ozone layer over the Antarctic
region. More recently, a similar hole was detected over
the arctic region.
Control of CFC Emissions
CFC emissions can be controlled mainly by finding and
using alternative chemicals for refrigeration and air
conditioning, foam blowing agents, and solvent
And, by developing better alternative refrigeration
processes which do not require refrigerant gases similar
This process is being forced by a variety of national
laws world wide, and by the Montreal Protocol, an
international agreement signed in Montreal Canada in
1987. In essence, the Montreal Protocol requires the
phaseout of the most dangerous CFCs by 1997 for developed
countries, and by 2007 for developing nations.
This agreement should lead to substantial reductions
in global CFC emissions. This phaseout of CFCs will
result in an improvement in stratospheric ozone.
However, because CFCs have atmospheric lifetimes of
60 to 400 years, near term expectations are poor. Further
reductions in US CFC emissions, in excess of the Montreal
Protocol, are required by the 1990 Clean Air Act
Amendments. But, with CFCs implicated in both greenhouse
warming and ozone depletion, former President George Bush
issued a presidential directive banning production of
CFCs by 1996, faster than either the Montreal Protocol or
the Clean Air Act Amendments.
Elimination of CFC emissions in the U.S. is important
because the United States is responsible for
approximately one-quarter to one-third of world CFC
In an effort to accomplish the goal of CFC
elimination, many industries have joined a global effort
to find acceptable substitutes to CFCs.
In the short term the substitute may be
hydrofluorocarbons (HFCs). However, HFCs also damage the
ozone layer, but have much shorter atmospheric lives than
Thus, although not ideal, they are much better than
In the longer term, it is expected that other
substitute chemicals and possibly different refrigeration
processes, will be developed which have zero ozone
depleting potential, and are not greenhouse gases.
Since the 1970s we have improved much
in air pollution reduction and control. We understand air
emissions, their sources, and their effects much better now than
then. We are doing much better in many air pollution aspects, but
much improvement is still needed
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