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Background
Number of People Living in
Counties that Experienced Air
Pollution Levels above Standards
for Public Health in 1986
Most air pollution comes either from "stationary
sources" such as factories, power plants, and smelters,
from "mobile sources" that include cars, buses, planes,
trucks, and trains, or from natural sources such as
wildfires. Both kinds of man-initiated sources are
regulated by EPA under the Clean Air Act which
provides the principal framework for state and national
efforts to protect air quality Under the Act, EPA is
responsible for
• Setting standards (called "National Ambient Air
Quality Standards" or NAAQS) for pollutants considered
harmful to public health or welfare.
• In cooperation with the states, enforcing compliance
with the standards through state implementation plans
(SIPs) and regulations controlling emissions from
automobiles and new industrial sources
The law provides for two types of standards. Primary
standards set limits protective of public health,
including the health of "sensitive" populations such as
asthmatics, children, or the elderly; secondary
standards set limits to protect vegetation, wildlife, and
materials.
EPA has set primary and secondary standards for six
principal pollutants ozone, particulate matter (total
suspended particulates or TSP), carbon monoxide,
nitrogen dioxide, lead, and sulfur dioxide. The deadline
for meeting these standards was December 31, 1987
and many areas were able to meet the standards for all
the pollutants by that date
These are significant achievements. Yet the fact
remains that millions of U.S. citizens still live in areas
with unhealthy levels of major air pollutants (See
Figure) More than 60 major urban areas will not be
able to meet the standards for one or more of the six
pollutants, chiefly those related to mobile
sources—ozone and carbon monoxide. Nevertheless,
the latest measurements of air quality are encouraging
They show that levels of all six pollutants are lower, in
some cases dramatically lower, than they were a
decade ago, and that considerable progress has been
made in reducing air pollution
Summary
This report summarizes data accumulated on the six
NAAQS pollutants between 1977 and 1986 from more
than 4,000 monitoring stations around the country. All
data are from sites monitored for at least eight of those
years. A complete analysis appears in the EPA
publication National Air Quality and Emissions Trends
Report, 1986.
Measurements at selected monitoring sites show
that since 1977:
• Ozone levels have fallen 21 percent Because of a
change in calibration methods between 1978 and 1979,
1
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however, EPA has analyzed the data separately for the
period 1979-1986 During that time, ozone levels
decreased by 13 percent
• Total suspended particulate (TSP) levels have fallen
23 percent
• Carbon monoxide (CO) levels have fallen 32
percent
• Nitrogen dioxide (N02) levels have fallen 14 percent
overall, despite increases from 1976 to 1979, and a
slight increase during 1984
• Lead levels have fallen a dramatic 87 percent
• Sulfur dioxide (S02) levels have fallen 37 percent
How
Air Quality
is Determined
Most of our information on air quality is based on data
from three related indicators
• Measurements of pollutants in the ambient air
• Estimates of total national pollution emissions
• The number of times that air quality standards are
violated
National Trends
of Pollutants
in the Ambient Air
National trends in air quality are derived from routine
measurements recorded over time in areas of high
population exposure and high pollutant concentrations,
as well as other representative areas. Monitoring
stations are operated by state and local government
agencies and by some federal agencies. The trends
calculated for this report were derived by averaging
direct .measurements from monitoring sites, and appear
in the "A" graph shown for each pollutant
National Trends
in Estimated
Total Emissions
Another factor in calculating air quality trends is
estimated total nationwide emissions. These estimates
are based on engineering calculations of the amounts
and kinds of pollutants emitted by automobiles,
factories, and other sources at a given time. Trends for
total emissions appear in the "B" graph shown for each
pollutant
Note: Pollutant concentrations do not correlate
exactly with pollutant emissions. In the first place, three
of the pollutants measured as emissions have different
names from the pollutants they help to form in the
ambient air Thus, emissions of sulfur oxide help to
form the NAAQS pollutant sulfur dioxide, emissions of
oxides of nitrogen contribute to nitrogen dioxide
pollution; and volatile organic compounds (VOCs) and
nitrogen oxides are the principal sources of the
pollutant ozone.
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Secondly, reductions of pollutant concentrations in
the air do not always match reductions of estimated
pollutant emissions For example
• Average ambient concentrations of sulfur dioxide
declined 37 percent from 1977 to 1986, even though
estimated total emissions of sulfur oxides declined only
21 percent This is because sulfur dioxide is monitored
primarily m high-population urban centers, whereas the
major emitters, such as smelters, large power plants,
and other industrial facilities, are located in more rural
areas where there are fewer monitors Another factor
in the difference between concentrations and
emissions reductions is that emitting sulfur oxides
through increasingly higher smokestacks allows
concentrations at ground level to decrease at a faster
rate than emissions
• Ambient carbon monoxide concentrations dropped 32
percent between 1977 and 1986, while estimated total
emissions of carbon monoxide decreased only 26
percent Both figures reflect improvements as a result
of federal emission standards on newer motor vehicles
Since motor vehicles are the largest contributors to
carbon monoxide emissions, it is noteworthy that these
reductions were achieved despite a 24-percent increase
in vehicle miles travelled throughout the United States
during this period Carbon monoxide concentrations,
however, are generally monitored in center city areas
which don't experience significant increases in vehicular
travel once traffic has reached a certain saturation
point
National Trends
in NAAQS Violations
While measurements of air quality and emissions can
show the overall reductions in NAAQS pollutants, actual
improvement in air quality is measured by comparing
recorded ambient air pollution levels against the levels
required by national standards As a reasonable
alternative to listing the findings from thousands of
sites, EPA has charted trends in violations for ozone,
sulfur dioxide, and carbon monoxide National Violation
Trends (NVTs) appear for these pollutants in the "C"
graphs.
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Ozone
Nature and
Sources of the
Pollutant
Health
Effects
Trends in
Ozone Levels
Ozone is the most complex, difficult to control, and
pervasive of the six NAAQS pollutants Many more
Americans live in areas with unhealthy levels of ozone
than any of the other major pollutants, and levels far in
excess of health standards still occur in many heavily
populated areas, including some that have instituted
strict control measures
Unlike other pollutants, ozone is not emitted directly
into the air by specific sources A poisonous form of
pure oxygen, it is created by sunlight acting on nitrogen
oxides and volatile organic compounds (VOCs) in the
air Often, these "precursor" gases are emitted in one
area, but the actual chemical reactions, stimulated by
sunlight and temperature, take place in another
Combined emissions from motor vehicles and
stationary sources can be carried hundreds of miles
from their origins, forming high ozone concentrations
over very large regions
There are literally thousands of sources of these
gases, which can come from gasoline vapors, chemical
solvents, the combustion products of various fuels, and
even common consumer products Sources include not
only large industrial facilities and motor vehicles, but
also small businesses such as bakeries, dry cleaners,
and gas stations
Because it is triggered by sunlight, ozone reaches
peak levels in most parts of the country during the
summer months, particularly when the air is stagnant
for extended periods In 1986, the highest levels of
ozone were recorded in the greater Los Angeles basin
and in other parts of southern California as they have
been for several decades High levels also persist in the
Texas Gulf Coast area, much of the Northeast, and in
several other heavily populated areas
Ozone severely irritates the eyes and the mucous
membranes of the nose and throat, as well as the
mucous membranes leading to the lungs Even in
healthy individuals, it can directly affect lung function,
reducing the ability to perform physical exercise and
leading to chest pain, coughing, wheezing, and
pulmonary congestion It also appears to have effects
on the body's immune system
Length of exposure, frequency of exposure, and level
of concentration are significant factors in determining
these effects, but they are always more severe in
individuals with chronic lung disease, asthma, or
diseases of the heart and circulatory system Studies
also show that ozone in combination with sulfur dioxide
has a greater effect on respiratory functions than does
either pollutant alone
Ozone concentrations nationwide decreased by 21
percent between 1977 and 1986, as measured at 242
sites Because of a change in calibration methods
4
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Typical average for
more polluted locations
Typical average for
cleaner locations
National Trend in Ozone
Concentrations, 1977-1986
(Graph A)
Average ozone concentrations
decreased overall by 21 percent
as measured at 242 sites
between 1977 and 1986
Because of a change in
calibration methods, however,
the period 1979-1986 shows a 13
percent decrease
Note Because sunlight is
crucial to ozone formation, the
length of monitoring for the
"ozone season" varies among
parts of the country, ranging from
12 months per year in the South
and Southwest to a few months
per year in the far North These
factors are taken into account for
calculating purposes
affecting data prior to 1979, levels from 1979 to 1986
were analyzed separately, for that period, ozone
concentrations decreased by 13 percent (The increase
in 1983 is likely due to weather conditions in some
areas of the country being more favorable that year for
ozone formation, such as warmer temperatures )
Estimated VOC emissions for 1979-1986 dropped 20
percent
The most significant trend has been the decline in
ozone formation attributable to mobile sources, which
has occurred despite a 24-percent increase in miles
travelled by vehicles EPA estimates that without
current emission controls on new vehicles and
industrial sources and the vehicle inspection and
maintenance programs in 31 states, VOC emissions
would be 83 percent higher than they are today
Nevertheless, most of the major population centers
do not meet the current ozone standard To bring these
areas into attainment may require extraordinary
measures such as tougher tail-pipe emissions tests,
restrictions on driving and new growth and
development, new or expanded controls on industrial
sources, and even restrictions on the use of some
consumer products
National Trend in VOC
Emissions, 1977-1986
(Graph B)
Estimated VOC emissions
decreased 19 percent from 1977
to 1986, with VOC emissions
from transportation sources
decreasing by 35 percent
Emissions from industrial-process
sources also declined
National Violation Trends for
Ozone, 1979-1986 (Graph C)
The average number of days that
ozone standards were violated
dropped sharply, from about 11
days in 1979 to less than seven
days in 1986 Despite this overall
trend to shorter and fewer
exceedances of the standard,
ozone levels continued to reach
very high levels IP seven' T°-
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Nature and
Sources of the
Pollutant
Total Suspended Particulates (TSP)
Participate matter is the general term for solid or liquid
particles found in the atmosphere Some particles are
large or dark enough to be seen as soot or srnoke,
others are so small they can be detected only with an
electron microscope Because particles originate from a
variety of mobile and stationary sources, their chemical
and physical compositions vary widely depending on
location and time of year
This report summarizes trends based on the
measurements for total suspended particulates, which
include particles ranging from small to relatively large
sizes Recently, however, EFV\ revised the particulate
standards to include only those particles that pose a
risk to health because they are small enough to
penetrate the most sensitive regions of the respiratory
tract Future measurements will be based on these
smaller particulates
During 1986, the highest TSP concentrations were
recorded in the industrialized Midwest and in and
sections of the West Most violations of the TSP
standards are caused by activities that generate soot
and dust, and by industrial emissions as well as natural
dust
Health
Effects
Inhaled particles can irritate or damage the respiratory
system, causing acute respiratory illnesses much as
gaseous pollutants do, and prolonged inhalation of
certain particles may increase the number and seventy
of chronic respiratory diseases In addition, metal,
sulfate, and organic chemical particulates may
specifically contribute to other adverse health effects
Trends
in TSP Levels
Average composite TSP levels decreased by 23 percent
between 1977 and 1986, as measured at 1,435 sites
Estimated TSP emissions declined overall by 25 percent
during the same period These measurements are
considered valid despite technical problems with filters
used from 1979 through 1981, and are primarily
attributable to reductions in industrial emissions
nationwide through use of new control equipment and
reduced coal-burning by electric utilities.
The decrease in TSP levels and TSP emissions were
similar, although ambient levels are not expected to
improve proportionally with reductions in particulate
emissions Levels can be influenced by factors such as
dust from construction and other activities, as well as
by gases such as sulfur dioxide that are transformed
into particles in the atmosphere The other major factor
affecting TSP levels is precipitation, which reduces
reentramment of particles and washes particulates out
of the air
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100
Typical average for
more polluted locations
National Trend in TSP
Concentrations, 1977-1986
(Graph A)
Average TSP concentrations
decreased by 23 percent
between 1977 and 1986, as
measured at 1,435 sites Yearly
changes between 1978 and 1982
can be attributed in part to a
change in measurement method
National Trend in TSP
Emissions, 1977-1986
(Graph B)
Emissions of particulates
decreased by 25 percent
between 1977 and 1986, largely
because of emission reductions
in industrial processes
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Carbon Monoxide
Nature and
Sources of the
Pollutant
Carbon monoxide is a colorless, odorless, poisonous
gas formed when carbon in fuels is not burned
completely Its major source is motor vehicle exhaust,
which contributes more than two-thirds of all emissions
nationwide In cities or other areas with heavy traffic
congestion, however, automobile exhaust can cause as
much as 95 percent of all emissions, and carbon
monoxide concentrations can reach very high levels
Other sources include industrial processes and
non-transportation fuel combustion
Despite an overall downward trend in concentrations
and emissions of carbon monoxide, many metropolitan
areas still experience higf levels of the pollutant During
1985, the highest levels were recorded in large urban
areas with heavy traffic congestion and m high-altitude
areas of the Far West and Rocky Mountains
Health
Effects
Carbon monoxide binds chemically to hemoglobin, the
substance in the blood that carries oxygen to the cells,
and thus reduces the amount of oxygen available to the
body tissues The amount of oxygen reduction depends
on amount of air inhaled, carbon monoxide
concentrations, and length of exposure
Carbon monoxide also weakens heart contractions,
reducing the amount of blood pumped This in turn
reduces the amount of oxygen available to the muscles
and organs Such oxygen depletion impairs the
functioning even of healthy individuals, and can be life
threatening to those with heart disease Even at
relatively low concentrations, carbon monoxide can
affect mental functioning, visual acuity, and alertness
Cigarette smokers, those living at high altitudes, and
persons suffering from anemia, emphysema, and other
lung diseases are likely to be more susceptible to the
effects of carbon monoxide
Trends in Carbon
Monoxide Levels
Carbon monoxide concentrations decreased 32 percent
between 1977 and 1986, as measured at 182 urban
sites Overall, estimated carbon monoxide emissions
decreased 26 percent during the same period,
however, estimated emissions from motor vehicle
exhaust—the major source of carbon monoxide
emissions—declined by 34 percent These emissions
reductions occurred even with an estimated increase of
24 percent in vehicle miles traveled during the same
time The difference between concentration reductions
and emissions reductions can be affected by the
placement of monitors, which typically are located in
areas of chronic traffic problems In such areas, vehicle
miles travelled tend to remain constant, while
emissions decline as control technology improves The
result is that concentrations monitored at these
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locations may show greater reductions than do
estimated emissions
Nevertheless, the declines in both concentrations and
emissions show that federal emissions-control
requirements for new vehicles have had a major impact
in controlling carbon monoxide releases
Typical average for
more polluted locations
fe Typical average for
° cleaner locations
77 78 79
81 82 83 84
National Trend in Carbon
Monoxide Concentrations,
1977-1986
(Graph A)
Average concentrations of carbon
monoxide declined 32 percent, as
measured at 182 urban sites
between 1977 and 1986 This
improvement reflects the impact
of emissions control standards
for new cars since the beginning
of the monitoring period, as well
as the impact of other measures
to control carbon monoxide
emissions in traffic-saturated
areas Some improvement also
may be due to meteorological
conditions or changes in the
vehicle mix at some locations
"S5
a> Transportation
National Trend in Carbon
Monoxide Emissions,
1977-1986
(Graph B)
Total carbon monoxide emissions
decreased 26 percent from 1977
to 1986, but emissions from
motor vehicle exhaust decreased
34 percent This decrease took
place despite an increase of 24
percent in vehicle miles traveled
uo
National Violation Trends for
Carbon Monoxide, 1977-1986
(Graph C)
The average number of times
that carbon monoxide standards
were violated dropped sharply
from about 21 days in 1977 to
about two days in 1986 Despite
the overall decline, however,
some areas exceed the standard
a far higher number of times than
the average suggests
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Nature and
Sources of the
Pollutant
Nitrogen Dioxide
Nitrogen dioxide belongs to a family of poisonous,
highly reactive gases called nitrogen oxides These
gases form when fuel is burned at high temperatures
They come principally from motor vehicle exhaust
and stationary sources such as electric utility and
industrial boilers
A suffocating, brownish gas, nitrogen dioxide is a
strong oxidizing agent that reacts with water to form
corrosive nttnc acid It also plays a major role in the
atmospheric reactions that produce ozone
Los Angeles, California, was the only urban area that
recorded violations of the health standards for nitrogen
dioxide during 1986 Monitoring from all other areas
showed levels of the pollutant that were below the
standards
Health
Effects
Nitrogen oxides can irritate the lungs, cause bronchitis
and pneumonia, and lower resistance to respiratory
infections such as influenza. The effects of short-terrn
exposures are still under study, but continued or
frequent exposure to concentrations higher than those
normally found in the ambient air can cause pulmonary
edema
Trends in
Nitrogen Dioxide
Levels
Despite some yearly fluctuations, average nitrogen
dioxide concentrations as measured at 111 sites
decreased by 14 percent between 1977 and 1986 Total
estimated emissions of nitrogen oxides declined by
eight percent, although emissions from motor vehicles
dropped by 13 percent This decline occurred even
though vehicle miles traveled increased by 24 percent
during the same time
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££. Transportation
15 o
77 78 79 80
National Trend in Nitrogen
Dioxide Concentrations,
1977-1986
(Graph A)
Nitrogen dioxide does not
present a significant air quality
problem at this time for most
areas of the country With some
fluctuations, average
concentrations of nitrogen
dioxide measured at 111 sites
decreased by 14 percent from
1977 to 1986
National Trend in Nitrogen
Oxide Emissions, 1977-1986
(Graph B)
Estimated nitrogen oxide
emissions declined by eight
percent from 1977 to 1986, this
decline was accomplished
against a 24-percent increase in
vehicle miles traveled during the
same time
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Sources and
Nature of the
Pollutant
Lead
Non-ferrous smelters, battery plants, and lead additives
in gasoline are the major sources of lead emissions to
the atmosphere, of these, leaded gasoline is the most
significant source, contributing 38 percent of total ead
emissions in 1986, down sharply from 69 percent n
1985
During 1986, the highest concentrations of lead were
found in locations that contain non-ferrous smelters or
other stationary sources of lead emissions Most such
sources are located in the Midwestern United States
Health
Effects
Lead accumulates in the body in blood, bone, and soft
tissue Because it is not readily excreted, lead also
affects the kidneys, nervous system, and blood-forming
organs Ingesting excessive amounts of lead may cause
neurological impairments such as seizures, mental
retardation, and/or behavioral disorders, infants and
children in particular are susceptible to central nervous
system damage Recent studies have also shown that
lead may be a factor in high blood pressure and
subsequent heart disease
Trends in
Lead Levels
Average ambient concentrations of lead decreased by
87 percent between 1977 and 1986, as measured at 82
urban sites Measurements for the period 1982 to 1986
at an additional 326 sites in 43 states showed a 68
percent reduction in ambient lead levels Estimated
emissions of lead for the same periods dropped by 94
percent and 84 percent, respectively
Although controls on stationary sources such as
smelters and battery plants have also helped, these
reductions are mainly the result of two factors stricter
controls on automobile emissions, beginning with the
1975 model-year, and reductions in the amount of lead
permitted in leaded gasoline to the current limit of
0.10 grams per gallon
Since 1975, EPA has increasingly restricted
automobile emissions As a result, all new cars since
then have been equipped with catalytic converters,
muffler-like devices that reduce emissions of
hydrocarbons, carbon monoxide, and nitrogen oxides
Because lead destroys the effectiveness of these
converters, the use of unleaded gasoline has increased
dramatically, with corresponding decreases in lead
emissions from exhaust EPA has moved to accelerate
this progress by phasing out and ultimately by banning
all lead in gasoline during the1980's The overall eflect
of these control programs has been a major reducton
in the amount of lead in the environment
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Typical average for
re polluted locations
Typical aver
for cleaner locations
100
50
o>
Transportation
Fuel combustion
' Industrial processes
National Trend in Lead
Concentrations, 1977-1986
(Graph A)
Average lead concentrations
measured at 82 urban sites
between 1977 and 1986
decreased by 87 percent This
improvement was due mainly to
two related factors Because
post-1975 cars run on unleaded
gasoline, the use of leaded gas
has declined sharply, and with it,
the emission of lead in
automobile exhausts Secondly,
the amount of lead in leaded gas
itself has been reduced
National Trend in Lead
Emissions, 1977-1986
(Graph B)
Estimated lead emissions
decreased 94 percent from 1977
to 1986 Most of this reduction
came from decreases in the use
of leaded gas, as well as
decreases in the amount of lead
in leaded gas Emissions were
also reduced from fuel
combustion and industrial
processes
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Sulfur Dioxide
Nature and
Sources of the
Pollutant
Health
Effects
Sulfur dioxide belongs to the family of sulfur oxtde
gases These gases are formed from the burning of
sulfur-containing fuel, mainly coal and oil, and also from
metal smelting and other industrial processes
Most sulfur dioxide monitoring stations are located in
urban areas During 1986, the highest monitored
concentrations of the pollutant were primarily recorded
in industrial communities of the Midwest, although
most urban areas were well within the NAAQS
standards High concentrations of sulfur dioxide may
also be occurring in many other rural areas near
smelters, power plants where there are no monitoring
stations, or industrial complexes
Sulfur oxides are associated with many types of
respiratory diseases, including coughs and colds,
asthma, bronchitis, and emphysema High levels of
sulfur oxides obstruct breathing, an effect that is
enhanced by the presence of high concentrations of
participate matter, and studies have found mcreasec
death rates from high sulfur oxide levels among people
with existing heart and lung disease Lower levels also
cause a noticeable increase in acute and chronic
respiratory diseases
Sulfur dioxide reacts in the atmosphere to form other
compounds such as sulfunc acid, sulfates, and sulfites
Although these may be even more irritating to the
respiratory system than sulfur dioxide, not enough is
known about them at present for EPA to control them
specifically Controlling sulfur dioxide, however,
generally lowers the concentrations of other sulfur
compounds as well.
Trends in Sulfur
Dioxide Levels
Average concentrations of sulfur dioxide measured at
302 sites decreased by 37 percent between 1977 arid
1986 Estimated emissions of sulfur oxides decreased
by 21 percent during the same time
Sulfur oxides are emitted mainly by electric utilities
that burn coal or oil. Emissions reductions were due
mainly to new controls at coal-fired generating stations,
to use of lower-sulfur coal, and to decreased use of
high-sulfur fuel oil. Emissions were also controlled from
nonferrous smelters and from sulfunc acid
manufacturing plants.
With the exception of some daily violations in a few
urban areas, almost all urban monitoring sites had
achieved the standard. Violations do still occur in the
vicinity of smelters and some large power plants in
rural areas.
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030 NAAQS
Typical average for
more polluted locations
77 78 79
77 78 79
National Trend in Sulfur
Dioxide Concentrations,
1977-1986
(Graph A)
Average sulfur dioxide
concentrations measured at 302
sites declined by 37 percent
between 1977 and 1986 This
improvement resulted mainly
from: reductions in average
sulfur content of fuels burned,
installation of flue-gas control
equipment at coal-fired
generating plants; reduced
emissions from industrial
processing facilities such as
smelters and sulfunc acid
manufacturing plants; and the
use of cleaner fuels in residential
and commercial burners
National Trend in Emissions
of Sulfur Oxides, 1977-1986
(Graph B)
Estimated sulfur oxide emissions
declined 21 percent between
1977 and 1986 One reason for
this decline is that most
high-sulfur fuel use has shifted
away from urban sites—where
most of the monitors are
located—to rural areas with
fewer recording stations. At
urban sites, however, sulfur
oxide emissions have declined
proportionately with
concentrations as a result of
energy conservation measures
and the use of low-sulfur fuel
National Violation Trends for
Sulfur Dioxide, 1977-1986
(Graph C)
The average number of days that
sulfur dioxide standards were
violated dropped from about 0 9
days per year in 1977 to 0 02
days in 1986 Essentially, the
standard is being achieved
nationwide
15
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Other Major Air Quality Issues
Although pollutants such as carbon monoxide, ozone,
TSP, and the sulfur and nitrogen oxides have been the
primary focus of control programs since 1970,
Americans have become increasingly aware of other
serious air quality problems
Toxic
Air Pollutants
Acid
Precipitation
The Clean Air Act requires special controls, called
NESHAPS (National Emissions Standards for Hazardous
Pollutants), for pollutants so toxic that even small
emissions are dangerous Thus far, EPA has established
NESHAPS for six substances: arsenic, asbestos,
benzene, berylium, mercury, and vinyl chloride
Some toxic substances, however, get into the air not
from normal industrial emissions, but because of
sudden, accidental releases The danger of such
releases was vividly illustrated by the catastrophic
explosion of a chemical plant in Bhopal, India, in 1985,
and by several incidents in the United States Because
even small amounts of toxics can threaten the health of
nearby people, EPA has focused on determining the
health effects of such pollutants and on establishing the
most feasible measures for controlling them
Acid precipitation refers to a chain of complex
processes that starts with emissions from utilities,
industry, and motor vehicles, as well as from natural
sources When these emissions interact with sunlight
and vapors in the air, they change into acidic
compounds that can be transported long distances to
other areas and subsequently deposited on the earth's
surface with ram or snow, or as dry compounds These
deposits may harm fish and other wildlife, lakes,
forests, crops, and manmade materials and objects
such as buildings and statues
While certain aspects of the acid rain process are
generally accepted by the scientific community, others
are uncertain Unanswered questions include the
geographic range of damage from acid ram, the origin
of the pollutants involved in its formation, and the rate
at which acidification takes place The role of sulfur
emissions in acid rain has been studied most, but other
pollutants, including oxides of nitrogen, are also known
contributors
At present, EPA believes there is not enough
knowledge about acid precipitation to institute specific
control measures beyond those in effect for the six
NAAQS pollutants However, an extensive research
program is underway to help determine the specific
causes and effects of acid ram, and new controls could
be imposed based on its findings
Indoor Ope °ftne newest concerns about air quality involves
Air Pollution indoor pollutants. Recent studies have shown that
people are more exposed to chemical pollutants in their
own homes than they are to industrial emissions
16
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outdoors The reasons are simple' people spend more
time indoors, and pollutants do not disperse as easily
inside as they do outdoors, especially in newer
buildings that have been tightly insulated to conserve
energy. These indoor pollutants can include radon gas,
asbestos, formaldehyde, and several volatile organic
compounds, as well as tobacco smoke, certain building
materials, pesticides, cleaning agents, and a host of
commercial and consumer products.
Of these pollutants, those considered most
threatening are asbestos, radon gas, and formaldehyde,
and they are being addressed by a wide range of
regulatory and non-regulatory actions at the federal,
state, and local levels.
Asbestos is the name for a group of natural minerals
that separate into strong, very fine fibers The fibers are
heat-resistant and extremely durable, and these
qualities have made asbestos very useful in
construction and industry.
The properties that give asbestos its usefulness,
however, are also linked to serious health effects,
among which are asbestosis, lung cancer, and
mesothelioma Asbestos' tiny fibers can remain
suspended in the air for long periods of time, and
remain in the body when inhaled Because each
exposure can increase the burden of asbestos in the
body, federal control programs are aimed principally at
protecting school children, persons whose work
involves exposure to asbestos, and other persons in
exposure situations EPA already has prohibited most
asbestos use, and is currently considering a total ban
Federal, state, and local programs are also seeking to
reduce exposure to radon gas Radon is a colorless,
odorless radioactive gas that occurs naturally in soil gas,
underground water, and outdoor air at various levels
throughout the United States. Prolonged exposure to
high levels of radon decay products has been
associated with increased risk of lung cancer
Radon gas from soil enters homes through exposed
soil in crawl spaces, through cracks and openings in
slab-on-grade floors, and through below-grade walls and
floors When radon-containing water is heated or
agitated—as in a shower or washing machine—it, too,
can give off small quantities of radon. (Radon in the
outside air is diluted to such low concentrations that it
does not present a health hazard )
EPA provides technical assistance to states to help
communities with severe radon gas problems The
Agency also has developed training, demonstration, and
public information programs to support its technical
assistance efforts
While EPA has no regulatory program for
formaldehyde, other federal agencies have assessed
the risks posed by its presence in building materials
and have concluded that it probably increases the risk
of cancer when inhaled indoors
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Global Air Quality Problems
Finally, there are growing concerns in the international
community about two global phenomena that could
seriously affect the health and welfare of future
generations These are the depletion of the
stratospheric ozone layer, and global climate change
brought about by the ever-increasing concentrations of
air pollutants in the earth's atmosphere.
Depletion of the
Stratospheric
Ozone Layer
Global
Climate Change
Stratospheric ozone (not to be confused with ozone at
ground level, where it is a serious pollutant) protects
Earth's inhabitants and ecosystems by shielding them
from the sun's harmful ultraviolet radiation Since the
early 1970s, scientists have predicted that emissions of
chlorofluorocarbons (CFCs) and other chemicals would
ultimately begin to deplete this essential layer In 1978,
EPA banned the use in this country of CFCs in
nonessential aerosol propellants, at that time the largest
source of CFC emissions Emissions of CFCs from other
sources, however, such as refrigerants, air conditioners,
and various solvents, have continued to increase
Worldwide CFC emissions also have increased, in part
because many countries still use CFCs in aerosol sprays
and spray products
Most scientific researchers are convinced that global
CFC emissions must be reduced substantially to avoid
depletion of the stratospheric ozone layer and its
consequences for the planet Such depletion, with
subsequent increases in ultraviolet radiation, would
most likely lead to severe and widespread health
problems, ranging from increased cases of skin cancer
and eye cataracts to suppression of immune system
functioning Ozone depletion may also accelerate the
formation of ground-level pollutants and damage
agriculture, plants, and fragile aquatic ecosystems
During late 1986, concern about these effects
heightened when a very large seasonal depletion of
ozone was discovered in the atmosphere over
Antarctica; a year later, ozone levels had dropped even
further to the lowest levels ever observed there since
measurements began more than a decade ago These
findings came just as more than 60 nations under the
auspices of the United Nations Environment
Programme were negotiating an agreement to curtail
CFC production sharply The final agreement, which
includes all the world's major CFC producers, freezes
CFC production levels in the short run, and in the future
will cut worldwide production by half
Increased economic and industrial activity have produced
ever greater concentrations of carbon dioxide, CFCs,,
methane, nitrous oxides, and other trace gases in Earth's
atmosphere In a phenomenon known as the "greenhouse
effect," these gases trap heat in the atmosphere, causing
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world temperatures to rise—an effect likely to alter the
environment.
While difficult to predict with certainty, the economic
disruptions and environmental dislocations of climate
change could devastate whole regions of the planet Sea
levels would certainly rise, threatening major coastal
population centers with severe flooding; coastal wetlands
and other fragile habitats that incubate critical fish and
shellfish species would be wiped out Agriculture and
forests would also suffer from marked change in world
temperatures or climate patterns. The timetables for
many of these prospective changes cannot be predicted
with certainty Many contributing factors, such as the
role of agricultural emissions, are still far too unclear
One known factor, however, is the rapidly
accelerating destruction of the world's tropical ram
forests These forests absorb the greenhouse pollutants
and give off pure oxygen back into the atmosphere.
They also play an indispensable role m maintaining the
stability of global weather patterns Yet if current rates
of destruction persist, most of these forests will be
gone within the next three decades, certainly within the
next hundred years.
There is a growing concensus that those problems
must be addressed as quickly as possible Most
scientists believe that by the time visible manifestations
of these problems appear, it may well be too late to
reverse them Measures to avoid them may include
international controls, massive reforestation programs,
and greatly increased use of non-fossil fuels
At the request of Congress, EPA is preparing two
reports on global climate change These reports will
focus on the effects of climate change and on
strategies to stabilize the atmospheric concentrations of
trace gases.
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