United States
Environmental Protection
Agency
Office ;of Air Quality
Planning and Standards
Research Triangle Park, NC 27711
September 1995
EPA-454/F-95-003
& EPA Air Quality Trends
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AIR
QUALITY
TRENDS
The overall quality of our nation's air continues to improve.
This brochure highlights the United States Environmental
Protection Agency's (EPA's) most recent analysis of trends
in air pollution emissions and air quality concentrations.
Highlights include:
• Emissions of the six principal pollutants increased
significantly between 1900 and 1970. However, since
1970 (the year the Clean Air Act was signed into law),
emissions of all but one of these pollutants have
declined, in some cases dramatically.
• Economic growth and environmental protection can
go hand-in-hand. Between 1970 and 1994, total
emissions of the six principal pollutants decreased
while gross domestic product, population, and total
vehicle miles traveled all increased significantly.
• Between 1985 and 1994, air quality continued to
improve as monitored concentrations of each of the
six pollutants declined.
• Short-term trends between 1993 and 1994 showed
slight increases in monitored concentration levels of
nitrogen dioxide and carbon monoxide. Monitored
concentration levels of lead, ozone, and sulfur dioxide
continued to decrease, while particulate matter
remained unchanged. During this same 1 -year period,
emissions of carbon monoxide, nitrogen oxides,
particulate matter, and volatile organic compounds also
increased.
• Despite the improvements to date in air quality since
1970, approximately 62 million people lived in
counties where air quality levels exceeded the national
air quality standards for at least one of the six
principal pollutants in 1994.-
• Toxic air emissions from sources such as organic
chemical plants, oil refineries, dry cleaning operations,
and aerospace manufacturing are decreasing as
federal air toxic regulations take effect.
Background
Air pollution comes from many different sources.
"Stationary sources" such as factories, power plants, and
smelters — "mobile sources" including cars, buses,
planes, trucks and trains — and "natural sources" such as
wildfires, windblown dust and volcanic eruptions —
contribute to air pollution in the United States. The Clean
Air Act provides the principal framework for State, tribal,
national and local efforts to protect air quality. Under the
Clean Air Act, which was last amended in 1990, EPA has a
number of responsibilities, including:
• Setting National Ambient Air Quality Standards
(NAAQS) for pollutants considered harmful to public
health and the environment.
• Ensuring that these air quality standards are met or
attained (in cooperation with States) through national
standards and strategies to control air emissions from
sources such as automobiles and factories.
• Ensuring that sources of toxic air pollutants are well
controlled.
The Clean Air Act established two types of national air
quality standards. Primary standards set limits to protect
public ihealth, including the health of "sensitive"
populations such as asthmatics, children, and the elderly.
Secondary air quality standards set limits to protect public
welfare, including protection against decreased visibility,
damage to animals, crops, vegetation, and buildings.
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EPA has set national air quality standards for six principal
pollutants (referred to as "criteria" pollutants): carbon
monoxide (CO), lead (Pb), nitrogen dioxide (NC>2), ozone (O3),
partteulate matter (PM-10), and sulfur dioxide (SO2). [Note:
The pollutant ozone is not emitted directly to the air, but is
formed by sunlight acting on emissions of nitrogen oxides
(NOX) and volatile organic compounds (VOC).
For the past 22 years, EPA has examined air pollution trends
of each of the six principal pollutants in this country. EPA
examines changes in air pollution levels over time and
summarizes the current air pollution status. Each year, EPA
publishes a comprehensive technical document titled
"National Air Quality and Emissions Trends Report." The
1994 report is scheduled for publication in late October
1995. This brochure is a summary of trends in the nation's
air quality for the last 10 years.
Emissions of some particulate matter and some volatile
organic compounds, as well as other chemicals, may be
more dangerous and have been designated as toxic air
pollutants. The Clean Air Act contains requirements for
reducing air toxics. EPA has responsibility for developing
regulations to control toxic air pollutants from industrial
factories and other sources. This brochure also provides an
overview of trends in toxic air pollution, sources of toxic air
emissions and the process EPA has developed for controlling
toxic air pollution.
Long-Term Emissions Trends
Before the Clean Air Act was signed into law in 1970, the
20th century witnessed a significant, continued increase in
air pollution levels. Although efforts made during the 1960's
by State and local air pollution agencies in particular polluted
cities in the Northeast did help reduce pollution in some local
areas, emissions continued to increase on a national level.
Between 1900 and 1970, emissions of nitrogen oxides
Increased 690 percent, volatile organic compounds
increased 260 percent, and sulfur dioxide increased 210
percent. Emissions of these pollutants have decreased
significantly since the 1970 Clean Air Act was passed.
Without passage of the Clean Air Act in 1970, emissions
would have continued to increase as illustrated in the charts.
Without the passage of the Clean Air Act in 1970,
emissions would have increased at a higher rate.
Without the passage of the Clean Air Act in 1970,
emissions would have continued to increase.
Without the passage of the Clean Air Act in 1970,
emissions would have continued to increase.
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Summary of Air Quality and Emissions Trends
The 1994 Trends Report tracks two kinds of trends: air
concentrations based on actual measurements of
pollutant concentrations in the air at selected sites
throughout the country, and emissions based on
engineering estimates of the total tonnage of these
pollutants released into the air annually.
Each year, EPA gathers and analyzes air quality
concentration data from more than 4,000 monitoring
stations around the country. Monitoring stations are
operated by State, tribal, and local government agencies
as well as some federal agencies, including EPA. Trends
for 1994 are derived by averaging direct measurements
from these monitoring sites. During the last 10 years
(1985 through 1994), air quality has continued to improve
as shown in the chart below. The most notable
improvements were an 86 percent decrease in lead
concentrations and a 28 percent decrease in carbon
monoxide concentrations. Improvements in measured
concentrations were also noted for the other principal
pollutants including nitrogen dioxide, ozone, particulate
matter and sulfur dioxide during this timeframe.
PERCENT DECREASE IN CONCENTRATIONS
(1985-1994)
CO
Lead
N02
Ozone
PM-10
S02
28%
86%
12%
20%
25%
developments, fuel consumption, vehicle miles of travel,
and other activities that cause air pollution. Emissions
trends also reflect changes in air pollution regulations and
installation of emissions controls. Over the last 10-year
period (1985 through 1994), air emissions have shown
improvement (decreased) for all pollutants except nitrogen
oxides as shown in the chart below. The slight emissions
increase (3 percent) observed for nitrogen oxides can be
attributed to increased processing or manufacturing by
industry and increased amounts of fuels burned by electric
utility plants.
PERCENT DECREASE IN EMISSIONS
(1985-1994)*
CO
Lead
VOC
PM-10
S02
,15%
75%
10%
12%
9%
*
Unlike the other pollutants, NOX emissions increased 3 percent.
EPA estimates nationwide air emissions trends based on
engineering calculations of the amounts and types of
pollutants emitted by automobiles, factories, and other
sources. Emission trends are based on many factors,
including the level of industrial activity, technology
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As illustrated in the following charts, since
1970, the combined emissions of the six
principal pollutants decreased 24 percent,
while U.S. population increased 27 percent,
vehicle miles traveled increased 111 percent,
and gross domestic product increased 90
percent. These dramatic improvements in
emissions and air quality occurred
simultaneously with significant increases in
economic growth and population. The
improvements are a direct result of effective
implementation of clean air laws and
regulations.
Comparison of 1970 and 1994 Emissions
(24% decrease for all pollutants)
Million Tons/Year Thousand Tons/Year
30
— 50
NOX
(+14%)
VOC
(-24%)
PM-10
(-78%)
S02
(-32%)
Although some areas of the United States are experiencing air quality
problems, overall air quality continues to show improvement, despite
extensive national growth.
Total U.S. Population Vehicle Miles Traveled Gross Domestic Product
, ' (27% increase, 1970-94)
(90% increase, 1970-94
(111% increase, 1970-94)
rfaam&it ..... srsiiaai mfratOHoninivetirwiqMnHnrwiMCWmhmainiri
200 250 300 0 500 1000 1500 2000 2500
0 --.50 100 t50
le Vehicle Miles Traveled (Billions Miles Gross Domestic Product (Billions Dollars)
"
Since 1970, the United States has experienced extensive national growth.
PM-10
AnyNAAQS
Lead
Ozone
10 20 30 40 50 60 70
Millions of People
Despite great progress in air quality improvement, in
1994 approximately 62 million people nationwide lived
in counties with air quality levels above the primary
national air quality standards.
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Six
PRINCIPAL
POLLUTANT
CARBON MONOXIDE (CO)
Nature and Sources of the Pollutant: Carbon
monoxide is a colorless, odorless, poisonous gas formed
when carbon in fuels is not burned completely. It is a by-
product of motor vehicle exhaust, which contributes more
than two-thirds of all CO emissions nationwide. In cities,
automobile exhaust can cause as much as 95 percent of
all CO emissions. These emissions can result in high
concentrations of CO, particularly in local areas with heavy
traffic congestion. Other sources of CO emissions include
industrial processes and fuel combustion in sources such
as boilers and incinerators. Despite an overall downward
trend in concentrations and emissions of CO, some
metropolitan areas still experience high levels of CO.
Health and Other Effects: Carbon monoxide enters
the bloodstream and reduces oxygen delivery to the
body's organs and tissues. The health threat from CO is
most serious for those who suffer from cardiovascular
disease. Healthy individuals are also affected, but only at
higher levels of exposure. Exposure to elevated CO levels
is associated with visual impairment, reduced work
capacity, reduced manual dexterity, poor learning ability,
and difficulty in performing complex tasks. EPA's health-
based national air quality standard for CO is 9 parts per
million (ppm) [measured over 8 hours].
Trends in Carbon Monoxide Levels: Long-term
improvements continued between 1985 and 1994.
National average CO concentrations decreased 28 percent
while CO emissions decreased 15 percent. Long-term air
quality improvement in CO occurred despite a 32 percent
increase in vehicle miles traveled in the U.S. during the
past TO years. Between 1993 and 1994, national average
CO concentrations increased 2 percent while total CO
emissions increased 4 percent. Transportation sources
now account for 78 percent of the nation's total CO
emissions. The observed increase in CO emissions
between 1993 and 1994 is attributed to two sources:
transportation emissions (up 2%) and wildfire emissions
(up 160%).
CO CONCENTRATION TRENDS
15
1985-94: 28% decrease
1993-94: 2% increase
90% of monitor sites had
concentrations less than this line
1985 1986 1987 1988 1989 1990 1991 1992 1993 1994
CO EMISSIONS TRENDS
Fuel Combustion E3 Industrial Processing
Transportation Q Miscellaneous
20
•-0
1985 1986 1987 1988 1989 1990 1991 1992 1993 1994
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LEAD (Pb)
Nature and Sources of the Pollutant: Smelters and
battery plants are the major sources of the pollutant "lead" in
the air. The highest concentrations of lead are found in the
vicinity of nonferrous smelters and other stationary sources of
lead emissions.
Health Effects: Exposure to lead mainly occurs through
inhalation of air and ingestion of lead in food, paint, water,
soil, or dust. Lead accumulates in the body in blood, bone,
and soft tissue. Because it is not readily excreted, lead can
also affect the kidneys, liver, nervous system, and other
organs. Excessive exposure to lead may cause anemia,
kidney disease, reproductive disorders, and neurological
impairments such as seizures, mental retardation, and/or
behavioral disorders. Even at low doses, lead exposure is
associated with changes in fundamental enzymatic, energy
transfer, and other processes in the body. Fetuses and
children are especially susceptible to low doses of lead, often
suffering central nervous system damage or slowed growth.
Recent studies show that lead may be a factor in high blood
pressure and subsequent heart disease in middle-aged white
mates. Lead may also contribute to osteoporosis in post-
menopausal women. EPA's health-based national air quality
standard for lead is 1.5 micrograms per cubic meter (|j.g/m3)
[measured as a quarterly average].
Trends In Lead Levels: Between 1985 and 1994, average
lead concentrations in urban areas throughout the country
decreased 86 percent while total lead emissions decreased
LEAD CONCENTRATION TRENDS
1.5
NAAQS
1985-94: 86% decrease
1993-94: 20% decrease
Q 5 L 90% of monitor sites had concentrations
less than this line
Average for all sites
1985 1986 1987 1988 1989 1990 1991 1992 1993 1994
LEAD EMISSIONS TRENDS
25,000 -
20,000
I Fuel Combustion H Industrial Processing
I Transportation
1985-94: 75% decrease
1993-94: No Change
1985 1986 1987 1988 1989 1990 1991 1992 1993 1994
75 percent. These reductions are a direct result of the use of
unleaded gasoline in automobiles. The large reduction in lead
emissions from transportation sources has changed the
nature of the air quality problem for lead in the U.S.
Violations of the lead air quality standard still occur, but tend
to occur near large industrial complexes such as lead
smelters. Between 1993 and 1994, lead emissions remained
unchanged while national average lead concentrations
decreased 20 percent.
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NITROGEN DIOXIDE (NO2)
Nature and Sources of the Pollutant: Nitrogen
dioxide belongs to a family of highly reactive gases called
nitrogen oxides (NOX). These gases form when fuel is
burned at high temperatures, and come principally from
motor vehicle exhaust and stationary sources such as
electric utilities and industrial boilers. A suffocating,
brownish gas, nitrogen dioxide is a strong oxidizing agent
that reacts in the air to form corrosive nitric acid, as well as
toxic organic nitrates. It also plays a major role in the
atmospheric reactions that produce ground-level ozone (or
smog).
Health and Other Effects: Nitrogen dioxide can irritate
the lungs and lower resistance to respiratory infections
such as influenza. The effects of short-term exposure are
still unclear, but continued or frequent exposure to
concentrations that are typically much higher than those
normally found in the ambient air may cause increased
incidence of acute respiratory illness in children. ERA'S
health-based national air quality standard for NC>2 is 0.053
ppm (measured as an annual average). Nitrogen oxides
are important in forming ozone and may affect both
terrestrial and aquatic ecosystems. Nitrogen oxides in the
air are a potentially significant contributor to a number of
environmental effects such as acid rain and eutrophication
in coastal waters like the Chesapeake Bay. Eutrophication
occurs when a body of water suffers an increase in
nutrients that reduce the amount of oxygen in the water,
producing an environment that is destructive to fish and
other animal life.
NO2 CONCENTRATION TRENDS
0.06
0,05
0.04
0.03
0.02
0.01 -
1985 1986 1987 1988 1989 1990 1991 1992 1993 1994
NOX EMISSIONS TRENDS
30
25
20
15
10
I Fuel Combustion E3 Industrial Processing
§ Transportation 0 Miscellaneous
1985-94: 3% increase
1993-94: 1% increase
Trends in Nitrogen Dioxide Levels: Nationally, annual
NC>2 concentrations remained relatively constant through-
out the 1980's, followed by decreasing concentrations in
the 1990's. Average NC>2 concentrations in 1994 were 9
percent lower than the levels recorded in 1985. National
total NOX emissions increased 3 percent since 1985. The
two primary sources of the NOX emissions in 1994 were
fuel combustion (50 percent) and transportation (45
percent). Since 1985, emissions from highway vehicles
decreased 7 percent while fuel combustion emissions
1985 1986 1987
1990 1991 1992 1993 1994
increased 8 percent. Between 1993 and 1994, NOX
emissions and NO2 concentrations increased. The
emissions increases are attributed to increased emissions
from off-highway vehicles and wildfires. Even with an
increase in NOX emissions, 1994 is the third year in a row
that all monitoring locations across the nation, including
Los Angeles, met the federal NC>2 air quality standard.
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OZONE CONCENTRATION TRENDS
it^lOZONE(°3)
HI Nature and Sources of the Pollutant: Ground-level ozone
(the primary constituent of smog) is the most complex, difficult
to control, and pervasive of the six principal pollutants. Unlike
other pollutants, ozone is not emitted directly into the air by
specific sources. Ozone is created by sunlight acting on NOX
and VOC emissions in the air. There are literally thousands of
sources of these gases. Some of the more common sources
include gasoline vapors, chemical solvents, combustion
products of various fuels, and consumer products. They can
originate from large Industrial facilities, gas stations, and small
businesses such as bakeries and dry cleaners. 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. Approximately 50 million people lived in counties with
air quality levels above EPAfe health-based national air quality
standard in 1994. The highest levels of ozone were recorded in
Los Angetes. High levels also persist in other heavily populated
areas Ike the Texas Gulf Coast and much of the Northeast.
Health and Other Effects: Scientific evidence indicates that
ground-level ozone not only affects people with impaired
respiratory systems (such as asthmatics), but healthy adults and
children as well. Exposure to ozone for 6 to 7 hours, even at
relatively tow concentrations, significantly reduces lung function
and induces respiratory inflammation in normal, healthy people
during periods of moderate exercise. It can be accompanied by
symptoms such as chest pa'n, coughing, nausea, and
pulmonary congestion. Recent studies provide evidence of an
association between elevated ozone levels and increases in
hospital admissions for respiratory problems in several U.S.
cities. Results from animal studies indicate that repeated
exposure to high levels of ozone for several months or more can
produce permanent structural damage in the lungs. EPA's
health-based national air quality standard for ozone is 0.12 ppm
(measured at the highest hour during the day). Ozone is also
responsible for several billion dollars of agricultural crop yield
toss in the U.S. each year. Ozone also damages forest eco-
systems in California and the eastern U.S.
Trends in Ozone Levels: Ground-level ozone has been a
pervasive pollution problem throughout the U.S. Ozone
0.25
0.20
0.15
1985-94: 12% decrease
1993-94: 1% decrease
90% of monitor sites had
concentrations less than this line
NAAQS
0.05
0.00
1985 1986 1987 1988 1989 1990 1991 1992 1993 1994
VOC EMISSIONS TRENDS
>•
S.
30
25
20
15
10 H
5 -t
I Fuel Combustion H Industrial Processing
1 Transportation Q Miscellaneous
1985 1986 1987 1988 1989 1990 1991 1992 1993 1994
concentration trends are influenced by year-to-year changes in
meteorological conditions as well as emission reductions from
ongoing control measures. Although meteorological conditions
in 1994 were conducive to ozone formation (especially in the
Southeast), national ozone levels were 12 percent lower than
those in 1985. Levels in 1994 are the second lowest national
average for the period between 1985 and 1994. The lowest
level was recorded in 1992, and the highest in 1988. Recent
control measures include regulations to reduce evaporation of
fuel and limit NOX and VOC emissions from tailpipe exhaust.
Emissions of VOCs (which contribute to ozone formation)
decreased 10 percent between 1985 and 1994, despite a slight
increase between 1993 and 1994.
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PM-10 CONCENTRATION TRENDS
PARTICULATE MATTER (PM-10)
Nature and Sources of the Pollutant: Particulate
matter is the term for solid or liquid particles found in the air.
Some particles are large or dark enough to be seen as soot
or smoke. Others are so small they can be detected only
with an electron microscope. Because particles originate
from a variety of mobile and stationary sources (diesel
trucks, wood stoves, power plants, etc.), their chemical and
physical compositions vary widely.
Health and Other Effects: In 1987, EPA replaced the
earlier Total Suspended Particulate (TSP) air quality standard
with a PM-10 standard. The new standard focuses on
smaller particles that are likely responsible for adverse health
effects because of their ability to reach the lower regions of
the respiratory tract. The PM-10 standard includes particles
with a diameter of 10 micrometers or less (0.0004 inches or
one-seventh the width of a human hair). EPA's health-based
national air quality standard for PM-10 is 50 ng/m3
(measured as an annual average) and 150 |j,g/m3
(measured as a daily average). Major concerns for human
health from exposure to PM-10 are: effects on breathing
and respiratory systems, damage to lung tissue, cancer, and
premature death. The elderly, children, and people with
chronic lung disease, influenza, or asthma, tend to be
especially sensitive to the effects of paniculate matter.
Acidic PM-10 can also damage manmade materials and is a
major cause of reduced visibility in many parts of the U.S.
Trends in PM-10 Levels: Air monitoring networks were
changed in 1987 to measure PM-10 (replacing the earlier
TSP monitors). Between 1988 and 1994, average PM-10
'70-
60
1988-94: 2O% decrease
1993-94: No change
NAAQS
0.00
1988 1989 1990 1991 1992 1993 1994
PM-10 EMISSIONS TRENDS
Fuel Combustion H Industrial Processing
ransportation
1988
1989
1990
1991
1992
1993
1994
concentrations decreased 20 percent, while PM-10
emissions decreased 12 percent. Particulate matter
emissions from sources such as fuel combustion, industrial
processes, and transportation decreased 17 percent since
1985. Emissions from residential wood combustion
decreased 50 percent in the past 10 years. Although not
included in the above chart, fugitive emissions (such as
those from construction) are also a significant source of
particulate matter in the air. Between 1993 and 1994, PM-
10 concentrations remained unchanged. Between 1993
and 1994, emissions of PM-10 increased 1 percent due to
emissions from transportation, industrial sectors, and
wildfire's.
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SULFUR DIOXIDE (SO2)
Nature and Sources of the Pollutant: Sulfur dioxide
belongs to the family of sulfur oxide gases (SOX). These
gases are formed when fuel containing sulfur (mainly coal and
oil) is burned, and during metal smelting and other industrial
processes.
Health and Other Effects: The major health concerns
associated with exposure to high concentrations of SC>2
Include effects on breathing, respiratory illness, alterations in
pulmonary defenses, and aggravation of existing
cardiovascular disease. Major subgroups of the population
that are most sensitive to SO2 include asthmatics and
individuals with cardiovascular disease or chronic lung
disease (such as bronchitis or emphysema) as well as
children and the elderly. EPA's health-based national air
quality standard for SO£ is 0.03 ppm (measured on an annual
average) and 0.14 ppm (measured over 24 hours). Emissions
of SO2 also can damage the foliage of trees and agricultural
crops. Together, SC>2 and NOX are the major precursors to
acid rain, which is associated with the acidification of lakes
and streams, accelerated corrosion of buildings and
monuments, and reduced visibility.
SO2 CONCENTRATION TRENDS
0.035
0.030
0.025
E- 0.020
0.015
0.010
0.005
NAAQS
1985-94: 25% decrease
1993-94: 4% decrease
90% of monitor sites had concentrations
less than this Bne I
1985 1986 1987 1988 1989 1990 1991 1992 1993 1994
30
25
20
SO2 EMISSIONS TRENDS
I Fuel Combustion H Industrial Processing
1 Transportation
15 -I
10
1985-94: 9% decrease
1993-94: 2% decrease
1985 1986 1987 1988 1989 1990 1991 1992 1993 1994
Trends in Sulfur Dioxide Levels: Between 1985 and
1994, SC>2 emissions decreased 9 percent while national
SC>2 concentrations decreased 25 percent. Between 1993
and 1994, national SC>2 concentrations decreased 4 percent
and SC>2 emissions decreased 2 percent. EPA's Acid Rain
Program calls for major reductions of SC>2 and NOX, the
pollutants that cause acid rain. The program sets a
permanent cap on the total amount of SC>2 that may be
emitted by electric utilities nationwide, about one-half the
amount emitted in 1980..
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VISIBILITY
Nature and Sources of the Problem: Visibility
impairment is caused by the presence of particles in the air.
It is most simply described as the haze which obscures the
clarity, color, texture, and form of what we see, and is
actually a complex problem that relates to several
pollutants. Visibility impairment is primarily a result of fine
particles (even smaller than PM-10) in the air. These
particles cause light to be scattered or absorbed, thereby
reducing visibility.
Long Term Trends: Visibility impairment has been
analyzed using data collected since 1960 at 280 monitoring
stations located at airports across the country. At these
stations, measurements of visual range (the maximum
distance at which an observer can discern the outline of an
object) were recorded. Long-term records of visual range
(derived from weather data) help reveal trends in visibility.
The following maps display U.S. visibility trends derived
from such data.
The maps show the amount of haze during the summer
months of 1970,1980, and 1990. The greater the haze,
the poorer the visibility. The dark blue color represents the
best visibility and red represents the worst visibility. Overall,
these maps show that visibility impairment in the eastern
U.S. increased greatly between 1970 and 1980, and
decreased slightly in 1990. This follows the overall trends
in SOX emissions during these periods. Sulfur oxides are a
major source of fine particles.
New Monitoring Network: EPA and the National Park
Service established a long-term visibility monitoring
program at locations throughout the U.S. The effort has
been expanded to incorporate other federal and regional
monitoring programs. The network is the largest in the
country devoted to fully characterizing visibility. Sulfates are
.the largest single contributor to haze, or visibility reduction,
in many parts of the U.S. Data from this monitoring
network reveals that sulfates account for 68 percent of the
visibility reduction in the Appalachian Mountains in the East.
Organic carbon, the next-largest contributor, causes 16
percent of visibility reduction. In most areas of the western
U.S. and Alaska, sulfates and organic particles contribute
equally to haze. In southern California, nitrate particles are
the greatest contributor to haze.
Best
Map of haze from airport visual data (July-September).
11
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Programs to Improve Visibility: In April 1994, EPA
announced development of its new regional haze program to
address visibility impairment in national parks and wilderness
areas. This program will introduce new approaches to
monitoring and modeling regional haze as well as define a policy
for achieving "reasonable progress" toward the reduction of
visibility impairment. The program will build on efforts of the
Grand Canyon Visibility Transport Commission which was
established to address visibility impairment in the region around
the Grand Canyon National Park. This commission is in the
process of developing recommendations for EPA regarding
protection of the national park areas on the Colorado Plateau in
the western United States. In addition, it is expected that better
controls for sources of pollutants such as sulfur oxides as a
result of the Acid Rain Program will also lead to improvements
Invisibility.
Toxic AIR
POLLUTANTS
Nature and Source: Toxic air pollutants are those pollutants
known to or suspected of causing cancer or other serious
health effects such as birth defects or reproductive effects.
Examples of toxic air pollutants include dioxins, benzene,
arsenic, beryllium, mercury, and vinyl chloride. The Clean Air
Act lists 189 toxic air pollutants to be regulated by EPA. They
are emitted from all types of sources, including motor vehicles
and stationary sources such as factories. Control of toxic air
pollutants differs in focus from control of the six principal
pollutants for which EPA has established national air, quality
standards (discussed earlier). For the six principal pollutants,
a variety of control strategies are used in geographic areas
where the national air quality standards have been violated.
In contrast, for toxic air pollutants, EPA has focused on
identifying all major sources that emit these pollutants and
developing national technology-based performance
standards to significantly reduce their emissions. The
objective is to ensure that major sources of toxic air pollution
are well controlled regardless of geographic location.
The air toxics program and the NAAQS program
complement each other. Many air toxics are emitted in the
form of particulates or as volatile organic compounds.
Control programs to meet the NAAQS for ozone and PM-10
also reduce toxic air emissions. Likewise, emission
requirements under the toxic air pollutant program can
significantly reduce emissions of the six principal pollutants
for which EPA has national ambient air quality standards.
For example, EPA's final toxic air pollutant regulation for
organic chemical manufacturing is expected to reduce VOC
emissions (which form ground-level ozone or smog) by an
amount equivalent to removing millions of cars from the road.
The toxic air pollutant program is especially important in
reducing air emissions at or near industrial locations and in
controlling pollutants that are toxic even when emitted in
small amounts. Companies handling toxic chemicals are
required by EPA to develop plans to prevent accidental
releases and to contain any releases in the event they should
occur.
Health and Other Effects: At sufficient concentrations .
and exposure durations, human health effects from toxic air
pollutants can include cancer, poisoning, and rapid onset of
sickness such as nausea and difficulty in breathing. Other
less measurable effects include immunological, neurological,
reproductive, developmental, and respiratory effects. Toxic .
air pollutants may also be deposited onto soil or into lakes
and streams, thereby affecting ecological systems and
eventually human health through consumption of
contaminated food (mainly freshwater fish).
Trends in Toxic Air Pollutants: In 1993, industrial sources
emitted toxic air pollutants totalling 1.2 billion pounds
12
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nationally, as reported in EPA's toxic release inventory (TRI).
Reporting under TRI is required for manufacturers handling
toxic chemicals and represents only a subset of total
nationwide emissions. This total represents a decrease of
approximately 600 million pounds (or 33 percent) from 1989
levels and reduction of 110 million pounds (or 8 percent)
from 1992 levels.
These downward trends in emissions are expected to
continue. The 1990 Clean Air Act Amendments greatly
expanded the number of industries that will be affected by
national air toxic emission controls. The emission
reductions from these controls are just beginning to be
realized for some industries. Large industrial complexes
such as chemical plants, oil refineries, aerospace
manufacturers, and steel mills are some of the industries
being controlled for toxic air pollution. It is necessary to
control smaller sources of toxic air pollution such as dry
cleaning operations, solvent cleaning, and chrome plating.
Within the next 10 years, the air toxics program is projected
to reduce emissions of toxic air pollutants by at least 1
billion pounds.
CONCLUSIO
Since EPA was established in 1970, air quality in the U.S.
has improved tremendously. Many of these improvements
can be attributed to pollution control programs instituted
by EPA, State and local agencies and industry. Because
air pollution problems continue in many parts of the
country, EPA and states are actively seeking innovative
and more cost-effective programs to further reduce
emissions. Market-based programs like emissions trading
provide incentives for industry to develop new pollution
control technologies or pollution prevention approaches.
Through continued interaction with the regulated
community, environmental groups, State, tribal, and local
governments, and concerned citizens, EPA is working to
develop effective common-sense control strategies to
improve our nation's air quality.
For Further Information:
Call (919)541-5285
National Air Pollutant Emission Trends,
1900-1994 (EPA-454/R-95-011)
(919)541-5558
National Air Quality and Emissions Trends,
1994 (EPA-454/R-95-014) -
Internet Users: EPA Homepage "at:
(http://www.epa.gov/docs/oar/oarhome.html)
!
Technology Transfer Network (TTN) Users:
• Access by modem, dial: (919) 541-5742
• Access by Internet, use telnet address:
(ttnbbs.rtpnc.epa.gov)
ACRONYMS
Principal Pollutants:
CO Carbon Monoxide
Pbj Lead
NO2, NOX Nitrogen Dioxide, Nitrogen Oxides
03 !.. .. Ozone
PM-10 Particulate Matter
SO2, SOX Sulfur Dioxide, Sulfur Oxides
EPA ., Environmental Protection Agency
NAAQS National Ambient Air Quality Standard
TRI Toxic Release Inventory
TSP.
VOC.
. Total Suspended Particulates
. Volatile Organic Compounds
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