United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park, NC 27711
December 1998
EPA-454/F-98-009
&EPA Latest Findings on National Air
Quality: 1997 Status and Trends
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&EPA Latest Findings on National Air
Quality: 1997 Status and Trends
Table of Contents
National Air Quality 1
Highlights 1
Background 2
Six Principal Pollutants 3
Long-Term Emissions Trends 3
Summary of Air Quality and Emissions Trends 3
Carbon Monoxide (CO) 5
Lead(Pb) 6
Nitrogen Dioxide (N02) 7
Ground-Level Ozone (03) 8
Particulate Matter (PM-10) 10
Sulfur Dioxide (S02) 11
Acid Rain 12
Visibility 14
Toxic Air Pollutants 16
Stratospheric Ozone 18
Global Warming and Climate Change 20
Conclusion 22
Acronyms 22
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NATIONAL
AIR
QUALITY
This brochure
highlights the U.S.
Environmental
Protection Agency's
(EPA's) most recent
evaluation of status
and trends in our
nation's air quality.
Highlights include:
National air quality standards have been set for six principal
air pollutants (also referred to as "criteria pollutants"): carbon
monoxide (CO), lead (Pb), nitrogen dioxide (N02), ozone (03),
particulate matter (PM), and sulfur dioxide (S02). Emissions
of these pollutants, or their precursors, increased significantly
between 1900 and 1970.
Since the 1970 Clean Air Act was signed into law, emissions
of each of the six pollutants decreased, with the exception of
nitrogen oxides (N0x). Between 1970 and 1997, emissions
of N0x have increased 11 percent. Emissions of N0x
contribute to the formation of ground-level ozone (smog) and
acid rain. In 1998, EPA issued a rule that will significantly
reduce emissions of N0x across 22 states in the eastern half
of the United States, and, in turn, reduce the regional
transport of ground-level ozone and acid rain formation.
Nationally, air quality concentration data taken from
thousands of monitoring stations across the country has
continued to show improvement since the 1980's for CO, Pb,
N02, 03, PM, and S02. In fact, all the years throughout the
1990's have shown better air quality than any of the years in
the 1980's. This steady trend of improvement resulted
despite the fact that weather conditions in the 1990's were
generally more conducive to higher pollution levels, such as
ground-level ozone formation.
In 1997, despite continued improvements in air quality,
approximately 107 million people lived in counties with
monitor data showing unhealthy air for one or more of the six
principal pollutants. While many of the more industrialized
areas have high pollution levels due to increased use of motor
vehicles and local industries in their vicinity, some rural
locations also are experiencing increased air pollution levels.
Some national parks have experienced high air pollution
concentrations as a result of pollutants being transported
many miles from their original source. For example, ground-
level ozone concentrations in remote locations of the Great
Smoky Mountains National Park have increased nearly 20
percent over the last 10 years.
Exposure to air pollutants is associated with numerous effects
on human health, including increased respiratory symptoms or
decreased lung function, hospitalization for heart or lung
diseases, or premature death. Because children's respiratory
systems are still developing, and they breathe even more air
per pound of body weight, they are generally more susceptible
than adults to environmental threats.
When Congress passed the Clean Air Act Amendments in
1990, they required EPA to address 188 hazardous air
pollutants commonly called toxic air pollutants. Since 1990
EPA has issued 27 air standards which when fully
implemented will reduce 1 million tons per year of toxic air
emissions. Exposure to toxic air pollutants may lead to an
increased chance of getting cancer or experiencing other
serious health effects. EPA is now developing strategies to
address the effects of toxic air pollutants in urban areas.
Air pollution, such as acid rain, ground-level ozone, and air
toxics, can also significantly affect ecosystems. For
example, ground-level ozone is responsible for over 500
million dollars in annual reductions of agricultural and
commercial forest yields, and airborne releases of nitrogen
oxides are one of the largest sources of nitrogen pollution to
the Chesapeake Bay.
Certain pollutants (such as some metals and organic
chemicals) that are emitted from industrial sources can be
deposited into water bodies and magnified through the food
web, adversely affecting fish-eating animals and humans.
Currently, about 2,300 U.S. water bodies are under fish
consumption advisories, resulting from chemicals such as
PCB's, chlordane, dioxins, and mercury.
Many of the improvements in air quality can be attributed to
pollution control programs instituted under the Clean Air Act,
state and local laws, and actions taken by industry. EPA and
state efforts are continuing to help address such concerns as
reducing sulfur in fuels, tightening tailpipe standards for cars
and diesel engines, and reducing air pollutants from power
plants and other industrial plants.
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While the focus of this document is on national a\r pollutant
issues, global air pollution issues such as destruction of the
stratospheric ozone layer and the effect of global warming on
the Earth's climate are major concerns and are also addressed
in this brochure. EPA continues to work with states, industry,
and other partners to find cost-effective and innovative ways to
address these and other air pollution problems.
Background
Air pollution comes from many different sources. "Stationary
sources," such as factories, power plants, and smelters; "area
sources," which are smaller stationary sources such as dry
cleaners and degreasing operations; "mobile sources," such as
cars, buses, planes, trucks, and trains; and "natural sources,"
such as windblown dust, and volcanic eruptions, all contribute
to air pollution. The Clean Air Act provides the principal
framework for national, state, Tribal, 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 the
six principal pollutants which are considered harmful to public
health and the environment.
Ensuring that these air quality standards are met, or attained,
(in cooperation with the state, Tribal, and local governments)
through national standards and strategies to control air
pollutant emissions from automobiles, factories, and other
sources.
Reducing emissions of sulfur dioxide and nitrogen oxides that
cause acid rain.
TREND IN EMISSIONS OF NITROGEN OXIDES
(1900-1990)
35 -
30 -
25 -
Without the passage of the Clean Air Act
Amendments in 1970, emissions would have
increased at a higher rate.
1910 1930 1950 1970
1990
TREND IN EMISSIONS OF VOLATILE
ORGANIC COMPOUNDS
(1900-1990)
Without the passage of the Clean Air Act
Amendments in 1970, emissions would have
continued to increase.
1910
1930
1950
1970
1990
Reducing air pollutants such as particulate matter, sulfur
oxides, and nitrogen oxides that can cause visibility
impairment across large regional areas, including many of the
nation's most treasured parks and wilderness areas.
Ensuring that sources of toxic air pollutants that cause or
may cause cancer, other adverse human health problems, or
adverse environmental effects are well controlled and that
risks to public health and the environment are substantially
reduced.
Limiting use of chemicals that damage the stratospheric
ozone layer, in order to prevent increased levels of harmful
ultraviolet radiation.
This brochure provides an overview of trends in these air
pollution problems, as well as global warming issues and the
processes EPA has developed for controlling pollutants that
contribute to global warming.
TREND IN EMISSIONS OF SULFUR OXIDES
(1900-1990)
Without the passage of the Clean Air Act
Amendments in 1970, emissions would have
continued to increase.
1910
1930
1950
1970
1990
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Six
PRINCIPAL
POLLUTANTS
The Clean Air Act
established two types
of national air quality
standards. "Primary"
standards are
designed to establish
limits to protect public
health, 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 and damage to animals, crops, vegetation, and buildings.
EPA has set national air quality standards for six principal
pollutants (referred to as "criteria" pollutants): carbon monoxide
(CO), lead (Pb), nitrogen dioxide (N02), ozone (03), particulate
matter (PM), and sulfur dioxide (S02). [Note: The pollutant ozone
is not emitted directly into the air, but is formed when sunlight
acts on emissions of nitrogen oxides (N0x) and volatile organic
compounds (VOC).]
For the past 25 years, EPA has examined air pollution trends in
concentrations and emissions of each of the six principal
pollutants in this country. Each year EPA examines changes in
air pollution levels over time and summarizes the current air
pollution status. The following sections summarize trends in air
quality and emissions during the last 10 years.
Long-Term Emissions Trends
Before the Clean Air Act was signed into law in 1963, the 20th
century had witnessed a significant and continued increase in
air pollution levels. Although efforts made during the 1960's by
state and local air pollution agencies in certain polluted cities in
the Northeast helped reduce pollution in some local areas,
emissions continued to increase on a national level. Between
1900 and 1970, emissions of N0x increased 690 percent, VOC
increased 260 percent, and S02 increased 210 percent.
Without the pollution controls resulting from amendments to the
Clean Air Act, emissions would have continued to increase at a
higher rate, as shown in the three graphs to the left.
Summary of Air Quality and Emissions Trends
EPA tracks two kinds of trends: air concentrations based on
actual measurements of pollutant concentrations in the ambient
(outside) air at selected monitoring sites throughout the country,
and emissions based on engineering estimates of the total
tonnage of these pollutants released into the air annually. In
addition, starting in 1994, under the Acid Rain Program, EPA
began tracking emissions of S02 and N0x based on data from
continuous emission monitors for the electric utility industry.
Generally there are similarities between air quality trends and
emission trends for any given pollutant. However, in some
cases, there are notable differences between the percent of
change in ambient concentrations and the percent of change in
emissions. These differences can mainly be attributed to the
location of air quality monitors. Because most monitors are
positioned in or near urban areas, trends in air quality tend to
more closely track changes in urban emissions rather than
changes in total national emissions.
Each year, EPA gathers and analyzes air quality concentration
data from thousands of 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 are derived by
averaging direct
measurements from these
monitoring sites on a yearly
basis. During the last 10
years (1988 through 1997),
air quality has continued to
improve.
Revised Ozone and
Particulate Matter
Standards - In 1997, EPA
revised the ozone (OJ and
particulate matter (PM)
national air quality
standards. Prior to this
time, the PM standard
applied to particles less than
or equal to 10 micrometers
in size, or PM-10. With the
revised standards, EPA
strengthened protection
against smaller particles by
adding an indicator for
PM-2.5 (those less than or
equal to 2.5 micrometers).
As shown in the following chart, the most notable
improvements are a 67 percent decrease in Pb concentrations,
a 38 percent decrease in CO concentrations, and a 39 percent
decrease in S02 concentrations. Improvements in measured
Percent Decrease
in Concentrations
(1988- 1997)
Percent Decrease
in Emissions
(1988- 1997)
CO
Pb
N02
38
67
14
25
44
1 (NOJ
19 (Pre-existing NAAQS) 20 (VOC)
16 (Revised NAAQS)
PM-10
so.
26
39
12
12
3
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Comparison of Growth Areas and Emission Trends
Vehicle Miles Traveled Increased 127%
U.S. Gross Domestic Product Increased 114%
U.S. Population Increased 31%
Aggregate Emissions Decreased 31%
(Six Principal Pollutants)
1970
1980
1990
1997
Between 1970 and 1997, U.S. population increased 31 percent, vehicle miles traveled increased 127 percent, and gross
domestic product increased 114 percent. At the same time, total emissions of the six principal air pollutants decreased
31 percent.
concentrations are also noted for the other principal pollutants,
including NO2, ozone, and PM-10 during this same time frame.
EPA estimates nationwide emissions trends based on actual
monitored readings or 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
developments, fuel consumption, vehicle miles traveled, 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, emissions
have shown improvement (decreased emissions) for all six
principal air pollutants.
Comparison of 1970 and 1997 Emissions
(31 % decrease for all principal pollutants)
The dramatic improvements in emissions and air quality
occurred simultaneously with significant increases in economic
growth and population. The improvements are a result of
effective implementation of clean air laws and regulations, as
well as improvements in the efficiency of industrial technologies.
Despite great progress in air quality improvement, in 1997 there
were still approximately 107 million people nationwide who lived
in counties with monitored air quality levels above the primary
national air quality standards.
Number of People Living in Counties with Air Quality
Concentrations Above the Level of the NAAQS in 1997
Million Tons/Year
150
Thousand Tons/Year
250
CO
Pb
NO2
03
PM-10
PM-2.5
SO2
Any
NAAQS
19.1
12.4
0
|4/.9 (pre-existing NAAQS)
|1U1 .0
. , (revised NAAQS)
|7.9 (pre-existing NAAQS)
19.7 (revised NAAQS)
Data not yet available
0.1
| bZfci (pre-existing NAAUbJ
|107
(revised NAAQS)
20
40 60 80
Millions of Persons
100
120
Blue bars represent revised standards for
ozone and PM.
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Six
PRINCIPAL
POLLUTANTS
1
CARBON
MONOXIDE (CO)
Nature and Sources
of the Pollutant:
Carbon monoxide (CO)
is a colorless, odorless
and at high levels, a
poisonous gas, formed when carbon in fuel is not burned
completely. It is a component of motor vehicle exhaust, which
contributes about 60 percent of all CO emissions nationwide.
High concentrations of CO generally occur in areas with heavy
traffic congestion. In cities, as much as 95 percent of all CO
emissions may come from automobile exhaust. Other sources of
CO emissions include industrial processes, non-transportation
fuel combustion, and natural sources such as wildfires. Peak
CO concentrations typically occur during the colder months of
the year when CO automotive emissions are greater and
nighttime inversion conditions (where air pollutants are trapped
near the ground beneath a layer of warm air) are more frequent.
Health and Environmental Effects: Carbon monoxide
enters the bloodstream through the lungs and reduces oxygen
delivery to the body's organs and tissues. The health threat from
lower levels of CO is most serious for those who suffer from
cardiovascular disease, such as angina pectoris. At much higher
levels of exposure, CO can be poisonous and even healthy
individuals may be affected. Visual impairment, reduced work
capacity, reduced manual dexterity, poor learning ability, and
difficulty in performing complex tasks are all associated with
exposure to elevated CO levels.
Trends in CO Levels: Long-term improvements in CO
continued between 1988 and 1997. Ambient CO concentrations
decreased 38 percent, and the estimated number of
exceedances of the national standard decreased 95 percent.
While CO emissions from highway vehicles alone have decreased
29 percent, total CO emissions decreased only 25 percent
overall. Long-term air quality improvement in CO occurred
despite a 25 percent increase in vehicle miles traveled in the
United States during this 10-year period. Between 1996 and
1997, ambient CO concentrations decreased 7 percent, while CO
emissions decreased 3 percent. Transportation sources
(including highway and off-highway vehicles) now account for 77
percent of national total CO emissions.
CO Air Quality, 1988-97
Annual 2nd Maximum 8-Hour Average
1988-97: 38% decrease
1996-97: 7% decrease
Concentration, ppm
10
9
NAAQS
-T- 90th Percentile
- Mean
Median
-L 10th Percentile
88 89 90 91 92 93 94 95 96 97
Bold line indicates national air standard.
CO Emissions, 1988-97
1988-97: 25% decrease
1996-97: 3% increase
Thousand Short Tons Per Year
140,000,
120,000
100,000
80,000
60,000
40,000
20,000
fj Fuel Combustion | Industrial Processing
fj Transportation rj Miscellaneous
88 89 90 91 92 93 94 95 96 97
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2
LEAD (Pb)
Nature and Sources of the Pollutant: In the past,
automotive sources were the major contributor of Pb emissions
to the atmosphere. As a result of EPA's regulatory efforts to
reduce the content of Pb in gasoline, the contribution from the
transportation sector has declined over the past decade.
Today, metals processing is the major source of Pb emissions to
the atmosphere. The highest air concentrations of Pb are found
in the vicinity of nonferrous and ferrous smelters, and battery
manufacturers.
Health and Environmental Effects: Exposure to Pb
occurs mainly through inhalation of air and ingestion of Pb in
food, water, soil, or dust. It accumulates in the blood, bones,
and soft tissues. Lead can adversely affect the kidneys, liver,
nervous system, and other organs. Excessive exposure to Pb
may cause neurological impairments, such as seizures, mental
retardation, and behavioral disorders. Even at low doses, Pb
exposure is associated with damage to the nervous systems of
fetuses and young children, resulting in learning deficits and
lowered IQ. Recent studies also show that Pb may be a factor
in high blood pressure and subsequent heart disease. Lead
can also be deposited on the leaves of plants, presenting a
hazard to grazing animals.
Trends in Pb Levels: Between 1988 and 1997, ambient Pb
concentrations decreased 67 percent, and total Pb emissions
decreased 44 percent. Since 1988, Pb emissions from highway
vehicles have decreased 99 percent due to the phase-out of
leaded gasoline. The large reduction in Pb emissions from
X
transportation sources has changed the nature of the pollution
problem in the United States. While there are still violations of
the Pb air quality standard, they tend to occur near large
industrial sources such as lead smelters. Between 1996 and
1997, Pb concentrations and emissions remained unchanged.
Lead (Pb) Air Quality, 1988-97
Annual Maximum Quarterly Average
1988-97: 67% decrease
1996-97: no change
Concentration, ug/m3
1.5
1.0
0.5
0.0
NAAQS
^-90th Percentile
i-Mean
Median
_10th Percentile
88 89 90 91 92 93 94 95 96 97
Bold line indicates national air standard.
Lead (Pb) Emissions, 1988-97
1988-97: 44% decrease
1996-97: no change
Short Tons Per Year
8,000
uel Combustion | Industrial Processing Q Transportation
6,000
4,000
2,000
88 89 90 91 92 93 94 95 96 97
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3
NITROGEN DIOXIDE (NO2)
Nature and Sources of the Pollutant: Nitrogen dioxide
(N02) is a reddish brown, highly reactive gas that is formed in
the ambient air through the oxidation of nitric oxide (NO).
Nitrogen oxides (N0x), the term used to describe the sum of
NO, N02 and other oxides of nitrogen, play a major role in the
formation of ozone. The major sources of man-made N0x
emissions are high-temperature combustion processes, such as
those occurring in automobiles and power plants. Home
heaters and gas stoves also produce substantial amounts of
N02 in indoor settings.
Health and Environmental Effects: Short term exposures
(e.g., less than 3 hours) to current nitrogen dioxide (N02)
concentrations may lead to changes in airway responsiveness
and lung function in individuals with pre-existing respiratory
illnesses and increases in respiratory illnesses in children (5-12
years old). Long-term exposures to N02 may lead to increased
susceptibility to respiratory infection and may cause alterations
in the lung. Atmospheric transformation of N0x can lead to the
formation of ozone and nitrogen-bearing particles (most notably
in some western urban areas) which are both associated with
adverse health effects.
Nitrogen oxides also contribute to the formation of acid rain.
Nitrogen oxides contribute to a wide range of environmental
effects, including potential changes in the composition and
competition of some species of vegetation in wetland and
terrestrial systems, visibility impairment, acidification of
freshwater bodies, eutrophication (i.e., explosive algae growth
leading to a depletion of oxygen in the water) of estuarine and
coastal waters (e.g., Chesapeake Bay), and increases in levels
of toxins harmful to fish and other aquatic life.
Trends in NO2 Levels: Over the past ten years, ambient N02
concentrations decreased 14 percent. Between 1996 and
1997, national average annual mean N02 concentrations remain
unchanged. In the last 10 years, N0xemissions levels have
remained relatively constant.
Between 1988 and 1997,
N0x emissions declined 1
percent, while they
increased slightly (by 1
percent) between 1996 and
1997. However, over the
longer term since 1970, total
N0x emissions have
increased 11 percent and
N0x emissions from coal-
fired power plants have
increased 44 percent.
NO2 Air Quality, 1988-97
Annual Arithmetic Mean
1988-97: 14% decrease
1996-97: no change
Concentration, ppm
0.053
0.04
0.03
0.02
0.01
0.00
NAAQS
90th Percentile
=Mean
Median
_10th Percentile
88 89 90 91 92 93 94 95 96 97
Bold line indicates national air standard.
NO Emissions, 1988-97
1988-97: 1% decrease
1996-97: 1% increase
Thousand Short Tons Per Year
30,000
25,000
20,000
15,000
10,000
5,000
0
Q Fuel Combustion | Industrial Processing
Q Transportation Q Miscellaneous
88 89 90 91 92 93 94 95 96 97
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4
GROUND-LEVEL OZONE (O3)
Nature and Sources of the Pollutant: Ground level ozone
(the primary constituent of smog) continues to be a pervasive
pollution problem throughout many areas of the United States.
Ozone is not emitted directly into the air but is formed by the
Ozone occurs naturally in the stratosphere and provides
a protective layer high above the Earth. See page 18 for
more information on stratospheric ozone.
reaction of VOCs and N0x in the presence of heat and sunlight.
Ground-level ozone forms readily in the atmosphere, usually
during hot summer weather. VOCs are emitted from a variety of
sources, including motor vehicles, chemical plants, refineries,
factories, consumer and commercial products, and other
industrial sources. Nitrogen oxides are emitted from motor
vehicles, power plants, and other sources of combustion.
Changing weather patterns contribute to yearly differences in
ozone concentrations from city to city. Ozone and the
precursor pollutants that cause ozone also can be transported
into an area from pollution sources found hundreds of miles
upwind.
Health and Environmental Effects: Short term (1 3 hours)
and prolonged (6-8 hours) exposures to ambient ozone have
been linked to a number of health effects of concern. For
example, increased hospital admissions and emergency room
visits for respiratory causes have been associated with ambient
ozone exposures. Repeated exposures to ozone can make
people more susceptible to respiratory infection, result in lung
inflammation, and aggravate pre-existing respiratory diseases
such as asthma. Other health effects attributed to ozone
exposures include significant decreases in lung function and
increased respiratory symptoms such as chest pain and cough.
These effects generally occur while individuals are engaged in
moderate or heavy
exertion. Children active
outdoors during the
summer when ozone levels
are at their highest are
most at risk of
experiencing such effects.
Other at-risk groups
include adults who are
active outdoors (e.g., outdoor workers), and individuals with
pre-existing respiratory disease such as asthma and chronic
obstructive lung disease. In addition, longer-term exposures to
moderate levels of ozone present the possibility of irreversible
changes in the lungs which could lead to premature aging of
the lungs and/or chronic respiratory illnesses.
0.20
0.15
0.12
0.10
0.05
0.00
Ozone Air Quality, 1988-97
Annual 2nd Daily 1 -Hour Maximum
1988-97: 19% decrease
1996-97: no change
Concentration, ppm
-90th Percentile
-MeanNAAQS
Median
-10th Percentile
88 89 90 91 92 93 94 95 96 97
Bold line indicates pre-existing
national air standard.
VOC Emissions, 1988-97
1988-97: 20% decrease
1996-97: no change
Thousand Short Tons Per Year
35,000
30,000
25,000
20,000
15,000
10,000
5,000
88 89 90 91 92 93 94 95 96 97
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Ozone also affects vegetation and ecosystems, leading to
reductions in agricultural and commercial forest yields, reduced
growth and survivability of tree seedlings, and increased plant
susceptibility to disease, pests, and other environmental
stresses (e.g., harsh weather). In long-lived species, these
effects may become evident only after several years or even
decades, thus having the potential for long-term effects on
forest ecosystems. Ground-level ozone damage to the foliage
of trees and other plants also can decrease the aesthetic value
of ornamental species as well as the natural beauty of our
national parks and recreation areas.
Revised Ozone Standards: In 1997, EPA revised the
national ambient air quality standards for ozone by
replacing the 1-hour ozone 0.12 parts per million (ppm)
standard with a new 8-hour 0.08 ppm standard. The
revision to the O3 standard was set such that the 1-hour
standard will no longer apply once an area has air
quality data meeting the 1-hour standard. Although
areas that do not meet the new 8-hour standard will not
be designated "nonattainment" until the year 2000, EPA
is beginning to track trends in 8-hour levels of ozone.
Ozone Air Quality, 1988-97
Annual 4th Daily 8-Hour Maximum
1988-97: 16% decrease
1996-97: 1% decrease
Concentration, ppm
0.15
0.10
0.08
0.05
0.00
_90th Percentile
^Mean NAAQS
^Median
"10th Percentile
88 89 90 91 92 93 94 95 96 97
Bold line indicates revised national air standard.
Trends in Ozone Levels: Ambient ozone trends are
influenced by year-to-year changes in meteorological
conditions, population growth, loadings of VOC and N0x in
the atmosphere, and by changes in emissions from ongoing
control measures. As shown in the chart to the left, between
1988 and 1997, ambient ozone concentrations decreased 19
percent, based on the pre-existing standard. Between 1996
and 1997, ambient ozone concentrations did not change based
on the pre-existing standard.
Nationally, 8-hour levels of ozone have
decreased 16 percent over the past 10 years.
Between 1996 and 1997, 03 concentrations
decreased 1 percent based on the revised
standard.
In order to address ozone pollution, EPA has
traditionally focused its control strategies on
reducing emissions of VOC in nonattainment
areas. However, EPA and the states have
recognized a need for an aggressive program
to reduce regional emissions of N0x. In 1998,
EPA issued a rule that will significantly reduce
regional emissions of N0x in 22 states and the
District of Columbia, and, in turn, reduce the
regional transport of ozone. National trends in
emissions of N0x and VOC underscore the importance of this
new approach. Volatile organic compound emissions
decreased 20 percent between 1988 and 1997, while N0x
emissions decreased only 1 percent. VOC emissions from
highway vehicles have declined 38 percent since 1988, while
highway vehicle N0x emissions have declined 8 percent since
their peak level in 1994. Further, between 1970 and 1997
emissions of VOCs have decreased 38 percent whereas
emissions of N0x have increased 11 percent and N0x emissions
from coal-fired power plants have increased 44 percent.
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5
PARTICULATE MATTER (PM-10)
Nature and Sources of the Pollutant: Particulate matter (PM) is
the general term used for a mixture of solid particles and liquid droplets
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. These particles, which come in a wide range
of sizes ("fine" particles are less than 2.5 micrometers in diameter and
coarser-size particles are larger than 2.5 micrometers), originate from
many different stationary and mobile sources as well as from natural
sources. Fine particles (PM-2.5) result from fuel combustion from
motor vehicles, power generation, and industrial facilities, as well as
from residential fireplaces and wood stoves. Coarse particles (PM-10)
are generally emitted from sources, such as vehicles traveling on
unpaved roads, materials handling, and crushing and grinding
operations, as well as windblown dust. Some particles are emitted
directly from their sources, such as smokestacks and cars. In other
cases, gases such as sulfur oxide and S02, N0x, and VOC interact
with other compounds in the air to form fine particles. Their chemical
and physical compositions vary depending on location, time of year,
and weather.
Health and Environmental Effects: Inhalable PM includes both
fine and coarse particles. These particles can accumulate in the
respiratory system and are associated with numerous health effects.
Exposure to coarse particles is primarily associated with the
aggravation of respiratory conditions, such as asthma. Fine particles
are most closely associated with such health effects as increased
hospital admissions and emergency room visits for heart and lung
disease, increased respiratory symptoms and disease, decreased
lung function, and even premature death. Sensitive groups that
appear to be at greatest risk to such effects include the elderly,
individuals with cardiopulmonary disease, such as asthma, and
children. In addition to health problems, PM is the major cause of
reduced visibility in many parts of the United States. Airborne
particles also can cause damage to paints and building materials.
Revised Particulate Matter Standards: In 1997, EPA
added two new PM-2.5 standards, set at 15 micrograms
per cubic meter fag/m3) and BS^ig/m3, respectively, for
the annual and 24-hour standards. In addition, the form of
the 24-hour standard for PM-10 was changed. EPA is
beginning to collect data on PM-2.5 concentrations.
Beginning in 2002, based on 3 years of monitor data, EPA
will designate areas as nonattainment that do not meet the
new PM-2.5 standards.
Trends in PM-10 Levels: Between 1988 and 1997, average
PM-10 concentrations decreased 26 percent. Short-term trends
between 1996 and 1997 showed a decrease of 1 percent in
monitored PM-10 concentration levels.
Emissions of PM-10 shown in the chart are based on estimates of
anthropogenic emissions including fuel combustion sources, industrial
processes, and transportation sources, which account for only 6
PM-10 Air Quality, 1988-97
Annual Arithmetic Mean
1988-97: 26% decrease
1996-97: 1% decrease
Concentration, ug/m3
50
40
30
20
10
0
NAAQS
-90th Percentile
-Mean
^Median
-10th Percentile
88 89 90 91 92 93 94 95 96 97
Bold line indicates pre-existing national air standard.
PM-10 Emissions, 1988-97
1988-97: 12% decrease
1996-97: 1% decrease
Thousand Short Tons Per Year
Fuel Combustion
| Industrial Processing rj Transportation
4,000
3,000
2,000
1,000
88 89 90 91 92 93 94 95 96 97
percent of the total PM-10 emissions nationwide. Between 1988 and
1997, PM-10 emissions for these sources decreased 12 percent.
Emissions of PM-10 between 1996 and 1997 decreased 1 percent.
The emissions estimates presented above do not include
emissions from natural and miscellaneous sources, such as fugitive
dust (unpaved and paved roads), agricultural and forestry activities,
wind erosion, wildfires, and managed burning. These emissions
estimates also do not account for PM that is secondarily formed in
the atmosphere from gaseous pollutants (i.e., S02 and N0x).
10
-------
6
SULFUR DIOXIDE (SO2)
Nature and Sources of the Pollutant: Sulfur dioxide
belongs to the family of sulfur oxide gases. These gases are
formed when fuel containing sulfur (mainly, coal and oil) is
burned and during metal smelting and other industrial
processes. Most S02 monitoring stations are located in urban
areas. The highest monitored concentrations of S02 are
recorded in the vicinity of large industrial facilities.
Health and Environmental Effects: High concentrations of
S02 can result in temporary breathing impairment for asthmatic
children and adults who are active outdoors. Short-term
exposures of asthmatic individuals to elevated S02 levels while
at moderate exertion may result in reduced lung function that
may be accompanied by such symptoms as wheezing, chest
tightness, or shortness of breath. Other effects that have been
associated with longer-term exposures to high concentrations
of S02, in conjunction with high levels of PM, include respiratory
illness, alterations in the lungs' defenses, and aggravation of
existing cardiovascular disease. The subgroups of the
population that may be affected under these conditions include
individuals with cardiovascular disease or chronic lung disease,
as well as children and the elderly.
SO2 Air Quality, 1988-97
Annual Arithmetic Mean
1988-97: 39% decrease
1996-97: 4% decrease
Concentration, ppm
0.03
0.02
0.01
0.00
NAAQS
-90th Percentile
=Mean
Median
-10th Percentile
38 89 90 91 92 93 94 95 96 97
Bold line indicates national air standard.
Together, S02 and N0x are the major precursors to acidic
deposition (acid rain), which is associated with the acidification
of soils, lakes, and streams, accelerated corrosion of buildings
and monuments, and reduced visibility. Sulfur dioxide also is a
major precursor to PM-2.5, which is a significant health concern
as well as a main pollutant that impairs visibility.
Trends in SO2 Levels: Between 1988 and 1997, national
S02 concentrations decreased 39 percent and S02 emissions
decreased 12 percent. Between 1996 and 1997, national S02
concentrations decreased 4 percent and S02 emissions
increased 3 percent. Sulfur dioxide emissions from electric
utilities decreased 12 percent between 1994 and 1997. These
recent reductions are
due, in large part, to
controls implemented
under EPA's Acid Rain
Program. The 3
percent increase that
occurred between
1996 and 1997 is
primarily due to
increased demand for
electricity.
SO, Emissions, 1988-97
1988-97: 12% decrease
1996-97: 3% increase
Thousand Short Tons Per Year
30,000
25,000
20,000
15,000
10,000
5,000
0
Q Fuel Combustion
Q Transportation
^ Industrial Processing
2 Miscellaneous
88 89 90 91 92 93 94 95 96 97
11
-------
ACID RAIN
Nature and Source of the Problem: Acidic deposition or
"acid rain" occurs when emissions of sulfur dioxide (S02) and
oxides of nitrogen (N0x) in the atmosphere react with water,
oxygen, and oxidants to form acidic compounds. These
compounds fall to the Earth in either dry form (gas and particles)
or wet form (rain, snow, and fog). Some are carried by the
wind, sometimes hundreds of miles, across state and national
borders. In the United States, about 64 percent of annual S02
emissions and 26 percent of N0x emissions are produced by
electric utility plants that burn fossil fuels.
Acid Rain Formation
Acid Run
Coal-fired electric utilities
and other sources that burn fossil
fuels emit sulfur dioxide and nitrogen oxides.
Health and Environmental Effects: Before falling to the
Earth, S02 and N0x gases and related particulate matter
(sulfates and nitrates) contribute to poor visibility and impact
public health. Major human health concerns associated with
their exposure include effects on breathing and the respiratory
system, damage to lung tissue, and premature death. In the
environment, acid rain raises the acid levels in soils and water
bodies (making the water unsuitable for some fish and other
wildlife), and damages trees at some high elevations. It also
speeds the decay of buildings, statues, and sculptures that are
part of our national heritage.
Program Structure: The goal of EPA's Acid Rain Program,
established by the Clean Air Act, is to improve public health and
the environment by reducing emissions of S02 and N0x. The
program is being implemented in two phases: Phase I began in
1995 for S02 and targets the largest and highest-emitting power
plants (boilers). Phase I for N0x began in 1996 and targets coal-
fired power plants. Phase II for both pollutants begins in 2000
and will set restrictions on smaller coal-, gas-, and oil-fired plants.
The Acid Rain Program will reduce annual S02 emissions by 10
million tons between 1980 and 2010. The program sets a
permanent cap on the total amount of S02 that may be emitted
by power plants nationwide at about half of the amount emitted
in 1980. An emissions trading program is in effect to achieve
the required emission reduction more cost effectively. This
approach gives utilities the flexibility and incentive to reduce
emissions at the lowest cost, while ensuring that the overall
emission limit is met.
The N0x component of the Acid Rain Program establishes an
emission rate limit for all affected utilities, resulting in a 2 million
ton reduction compared to 1980 levels. Under this program,
the industry can choose to over-control at units where it is
technically easier to control emissions, average these emissions
with those at their other units, and thereby achieve overall
emissions reductions at lower cost.
Reductions in S02 and N0x will decrease levels of sulfates,
nitrates, and ground-level ozone (smog), leading to
improvements in public health and other benefits such as better
water quality in lakes and streams. Visibility will improve,
enhancing the beauty of our country's scenic vistas, including
those in national parks. Likewise, damage to the trees that
populate mountain ridges from Maine to Georgia will be
reduced, and deterioration of our historic buildings and
monuments will be slowed.
Emissions and Atmospheric Trends: S02 emissions
reductions have been significant in the first 3 years of
compliance with EPA's Acid Rain Program. As shown in the
graph below, the 263 core Phase I utility units continued to emit
SO2 Emissions from 263 Highest-Emitting Phase I Units
Allowable
Emissions
1980 1990 1995 1996 1997
In 1997, emissions at the Phase I units were 1.2 million
tons below their allowed level.
12
-------
NO Emissions from 263 Phase I Units
1990 1996 1997
1997 emissions from NOx Phase I Units decreased 32
percent from 1990 levels.
well below the allowable emission levels required by the Clean
Air Act. Additional units elected to participate early, bringing the
total number of Phase I units to 423 in 1997. Total Phase I units
emitted 5.5 million tons, which was still well below the 1997
allowable emissions level for S02.
As shown in the chart to the left, actual N0x emissions
decreased by approximately 400,000 tons (32 percent)
compared to 1990 levels. N0x emissions in 1997 increased
slightly from 1996, attributable to greater electrical production.
In 1995 and 1996, concentrations of sulfates in precipitation
over a large area of the eastern United States exhibited a
dramatic and unprecedented reduction. Sulfates have been
estimated to be 10 to 25 percent lower than they would have
been if the trend from 1983 through 1994 had continued (see
figure below). These reductions in acid precipitation are directly
related to the large regional decreases in S02 emissions
resulting from Phase I of the Acid Rain Program. The largest
reductions in sulfate concentrations occurred along the Ohio
River Valley and in states immediately downwind. Reductions in
the East in hydrogen ion concentrations, the primary indicator of
precipitation acidity, were similar to those of sulfate
concentrations, both in magnitude and location. Nitrate
concentrations were not appreciably different in 1995 to 1996
from historical levels.
Percent Change in Sulfate Levels Occurring in 1996 Precipitation
(compared to 1983-1994 predicted levels)
-25 -20 -15 -10
The level of sulfates in rain is an indicator of acidity. A 10 to 25 percent decrease in sulfate levels in rainfall was
observed in 1996, particularly in some of the most acid-sensitive regions of the United States.
13
-------
VISIBILITY
Nature and Sources of the Problem: Visibility impairment
occurs as a result of the scattering and absorption of light by
air pollution, including particles and gases. In addition to limiting
the distance that we can see, the scattering and absorption of
light caused by air pollution can also degrade the color, clarity,
and contrast of scenes. The same particles that are linked to
serious health effects can also significantly affect our ability
to see.
Both primary emissions and secondary formation of particles
contribute to visibility impairment. "Primary" particles, such as
dust from roads or elemental carbon (soot) from wood
combustion, are emitted directly into the atmosphere.
"Secondary" particles are formed in the atmosphere from
primary gaseous emissions. Examples include sulfate, formed
from sulfur dioxide (SO2), and nitrates, formed from NOx. In the
Eastern United States, reduced visibility is mainly attributable to
secondarily-formed particles. While these secondarily-formed
particles still account for a significant amount in the West,
primary emissions from sources like wood smoke contribute a
larger percentage of the total particulate loading than in the
East.
Humidity can significantly increase the effect of pollution on
visibility. Some particles, such as sulfates, accumulate water
and grow in size, becoming more efficient at scattering light and
causing visibility impairment. Annual average relative humidity
levels are 70-80 percent in the East as compared to 50-60
percent in the West. Poor summer visibility in the eastern
United States is primarily the result of high sulfate
concentrations combined with high
humidity levels.
Long-term Trends: Visibility
impairment has been
analyzed using visual range
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. The maps below show the amount
of haze during the summer months of 1970, 1980, and 1990.
The dark blue color represents less haze and red represents more
haze. Overall, the maps show that visibility impairment in the
Eastern United States increased greatly between 1970 and 1980
and decreased slightly between 1980 and 1990. This follows the
overall trend in emissions of SOx during these periods.
Visibility Monitoring Network: In 1987, a visibility
monitoring network was established as a cooperative effort
between the EPA, states, National Park Service, U.S. Forest
Service, Bureau of Land Management, and U.S. Fish and
Wildlife Service. The network is designed to track progress
toward the Clean Air Act's national goal of remedying the
existing and preventing future visibility impairment in the 156
national parks and wilderness areas. Each of these sites
contains over 5,000 acres. The network is the largest in the
country devoted to fully characterizing visibility. It also provides
information for determining the types of pollutants and sources
primarily responsible for reduced visibility.
Visibility impairment is generally worse in the rural East
compared to most of the West. This is primarily due to higher
concentrations of man-made pollution, slightly higher
background levels of fine particles, and higher relative humidity
levels in the East. The chart to the right shows the relative levels
of pollutants that contribute to visibility impairment in the
Eastern and Western parts of the United States.
1980
Maps from airport visual data
show the amount of summertime
haze (visibility impairment). Haze in
the Eastern United States increased
significantly between 1970 and 1980 and
decreased slightly between 1980 and 1990.
1970
14
-------
lllj
Great Smoky Mountains National Park under a range of visibility conditions.
Programs to Improve Visibility: EPA proposed a new
regional haze program in 1997 to address visibility impairment in
national parks and wilderness areas caused by numerous
sources located over broad regions. When finalized, the
program will lay out a framework within which states develop
implementation plans to achieve "reasonable progress" toward
the national visibility goal of remedying any existing and
preventing any future human-caused impairment. These plans
will include emission management strategies to improve visibility
over time in national parks, particularly for the worst visibility
days. States will be required to periodically track progress and
revise any strategies as necessary. Because fine particles are
frequently transported hundreds of miles, pollution that occurs
in one state may contribute to the visibility impairment in
another state. Thus, to effectively address the regional haze
problem, states are encouraged to coordinate with each other
in developing strategies to improve visibility and to comply with
the PM-2.5 and ozone NAAQS.
Other air quality programs are expected to lead to emission
reductions that will improve visibility in certain regions of the
country. The Acid Rain Program is designed to achieve
significant reductions in S0x emissions, which is expected to
reduce sulfate haze, particularly in the Eastern United States.
Additional control programs on sources of N0x to reduce
formation of ozone can also improve regional visibility
conditions. In addition, programs, such as the national ambient
air quality standards, controls on diesel-powered mobile
sources, and programs to improve wood stove efficiency can
benefit areas adversely impacted by visibility impairment.
Sulfates
Organic Carbon
Nitrates
Elemental Carbon (soot)
Crustal Material (soil dust)
25-65%
15-35%
5-45%
15-25%
10-20%
>60%
10-15%
10-15%
10-15%
10-15%
Pollutants that contribute to visibility impairment in the eastern and western parts of the United
States. Sulfates are generally the largest contributor in both the East and the West.
15
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Toxic AIR
POLLUTANTS
Nature and Sources:
Toxic air pollutants are
those pollutants that
cause or may cause
cancer or other serious
health effects, such as
reproductive effects or
birth defects, or adverse
environmental and ecological effects. The Clean Air Act requires
EPA to address 188 toxic air pollutants. Examples of toxic air
pollutants include benzene, found in gasoline; perchloroethylene,
emitted from some dry cleaning facilities; and methylene chloride,
used as a solvent and paint stripper by a number of industries.
Some air toxics are released from natural sources such as
volcanic eruptions and forest fires. Most, however, originate from
human-made sources, including both mobile sources (e.g., cars,
trucks, buses) and stationary sources (e.g., factories, refineries,
power plants).
decreased fertility, decreased hatching success, damaged
reproductive organs, and altered immune systems.
Program Structure: Control of toxic air pollutants differs
from the control of the six principal pollutants for which EPA has
established national air quality standards. For the six principal
pollutants, the Clean Air Act requires states to develop plans to
meet the national air quality standards by specific deadlines. In
contrast, for toxic air pollutants, the Act requires EPA to have a
two-phased program. The first phase consists of identifying the
sources of toxic pollutants and developing technology-based
standards to significantly reduce their emissions. The second
phase consists of strategies and programs for evaluating the
remaining risks and ensuring that the overall program has
achieved substantial reduction in risks to public health and the
environment. The objective is to ensure that on a national basis
sources of toxic air pollution are well controlled and that risks to
public health and the environment are substantially reduced.
In addition, the toxic air pollutant program is important in
reducing highly localized emissions near industrial sources and
in controlling pollutants that are toxic even when emitted in
small amounts. Companies handling extremely hazardous
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 Environmental Effects: People exposed to
toxic air pollutants at sufficient concentrations and for sufficient
durations have an increased chance of getting cancer or
experiencing other serious health effects. These health effects
can include damage to the immune system, as well as
neurological, reproductive (i.e., reduced fertility), developmental,
respiratory and other health problems. Some toxic air pollutants
pose particular hazards to people at a certain stage in life, such
as young children or the elderly. Some health problems occur
very soon after a harmful exposure. Health effects associated
with long-term exposures to toxic air pollutants, however, may
develop slowly over time or not appear until many months or
years after the initial exposure.
Toxic pollutants in the air or deposited on soils or surface waters
can have a number of environmental impacts. Like humans,
animals experience health problems if exposed to sufficient
concentrations of air toxics over time. Persistent toxic air
pollutants that can accumulate in plants and animals are of
particular concern in aquatic ecosystems because the
pollutants accumulate in tissues of animals, magnifying up the
food chain to levels many times higher than in the water. Toxic
pollutants that disrupt the endocrine system also pose a threat.
In some wildlife, for example, exposures to pollutants such as
DDT, dioxins, and mercury have been associated with
1993 National Toxic Air Pollutant Emissions by Source
Small
Stationary
Sources (Area)
18%
Mobile
Sources
21%
Large Industrial
Complexes
(Point Sources)
61%
According to National Toxics Inventory data, smaller
stationary sources account for 18 percent of U.S. toxic
emissions, mobile sources account for 21 percent, and
larger industrial sources for 61 percent.
16
-------
Trends in Toxic Air Pollutants: EPA is using the National
Toxics Inventory (NTI) to track nationwide emissions trends for
toxic air pollutants listed in the Clean Air Act. The NTI includes
emissions information for 188 hazardous air pollutants from
more than 900 stationary sources based on a 1993 survey.
There are approximately 8.1 million tons of air toxics released to
the air each year according to NTI. As illustrated in the chart,
NTI includes emissions from large industrial or "point" sources,
smaller stationary sources called "area" sources, and mobile
sources. The NTI estimates of the large point source and
mobile source contributions to the national emissions of toxic air
pollutants are approximately 61 and 21 percent, respectively.
Currently, EPA has issued 27 air toxics emissions standards
under the first (technology-based) phase of the regulations
program. These standards affect 52 categories of major
industrial sources, such as chemical plants, oil refineries,
aerospace manufacturers, and steel mills, as well as eight
categories of smaller sources, such as dry cleaners, commercial
sterilizers, secondary lead smelters, and chromium
electroplating facilities. EPA has also issued two standards to
control emissions from solid waste combustion facilities.
Together these standards reduce emissions of over 100
different air toxics. When fully implemented, these standards
will reduce air toxics emissions by about 1 million tons per year
- almost ten times the reductions achieved prior to 1990. In
addition, controls for toxic air pollutants will also reduce VOC
and PM emissions by more than 2.5 million tons per year over
the same time period.
EPA is now moving into the second (risk-based) phase of the
regulatory program. EPA has recently published a draft
integrated strategy that will address cumulative risks from multiple
sources (both stationary and mobile) of toxic pollutants and from
combined exposures of these pollutants in urban areas.
EPA collects data through its Photochemical Assessment
Monitoring Stations (PAMS) program on concentrations of
ozone and its precursors in 22 areas across the nation with the
most significant ozone problems. The PAMS program requires
routine measurement of ten pollutants that contribute to ozone
formation and which also are toxic air pollutants: acetaldehyde,
benzene, ethyl benzene, formaldehyde, hexane, styrene,
toluene, m/p-xylene, o-xylene, and 2,2,4-trimethylpentene.
Preliminary analysis of the monitoring data indicates that
concentrations of some of these toxic VOC in the areas
monitored are declining. Monitoring networks now being set up
will provide more toxics data in the future.
17
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STRATOSPHERIC
OZONE
Nature and Sources of the Problem: The stratosphere,
located about 6 to 30 miles above the Earth, contains a layer of
ozone gas that protects living organisms from harmful ultraviolet
radiation (UV-b) from the sun. Over the past two decades,
however, this protective shield has been damaged. Each year,
an "ozone hole" forms over the Antarctic, and ozone levels fall
to 70 percent below normal. Even over the United States,
ozone levels are about 5 percent below normal in the summer
and 10 percent below normal in the winter. The trend line in the
figure below shows a 3.4 percent decrease per decade in
average total ozone over Northern Hemisphere mid-latitudes
since 1979.
As the ozone layer thins, more UV-b radiation reaches the
Earth. In 1996, scientists demonstrated for the first time that
UV-b levels over most populated areas have increased.
Scientists have linked several substances associated with
human activities to ozone depletion, including the use of
chlorofluorocarbons (CFCs), halons, carbon tetrachloride, and
methyl chloroform. These chemicals are emitted from home air
conditioners, foam cushions, and many other products.
Strong winds carry them through the lower part of the
atmosphere, called the troposphere, and into the stratosphere.
There, strong solar radiation releases chlorine and bromine
atoms that attack protective ozone molecules. Scientists
estimate that one chlorine atom can destroy 100,000 ozone
molecules.
Health and Environmental Effects: Some UV-b radiation
reaches the Earth's surface even with normal ozone levels.
However, because the ozone layer normally absorbs most UV-b
radiation from the sun, ozone depletion is expected to lead to
increases in harmful effects associated with UV-b radiation. In
humans, UV-b radiation is linked to skin cancer, including
melanoma, the form of skin cancer with the highest fatality rate.
It also causes cataracts and suppression of the immune
system.
The effects of UV-b radiation on plant and aquatic ecosystems
are not well understood. However, the growth of certain food
plants can be slowed by excessive UV-b radiation. In addition,
some scientists suggest that marine phytoplankton, which are
the base of the ocean food chain, are already under stress from
UV-b radiation. This stress could have adverse consequences
for human food supplies from the oceans. Because they
absorb C02 from the atmosphere, significant harm to
phytoplankton populations could increase global warming (see
following section on Global Warming and Climate Change).
Programs to Restore the Stratospheric Ozone Layer:
In 1987, 27 countries signed the Montreal Protocol, a landmark
treaty that recognized the international nature of ozone
depletion and committed the world to limiting the production of
375
350
325
Q^
01
e
8
o
§ 300
275
78
80
82
84
86
88 90
Year
92
94
96
Trend:
3.4 percent
decrease
Source: National Oceanic and Atmospheric Administration, 1998.
Monthly average total ozone measured in Dobson Units (DU) at four mid-latitude stations across the United States from
1979 to 1997. The trend line shows a 3.4 percent decrease in average total ozone over mid-latitudes in the United States
since 1979. The large annual variation shown in each of the four cities is a result of ozone transport processes which
cause increased levels in the winter and spring and lower ozone levels in the summer and fall at these latitudes.
18
-------
UV-b Radiation Increases by Latitude
BSN: 6.8%
5SN: 7.3%
45N: 5.0%
35N:
25W: 1.2%
1SN: 0.1%
Equator
45S: 5.5%
55S: 9.9%
65S: 11.0%-
^4 7PP<5 5/Mc/V using satellite-based analyses of UV-b trends demonstrated that UV-b levels had increased at ground level.
This figure shows the percent increases in average annual UV-b reaching the surface over the past 10 years. UV-b
incidence is strongly dependent on latitude. At latitudes that cover the United States, UV-b levels are 4 to 5 percent
higher that they were 10 years ago.
ozone-depleting substances. Today, over 160 nations have
signed the Protocol, which has been strengthened four times
and now calls for the elimination of those chemicals that deplete
ozone.
The 1990 Clean Air Act Amendments established a U.S.
regulatory program to protect the stratospheric ozone layer.
In January 1996, U.S. production of many ozone-depleting
substances virtually ended, including CFCs, carbon
tetrachloride, and methyl chloroform. Production of halons
ended in January 1994. Many new products that either do not
affect or are less damaging to the ozone layer are now gaining
popularity. For example, computer-makers are using
ozone-safe solvents to clean circuit boards, and automobile
manufacturers are using HFC-134a, an ozone-safe refrigerant,
in new motor vehicle air conditioners. In some sectors, the
transition away from ozone-depleting substances has already
been completed. EPA is also emphasizing new efforts like the
UV Index, a daily forecast of the strength of UV radiation people
may be exposed to outdoors, to educate the public about the
health risks of overexposure to UV radiation and the steps they
can take to reduce those risks.
Trends in Stratospheric Ozone Depletion: Scientific
evidence shows that the approach taken under the Montreal
Protocol has been effective. In 1996, measurements showed
that the tropospheric concentrations of methyl chloroform had
started to fall, indicating that emissions had been greatly
reduced. Tropospheric concentrations of other ozone-depleting
substances, like CFCs, are also beginning to decrease. It takes
several years for these substances to reach the stratosphere
and release chlorine and bromine. For this reason,
stratospheric chlorine levels are expected to continue to rise,
peak by the year 2000, and then slowly decline. Because of the
stability of most ozone-depleting substances, chlorine will be
released into the stratosphere for many years, and the ozone
layer will not fully recover until well into the next century.
In 1996, scientists developed a new technique allowing them to
draw conclusions about UV-b radiation at ground level.
According to satellite-based trend analyses, major populated
areas have experienced increasing UV-b levels over the past 15
years. As shown by the figure above, at latitudes that cover the
United States, UV-b levels are 4 to 5 percent higher than they
were 10 years ago.
19
-------
GLOBAL WARMING
AND CLIMATE CHANGE
Nature and Sources: The Earth's climate is fueled by the
Sun. Most of the Sun's energy, called solar radiation, is
absorbed by the Earth, but some is reflected back into space.
A natural layer of atmospheric gases absorbs a portion of this
reflected solar radiation, eventually releasing some of it into
space, but forcing much of it back to Earth. There it warms the
Earth's surface creating what is known as the natural
"greenhouse effect," as illustrated in the diagram below.
Without the natural greenhouse effect, the Earth's average
temperature would be much colder, and the planet would be
covered with ice.
Recent scientific evidence shows that the greenhouse effect is
being increased by release of certain gases to the atmosphere
that cause the Earth's temperature to rise. This is called "global
warming." Carbon dioxide (C02) accounts for about 85 percent
of greenhouse gases released in the United States. Carbon
dioxide emissions are largely due to the combustion of fossil
fuels in electric power generation. Methane (CH4) emissions,
which result from agricultural activities, landfills, and other
sources, are the second largest contributor to greenhouse
gases in the United States.
Industrial processes such as foam production, refrigeration, dry
cleaning, chemical manufacturing, and semiconductor
manufacturing produce other greenhouse gas emissions, such
as hydrofluorocarbons (MFCs). Smelting of aluminum produces
another greenhouse gas called perfluorinated compounds
(PFCs). Emissions of N0x and VOC from automobile exhaust
and industrial processes contribute to the formation of ground-
level ozone or smog, also a greenhouse gas.
The
Effect
Some solar radiation
is reflected by the Earth
and the atmosphere.
Solar
radiation
passes
through
the clear
atmosphere.
Some of the infrared
radiation passes through
the atmosphere, and
some is absorbed and
re-emitted in all directions
by greenhouse gas molecules.
The effect of this is to
warm the Earth's surface and
the lower atmosphere.
radiation is absorbed
y the Earth's surface and
varms it.
Infrared radiation
is emitted from the
Earth's surface.
Source: U.S. Department of State, 1992
The greenhouse effect is being accelerated by releases of certain gases to
the atmosphere that are causing the Earth's temperature to rise.
20
-------
Health and Environmental Effects: Greenhouse gas
emissions could cause a 1.8° to 6.3° Fahrenheit rise in
temperature during the next century, if atmospheric levels are
not reduced. Although this change may appear small, it could
produce extreme weather events, such as droughts and floods;
threaten coastal resources and wetlands by raising sea level;
and increase the risk of certain diseases by producing new
breeding sites for pests and pathogens. Agricultural regions
and woodlands are also susceptible to changes in climate that
could result in increased insect populations and plant disease.
This degradation of natural ecosystems could lead to reduced
biological diversity.
International Developments: In 1988, the Intergovernmen-
tal Panel on Climate Change (IPCC) was formed to assess the
available scientific and economic information on climate change
and formulate response strategies. In 1995, the IPCC pub-
lished a report representing the work of more than 2,000 of the
world's leading scientists. The IPCC concluded that humans
are changing the Earth's climate, and that "climate change is
likely to have wide-ranging and mostly adverse impacts on
human health, with significant loss of life."
In 1992,150 countries signed the "Framework Convention on
Climate Change" (FCCC), which has the objective of stabilizing
the concentration of greenhouse gases in the atmosphere at
levels that would prevent dangerous interference with the climate
system. Under the FCCC, industrialized countries agreed to aim
to reduce greenhouse gas emissions to 1990 levels by the year
2000. It now appears that most industrialized countries,
including the United States, will not meet this target. In light of
the 1995 scientific findings of the IPCC and the continued rise in
greenhouse gas emissions, parties to the FCCC formulated the
"Kyoto Protocol" at a 1997 conference held in Kyoto, Japan. The
Kyoto Protocol includes greenhouse gas emission targets for
industrialized countries for the period of 2008-2012. The average
reduction target for all industrialized countries for this period is 5
percent below 1990 emission levels. The reduction target varies
across countries to account for differing circumstances, with the
United States' target being a 7 percent reduction below 1990
levels. The Kyoto Protocol also provides for market-based
measures, such as international emissions trading, to help
countries meet their commitments at the lowest possible cost.
(The U.S. Administration will seek the Senate's consent for
ratification of the Kyoto Protocol after working for further progress
on the details of the market mechanisms and on the involvement
of key developing countries.)
U.S. Programs to Mitigate Climate Change: The United
States adopted a Climate Change Action Plan (CCAP) in 1993
to reduce greenhouse gas emissions. Thousands of companies
and nonprofit organizations are working together to effectively
reduce their emissions. The Plan involves more than 40
programs implemented by EPA, the Department of Energy, the
Department of Agriculture, and other government agencies.
In 1997, these voluntary programs reduced greenhouse gas
emissions by more than 15 million tons of carbon, while
partners saved over $1 billion from energy bill savings.
1996 Greenhouse Gas Emissions
Fluorinated
Compounds
2%
Nitrous Oxide
6%
Methane
10%
Carbon Dioxide
82%
1996 total greenhouse gas emissions
rose 9.5 percent from 1990 baseline
levels. The major contributor to
these emissions is carbon dioxide
(CO J from fossil fuel combustion.
Other contributors include methane
gas (CHJ from landfills, fermentation,
natural gas systems, and coal mining;
nitrous oxide (Nf>) from agricultural
management and mobile sources, and
fluorinated compounds from such processes as
aluminum and magnesium production and
electrical transmission and distribution systems.
21
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CONCLUSION
ACRONYMS
The Clean Air Act has been the impetus for many improvements
in the quality of the air in the United States. Scientific and
international developments continue to have an effect on the air
pollution programs that are implemented by the U.S.
Environmental Protection Agency. New data helps identify
sources of pollutants and the properties of these pollutants.
Although much progress has been made to clean up our air,
work must continue to ensure steady improvements in air
quality, especially because our lifestyles create more pollution
sources. Many of the strategies developed by EPA have been
adopted by state, local, and Tribal governments as well as
business and industry. Air quality improvements are the result of
partnerships with government, industry, and the public.
For further information:
National Air Pollutant Emission Trends, 1900-1997
Call: (919)541-5285
Internet: http ://www. epa. gov/oar/oaq ps/efig
National Air Quality and Emissions Trends Report,
1997 (EPA-454/R-98-016)
Call: (919)541-5558
Internet: http://www.epa.gov/oar/aqtrnd97
This brochure is available on the Internet at:
http://www.epa.gov/oar/aqtrnd97/brochure
Acid Rain Hotline: (202) 564-9620
Energy Star (Climate Change) Hotline: (888) STAR YES
Mobile Sources National Vehicles and Fuel
Emissions Lab: (734)214-4200
Stratospheric Ozone Hotline: (800) 296 1996
Principal Pollutants:
CO
Pb
N02, N0x
3
PM-10
PM-2.5
S02,SOx
Carbon Monoxide
Lead
Nitrogen Dioxide, Nitrogen Oxides
Ozone
Particulate Matter (10 micrometers
in diameter or less)
Particulate Matter (2.5 micrometers
in diameter or less)
Sulfur Dioxide, Sulfur Oxides
Other Pollutants:
CFCs
CH4
C02
HFCs
N20
PFCs
VOC
Chlorofluorocarbons
Methane
Carbon Dioxide
Hydrofluorocarbons
Nitrous Oxide
Perfluorinated Carbons
Volatile Organic Compounds
Other Acronyms:
DU Dobson Unit(s)
EPA Environmental Protection Agency
FCCC Framework Convention on Climate Change
IPCC Intergovernmental Panel on Climate Change
NAAQS National Ambient Air Quality Standard
NTI National Toxics Inventory
PAMS Photochemical Assessment Monitoring Stations
ppm parts per million
ng/m3 micrograms per cubic meter
UV-b Ultraviolet radiation
22
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