United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park NC 27711
August 2000
EPA-454/F-00-002
Air
EPA Latest Findings on National Air
Quality: 1999 Status and Trends
www.epa.gov/airtrends
Recycled/Recyclable • Printed with Vegetable Oil Based Inks on Recycled Paper (Minimum 30% Postconsumer)
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EPA Latest Findings on National Air
Quality: 1999 Status and Trends
National Air Quality 2
Six Principal Pollutants 4
Acid Rain 16
Visibility 18
Toxic Air Pollutants 20
Stratospheric Ozone 22
Global Warming & Climate Change 24
Conclusion 26
Acronyms 26
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National Air Quality
Six Principal Air Pollutants Tracked
Nationally
• Carbon Monoxide (CO)
• Lead(Pb)
• Nitrogen Dioxide (NO2)
• Ozone (O3) - formed by volatile organic
compounds (VOCs) and nitrogen
oxides (NOX)
• Particulate Matter (PM)
• Sulfur Dioxide (SO2)
Comparison of 1970 and 1999 Emissions
Million tons
Thousand tons
140
120
100
80
60
40
20
Ih
ru
CO NOX VOC S02 PM10
(-29%) (+17%) (-43%) (40%) (-77%)
100
50
This summary report highlights the U.S. Environ-
mental Protection Agency's (EPA's) most recent
evaluation of status and trends in our nation's air
quality.
More detailed information on air pollution
trends is available at www.epa.gov/airtrends.
Highlights
• Overall, national air quality levels measured at
thousands of monitoring stations across the
country have shown improvement over the
past 20 years for all six principal pollutants.
• Despite this progress, over 150 million tons of air pollution were released into
the air in 1999 in the United States, and approximately 62 million people lived
in counties where monitored data showed unhealthy air for one or more of
the six principal pollutants.
• While the national trends continue to improve, air quality trends for some
areas, including rural locations, have actually worsened. Some national parks,
including the Great Smoky Mountains and Shenandoah, have high air
pollution concentrations resulting from the transport of pollutants many miles
from their original sources. In 1999, for the second consecutive year, average
rural 1-hour ozone (smog) levels were greater than the average levels
observed for urban sites.
• Between 1900 and 1970, emissions of the six principal pollutants increased
significantly. For example, estimated emissions of nitrogen oxides (NOX)
increased 690 percent, volatile organic compounds increased 260 percent, and
sulfur dioxide 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.
• Since the 1970 Clean Air Act was signed into law, emissions of each of the six
pollutants decreased, with the exception of NOX. Between 1970 and 1999,
emissions of NOX increased 17 percent. The majority of this increase can be
attributed to heavy-duty diesel vehicles and coal-fired power plants. EPAhas
major initiatives to reduce emissions of NOX considerably from these sources.
Emissions of NOX contribute to the formation of ground-level ozone (smog),
acid rain, and other environmental problems, even after being carried by the
wind hundreds of miles from their original source.
• Estimates of nationwide air toxic emissions have dropped approximately 23
percent between 1990 and 1996. For example, perchloroethylene monitored
in 16 urban sites in California showed a drop of 60 percent from 1989 to 1998.
Benzene is another widely monitored toxic air pollutant. It is emitted from
cars, trucks, oil refineries, and chemical processes. Measurements taken from
84 urban monitoring sites around the country show a 39-percent drop in
benzene levels from 1993 to 1998.
• Since implementation of EPA's acid rain program in 1995, there have been
dramatic reductions (10 to 25 percent) in sulfates deposited in many of the
most acid sensitive ecosystems located in the Northeastern United States.
• 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
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humans. Currently, about 2500 U.S. water bodies are under fish consumption
advisories resulting from chemicals such as PCBs, chlordane, dioxins, and mercury.
• Scientific evidence shows that efforts taken to protect the stratospheric ozone
layer have been effective to date. In 1996, measurements in the upper layers of
the atmosphere showed concentrations of methyl chloroform had started to
fall, indicating emissions had been greatly reduced. Concentrations of other
ozone-depleting substances, like chlorofluorocarbons, are also beginning to
decrease.
Air Pollution
The Concern
Exposure to air pollution is associated with numerous effects on human
health, including respiratory problems, hospitalization for heart or lung
diseases, and even premature death. The average American breathes 3,400
gallons of air each day. Children are at greater risk because they are more
active outdoors and their lungs are still developing. The elderly are also more
sensitive to air pollution because they often have heart or lung diseases.
Air pollution, such as acid rain, ground-level ozone, and air toxics, can also
significantly affect ecosystems. For example, ground-level ozone has been
estimated to cause over $500 million in annual reductions of agricultural and
commercial forest yields, and airborne releases of NOX are one of the largest
sources of nitrogen pollution in certain water bodies such as the Chesapeake Bay.
The Causes
Air pollution comes from many different sources. "Stationary sources," such
as factories, power plants, and smelters; "area sources," which are smaller
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 wildfires, all contribute to air pollution.
The Law
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, EPAhas a number of responsibilities, including:
• Setting national ambient air quality standards (NAAQS) for the six principal
pollutants that are considered harmful to public health and the environment.
• Ensuring that these air quality standards are met (in cooperation with the state,
tribal, and local governments) through national standards and strategies to
control air pollutant emissions from vehicles, factories, and other sources.
• Reducing emissions of sulfur dioxide and nitrogen oxides that cause acid rain.
• 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 and
other adverse human health and environmental effects are well controlled, and
that risks to public health and the environment are substantially reduced.
• Limiting the use of chemicals that damage the stratospheric ozone layer in
order to prevent increased levels of harmful ultraviolet radiation.
While the focus of this report is on national air pollution, 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
discussed.
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Six Principal Pollutants
Revised Ozone and Particulate Matter
Standards
In 1997, EPA revised national air quality
standards for ozone and particulate
matter. The PM standard added an
indicator for PM2.s (particles less than or
equal to 2.5 micrometers) to strengthen
protection against smaller particles. The
ozone standard changed from a 1-hour
standard to an 8-hour standard to better
reflect ozone health studies. In May 1999,
1he U.S. Court of Appeals for the District
of Columbia Circuit remanded these
standards back to EPA for further
consideration. Following a denial of a
petition for a rehearing by the D.C. Circuit,
the Supreme Court has agreed to hear the
case. Updates on this action can be
found at http://www.epa.gov/airiinks.
Percent Change in Air Quality
1980-1999 1990-1999
Pb
NO2
O31-hr
8-hr
PM10
-57
-94
-25
-20
-12
-36
-60
-10
-4
no change
-18
Percent Change in Emissions
1980-1999 1990-1999
CO
Pb
NOX
VOC
PM10
-23
+2
-15
-16
Air quality concentrations do not always track
nationwide emissions. Because most monitors are
located in or near urban areas, air quality trends
are affected by urban emissions which are
sometimes different than nationwide emissions.
year-to-year air quality trends can also be affected by
atmospheric conditions and other factors.
Under the Clean Air Act, EPA
establishes air quality standards
to protect public health, includ-
ing the health of "sensitive"
populations such as asthmatics,
children, and the elderly. EPA
also sets 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
(also referred to as criteria pollutants): carbon monoxide (CO), lead
(Pb), nitrogen dioxide (NO2), ozone (O3), particulate matter (PM), and
sulfur dioxide (802). [Note: The pollutant ozone is not emitted directly
into the air, but is formed when sunlight acts on emissions of nitrogen
oxides (NOX) and volatile organic compounds (VOCs).]
Each year EPA examines changes in levels of these pollutants over
time and summarizes the current air pollution status.
Summary of Air Quality and Emissions Trends
EPA tracks trends in air quality based on actual measurements of
pollutant concentrations in the ambient (outside) air at monitoring
sites across 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 stations on a yearly basis. The
chart at the left shows that the air quality based on concentrations of
the principal pollutants has improved nationally over the last 20
years (1980-1999). The most notable improvements are seen for Pb,
CO, and SO2 with 94-, 57- and 50-percent reductions, respectively.
EPA estimates nationwide emissions based on actual monitored
readings or engineering calculations of the amounts and types of
pollutants emitted by vehicles, factories, and other sources. Emis-
sion estimates 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 estimates also reflect changes in air pollution regulations
and installation of emissions controls. The 1999 emissions reported
in this summary report are projected numbers based on available
1999 information and historical trends. Check http://www.epa.gov/
ttn/chief for updated emissions information. As shown in the chart
at the lower left, emissions of the principal pollutants have de-
creased over the last 20 years (1980-1999), with the exception of
NOX. Nitrogen oxides emissions increased 1 percent over the last 20
years and 2 percent over the more recent 10-year period, 1990 to
1999.
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Comparison of Growth Areas and Emission Trends
U.S. Gross Domestic Product Increased 147%
Vehicle Miles Traveled Increased 140%
U.S. Population Increased 33%
Aggregate Emissions Decreased 31%
(Six Principal Pollutants)
1970
1980
1990
1999
Between 1970 and 1999, U.S. population increased 33 percent, vehicle miles traveled increased 140 percent, and gross domestic
product increased 147 percent. At the same time, total emissions of the six principal air pollutants decreased 31 percent.
Between 1970 and 1999, total emissions of the six principal
air pollutants decreased 31 percent. This dramatic im-
provement 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, approxi-
mately 62 million people nationwide still lived in counties
with pollution levels above the national air quality stan-
dards in 1999. This number does not take into consider-
ation the 8-hour ozone standard.
Number of People Living in Counties with
Air Quality Concentrations Above the Level
of the NAAQS in 1999
CO
Pb
N02
U3
PM10
PM25
S02
• 9.1
0.4
0
53.8 (1-hour)
(8-hour) 1 122.5
|20.3
Data not yet available.
0
1 62.1 (1-hour)
(8-hour) 125.3
20 40 60 80 100 120 140
Millions of People
Blue bars represent 8-hour standard for ozone.
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1
Ground-Level Ozone (O3)
VOC Emissions, 1980-1999
Thousand Tons Per Year
30,000
D Fuel Combustion • Industrial Processing
DTransportafion D Miscellaneous
1980-99: 33% decrease
1990-99: 15% decrease
Air quality concentrations do not always track
nationwide emissions. Because most monitors are
located in or near urban areas, air quality trends
are affected by urban emissions which are
sometimes different than nationwide emissions.
Year-to-year air quality trends can also be affected by
atmospheric conditions and other factors.
Ozone Air Quality, 1980-1999
(Based on Annual 2nd Daily 1-Hour Maximum)
Concentration, ppm
0.2
0.15
0.1
0.05
90% of sites have concentrations below this line
441 Sites
National Standard
703 Sites
10% of sites have concentrations below this line
80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99
1980-99: 20% decrease
1990-99: 4% decrease
Because few sites have 20 years of data, EPA used
two consecutive 10-year periods to construct this
20-year trend.
Nature and Sources
of the Pollutant
Ground-level ozone (the
primary constituent of
smog) continues to be a
pollution problem
throughout many areas of
the United States.
Ozone occurs naturally in the stratosphere and provides a
protective layer high above the Earth. See page 22 for more
information on the stratospheric ozone layer.
Ozone is not emitted directly into the air but is formed by the
reaction of VOCs and NOX 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 region to region.
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 emer-
gency room visits for respiratory causes have been associated with
ambient ozone exposures. Exposures to ozone can make people
more susceptible to respiratory infection, result in lung inflamma-
tion, 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 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., some outdoor workers)
and individuals with pre-existing respiratory disease such as
asthma and chronic lung disease. In addition, longer-term expo-
sures to moderate levels of ozone present the possibility of irrevers-
ible changes in the lung structure which could lead to premature
aging of the lungs and worsen chronic respiratory illnesses.
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0.15
0.05
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.
Trends in Ozone Levels
In 1997, EPA revised the national ambient air quality
standard for ozone by setting a new 8-hour 0.08 ppm stan-
dard. Currently, EPA is tracking trends based on the 1-hour
and 8-hour data. As of the publication date of this report, the
8-hour standard is under legal challenge. Updates on this action can
be found at http://www.epa.gov/airlinks.
Over the past 20 years, ambient ozone levels decreased 20 percent
based on 1-hour data, and 12 percent based on 8-hour data. Be-
tween 1980 and 1999, emissions of VOCs have decreased 33 percent.
During that same time period, emissions of NOX increased 1 percent.
Because sunlight and heat play a major role in ozone formation,
changing weather patterns contribute to yearly differences in
ozone concentrations. To better reflect the changes that
emissions have on measured air quality concentrations,
EPA is able to make analytical adjustments to account for
this annual variability in meteorology. For 53 metropoli-
tan areas, the adjusted trend for 1-hour ozone levels
shows steady improvement from 1980 through the mid-
1990s. The adjusted ozone levels decreased an average of
1 percent per year through 1994. However, beginning in
1994, the improvement appears to slow.
Ozone Air Quality, 1980-1999
(Based on Annual 4th Daily 8-Hour Maximum)
Concentration, ppm
0.2
90% of sites have concentrations below this line
^^^^_ 705 Sites
"" National' Standard
10% of sites have concentrations below this line
80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99
1980-99:
1990-99:
12% decrease
no change
Because few sites have 20 years of data, EPA used
two consecutive 10-year periods to construct this
20-year trend.
Comparison of Actual and Meteorologically
Adjusted 1-hour Ozone Trends, 1980-1999
Concentration, ppm
0.12 |
0.11
0.10
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0.00
Selected Area Trend in Average Daily Maximum 1-Hour Concentrations
Mateorolaalcallv Adjusted Trend
BO 81 82 83 84 85
87 88 89 90 91 92 93 94 95 96 97 98 99
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Trend in 1-Hour Ozone Levels, 1980-1999
Averaged Across EPA Regions
(Based on Annual Second Highest Daily Maximum)
20*
Alaska is in EPA Region 10; Hawaii, EPA Region 9; and
Puerto Rico, EPA Region 2. Concentrations are ppm.
Trend in 1-Hour Ozone Levels, 1980-1999
by Location of Site
(Based on Annual Second Highest Maximum)
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
National Standard
Rural Suburban Urban
80 82 84 86 88 90 92 94
Trend in 8-Hour Ozone Levels, 1990-1999
At Rural Eastern U.S. Monitoring Locations
(Based on Annual Fourth Highest Maximum)
Concentration, ppm
0.12
0.1
0.08
0.06
0.04
0.02
0% of sites have concentrations below this line
34 Sites
10% of sites have concentrations below this line
For the period 1980 to 1999, the downward trend in 1-hour ozone
levels seen nationally is reflected in every broad geographic area in
the country. The Northeast and West exhibit the most substantial
improvement while the South has experienced the least rapid
progress in lowering ozone concentrations.
Across the country, the highest ambient ozone concentrations are
typically found at suburban sites, consistent with the downwind
transport of emissions from urban centers. During the past 20 years,
ozone concentrations decreased almost 25 percent at urban sites
(121 such sites between 1990 and 1999, and 96 between 1980 and
1989) and declined by 20 percent at suburban sites (325 such sites
between 1990 and 1999, and 215 between 1980 and 1989). For the
more recent 10-year period, urban sites show decreases of approxi-
mately 6 percent and suburban sites show 4-percent decreases.
However, at rural monitoring locations, 1-hour ozone levels for 1999
are only 14 percent lower than those in 1980 and only 2 percent
below 1990 levels. In 1999, for the second consecutive year, average
rural 1-hour ozone levels are greater than the levels observed for the
urban sites.
Over the last 10 years, 8-hour ozone levels in 25 of our national
parks increased nearly 8 percent. Nine monitoring sites in eight of
these parks experienced statistically significant upward trends in
8-hour ozone levels: Great Smoky Mountain (TN), Big Bend (TX),
Cape Remain (SC), Cowpens (SC), Denali (AK), Everglades (FL),
Mammoth Cave (KY), and Voyageurs (MN). For the remaining 17
parks, the 8-hour ozone levels at eight increased only slightly
between 1990 and 1999, while seven showed decreasing levels, and
two were unchanged.
Additional data from rural sites in the eastern United States show
increases in 8-hour ozone levels similar to those found in the
national parks over the last 10 years. The 8-hour ozone levels at
these 34 rural sites, which were the highest during the hot and dry
summers of 1991 and 1998, increased 6 percent over the last 10 years.
90 91 92 93 94 95 96 97 98 99
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Participate Matter (PM10)
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.
PM2.5 describes the "fine" particles that are less than or equal to
2.5 micrometers in diameter. "Coarse" particles refers to
particles greater than 2.5, but less than or equal to 10 microme-
ters in diameter. PMjo refers to all particles less than or equal to
10 micrometers in diameter. Ten micrometers are about one-
seventh the diameter of human hair. These particles originate
from many different stationary and mobile sources as well as
from natural sources. Fine particles result from fuel combustion
from motor vehicles, power generation, and industrial facilities,
as well as from residential fireplaces and wood stoves. Coarse
particles are generally emitted from sources such as vehicles traveling
on unpaved roads, materials handling, crushing and grinding
operations, and windblown dust. Some particles are emitted directly
from their sources, such as smokestacks and cars. In other cases,
gases such as SC>2, NOX, and VOCs interact with other compounds in
the air to form fine particles. Their chemical and physical composi-
tions vary depending on location, time of year, and weather.
Health and Environmental Effects
Particulate matter includes both fine and larger coarse particles.
When breathed, 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, de-
creased 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 impact vegetation
and ecosystems and can cause damage to paints and
building materials.
Trends in PM10
Levels
Between 1990 and
1999, average PM10
concentrations
decreased 18
percent, while PMjo
emissions decreased 16
percent.
PM10 Emissions from Man-Made Sources,
1980-1999
In (985, EPA retried its methods for estimating emissions.
Thousand Tons PerYfear
7,000
6,000
5,000
4,000
3,000
2,000
1,000
1980-99:
1990-99:
55%
16%
decrease
decrease
Air quality concentrations do not always track
nationwide emissions. Because most monitors are
located in or near urban areas, air quality trends
are affected by urban emissions which are
sometimes different than nationwide emissions.
Year-to-year air quality trends can also be affected by
atmospheric conditions and other factors.
PM10 Air Quality, 1980-1999
(Based on Annual Arithmetic Mean)
Concentration, ug/m3
60
so
40
30
20
10
National Standard
90% of sites have concentrations below this line
Ten-year trend
not available
before 1990.
10% of sites have concentrations below this line
80 81 82 83 84 85 86 87 88 89 90 91 92
94 95 96 97
1990-99: 18% decrease
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Fine Participate Matter (PM2.5)
New PM25 Monitoring Network
Characterizing PM2.5 Trends
EPA is not yet able to characterize long term trends for PM^.s for
urban areas. In early 1999 EPA initiated a new monitoring network
to begin assessing the nature of the PM2.s problem. By December
2000 the network will consist of approximately 1,700 monitors at
over 1,100 sites, as shown in the map on the left. EPA will begin
analyzing preliminary PM2.s monitoring data later in 2000 and
future reports will reflect data gathered from this new network.
EPA does have some air quality monitoring data for PM^.s from a
network that has tracked levels of this pollutant at National Parks
and other rural sites.
Revised Particulate Matter Standards
Complete data from the new PM2 5 monitoring network
will be available later in 2000. However, EPA is able to
present PM2 5 data from a preexisting monitoring
network of rural sites. The map below shows that rural
PM2 5 concentrations vary regionally, with sites in the
East typically having higher annual average
concentrations. The pie charts indicate the chemical
constituents ofPM2 5 at each location.
While these data
cannot be used for
compliance purposes
(i.e., to tell whether or
not an area meets the
PM2.5 standard), they
provide a good
indication of PM2.5
In 1997, EPA added two newPM2.5
standards, set at 15 micrograms per
cubic meter (ug/m3) and 65 ug/m3,
respectively, for the annual and 24-hour
standards. EPA is beginning to collect
monitoring data on PM2.s
concentrations.
1998 Annual Average PM25 Concentrations (in ug/m3) in Rural Areas
S.72
3.81
8.82,
Source: Interagency Monitoring of
Protected Visual Environments
Network, 1998.
Nitrates: predominately from automobiles and utijity and industrial boilers.
Organic Carbon: from sources such as automobiles, trucks, and industrial processes.
Elemental Carbon (soot): from diesel, wood, and other combustion.
Crustal Material (soil dust): from roads, construction, and agricultural activities.
Sulfate: predominately from utility and Industrial boilers.
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concentrations and trends in rural areas, as well as the
sources of the fine particles at the various locations.
As shown in the map, rural PM^.s concentrations vary
regionally. Sites in the rural east typically have higher
PM2.5 concentrations. Of the 12 eastern sites, 10 have
higher annual averages of measured PM^.s than any
sites in the west. Much of this difference can be attrib-
uted to the high amounts of sulfate at the eastern sites.
Sulfates predominately result from sulfur dioxide
emissions from coal-fired power plants and industrial
boilers.
Sulfate and organic carbon (from sources such as
automobiles, trucks, and industrial processes) constitute
most of the PM2.s concentrations in both the east and the
west. However, sites in the east have on average a much
higher percentage of sulfate concentrations than those in
the west.
Percent Contribution to PM25
by Pollutant, 1998
East West
Sulfate
Organic Carbon
Nitrate
Elemental Carbon (soot)
Crustal Material (soil dust)
56
27
5
5
7
33
36
8
6
17
PM2.5 Trends in Rural Areas
Because of the significant regional variations in rural
PM2.5 concentrations, the analysis in this report aggre-
gates the trends separately for the eastern and western
parts of the nation. In the rural east, average PM2.5
concentrations decreased 9 percent between 1992 to
1995, then increased 12 percent from 1995 to 1998.
Much of the recent increase tracks increased emissions
of sulfur dioxide from coal-fired power plants not yet
regulated under EPA's Acid Rain Program. Beginning
in 2000, these plants will be controlled under Phase II of
the Acid Rain Program. The net change in the average
PM2.5 concentrations in the rural East between 1992 and
1998 is a 2-percent increase.
Average PM2.5 trends in the rural west showed a
decrease of 5 percent from 1992 to 1998, and a decrease
of 11 percent over the longer, 10-year period from 1989 to
1998.
Average PM25 Concentrations,
1989-1998 at Rural Eastern U.S. Sites
Concentration, ug/m3
15
14
13
12
11
10
9
8
7
3 Sites
10 Sites
Measured PM2.5
Sulfate
Organic Carbon
89 90 91 92 93 94 95 96 97 98
This plot shows average concentrations for sites
having available trend data in the East. Ten sites
have trend data between 1992 and 1998, and
three of those 10 sites have trend data prior to 1992.
Crustal Material
Elemental Carbon
Nitrate
Average PM25 Concentrations,
1989-1998 at Rural Western U.S. Sites
Concentration, ug/m3
6
24 Sites
Measured PM2.5
Organic Carbon
Sulfate
Crustal Material
Nitrate
Elemental Carbon
89 90 91 92 93 94 95 96 97 98
This plot shows average concentrations for sites
having available trend data in the West.
11
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3
Carbon Monoxide (CO)
CO Emissions, 1980-1999
Thousand Tons Per Year
140,000
DFuel Combustion n Industrial Processing
DTransportation D Miscellaneous
In (985, EPA renneo/te methods for estimating emissions.
1980-99: 22% decrease
1990-99: 7% decrease
Air quality concentrations do not always track
nationwide emissions. Because most monitors are
located in or near urban areas, air quality trends
are affected by urban emissions which are
sometimes different than nationwide emissions.
Year-to-year air quality trends can also be affected by
atmospheric conditions and other factors.
CO Air Quality, 1980-1999
(Based on Annual 2nd Maximum 8-hour Average)
Concentration, ppm
16
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 com-
pletely. It is a component of motor vehicle exhaust, which contrib-
utes about 60 percent of all CO emissions nationwide. Non-road
vehicles account for the remaining CO emissions from the transpor-
tation sources category. 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
Nationally, the 1999 ambient average CO concentration is 57 percent
lower than that for 1980 and is the lowest level recorded during the
past 20 years. CO emissions levels decreased 22 percent over the
same period. Between 1990 and 1999, ambient CO concentrations
decreased 36 percent, and the estimated number of exceedances of
the national standard decreased 93 percent while CO emissions fell
7 percent. This improvement occurred despite a 30-percent increase
in vehicle miles traveled in the United States during this period.
80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99
1980-99:
1990-99:
57% decrease
36% decrease
Because few sites have 20 years of data, EPA used
two consecutive 10-year periods to construct this
20-year trend.
12
-------
Lead (Pb)
Tons Per Year
60,000 I
60,000
40,000
20,000
Nature and Sources of the
Pollutant
In the past, automotive sources
were the major contributor of
lead emissions to the atmo-
sphere. As a result of EPA's
regulatory efforts to reduce the
content of lead in gasoline, the
contribution from the transpor-
tation sector has declined over
the past decade. Today,
industrial processes, primarily metals processing, are the
major source of lead emissions to the atmosphere. The
highest air concentrations of lead are found in the vicinity of
nonferrous and ferrous smelters, and battery manufacturers.
Health and Environmental Effects
Exposure to lead occurs mainly through inhalation of air and
ingestion of lead 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 lead
may cause neurological impairments such as seizures, mental
retardation, and behavioral disorders. Even at low doses, lead
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 lead 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.
Lead Emissions, 1980-1999
DFuel Combustion • Industrial Processing
D Transportation
In 1985, EPA refined its methods for estimating emissions.
94 95 96 97 98
1980-99: 95% decrease
1990-99: 23% decrease
Air quality concentrations do not always track
nationwide emissions. Because most monitors are
located in or near urban areas, air quality trends
are affected by urban emissions which are
sometimes different than nationwide emissions.
Year-to-year air quality trends can also be affected by
atmospheric conditions and other factors.
Lead Air Quality, 1980-1999
(Based on Annual Maximum Quarterly Average)
Trends in Lead Levels
Because of the phase-out of leaded gasoline, lead emissions
and concentrations decreased sharply during the 1980s and
early 1990s. The 1999 average air quality concentration for
lead is 94 percent lower than in 1980. Emissions of lead
decreased 95 percent over that same 20-year period. Today,
the only violations of the lead national air quality standard
occur near large industrial sources such as lead smelters.
Concentration, ug/m3
80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99
1980-99: 94% decrease
1990-99: 60% decrease
Because few sites have 20 years of data, EPA used
two consecutive 10-year periods to construct this
20-year trend.
13
-------
5
Nitrogen Dioxide (NO2)
NOX Emissions, 1980-1999
Thousand Tons Per Year
D Fuel Combustion D Industrial Processing
DTransportation D Miscellaneous
25,000
20,000
15,000
10,000
5,000
In f 985, EPA refined Us methods for estimating emissions.
94 96 96 97
1980-99: 1% increase
1990-99: 2% increase
Air quality concentrations do not always track
nationwide emissions. Because most monitors are
located in or near urban areas, air quality trends
are affected by urban emissions which are
sometimes different than nationwide emissions.
Year-to-year air quality trends can also be affected by
atmospheric conditions and other factors.
NO2 Air Quality, 1980-1999
(Based on Annual Arithmetic Average)
Concentration, ppm
0.06
0.05
10% of sites have concentrations below this line
81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99
1980-99: 25% decrease
1990-99: 10% decrease
Because few sites have 20 years of data, EPA used
two consecutive 10-year periods to construct this
20-year trend.
Nature and Sources of the Pollutant
Nitrogen dioxide (NC>2) is a reddish brown, highly reactive gas that
is formed in the ambient air through the oxidation of nitric oxide
(NO). Nitrogen oxides (NOX), the term used to describe the sum of
NO, NO2 and other oxides of nitrogen, play a major role in the
formation of ozone, particulate matter, and acid rain. The major sources
of man-made NOX emissions are high-temperature combustion pro-
cesses, such as those occurring in automobiles and power plants.
Home heaters and gas stoves also produce substantial amounts of
NO2 in indoor settings.
Health and Environmental Effects
Short-term exposures (e.g., less than 3 hours) to low levels of nitro-
gen dioxide (NO2) 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 NO2 may lead to increased
susceptibility to respiratory infection and may cause permanent
alterations in the lung. Nitrogen oxides react in the air to form
ground-level ozone and fine particle pollution which are both
associated with adverse health effects.
Nitrogen oxides contribute to a wide range of environmental effects,
including the formation of acid rain and 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., excessive 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 20 years, monitored levels of NO2 have decreased 25
percent. All areas of the country that once violated the national air
quality standard for NO2 now meet that standard. While levels
around urban monitors have fallen, national emissions of nitrogen
oxides (which include NO, NO2 and other oxides of nitrogen) have
actually increased over the 20 years by one percent. This increase is
the result of a number of factors, the largest being an increase in
nitrogen oxides emissions from off-highway diesel vehicles. This
increase is of concern
because NOX emissions
contribute to the formation
of ground-level ozone
(smog), but also to other
environmental problems,
like acid rain and nitrogen
loadings to water bodies.
14
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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 SC>2 monitoring
stations are located in urban areas. The highest monitored
concentrations of SC>2 are recorded in the vicinity of large
industrial facilities. Fuel combustion, largely from coal-
fired power plants, accounts for most of the total SC>2
emissions.
SO2 Emissions, 1980-1999
5,000
Health and Environmental Effects
High concentrations of SC>2 can result in temporary
breathing impairment for asthmatic children and adults
who are active outdoors. Short-term exposures of asth-
matic individuals to elevated SO2 levels while at moderate
exertion may result in breathing difficulties that may be accom-
panied 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 SC>2, in conjunc-
tion with high levels of PM, include respiratory illness, alter-
ations 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.
In 1985, EPA refined Us methods for estimating emissions.
Thousand Tons Per Year
30,000
25,000
20,000
15,000
10,000
1980-99:
1990-99:
28%
21%
decrease
decrease
Together, SC>2 and NOX 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. Sulfur dioxide
also is a major precursor to PM^.s, which is a significant
health concern as well as a main pollutant that impairs
visibility.
Trends in SO2 Levels
Nationally, average SC>2 ambient concentrations have
decreased 50 percent from 1980 to 1999 and 36 percent over
the more recent 10-year period 1990-1999. SC>2 emissions
decreased 28 percent from 1980 to
1999 and 21 percent from 1990 to
1999. Reductions in SC>2 concentra-
tions and emissions since 1994 are
due, in large part, to controls
implemented under EPA's Acid
Rain Program beginning in 1995.
Air quality concentrations do not always track
nationwide emissions. Because most monitors are
located in or near urban areas, air quality trends
are affected by urban emissions which are
sometimes different than nationwide emissions.
year-to-year air quality trends can also be affected by
atmospheric conditions and other factors.
SO2 Air Quality, 1980-1999
(Based on Annual Arithmetic Mean)
Concentration,
0.04
ppm
0.03
0.02
0.01
National Standard
90% of sites have concentrations below this line
80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99
1980-99:
1990-99:
50%
36%
decrease
decrease
Because few sites have 20 years of data, EPA used
two consecutive 10-year periods to construct this
20-year trend.
15
-------
Acid Rain
Acid Rain Formation
Coal-fired electric utilities and other sources
that burn fossil fuels emit sulfur dioxide and
nitrogen oxides.
SO, Emissions from
Phase 1 Units
9.4
§
= 8-
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c
o
3 *"
I ,
uj 2-
£*
CO 0-
-1-
g.%
8J
7.4
4.5
/
MIO
7.1
4.8
6.0
4JJ
-mi
5SI
5.9
r7
sns
5.9
4J
4 —
Actual
Emissions
1980 1985 1990 1995 1996 1997 1998 1999
In 1999, actual emissions at the 263 highest-
emitting Phase I units were 1.6 million tons
below their allocated level.
NOX Emissions from
Phase I Units
1.4-
M
I 1.2-
1 1-
7 0.8-
§
3 °-6 -
iS 0.4-
d
z 0.2-
ri-
I.33
I
).91
(
J.92
(
1.94
1
).91
1990 1996 1997 1998 1999
1999 emissions from 265 NOX Phase I units
decreased 32 percent from 1990 levels.
Nature and Source of the Problem
Acidic deposition or "acid rain" occurs when emissions of sulfur
dioxide (802) and oxides of nitrogen (NOX) 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 SC>2 emissions and 26
percent of NOX emissions are produced by electric utility plants that
burn fossil fuels.
Health and Environmental Effects
Before falling to the Earth, SC>2 and NOX gases and related particu-
late 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 some trees
at high elevations. It also speeds the decay of buildings, statues, and
sculptures that are part of our national heritage. Reductions in SC>2
and NOX have begun to greatly reduce these negative environmental
effects and are leading to significant improvements in public health.
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 SC>2 and NOX. The program is being implemented in two
phases: Phase I began in 1995 for SC>2 and targets the largest and
highest-emitting coal-fired power plants (boilers). Phase I for NOX
began in 1996. Phase II for both pollutants began in 2000 and sets
restrictions on smaller coal-, gas-, and oil-fired plants.
The Acid Rain Program will reduce annual SC>2 emissions by 10
million tons from 1980 levels by 2010. The program sets a perma-
nent cap on the total amount of SC>2 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 NOX component of the Acid Rain Program establishes an
emission rate limit for all affected utilities, resulting in a 2 million
ton NOX reduction from 1980 levels by year 2000. 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.
-------
Emissions and Atmospheric Trends
SC>2 emissions reductions have been significant in the first 5 years of
compliance with EPA's Acid Rain Program. As shown in the graph
to the left, the Phase I utility units continued to emit well below the
allocated emission levels required by the Clean Air Act. Additional
units elected to participate early bringing the total number of Phase I
units to 398 in 1999. These 398 units emitted 4.9 million tons, which
continues to be well below (28 percent) the 1999 allocated emissions
level for SC>2.
Actual NOX emissions, as shown in the graph to the left, have also
declined since 1990. NOX emissions decreased by approximately
424,000 tons (32 percent) from 1990 levels. NOX emissions in 1999
decreased slightly (3 percent) from 1998 levels.
For all years from 1995 through 1998, both deposition and concen-
trations of sulfates in precipitation exhibited dramatic and unprec-
edented reductions over a large area of the eastern United States.
Deposition vs. Concentration
Think of putting the same amount of salt into two different
glasses of water (one full and one half-full). The total amount
(deposition) is the same, but the solution in the half-Hill glass has
a greater concentration.
Sulfate concentrations have been estimated to be 10 to 25 percent
lower than they would have been if the trend from 1983 through
1994 had continued. Similarly, sulfate deposition has also been
reduced (10 to 25 percent) over a large portion of the eastern United
States (see figures at right). These reductions in acid precipitation
are directly related to the large regional decreases in SC>2 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. The largest reductions
in wet sulfate depositions occurred across the Mid-Appalachian
and Northeast regions of the country. 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 apprecia-
bly different in 1995 to 1998 from historical levels.
These maps represent snapshots of wet sulfate
deposition over time. As shown in the lower
map, the most significant reductions occur
following the 1995 implementation of EPA's
Acid Rain Program. The greatest reductions
occur in the northeastern United States, where
many of the most acid sensitive ecosystems are
located.
Trends in Sulfate Deposition in
Precipitation
Less
sulfate
deposition
units are kilograms per hectare
More
sulfate
deposition
Source: J. A. Lynch, et al., 2000.
Atmospheric Environment and GAO Report
(GAO/RCED-00-47).
17
-------
Visibility
1970
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.
The Clean Air Act provides for the protection of visibility in national
parks and wilderness areas, also known as class I areas. These
include many of the best known and most treasured natural areas,
such as the Grand Canyon, Yosemite, Yellowstone, Mount Rainier,
Shenandoah, the Great Smokies, Acadia, and the Everglades. The
Clean Air Act's national goal calls for remedying existing visibility
impairment and preventing future impairment in these 156 class I
areas across the country.
Nature and Sources of the Problem
Visibility impairment is one of the most obvious effects of air pollution.
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 contrib-
ute 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 (802) emissions from power plants
and other industrial facilities; and nitrates, formed from nitrogen
oxides (NOX) emissions from power plants, automobiles, and other types
of combustion sources. In the Eastern United States, reduced visibility is
mainly attributable to secondarily-formed sulfates. 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 to 80
percent in the East as compared to 50 to 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 to the left 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
18
-------
between 1980 and 1990. This follows the overall trend in emissions
of sulfur oxides during these periods.
Visibility Monitoring Network and Current Conditions
In 1987, a visibility monitoring network for national parks and
wilderness areas 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.
The network is the largest in the country devoted to fully characteriz-
ing visibility. Data are collected and analyzed to determine the types
of sources and pollutants primarily responsible for reduced visibil-
ity. EPA is currently in the process of expanding the network to
include monitors in 110 national parks and wilderness areas across
the country.
Data collected from this network show that, currently, visibility
impairment is generally worse in the rural East compared to most of
the West. For example, the average visual range in most Eastern
class I areas is 15-25 miles as compared to estimated natural
visibility of about 90 miles. In the West, where pristine conditions
should be about 140 miles, the average visual range is 35-90 miles
for most class I areas.
Programs to Improve Visibility
EPA issued a new regional haze program in April 1999. The pro-
gram addresses visibility impairment in national parks and wilder-
ness areas caused by numerous sources located over broad regions.
The program sets a framework for states to develop goals for improv-
ing visibility on the worst visibility days each year and to adopt
emission strategies to meet these goals. Because fine particles are
frequently transported hundreds of miles, pollution that occurs in
one state may contribute to the visibility impairment in another state.
For this reason, EPA encourages states to coordinate through
regional planning organizations to develop regional strategies to
improve visibility and to reduce pollutants that contribute to fine
particles and ground-level ozone. States are also required to review
progress every five years and revise any strategies as necessary.
Other air quality programs are expected to lead to emission reduc-
tions that will improve visibility in certain regions of the country.
EPA's Acid Rain Program is designed to achieve significant reductions
in SOX emissions, which is expected to reduce sulfate haze, particularly
in the Eastern United States. Additional control programs on sources of
NOX to reduce the formation of ground-level ozone can also improve
regional visibility conditions. In addition, programs to meet the
national ambient air quality standards, mobile source and fuel stan-
dards, air toxics, and programs to improve wood stove efficiency can
benefit areas adversely impacted by visibility impairment.
Great Smoky Mountains National Park
under a range of visibility conditions.
East
West
Sulfates
60-80% 25-65%
Organic Carbon 10-30% 15-35%
Nitrates
5-15% 5-45%
Elemental Carbon 5-15% 5-15%
(soot)
Crustal Material 5-15% 5-20%
(soil dust)
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.
-------
Toxic Air Pollutants
National Air Toxics Emissions
Major Sources
(Large Industrial)
Smaller Area
and
Other Sources
Nonroad Mobile
Sources
Onroad Mobile
Sources
4.6 Million Tons
(1996)
Note: These emissions are from outdoor
sources. Also, mobile source emissions do
not include diesel particulates.
National Air Toxics Emissions
(Total for 188 Toxic Air Pollutants)
Million Tons
Baseline
(1990-1993)
1996
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. Examples of toxic air
pollutants include benzene, found in gasoline; perchloroethylene, emitted
from some dry cleaning facilities; and methylene chloride, used as a
solvent by a number of industries. Most air toxics originate from
man-made sources, including mobile sources (e.g., cars, trucks, construc-
tion equipment) and stationary sources (e.g., factories, refineries, power
plants), as well as indoor sources (e.g., building materials and activities
such as cleaning). Some air toxics are also released from natural sources
such as volcanic eruptions and forest fires.
Health and Environmental Effects
People exposed to toxic air pollutants at sufficient concentrations may
experience various health effects including damage to the immune system,
as well as neurological, reproductive (e.g., reduced fertility), developmen-
tal, respiratory and other health problems. Many of these may increase
the risk of developing cancer or experiencing other serious health effects.
In addition to exposure from breathing air toxics, risks also are associated
with the deposition of toxic pollutants onto soils or surface waters, where
they are taken up by plants and ingested by animals and eventually
magnified up through the food chain. Like humans, animals may
experience health problems due to air toxics exposure.
Trends in Toxic Air Pollutants
EPA and states do not maintain a nationwide monitoring network for air
toxics, as they do for many of the other pollutants discussed in this report.
EPA has developed a National Toxics Inventory (NTI) to estimate and
track national emissions trends for the 188 toxic air pollutants regulated
under the Clean Air Act. In the NTI, EPA divides emissions into four
types of sectors: 1) major (large industrial) sources; 2) area and other
sources, which include smaller industrial sources, like small drycleaners
and gasoline stations, as well as natural sources, like wildfires; 3) onroad
mobile, including highway vehicles; and 4) nonroad mobile sources, like
aircraft, locomotives, and construction equipment.
As shown in the pie chart, based on 1996 estimates, the most recent year
of available data, the sources of toxic air pollutants are relatively equally
divided between the four types of sources. However, this distribution
varies from city to city.
While EPA and the states collect monitoring data for a number of toxic air
pollutants, the chemicals monitored, and the geographic coverage of the
monitors varies from state to state. Together with the emissions data
from the NTI, the available monitoring data help track trends in toxic air
pollutants in various locations around the country. EPA is in the process of
expanding the national monitoring network for a number of toxic air
pollutants.
Based on the data in the NTI, estimates of nationwide air toxics emissions
have dropped approximately 23 percent between 1990 and 1996. Al-
though changes in how EPA compiled the national inventory over time
-------
may account for some differences, EPA and state regulations, as
well as voluntary reductions by industry, have played an important
role in achieving large reductions in overall air toxic emissions.
Individual trends for different air toxics vary from pollutant to
pollutant. For example, data taken from California's monitoring
network for 16 urban sites show a nearly 60-percent reduction in
measured levels of perchloroethylene for the period 1989 to 1998.
Perchloroethylene is a chemical widely used in the drycleaning
industry. The NTI estimates that nationwide perchloroethylene
emissions dropped 66 percent from 1990 to!996. These reductions
reflect state and federal efforts to regulate emissions of this
pollutant, and industry efforts to move to other processes using
less toxic chemicals.
Benzene is another widely monitored toxic air pollutant. It is
emitted from cars, trucks, oil refineries, and chemical processes.
The graph at the lower right shows measurements of benzene
taken from 84 urban monitoring sites around the country. These urban
areas generally have higher levels of benzene than other areas of the
country. Measurements taken at these sites show a 39-percent drop in
benzene levels from 1993 to 1998. During this period, EPA phased in new
(so-called "tier 1") car emission standards; required many cities to begin
using cleaner burning gasoline; and set standards that required significant
reductions in benzene and other pollutants emitted from oil refineries and
chemical processes. EPA estimates that nationwide benzene emissions
from all sources dropped 25 percent from 1990 to 1996.
Programs to Reduce Air Toxics
As mentioned above, EPA has put into place important controls for
fuels and is continuing to take additional steps to reduce air toxics
from vehicles. By 2020, EPA anticipates there will be a 75-percent
reduction in key air toxics from highway vehicles from 1990 levels.
EPA has also taken important steps to reduce toxic air emissions
from large industrial sources such as chemical plants, oil refineries,
and steel mills, as well as some smaller sources such as dry cleaners,
chrome electroplaters, and commercial sterilizers. When fully
implemented, emission standards covering 82 stationary source
categories (e.g., pulp and paper mills, steel mills, oil refineries) are
projected to reduce annual air toxic emissions by 1.5 million tons.
EPAis continuing to develop additional air toxic emissions standards for
the remaining (96) industrial categories.
As part of the Agency's National Air Toxics Assessment, EPA is using
emissions from the NTI together with computer models to estimate
population exposures in 1996 and potential health effects associated with
33 priority air toxic pollutants. This work will help focus future efforts to
reduce air toxics and resultant health effects. EPA, states, and others are
working to improve the NTI and to expand the air toxics monitoring
networks to obtain more data to better understand air toxic emissions and
ambient concentrations nationally and locally.
Ambient Perchloroethylene
Annual Average Urban Concentrations in CA
(58-percent reduction, 1989-1998)
1989 1990 1991 1992 1993 1994 1995
1997 19
1993
Ambient Benzene
Annual Average Urban Concentrations,
Nationwide
(39-percent reduction, 1993-1998)
1994
1995
1997
For more information about EPA's air
toxics program, visit the Agency's
website at http://www.epa.gov/ttn/uatw.
21
-------
Stratospheric Ozone
375
Q 350
2 from the atmosphere, significant
harm to phytoplankton populations could increase global warming
(see following section on Global Warming and Climate Change).
94 96
22
-------
Programs to Restore the Stratospheric
Ozone Layer
In 1987, 27 countries signed the Montreal Protocol, a
treaty that recognized the international nature of
ozone depletion and committed the world to limiting
the production of ozone-depleting substances. Today,
over 170 nations have signed the Protocol, which has
been strengthened five times and now calls for the
elimination of those chemicals that deplete strato-
spheric 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 to date. In 1996, measurements
showed that the concentrations of methyl chloroform had started to
fall, indicating that emissions had been greatly reduced. Concentra-
tions of other ozone-depleting substances in the upper layers of the
atmosphere, 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 peak early in 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 century. All nations
that signed the Protocol must complete implementation of ozone
protection programs if full repair of the ozone layer is to happen.
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 4-5 percent higher than they were 10 years ago.
UV-b Radiation Increases by Latitude
A 1996 study 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—5 percent higher that they were 10 years
ago.
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Global Warming & Climate Change
The Greenhouse Effect
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. Clouds and a natural layer of atmospheric gases
absorb a portion of Earth's heat and prevents it from escaping to
space. This keeps our planet warm enough for life and is known as
the natural "greenhouse effect," as illustrated in the diagram below.
Without the natural greenhouse effect, the Earth's average tempera-
ture would be much colder, and the planet would be uninhabitable.
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 (CC>2) accounts for about 81 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 and in the transportation and industrial sectors. Meth-
ane (CH4) emissions, which result from agricultural activities,
landfills, and other sources, are the next largest contributors to
greenhouse gas emissions in the United
States and worldwide.
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.
The greenhouse effect is being accelerated by
releases of certain gases to the atmosphere that are
causing the Earth's temperature to rise.
Industrial processes such as foam produc-
tion, refrigeration, dry cleaning, chemical
manufacturing, and semiconductor
manufacturing produce other greenhouse
gas emissions, such as hydrofluoro-
carbons (HFCs). Smelting of aluminum
produces another greenhouse gas called
perfluorinated compounds (PFCs).
Emissions of NOX and VOCs from automo-
bile exhaust and industrial processes
contribute to the formation of ground-level
ozone or smog, also a greenhouse gas.
Health and Environmental Effects
In 1988, the Intergovernmental Panel on
Climate Change (IPCC) was formed to
assess the available scientific and eco-
nomic information on climate change. In
1995, the IPCC published a report repre-
senting 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."
According to the IPCC, greenhouse gas emissions could cause a 2° to
6° Fahrenheit rise in temperature during the next century, if atmo-
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spheric levels are not reduced. Although this change may appear
small, it could lead to more 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 1992, 150 countries signed the Framework Convention on Climate
Change (FCCC), which has the objective of stabilizing the concentra-
tion 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 commit-
ments 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 implemented a Climate Change Action Plan
(CCAP) in 1993 to reduce greenhouse gas emissions and help
achieve the goals of the FCCC. Thousands of companies and
nonprofit organizations are working together to effectively reduce
their emissions. The Plan involves more than 40 programs imple-
mented by EPA, the Department of Energy, the Department of
Agriculture, and other government agencies. In 1999, EPA's volun-
tary programs reduced greenhouse gas emissions by 44 million tons
of carbon, equivalent to eliminating the greenhouse gas emissions
from about 35 million cars. By investing in products that use energy
more efficiently, consumers and businesses have also saved more
than $4 billion on their 1999 energy bills while achieving these
environmental benefits.
1998 Greenhouse Gas Emissions
in the United States
Carbon Dioxide
81%
Fluorinated Compounds
2%
Nitrous Oxide
7%
Methane
10%
1998 total greenhouse gas emissions rose
11 percent from 1990 baseline levels. The
major contributor to these emissions is
carbon dioxide (CO:2) from fossil fuel
combustion. Other contributors include
methane gas (CH4)from landfills,
fermentation, natural gas systems, and coal
mining; nitrous oxide (N2O)from
agricultural management and mobile
sources, and fluorinated compounds from
such processes as aluminum and
magnesium production and electrical
transmission and distribution systems.
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Conclusion
Acronyms
CO Carbon Monoxide
Pb Lead
NO2, NOX Nitrogen Dioxide,
Nitrogen Oxides
O3 Ozone
PM-io Participate Matter
(10 micrometers in
diameter or less)
PM25 Participate Matter
(2.5 micrometers
in diameter or less)
SO2, SOX Sulfur Dioxide,
Sulfur Oxides
Other Pollutants
CFCs Chlorofluorocarbons
CH4 Methane
CO2 Carbon Dioxide
MFCs Hydrofluorocarbons
N2O Nitrous Oxide
PCBs Polychlorinated Biphenyls
PFCs Perfluorinated Carbons
VOCs Volatile Organic Compounds
Other Acronyms
CCAP Climate Change Action Plan
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
Standards
NTI National Toxics Inventory
The Clean Air Act has resulted in many improvements in the quality
of the air in the United States. Scientific and international develop-
ments continue to have an effect on the air pollution programs that
are implemented by the U.S. Environmental Protection Agency and
state and local agencies. New data help identify sources of pollut-
ants 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 for air quality
improvement will continue to be developed through coordinated
efforts with EPA, state, local and tribal governments, as well as
industry and other environmental organizations.
For Further Information
Detailed information on Air Pollution Trends:
http://www.epa.gov/airtrends
Real-Time Air Quality Maps and Forecasts:
http://www.epa.gov/airnow
On-line Air Quality Data:
http://www.epa.gov/airsdata
Acid Rain Website: http://www.epa.gov/acidrain
Global Warming Emissions Information:
http://www.epa.gov/globalwarming/emissions/national/index.html
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
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