<>EPA
United States
Environmental Protection
Agency
Latest Findings on National
Air Quality
2001 STATUS AND TRENDS
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Cover Photo of Mount McKinley, Denali National Park, Alaska, by Kim Ferguson.Waynesville. North Carolina
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EPA 454/K-02-001
September 2002
cli 1
2001 STATUS AND TRENDS
Contract No. GS-10F-0283K
Task Order No. TO 1307
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Emissions, Monitoring, and Analysis Division
Research Triangle Park, North Carolina
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Contents
National Air Quality 1
Six Principal Pollutants 3
Acid Rain 16
Visibility 18
Toxic Air Pollutants 20
Stratospheric Ozone 23
Conclusions 25
Acronyms 26
More detailed information on air pollution trends is available at
www.epa.gov/airtrends.
Information on global warming and global climate change is available at
www.epa.gov/globalwarming/publications/emissions and
www.epa.gov/globalwarming/publications/car.
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National Air Quality
This summary report highlights the U. S. Environmental
Protection Agency's (EPA's) most recent evaluation of the
status and trends in our nation's air quality.
EPA tracks air pollution
in two ways:
• Air quality measured
from over 3,000
locations (over 5,200
monitors) across the
nation operated
primarily by state,
local, and tribal
agencies.
• Emissions from all
sources going back
30 years.
Highlights
• Since 1970, aggregate emissions of the six
principal pollutants tracked nationally have
been cut 25 percent. During that same time
period, U.S. gross domestic product increased
161 percent, energy consumption increased
42 percent, and vehicle miles traveled increased
149 percent.
I National air quality levels measured at thou-
sands of monitoring stations across the country
have shown improvements over the past
20 years for all six principal pollutants.
• Despite this progress, almost 170 million tons
of pollution are emitted into the air each year
in the United States, and approximately
133 million people live in counties where
monitored air in 2001 was unhealthy at times
because of high levels of at least one of the six
principal air pollutants.
• The vast majority of areas that experienced
unhealthy air did so because of one or both
of two pollutants—ozone and participate
matter (PM). EPA is focusing its efforts to
control these pollutants by implementing
more stringent National Ambient Air Quality
Standards for ozone and PM and rules
reducing emissions from on-road transporta-
tion and stationary combustion sources. These
rules will bring reductions in emissions over
the next few years. Additional reductions will
be needed to provide clean air in the future.
EPA has submitted to Congress Clear Skies
legislation that, if enacted, would mandate
reductions of particle- and ozone- forming
compounds from power generators by 70
percent from current levels through a nation-
wide cap and trade program. EPA also expects
to propose nonroad vehicle regulations that
would help improve ozone and PM air quality.
EPA, states, and tribes have only recently
begun to measure fine particles (known as
PM2 5) in the air on a broad national basis.
In many locations, EPA now has 3 years of air
quality monitoring data to use in comparing
to the health-based standards for PM2 5. Based
on those data, areas across the Southeast,
Mid-Atlantic, and Midwest regions and
California have air quality that is unhealthy
due to fine particles. Eligh PM concentrations
in the eastern United States are due to
regional emissions from power plants and
motor vehicles in combination with local
emissions from transportation and other
sources. In California, high PM concentrations
tend to be due to mobile source emissions.
Of the six tracked pollutants, progress has been
slowest for ground-level ozone. The Northeast
and West exhibited the greatest improvement,
•while the South and North Central regions
experienced slower progress in lowering ozone
concentrations. Despite this progress in most
regions of the country, the average ozone
(8-hour) levels in 33 of our national parks have
increased over the past 10 years.
Ground-level ozone is not emitted directly
into the air but is formed in the atmosphere
by the reaction of volatile organic compounds
(VOCs) and nitrogen oxides (NOJ in the
presence of heat and sunlight. Although
emissions ofVOCs have decreased 16 percent
over the past 20 years, the lack of significant
reductions in regional-scale emissions of NOX,
a family of chemicals that can contribute to
the formation of ozone hundreds of miles
downwind, has slowed progress in reducing
ozone levels. Between 1982 and 2001, NOX
emissions in the United States increased
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Six Principal Air Pollutants Tracked Nationally
• Nitrogen Dioxide (NO2)
• Ozone (O3) - formed by volatile organic
compounds (VOCs) and nitrogen oxides
(NOX)
• Sulfur Dioxide (SO2)
• Particulate Matter (PM) - formed by SO2,
NOX, ammonia, VOCs, and direct particle
emissions
• Carbon Monoxide (CO)
• Lead (Pb)
9 percent (with a 3 percent decrease in the
past 10 years). The majority of this increase
is attributed to growth in emissions from
nonroad engines (like construction and recre-
ation equipment) and diesel vehicles. Emissions
of NOX also contribute to acid rain, haze,
particulate matter, and damage to waterbodies
like the Chesapeake Bay.
Sulfates formed primarily from sulfur dioxide
(SO2) emissions from coal-fired power plants
are a major component of fine particles in the
eastern United States. SO2 emissions decreased
25 percent from 1981 to 2001 and 24 percent
from 1992 to 2001. Nationally average SO2
ambient concentrations have been cut 52 per-
cent from 1982 to 2001 and 35 percent over
the more recent 10-year period from 1992 to
2001. Reductions in SO2 concentrations and
emissions since 1990 are primarily due to
controls implemented under EPA's Acid
Rain Program.
Based on EPA's recent National-Scale Air
Toxics Assessment for 1996, 3 of 32 urban air
toxics (chromium, a metallic compound used
in industrial processes such as plating; benzene,
primarily emitted by mobile sources such as
Comparison of 1970 and 2001 Emissions
100
CO
o 80
c
0
= 60
40
20
o
.
-
1
mJ
h
• 1970
D2001
1 0=
CO NOX VOC S02 PMio
(-19%) (+15%) (-38%) (-44%) (-76%)
200
o 150
c
to
| 100
I —
50
n
-
-
-
_
I
Pb
(-98%)
cars and trucks; and formaldehyde, emitted
by mobile sources and formed when other
compounds chemically react in sunlight)
appear to pose the greatest nationwide cancer
risk. One air toxic, acrolein — a by product of
combustion in mobile and industrial sources
— is estimated to pose the highest potential
on a nationwide basis for significant chronic
adverse effects other than cancer.
Scientific evidence shows that the Montreal
Protocol has been effective in reducing strato-
spheric ozone depletion. Measurements have
shown that atmospheric concentrations of
methyl chloroform are falling, indicating that
emissions have been greatly reduced. Concen-
trations of other ozone-depleting substances
in the upper layers of the atmosphere, like
chlorofluorocarbons (CFCs), are also beginning
to decrease.
Air Pollution
The Concern
The average person breathes 3,400 gallons of air
each day. 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.
Children are at greater risk because they are
generally more active outdoors and their lungs
are still developing. The elderly and people with
heart or lung diseases are also more sensitive to
some types of air pollution.
Air pollution can also significantly affect ecosys-
tems. 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.
These include stationary sources such as factories,
power plants, and smelters; 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.
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Six Principal Pollutants
Under the Clean Air Act, EPA estab-
lishes air quality standards to protect public health,
including the health of "sensitive" populations
such as people with asthma, 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 air pollutants (also referred to as criteria
pollutants): nitrogen dioxide (NO2), ozone (O3),
Percent Change in Air Quality
1982-2001 1992-2001
NO2
03 1-h
8-h
SO2
-24
-18
-11
-52
-11
-3
0
-35
PMi0 — -14
PM2.5
CO
Pb
Trend
-62
-94
data not available
-38
-25
Percent Change in Emissions
1982-2001 1992-2001
NOX
voc
SO2
PM10*
PM2.5*
CO
Pb
+ 9
-16
-25
-51
—
0
-93
-3
-8
-24
-13
-10
+ 6
-5
^Includes only directly emitted particles.
Negative numbers indicate improvements in
air quality or reductions in emissions. Positive
numbers show where emissions have increased.
Air quality concentrations do not always track nationwide emissions. There
are several reasons for this. First, most monitors are located in urban areas
so air quality is most likely to track changes in urban air emissions rather
than in total emissions. Second, not all of the principal pollutants are
emitted directly to the air. Ozone and many particles are formed after
directly emitted gases react chemically to form them. Third, the amount of
some pollutants measured at monitoring locations depends on the chemical
reactions that occur in the atmosphere during the time it takes the pollutant
to travel from its source to the monitoring station. Finally, weather condi-
tions often contribute to the formation and buildup of pollutants in the
ambient air. For example, peak ozone concentrations typically occur during
hot, dry stagnant summertime conditions.
sulfur dioxide (SO2), participate matter (PM),
carbon monoxide (CO), and lead (Pb). Four of
these pollutants (CO, Pb, NO2, and SO2) result
primarily from direct emissions from a variety of
sources. PM results from direct emissions, but is
also commonly formed when emissions of nitro-
gen oxides (NOJ, sulfur oxides (SOJ, ammonia,
organic compounds, and other gases react in the
atmosphere. Ozone is not directly emitted but is
formed when NOX and volatile organic com-
pounds (VOCs) react in the presence of sunlight.
Each year EPA examines changes in levels of
these ambient pollutants and their precursor
emissions 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
tables to the left show that the air quality based
on concentrations of the principal pollutants has
improved nationally over the past 20 years
(1982-2001).
EPA estimates nationwide emissions of ambient
pollutants and their precursors based on actual
monitored readings or engineering calculations
of the amounts and types of pollutants emitted
by vehicles, factories, and other sources. Emission
estimates are based on many factors, including
the level of industrial activity, technology develop-
ments, fuel consumption, vehicle miles traveled,
and other activities that cause air pollution.
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200%
150% -
100%, -
Comparison of Growth Areas and Emissions
Gross Domestic Product
Energy Consumption
U.S. Population
Aggregate Emissions
(Six Principal Pollutants)
70 80 90 "95 96 97 98 99 00 01
Between i970 and 200i,gross domestic product increased i6i percent, vehicle miles traveled increased i49 percent, energy
consumption increased 42 percent, and U.S. population increased 39 percent. At the same time, total emissions of the six principal
air pollutants decreased 25 percent.
Emission estimates also reflect changes in air
pollution regulations and installation of emission
controls. The 2001 emissions reported in this
summary are projected numbers based on available
2000 information and historical trends. Emission
estimation methods continue to evolve and
improve over time. Methods have changed for
many significant categories beginning with the
years 1985,1990, and 1996, and, consequently,
the estimates are not consistently developed across
all years in this trend period. Because emissions
estimation methods for many significant categories
have changed over time, comparisons of the
estimates for a given year in this report to the same
year in a previous report may not be appropriate.
Check www.epa.gov/ttn/chieffor updated
emissions information.
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on
Emissions of all principal pollutants except NOX
have decreased or remained essentially unchanged
over the past 20 years (1982-2001), while all air
quality measures for the six principal pollutants
have gone down. Although NOX emissions have
increased, air quality measurements for NO2 across
the country are below the national air quality
standards. NOX plays an important role in a
number of air pollution issues. These compounds
contribute to the formation of ozone and particles
as well as the deposition of acids and nutrients and
visibility impairment.
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,
approximately 133 million people nationwide still
lived in counties with pollution levels above the
National Ambient Air Quality Standards (NAAQS)
in 2001. This annual "snapshot" view of the
nation's air quality can be used to show levels that
people might currently be experiencing across the
county. There are still 130 nonattainment areas out
of the 230 originally resulting from the 1990
Clean Air Act Amendments designation process.
Number of People Living in Counties
with Air Quality Concentrations above
the Level of the NAAQS in 2001
NO.
110.3 (8-hour)
The Clean Air Act
The Clean Air Act provides the principal frame-
work for national, state, tribal, and local efforts to
protect air quality. Under the Clean Air Act, EPA
has a number of responsibilities, including
Setting 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 SO2 and NOX that
cause acid rain.
Reducing air pollutants such as PM, SOX,
and NOX that can cause visibility impairment
across large regional areas, including many of
the nation's most treasured parks and wilder-
ness areas.
• Ensuring that sources of toxic air pollutants
that may cause cancer and other adverse
human health and environmental effects are
•well controlled and that the 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.
a
n
50 100
Millions of People
150
Multiple years of data are generally used to determine if an area
attains the NAAQS.
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NITROGEN DIOXIDE (NO.
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Nature and Sources of the Pollutant
Nitrogen dioxide is a reddish brown, highly reac-
tive gas that is formed in the ambient air through
the oxidation of nitric oxide (NO). Nitrogen
oxides (NOJ, 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, haze, and acid rain. While EPA tracks
national emissions of NOX, the national monitor-
ing network measures ambient concentrations of
NO2 for comparison to national air quality stand-
ards. The major sources of man-made NOX emis-
sions are high-temperature combustion processes,
such as those that occur in automobiles and power
NO2 Air Quality, 1982-2001
Based on Annual Arithmetic Average
0.06
10% of sites have concentrations below this line
82 83 84 85 86 87
89 90 91 92 93 94 95 96 97 98 99 00 01
1982-01: 24% decrease
1992-01: 11% decrease
Air quality concentrations do not always track nationwide
emissions. For a detailed explanation, see page 3.
NOX Emissions, 1982-2001
30,000
20,000
o 10,000
I Fuel Combustion CU Industrial Processes
D Transportation D Miscellaneous
In 1985, EPA refined its methods for estimating emissions.
82
85
92 93 94 95 96 97 98 99 00 01
1982-01: 9%
1992-01: 3%
increase
decrease
plants. Home heaters and gas stoves can 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 NO2 may lead to changes in airway
responsiveness and lung function in individuals
with preexisting respiratory illnesses and increases
in respiratory illnesses in children. Long-term
exposures to NO2 may lead to increased suscepti-
bility to respiratory infection and may cause irre-
versible alterations in lung structure. NOX reacts
in the air to form ground-level ozone and fine
particle pollution, which are both associated with
adverse health effects.
NOX contributes to a wide range of environmental
effects directly and/or when combined with other
precursors in acid rain and ozone (see environ-
mental discussion under Ozone and Acid Rain).
Nitrogen inputs to terrestrial and wetland systems
can alter existing competitive relationships among
plant species, leading to changes in community
composition and diversity. Similarly, direct nitrogen
inputs to aquatic ecosystems such as those found
in estuarine and coastal waters (e.g., Chesapeake
Bay) can lead to eutrophication (a condition that
promotes excessive algae growth, which can lead
to a severe depletion of dissolved oxygen and
increased levels of toxins harmful to fish and other
aquatic life). Nitrogen, alone or in acid rain, also
can acidify soils and surface waters. Acidification of
soils causes the loss of essential plant nutrients and
increased levels of soluble aluminum that are toxic
to plants. Acidification of surface waters creates
conditions of low pH and levels of aluminum that
are toxic to fish and other aquatic organisms.
Finally, NOX is a contributor to visibility impair-
ment.
Trends in NO2 Levels and NOX Emissions
Over the past 20 years, monitored levels of NO2
have decreased 24 percent. All areas of the country
that once violated the NAAQS for NO2 now
meet that standard. While air quality levels of NO2
around urban monitors have fallen, national emis-
sions of NOX have actually increased over the past
20 years by 9 percent. This increase is the result of
a number of factors, the most significant being an
increase in NOX emissions from nonroad engines
and diesel vehicles. This increase is of concern
because NOX emissions contribute to the forma-
tion of ground-level ozone (smog), but also to
other environmental problems like acid rain and
nitrogen loadings to waterbodies.
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GROUND-LEVEL OZONE
on
1
03
25,000 -
15,000 -
5,000
82
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 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 commer-
cial products, and other industrial sources. NOX is
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 pollutants that form ozone also can be trans-
ported into an area from pollution sources found
hundreds of miles upwind.
Ozone occurs naturally in the stratos-
phere and provides a protective layer
high above the Earth. See page 23 for
more information on the stratospheric
ozone layer.
VOC Emissions, 1982-2001
I Fuel Combustion CU Industrial Processes
IZl Transportation CU Miscellaneous
In 1985, EPA refined its methods for estimating emissions.
85
92 93 94 95 96 97 98 99 00 01
1982-01: 16% decrease
1992-01: 8% decrease
Air quality concentrations do not always track nation-
wide emissions. For detailed explanation, see page 3.
a
n
Health and Environmental Effects
Short-term (1- to 3-hour) and prolonged
(6- to 8-hour) exposures to ambient ozone have
been linked to a number of health effects of
concern. For example, health effects attributed to
ozone exposure include significant decreases in
lung function and increased respiratory symptoms
such as chest pain and cough. Exposures to ozone
can make people more susceptible to respiratory
infection, result in lung inflammation, and aggra-
vate preexisting respiratory diseases such as asthma.
Also, increased hospital admissions and emergency
room visits for respiratory problems have been
associated with ambient ozone exposures. These
effects generally occur while individuals are
actively exercising, working, or playing outdoors.
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
preexisting respiratory disease such as asthma and
chronic obstructive pulmonary disease. In addition,
longer-term exposures to moderate levels of ozone
present the possibility of irreversible changes in the
lung structure, which could lead to premature
aging of the lungs and worsening of chronic
respiratory illnesses.
Ozone also affects vegetation and ecosystems,
leading to reductions in agricultural crop and com-
mercial forest yields, reduced growth and surviv-
ability of tree seedlings, and increased plant suscep-
tibility 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 can also decrease the aesthetic value
of ornamental species as well as the natural beauty
of our national parks and recreation areas.
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Trends in Ozone Levels and Related
Emissions
In 1997, EPA revised the NAAQS for ozone by
setting new 8-hour 0.08-ppm standards. Currently,
EPA is tracking trends based on both 1-hour and
8-hour data.
Over the past 20 years, national ambient ozone
levels decreased 18 percent based on 1-hour data
and 11 percent based on 8-hour data. Between
Ozone Air Quality, 1982-2001
Based on Annual 4th Maximum 8-Hour Average
0.20
0.15
I
•jo 0.10
I
o
° 0.05
0.00
379 Sites
90% of sites have concentrations below this line
Average
NAAQS
10% of sites have concentrations below this line
82 83 84 85 86 87
89 90 91 92 93 94 95 96 97 98 99 00 01
1982-01: 11% decrease
1992-01: 0% change
Air quality concentrations do not always track nationwide
emissions. For a detailed explanation, see page 3.
Ozone Air Quality, 1982-2001
Based on Annual 2nd Maximum 1-Hour Average
0.20
0.15
Ł 0.10
0.05
0.00
.90% of sites have concentrations below this line
379 Sites
Average
T
10% of sites have concentrations below this line
82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01
1982-01: 18% decrease
1992-01: 3% decrease
1982 and 2001, emissions of VOCs decreased
16 percent. During that same time period,
emissions of NOX increased 9 percent.
For the period 1982 to 2001, the downward trend
in 1-hour ozone levels seen nationally is reflected
in every broad geographic area in the country.
The Northeast and West exhibited the most
substantial improvement, while the South and
North Central regions experienced the least
rapid progress in lowering ozone concentrations.
Similar to the 1-hour ozone trends, all regions
experienced improvements in 8-hour ozone levels
between 1982 and 2001 except the North Central
region, which showed little change during this
period. Again, the West and Northeast have exhib-
ited the most substantial reductions in 8-hour
ozone levels for the past 20 years.
Across the country, the highest ambient 1-hour
ozone concentrations are typically found at subur-
ban sites, consistent with the downwind transport
of emissions from urban centers. During the past
20 years, ozone concentrations decreased approxi-
mately 20 percent at urban and suburban sites.
In the past 10 years, urban sites show declines of
approximately 5 percent and suburban sites show
a 6 percent decrease. However, at rural monitoring
locations, national improvements have slowed.
One-hour ozone levels for 2001 are 11 percent
lower than those for 1982 but less than 1 percent
below 1992 levels. In 2001, for the sixth consecu-
tive year, rural 1-hour ozone levels, on average, are
greater than the levels observed for the urban sites,
but they are still generally lower than levels
observed at suburban sites.
Over the past 10 years, the average 8-hour ozone
level in 33 of our national parks increased almost
4 percent. Six monitoring sites in five of these
parks experienced statistically significant upward
trends in 8-hour ozone levels: Great Smoky
Mountains (Tennessee), Craters of the Moon
(Idaho), Mesa Verde (Colorado), Mammoth Cave
(Kentucky), and Yellowstone (Wyoming). Monitor-
ing data for two parks showed statistically signifi-
cant improvements over the same time period:
Saguaro (Arizona) and Sequoia (California). For
the remaining 26 parks where ozone monitoring
takes place, the 8-hour ozone levels at 18 increased
only slightly between 1992 and 2001, while 5
showed decreasing levels and 3 were unchanged.
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Trend in 1-Hour Ozone Levels, 1982-2001, Averaged across EPA Regions*
Based on Annual 2nd Highest Daily Maximum
on
vA.^
1982
10 .133 i-M \
.111 ^ .079 ^"^ x— x_^v^—^.
M, 29% 1982 2001 ^. .099 x j
^15% 1982 ~" 2001 f-17%2
.154 7 ^14% ^
8 -°9L^ -093 e- 'I^LA^=^
1982 2001 ** 1982 2
*32% J6o/o f10%
9 -1°^^v -098
6 .128 .108
1982 2001 4 *
f 16%
The National Trend E
.127 1Q4 |
1982 2001 *&
^18% 1
o
O
*EPA Regional Office contacts can be found at www.epa.gpv/epahome/locate2.htm.
Trend in 8-Hour Ozone Levels, 1 982-2001 , Averaged across EPA
Based on Annual 4th Maximum 8-Hour Average
.112
1982
.101 .093
.072 .057 ->~/\-\ — ^^,
*21% -089 ^ -081 *
•jr 9% 48% O
7^9% />
3
— n OQfi ,)Qf
— 074 074 A
.-..-, . .. . ^—^—
1982 2001 W
f24% 0% f4%
.082 .080
6 .090 .082
1982 2001 4
^^^^^^^^^ -f- 9%
The National Trend
.092 .082
.119
-^V^
2001
1
'
.
^^
001
Trend in 1-hour Ozone Levels,
1982-2001, by Location of Site
Based on Annual 2nd Highest
'>O - » V\\ NAAQS
0.10 - ^*~*
0.08 -
0.06 -
- — — Suburban
0.02 - urban
n nn
82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01
Regions
.090
— ^-^
2001
\ 1
\
• 20%
1982 2001
f- 11%
Concentrations are in parts per million (ppm).
n
i-«.
T3
BS
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SULFUR DIOXIDE (SO-
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Nature and Sources of the Pollutant
Sulfur dioxide belongs to the family of SOX gases.
These gases are formed when fuel containing
sulfur (mainly coal and oil) is burned and during
metal smelting and other industrial processes. Most
SO2 monitoring stations are located in urban areas.
The highest monitored concentrations of SO2
are recorded in the vicinity of large industrial
facilities. Fuel combustion, largely from coal-fired
power plants, accounts for most of the total
SO2 emissions.
SO2 Air Quality, 1982-2001
Based on Annual Arithmetic Average
0.04
E 0.03
0.02
I
o
o
0.01
0.00
253 Sites
NAAQS
90% of sites have concentrations below this line
10% of sites have concentrations below this line
82 83 84 85 86 87
89 90 91 92 93 94 95 96 97 98 99 00 01
1982-01: 52% decrease
1992-01: 35% decrease
Air quality concentrations do not always track nationwide
emissions. For a detailed explanation, see page 3.
SO2 Emissions, 1982-2001
• Fuel Combustion D Industrial Processes
D Transportation
In 1985, EPA refined its methods for estimating emissions.
85
92 93 94 95 96 97 98 99 00 01
Health and Environmental Effects
High concentrations of SO2 can result in tempo-
rary breathing impairment for asthmatic children
and adults who are active outdoors. Short-term
exposures of asthmatic individuals to elevated
SO2 levels during moderate activity may result
in breathing difficulties that can be accompanied
by symptoms such as wheezing, chest tightness,
or shortness of breath. Other effects that have
been associated with longer-term exposures to
high concentrations of SO2, in conjunction with
high levels of PM, include aggravation of existing
cardiovascular disease, respiratory illness, and alter-
ations in the lungs' defenses. The subgroups of
the population that may be affected under these
conditions include individuals with heart or lung
disease, as well as the elderly and children.
Together, SO2 and NOX are the major precursors
to acidic deposition (acid rain), which is associated
•with the acidification of soils, lakes, and streams
and accelerated corrosion of buildings and monu-
ments. SO2 also is a major precursor to PM2 5,
•which is a significant health concern as •well as a
main contributor to poor visibility. (See Acid Rain
section, page 16, for a more detailed discussion.)
Trends in SO2 Levels and Emissions
Nationally average SO2 ambient concentrations
have decreased 52 percent from 1982 to 2001 and
35 percent over the more recent 10-year period
1992 to 2001. SO2 emissions decreased 25 percent
from 1982 to 2001 and 24 percent from 1992
to 2001. Reductions in SO2 concentrations and
emissions since 1990 are due, in large part, to
controls implemented under EPA's Acid Rain
Program beginning in 1995.
1982-01: 25% decrease
1992-01: 24% decrease
-------
PARTICULATE MATTER
Nature and Sources of the Pollutant
Particulate matter is the general term used for a
mixture of solid particles and liquid droplets found
in the air. Some particles are large enough to be
seen as dust or dirt. 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 |j,m in diameter. "Coarse fraction" par-
ticles are greater than 2.5 |j,m, but less than or equal
to 10 |j,m in diameter. PM10 refers to all particles
less than or equal to 10 |j,m in diameter. A particle
10 |j,m in diameter is about one-seventh the diam-
eter of a human hair. PM can be emitted directly
PM10 Air Quality, 1992-2001
Based on Seasonally Weighted Annual Average
60
50
40
'•s so
20
10
0
770 Sites
90% of sites have concentrations below this line
Average
NAAQS
10% of sites have concentrations below this line
92 93 94 95 96 97 98 99 00 01
1992-01: 14% decrease
Air quality concentrations do not always track nationwide emissions.
For a detailed explanation, see page 3.
PM10 Emissions, 1982-2001
H Fuel Combustion D Industrial Processes
D Transportation
1
o
rn
^
c
cC
D
B
6,000
5,000
4,000
3,000
2,000
0
, In 1985, EPA refined its methods for estimating emissions.
-
_
Emission K
trends ^ ^
available. ^
W
82 85 92 93 94 95 96 97 98 99 00 01
1992-01: 13% decrease
or form in the atmosphere. "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 sulfates, formed from SO2 emis-
sions from power plants and industrial facilities, and
nitrates, formed from NOX emissions from power
plants, automobiles, and other types of combustion
sources. The chemical composition of particles
depends on location, time of year, and weather.
Generally, coarse PM is composed largely of
primary particles and fine PM contains many more
secondary particles.
Health and Environmental Effects
Particles that are small enough to get into the
lungs (those less than or equal to 10 |_im in dia-
meter) can cause numerous health problems and
have been linked with illnesses and deaths from
heart and lung diseases. Various health problems
have been associated with long-term (e.g., multi-
year) exposures as well as daily and even, poten-
tially, peak (e.g., 1-hour) exposures to particles.
Particles can aggravate respiratory conditions such
as asthma and bronchitis and have been associated
with cardiac arrhythmias (heartbeat irregularities)
and heart attacks. Particles of concern can include
both fine and coarse-fraction particles, although
fine particles have been more clearly linked to the
most serious health effects. People with heart or
lung disease, the elderly, and children are at highest
risk from exposure to particles. 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. (See Acid Rain, NO2, and SO2
sections.)
Trends in PM1O Levels and Direct Emissions
Between 1992 and 2001, average PM10 concentra-
tions decreased 14 percent, while direct PM10
emissions decreased 13 percent.
on
a
n
-------
c
PP!
_
(J-l
If enacted. President Bush's Clear Skies Initiative would
decrease PM concentrations by dramatically reducing
emissions of SO2 and NOX. This initiative would also
reduce mercury emissions (www.epa.gov/clearskies).
Trends in PM2.s Levels and Direct Emissions
The chart at right shows that direct PM2 5
emissions from man-made sources decreased 10
percent nationally between 1992 and 2001. This
chart tracks only directly emitted particles and does
not account for secondary particles formed when
emissions of NOX, SO2, ammonia, and other gases
react in the atmosphere. The principal types of sec-
ondary particles are sulfates and nitrates, which are
formed when SO2 and NOX react with ammonia.
The maps at right show how sulfates and nitrates,
along with other components, contribute to PM2 5
concentrations. The first map represents the most
recent year of data available from the Interagency
Monitoring of Protected Visual Environments
(IMPROVE) network, which was established in
1987 to track trends in pollutants, such as PM2 5,
that contribute to visibility impairment. Because
the monitoring sites are located in rural areas
throughout the country, the network is a good
source for assessing regional differences in PM2 5.
The second map represents the most recent year of
data from EPA's urban speciation network, which
was established in 1999. All of these sites are locat-
ed in urban areas.
Sites in the rural East typically have higher annual
average PM2 5 concentrations than those in the
rural West, as shown by the larger circles in the
East. Most of this regional difference is attributable
to higher sulfate concentrations in the eastern
United States. Sulfate concentrations in the East
largely result from SO2 emissions from coal-fired
power plants.
Sites in urban areas, as shown in the circles in the
map at right, generally have higher annual average
PM2 5 concentrations than nearby rural areas.
Carbon from soot and organic compounds
accounts for much of the difference, while sulfate
concentrations are about the same. Sites in central
California show that nitrates, in addition to carbon,
are responsible for higher urban concentrations in
that region.
Trends in rural PM2 5 concentrations can be exam-
ined with data from the IMPROVE network. At
the time of this report, 2000 and 2001 data were
not available. However, 36 sites have enough data
to assess trends from 1992 to 1999. In the East,
where sulfates contribute most to rural PM2 5, the
2,500 r
Direct PM2.s Emissions, 1992-2001
I Fuel Combustion IZl Industrial Processes
D Transportation
2,000
« 1,000
92 93 94 95 96 97 98 99 00 01
1992-01: 10% decrease
Annual Average PM2.s Concentrations (ug/m3)
and Particle Type in Rural Areas,1999
I I Sulfate
I Ammonium
M Nitrate Q
• Total Carbon O 15 ng/
• Crustal Material O 20 ug/m3
Source: Interagency Monitoring of Protected Visual Environments
Network, 1999.
Note: Direct comparisons of the information in these two maps should
take into consideration: the fact that they represent different years; that one
is an urban network and the other is a rural network; and that there are
also differences in instruments and measurement methods.
Annual Average PM2.5 Concentrations (ug/m3)
Particle Type in Urban Areas, 2001
I I Sulfate
I I Ammonium
• Nitrate Q
• Total Carbon O 15 ug/m3
^f Crustal Material O 20 ug/m3
Source: EPA Speciation Network, 2001.
-------
Annual Average PM2 5 Concentrations
in Rural Areas
14
12
E 10
o
O 4
Measured PM2 5 (Eastern U.S.-10 sites)
Sulfate (Eastern U.S.-10 sites)
^ ^
Measured PM25 (Western U.S.-26 sites)
Carbon (Eastern U.S.-10 sites)
92 93 94 95 96 97 98 99
Source: Interagency Monitoring of Protected Visual
Environments Network, 1999.
Annual Average PM2.5 Concentrations (ug/m3), 2001
Concentration (jig/m3)
• >20
D 15-20
• 12-15
• <12
D Do not meet minimum
data completeness
Source: U.S. EPA AIRS databases as of 7/8/02.
Minimum 11 samples per calendar quarter required.
Note: The NAAQSfor PM2.S is
i5 jjg/m3 but is based on the average of
3 years of monitoring data. In addition,
PM2 5 concentration measurements from
the new nationwide monitoring network
are not directly comparable to the
measurements from the IMPROVE
network due to differences in instruments
and measurement methods.
on?--
30
25
20
I
10
0 —
92
annual average across the 10 sites decreased 5 per-
cent from 1992 to 1999.The peak in 1998 is asso-
ciated with increases in sulfates and carbon from
soot and organic compounds. Average PM2 5 con-
centrations across the 26 sites in the West were less
than one-half of the levels measured at eastern sites
from 1992 to 1999.
In 1999, EPA and its state, tribal, and local air
pollution control partners deployed a monitoring
network to begin measuring PM2 5 concentrations
nationwide. The map at left shows annual average
PM2 5 concentrations by county. This map also
indicates that PM2 5 concentrations vary regionally.
Based on the monitoring data, parts of California
and much of the eastern United States have annual
average PM2 5 concentrations above the level of the
annual PM2 5 standard, as indicated by the orange
and red on the map. With few exceptions, the rest
of the country generally has annual average con-
centrations below the level of the annual PM2 5
health standard.
Now that there are 3 years of monitoring data
available, we have begun to examine trends at the
national level. Annual average PM2 5 concentrations
decreased 5 percent nationally from 1999 to 2001,
•with much of that decrease occurring between
2000 and 2001. This decrease may or may not
represent a trend, given the few years of data avail-
able at this time. The Southeast was responsible for
most of that reduction, where the monitored levels
of PM25 decreased 10 percent from 2000 to 2001.
Lower 2001 annual average concentrations in the
Southeast are due, in part, to less demand on utili-
ties during a very warm winter. This is illustrated
by the reduction in direct emissions of SO2 and
PM2 5 from fuel combustion in 2001.
PM25 Air Quality, 1999-2001
Based on Seasonally Weighted Annual Average
486 Sites
90% of sites have concentrations below this line
Trends monitoring data for
PM,,-not available.
NAAQS
1 Average
10% of sites have concentrations below this line
93 94 95 96 97 98
1999-01: 5% decrease
99
00
01
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c
PP!
CARBON MONOXIDE
C O
_
(J-l
Nature and Sources of the Pollutant
Carbon monoxide is a colorless and odorless gas,
formed when carbon in fuel is not burned com-
pletely. It is a component of motor vehicle exhaust,
•which contributes about 60 percent of all CO
emissions nationwide. Nonroad vehicles account
for the remaining CO emissions from transporta-
tion sources. 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,
CO Air Quality, 1982-2001
Based on Annual 2nd Maximum 8-hour Average
90% of sites have concentrations below this line
218 Sites
NAAQS
10% of sites have concentrations below this line
82 83 84 85 86 87
89 90 91 92 93 94 95 96 97 98 99 00 01
1982-01: 62% decrease
1992-01: 38% decrease
Air quality concentrations do not always track nationwide
emissions. For a detailed explanation, see page 3.
CO Emissions, 1982-2001
• Fuel Combustion D Industrial Processes
D Transportation D Miscellaneous
In 1985, EPA refined its methods for estimating emissions.
85
92 93 94 95 96 97 98 99 00 01
nontransportation 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
CO enters the bloodstream through the lungs and
reduces oxygen delivery to the body's organs and
tissues. The health threat from levels of CO some-
times found in the ambient air is most serious for
those who suffer from cardiovascular disease, such
as angina pectoris. At much higher levels of expo-
sure not commonly found in ambient air, 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 and Emissions
Nationally the 2001 ambient average CO concen-
tration is almost 62 percent lower than that for
1982 and is the lowest level recorded during the
past 20 years. CO emissions from transportation
sources, the major contributor to ambient CO
concentration, have decreased slightly during this
period. Between 1992 and 2001, ambient CO
concentrations decreased 38 percent. This air
quality improvement occurred despite an approxi-
mately 35 percent increase in vehicle miles traveled
in the United States during this 10-year period
and an increase in total CO emissions of 6 percent.
The recent increase in CO emissions was caused
by an extremely serious wildfire season in 2000.
Nearly twice the number of U.S. acres burned in
2000 compared to the average year since 1982.
14
1982-01: 0% change
1992-01: 6% increase
-------
LEAD
P b
on
Nature and Sources of the Pollutant
In the past, automotive sources were the major
contributor of lead emissions to the atmosphere.
As a result of EPA's regulatory efforts to reduce the
content of lead in gasoline, however, the contribu-
tion of air emissions of lead from the transportation
sector, and particularly the automotive sector, has
greatly declined over the past two decades. Today,
industrial processes, primarily metals processing, are
Lead Air Quality, 1982-2001
Based on Annual Maximum Quarterly Average
90% of sites nave concentrations below this line
10% of sites have concentrations below this line
0.0
82 83 84 85
87 88 89 90 91 92 93 94 95 96 97 98 99 00 01
1982-01: 94% decrease
1992-01: 25% decrease
Air quality concentrations do not always track nationwide
emissions. For a detailed explanation, see page 3.
Lead Emissions, 1982-2001
I Fuel Combustion CU Industrial Processes
D Transportation
In 1985, EPA refined its methods for estimating emissions.
85
92 93 94 95 96 97 98 99 00 01
1982-01: 93% decrease
the major source of lead emissions to the atmos-
phere. The highest air concentrations of lead are
usually found in the vicinity of 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 and can adversely affect the kidneys, liver,
nervous system, and other organs. Excessive expo-
sure 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 and humans through
ingestion.
Trends in Lead Levels and Emissions
Because of the phaseout of leaded gasoline, lead
emissions and concentrations decreased sharply
during the 1980s and early 1990s. The 2001
average air quality concentration for lead is 94
percent lower than in 1982. Emissions of lead
decreased 93 percent over that same 20-year
period. Today, the only violations of the lead
NAAQS occur near large industrial sources such
as lead smelters and battery manufacturers. Various
enforcement and regulatory actions are being
actively pursued by EPA and the states for cleaning
up these sources.
a
n
ID
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Acid Rain
Nature and Sources of the Problem
Acidic deposition or "acid rain" occurs when
emissions of sulfur dioxide and nitrogen oxides
in the atmosphere react with water, oxygen, and
oxidants to form acidic compounds. These
Acid Rain Formation
Coal-fired electric utilities and other sources that burn
fossil fuels emit SO2 and NOX.
SO2 Emissions Covered under
the Acid Rain Program
^u
18
16
14
12
10
8
6
4
2
-
17.30
9.40
16.09
9.30
15.73
8.70
D Phase I Sources D Phase II Sources
D All Affected Sources, 2000
11.87
12.51
-.
12.51
12.98
12.98
13.13
13.13
12.45
12.45
11.20
1980 1985 1990 1995 1996 1997 1998 1999 2000
i 11995-1999: Allowances issued for 263 Phase I units.
2000: Allowances issued for all affected sources.
NOX Emissions Covered under
the Acid Rain Program
8
7
0*6
o 5
o
1 3
2
1
8.1
• ••"""*
6.7 „.--•""
« • • ™ ™
-
~
-
-
-
6.66
5.53
6.09
5.54
5.91
5.44
6.04
5.49
5.97
5.29
5.49
4.82
5.11
4.48
1990 1995
1996
1997
1998 1999
2000
D Phase II units not affected for NOX
D Phase II NOX affected units (1,046)
• Projected NOX emissions without the Acid Rain Program
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
SO2 emissions and 26 percent of NOX emissions
are produced by electric utility plants that burn
fossil fuels.
Health and Environmental Effects
In the environment, acid deposition causes soils
and waterbodies to acidify (making the water
unsuitable for some fish and other wildlife) and
damages some trees, particularly at high elevations.
It also speeds the decay of buildings, statues, and
sculptures that are part of our national heritage.
The nitrogen portion of acid deposition contri-
butes to eutrophication in coastal ecosystems,
the symptoms of which include algal blooms
(some of which may be toxic), fish kills, and loss
of plant and animal diversity. Finally, acidification
of lakes and streams can increase the amount
of methyl mercury available in aquatic systems.
Most exposure to mercury comes from eating
contaminated fish. Reductions in SO2 and
NOX have begun to reduce some of these
negative environmental effects and are leading
to significant improvements in public health
(described previously).
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 SO2
and NOX. The program was implemented in two
phases: Phase I for SO2 began in 1995 and targeted
the largest and highest-emitting coal-fired power
plants. Phase I for NOX began in 1996. Phase II for
both pollutants began in 2000 and sets restrictions
on Phase I plants as well as smaller coal-, gas-,
and oil-fired plants. Over 2,000 sources are now
affected by the Acid Rain Program.
The Acid Rain Program will reduce annual SO2
emissions by 10 million tons from 1980 levels
by 2010. The program sets a permanent cap of
8.95 million tons on the total amount of SO2 that
may be emitted by power plants nationwide, about
half the amount emitted in 1980. It employs an
emissions trading program to reach that emissions
cap more efficiently and cost-effectively Sources
are allocated allowances efficiently each year (one
allowance equals 1 ton of SO2 emissions), which
can be bought or sold or banked for future use.
-------
Change in Deposition from Precipitation
1990-1994 to 1996-2000
Nitrate
Source: U.S. EPA analysis of National Atmospheric
Deposition Program data.
This approach gives sources the flexibility and
incentive to reduce emissions at the lowest cost
•while ensuring that the emission cap is met.
The NOX component of the Acid Rain Program
limits the emission rate for all affected utilities,
resulting in a 2 million ton NOX reduction from
1980 levels by 2000. There is no cap on total NOX
emissions, but under this program a source can
choose to over-control at units where it is techni-
cally 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
SO2 emissions reductions have been significant in
the first 6 years of EPA s Acid Rain Program. The
first year of compliance with Phase II of the Acid
Rain Program was 2000. Sources in the Acid Rain
Program emitted 11.2 million tons in 2000, down
from 16 million tons in 1990. Emissions of SO2
dropped 1 million tons between 1999 and 2000.
Sources began drawing down the bank of unused
allowances in 2000, resulting in emissions levels
greater than the allowances allocated in 2000 but
still lower than emissions during any previous year.
Actual NOX emissions, as shown in the graph
on the bottom left of page 16, have also declined
since 1990. NOX emissions decreased steadily from
6 tons in 1997 to just over 5 tons in 2000. The
more than 1,000 sources affected by Phase II
emitted 4.5 tons in 2000, over 1 million tons
(almost 20 percent) less than they did in 1990.
NOX emissions in 2000 were somewhat lower
(7 percent) than in 1999 and almost half of what
emissions were projected to have been in 2000
•without the Acid Rain Program.
For all years from 1995 through 2000, sulfate
deposition exhibited dramatic and unprecedented
reductions over a large area of the eastern United
States. Average sulfate deposition in 1996—2000
compared to 1990-1994 was 10 percent lower
nationwide and 15 percent lower in the East.
Similarly, sulfate air concentrations, which con-
tribute to human health and visibility problems,
•were reduced significantly, especially in the East.
Nitrate deposition decreased slightly in some places
but increased in others, causing an overall average
increase in nitrate deposition between 1990—1994
and 1996-2000 of 3 percent.
These reductions in acid precipitation are directly
related to the large regional decreases in SO2
and NOX emissions resulting from the Acid Rain
Program. The largest reductions in sulfate concen-
trations occurred along the Ohio River Valley
and in states immediately downwind. The largest
reductions in wet sulfate deposition 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. The largest reductions in wet nitrate
deposition were in the northeastern United States,
Michigan, and Texas. The Midwest, the Southeast,
and California showed the highest increases in
deposition even though emissions from acid rain
sources have not increased substantially there. Acid
rain sources account for only one-third of nation-
wide nitrogen emissions, so emissions trends in
other source categories, especially agriculture and
mobile sources, affect air concentrations and
deposition.
i/
-------
Visibility
In 2000, the IMPROVE Monitoring Network, used to track visi-
bility trends at national parks and wilderness areas, started an
expansion from 30 to 110 monitoring sites. The expansion
work was completed in the fall of 2001. However, due to the
level of resources required to complete the network expan-
sion, reporting of 2000 IMPROVE data will occur while this
brochure is being finalized. Therefore, no update is provided
for visibility trends reported in the 7999 Status and Trends
Brochure. Reporting of 2000 and 2001 visibility trends are
scheduled to be included in U.S. EPA's 2001 National Air
Quality and Emission Trends Report.
Nature and Sources of the Problem
Visibility impairment is one of the most obvious
effects of air pollution and occurs at many of
the best known and most treasured natural parks
and wilderness areas, such as the Grand Canyon,
Yosemite,Yellowstone, Mount Rainier, Shenan-
doah, and the Great Smoky Mountain National
Park, as well as in urban areas.
Visibility impairment results from the scattering
and absorption of light by air pollution, including
particles and gases. The scattering and absorption
by air pollution limits the distance we can see and
can also degrade the color, clarity, and contrast of
scenes. The same fine particles that are linked to
serious health effects and premature death can
also significantly affect our ability to see.
Some particles that contribute to visibility impair-
ment are emitted directly into the atmosphere
from their sources, such as dust from roads or
elemental carbon (soot) from wood combustion.
In other cases, particles are formed in the atmos-
phere from primary gaseous emissions such as
SO2 emissions from power plants and other indus-
trial facilities and nitrates formed from NOX emis-
sions from power plants, automobiles, and other
types of combustion sources. These types of parti-
cles are referred to as secondarily formed particles.
In the eastern United States, reduced visibility is
mainly attributable to secondarily formed sulfates.
Although these secondarily formed particles still
account for a significant amount of particulate
loading in the West, primary emissions from
sources like wood smoke contribute a larger per-
centage of the total particulate loading than in the
East.
Also, humidity can significantly increase the effect
of pollution on visibility, causing some particles
to become 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 concentra-
tions combined with high humidity levels.
Sulfates
Organic Carbon
Nitrates
Elemental Carbon (soot)
Crustal Material (soil dust)
East
60-86%
10-18%
7-16%
5-8%
5-15%
West
25-50%
25-40%
5-45%
5-15%
5-25%
This table shows pollutants that contribute to visi-
bility impairment in the eastern and western parts
of the United States. Sulfates are generally the
largest contributor in both the East and the West.
Program Structure
The Clean Air Act provides for the protection
of visibility in national parks and wilderness areas,
also known as Class I areas. 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
Class I Areas
The Clean Ah Act provides for the protection of visibility
in our national parks and wilderness areas, also known as
Class I areas. There are i56 Class I areas across the
United States as shown.
In 1987, the IMPROVE visibility network was
established as a cooperative effort among EPA,
states, National Park Service, U.S. Forest Service,
Bureau of Land Management, and U.S. Fish and
Wildlife Service. Data are collected and analyzed
from this network to determine the type of pollut-
ants primarily responsible for reduced visibility
18
-------
Shenandoah
National Park
under bad and
good visibility
conditions. The
visual range in
the top photo is
25 km while the
visual range in
the bottom photo
is 180 km.
Yosemite
National Park
under bad and
visi
conditions. The
visual range in
the top photo is
iii km while
the visual range
in the bottom
photo is greater
than 208 km.
o~
h^ •
M.
.rr
and to track progress toward the Clean Air Act's
national goal.
In April 1999, EPA initiated a new regional haze
program. The program addresses visibility impair-
ment in national parks and wilderness areas caused
by numerous sources located over broad regions.
The program sets a framework for states to develop
goals for improving 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 5 years and revise any
strategies as necessary.
Visibility Trends
Without the effects of pollution, a natural visual
range in the United States is approximately 75 to
150 km (45 to 90 miles) in the East and 200 to
300 km (120 to 180 miles) in the West.
Data collected by the IMPROVE network show
visibility impairment for the worst visibility in
the West is similar to days with the best visibility
in the East. In 1999, mean visual range for the
•worst days in the East was only 24 km (14.4 miles)
compared to 84 km (50.4 miles) for the best
visibility. In the West, visibility impairment for
the worst days remained relatively unchanged over
the 1990s, with the mean visual range for 1999
(80 km) nearly the same as the 1990 level (86 km).
Visibility Trends for Western
U.S. Class I Areas, 1990-1999
_| 200
0)150
11 100
w 50
0
Best Visibility
Mid-Range
AX -A- A -A- A — *— A-
Worst Visibility
I I I I I I I I
Best visibility
range is 177-208 km
Mid-range visibility
is 118-133 km
Worst visibility
90 91 92 93 94 95 96 97 98 99
Year
Visibility Trends for Eastern
U.S. Class I Areas, 1992-1999
_| 200
0)150
to
11 100
0
-
-
Best Visibility
Mid-Range
A A " " T 7
' Worst Visibility
I I I I I I
Best visibility
range is 79-90 km
Mid- range visibility
is 42-48 km
Worst visibility
92 93 94 95 96 97 98 99
Year
Extinction {Mm'1) 10
Declvlews (dv)
Visual Range (km) 400
30 40 SO 70 100
300 400 500 7001000
I
14
I
Mill
19 23
Mill
200
130 100 80 60 40
I
30
I
I
34
I
20
I
37
I
10
Visibility Metrics. Comparisons of extinction
(Mm'1), deciviews (dv), and visual range (km).
Notice the difference in the three scales: 10
Mm'1 corresponds to about 400 km visual
range and 0.0 dv, while 1,000 Mm'1 is about
4 km visual range and 46 dv.
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Toxic Air Pollutants
Nature and Sources of the Problem
Toxic air pollutants, or air toxics, are those
pollutants that cause or may cause cancer or other
serious health effects, such as reproductive effects
or birth defects. Air toxics may also cause 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, construction
equipment) and stationary sources (e.g., factories,
refineries, power plants), as well as indoor sources
(e.g., some building materials and cleaning
solvents). Some air toxics are also released from
natural sources such as volcanic eruptions and
forest fires. The Clean Air Act identifies 188
air toxics from industrial sources. EPA has identi-
fied 20 of these pollutants that are associated with
mobile sources and one additional mobile source
air toxic designated "diesel particulate matter and
diesel exhaust organic gases."
Health and Environmental Effects
People exposed to toxic air pollutants at sufficient
concentrations may experience various health
effects, including cancer, damage to the immune
system, as well as neurological, reproductive
(e.g., reduced fertility), developmental, respiratory,
and other health problems. 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 an extensive
nationwide monitoring network for air toxics as
they do for many of the other pollutants discussed
in this report. While EPA, states, tribes, and local air
regulatory agencies collect monitoring data for a
number of toxic air pollutants, both the chemicals
monitored and the geographic coverage of the
monitors vary from state to state. EPA is working
with these regulatory partners to build upon the
existing monitoring sites to create a national
monitoring network for a number of toxic air
pollutants. The goal is to ensure that those
compounds that pose the greatest risk are mea-
sured. The available monitoring data help air pollu-
tion control agencies track trends in toxic air pol-
lutants in various locations around the country.
EPA began a pilot city monitoring project in 2001
and is scheduled to include at least 12 months
of sampling in four urban areas and six small
city/rural areas (see map below). This program is
intended to help answer several important national
network design questions (e.g., sampling and
analysis precision, sources of variability, and mini-
mal detection levels). In addition, an initial 11-city
trends network is being established that will help
develop national trends for several pollutants of
concern. For the latest information on national
air toxics monitoring, see www.epa.gov/ttn/
amtic/air txfil.html.
EPA also compiles an air toxics inventory as
part of the National Emissions Inventory (NEI,
formerly the National Toxics Inventory) to esti-
mate and track national emissions trends for the
188 toxic air pollutants regulated under the Clean
Air Act. In the NEI, EPA divides emissions into
four types of sectors:
San Jacinto Rio Rancho
Tampa •
San Juan
Map of iO cities in monitoring pilot project
-------
/-v
«
n.
(1) major (large industrial) sources; (2) area and
other sources, which include smaller industrial
sources like small dry cleaners and gasoline
stations, as well as natural sources like wildfires;
(3) onroad mobile sources, including highway
vehicles; and (4) nonroad mobile sources like air-
craft, locomotives, and construction equipment.
As shown in this pie chart, based on 1996
estimates, the most recent year of available data,
the emissions of toxic air pollutants are relatively
equally divided between the four types of sources.
However, this distribution varies from city to city.
National Air Toxics Emissions, 1996
4.7M Tons
Nonroad
20%
Onroad
31%
Trends for individual air toxics vary from pollutant
to pollutant. Benzene, which is the most widely
monitored toxic air pollutant, is emitted from cars,
trucks, oil refineries, and chemical processes. The
graph below shows measurements of benzene
taken from 95 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, on average,
a 47 percent drop in benzene levels from 1994
to 2000. During this period, EPA phased in new
(so-called "tier 1") car emission standards; required
many cities to begin using cleaner burning gaso-
line; 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 20 percent from 1990 to 1996.
Ambient Benzene, Annual Average Urban
Concentrations, Nationwide, 1994-2000
Area/Other
25%
National Air Toxics Emissions
Total for 188 Toxic Air Pollutants
95
96 97 98
1994-00:47% decrease
99
00
Baseline 1996
(1990-1993)
Based on the data in the NEI, estimates of nation-
wide air toxics emissions have dropped approxi-
mately 24 percent between baseline (1990—1993)
and 1996. Thirty-three of these air toxics, which
pose the greatest threat to public health in urban
areas, have similarly dropped 31 percent. Although
changes in how EPA compiled the national inven-
tory over time may account for some differences,
EPA and state regulations, as well as voluntary
reductions by industry, have clearly achieved
large reductions in overall air toxic emissions.
Risk Assessment
EPA has developed a National-Scale Air Toxics
Assessment, which is a nationwide analysis of air
toxics. It uses computer modeling of the 1996 NEI
air toxics data as the basis for developing health
risk estimates for 33 toxic air pollutants (a subset of
the Clean Air Act's list of 188 air toxics plus diesel
PM). The national-scale assessment is intended to
provide state, local, and tribal agencies and others
with a better understanding of the risks from
inhalation exposure to toxic air pollutants from
outdoor sources. It will help EPA and states priori-
tize data and research needs to better assess risk in
the future and will provide a baseline to help
measure future trends in estimated health risks. The
next national-scale analysis will focus on 1999 data
and will be released by the end of 2003.
rr
5
hH
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c
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n
90% of sites nave concentrations below this line
10% of sites have concentrations below this line
-------
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The following map shows a pattern of the
distribution of relative cancer risk across the
continental United States as estimated by the
national-scale assessment. The highest ranking 20
percent of counties in terms of risk (622 counties)
contain almost three-fourths of the U.S. popula-
tion. Three air toxics (chromium, benzene, and
formaldehyde) appear to pose the greatest nation-
wide carcinogenic risk. This map does not include
the potential risk from diesel exhaust emissions.
This is because existing health data are not
sufficient to develop a numerical estimate of cancer
risk for this pollutant. However, exposure to diesel
exhaust is widespread and EPA has concluded that
diesel exhaust is a likely human carcinogen and
ranks with the other substances that the national-
scale assessment suggests pose the greatest relative
risk. One air toxic, acrolein, is estimated to pose
the highest potential nationwide for significant
chronic adverse effects other than cancer. For more
information, visit www.epa.gov/ttn/atw/nata.
County Risk Comparison
Estimated by National-Scale Assessment
Median County Risk
D Highest
D
D
D
D Lowest
This technical assessment represents an important
step toward characterizing air toxics nationwide.
It is designed to help identify general patterns in
air toxics exposure and risk across the country and
is not recommended as a tool to characterize or
compare risk at local levels (e.g., to compare risks
from one part of a city to another). More localized
assessments, including monitoring and modeling,
are under way to help characterize local-level risk.
Programs to Reduce Air Toxics
Since 1990, EPA's technology-based emission
standards for industrial sources (e.g., chemical
plants, oil refineries, and dry cleaners) have proven
extremely successful in reducing emissions of air
toxics. Once fully implemented, these standards
will cut annual emissions of toxic air pollutants
by nearly 1.5 million tons from 1990 levels.
EPA has also put into place important controls
for motor vehicles and their fuels, including
introduction of reformulated gasoline and low
sulfur diesel fuel, and is continuing to take addi-
tional steps to reduce air toxics from vehicles.
Furthermore, air toxics emissions will further
decline as the motor vehicle fleet turns over, with
newer vehicles replacing older higher emitting
vehicles. By the year 2020, these requirements are
expected to reduce emissions of a number of air
toxics (benzene, formaldehyde, acetaldehyde, and
1,3-butadiene) from highway motor vehicles by
about 75 percent and diesel PM by over 90 per-
cent from 1990 levels.
EPA has begun to look at the risk remaining
(i.e., the residual risk) after emission reductions
for industrial sources take effect and is also
investigating new standards for nonroad engines
such as construction equipment.
In addition to national regulatory efforts, EPA's
program includes work with communities on
comprehensive local assessments, as well as federal
and regional activities associated with protecting
waterbodies from air toxics deposition (e.g., the
Great Waters program, which includes the Great
Lakes, Lake Champlain, Chesapeake Bay, and many
coastal estuaries) and EPA initiatives concerning
mercury and other persistent and bioaccumulative
toxics. For indoor air toxics, EPA's program has
relied on education and outreach to achieve
reductions. Information about indoor air activities
is available at www.epa.gov/iaq/.
For more information about EPA's air toxics
program, visit the Agency's Web site at
www.epa.gov/ttn/atw.
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Stratospheric Ozone
400
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 three
decades, however, it has become clear that this
protective shield has been damaged. Each year, an
"ozone hole" forms over the Antarctic, and ozone
levels there can fall to 60 percent below normal.
Even over the United States, ozone levels are
about 3 percent below normal in the summer
and 5 percent below normal in the winter.
As the ozone layer thins, more UV-b radiation
reaches the Earth. The 1998 Scientific Assessment
of Stratospheric Ozone firmly established the link
between decreased ozone and increased UV-b
radiation. In the 1970s, scientists had linked
several substances associated with human activities
to ozone depletion, including the use of chloro-
fluorocarbons (CFCs), halons, carbon tetrachloride,
methyl bromide, and methyl chloroform. These
chemicals are emitted from commercial air condi-
tioners, refrigerators, insulating foam, and some
industrial processes. Strong winds carry them
225
78 80 82 84 86 88 90 92 94 96 98
Year
Source: National Oceanic and Atmospheric Administration (NOAA), 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 that cause increased levels
in the winter and spring and lower ozone levels in
the summer and fall at these latitudes.
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 scien-
tists 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.
Programs to Restore the Stratospheric
Ozone Layer
In 1987, 27 countries, including the United States,
signed the Montreal Protocol, a treaty that recog-
nized the international nature of ozone depletion
and committed the world to limiting the produc-
tion of ozone-depleting substances. Today, more
than 180 nations have signed the Protocol, which
has been strengthened five times and now calls for
the elimination of those chemicals that deplete
stratospheric ozone.
The 1990 Clean Air Act Amendments established
a U.S. regulatory program to protect the stratos-
pheric ozone layer. In January 1996, U.S. produc-
tion 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
-------
fl
O
N
O
U
65N: 6.8%
55N: 7.3%
45N: 5.0%
35N:3.9%
25N: 1.2%
15N:0.1%
Equator
153:2.3%
25S: 2.6%
35S: 2.9%
45S:5.5%-
55S:9.9%-
65S:11.0%-
UV-b Radiation Increases by Latitude
A 1996 study using
satellite-based analyses of
UV-b trends demonstrated
that UV-b level had
increased at ground level.
This figure shows the
percent increases in average
annual UV-b reaching the
surface from 1986 to
1996. UV-b incidence
is strongly dependent on
latitude. At latitudes that
cover the United States,
UV-b levels are 4 to 5
percent higher than they
were in 1986.
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
industries, the transition away from ozone-deplet-
ing substances has already been completed. EPA is
also emphasizing new efforts like the UV Index, a
daily forecast of the strength of UV radiation to
which people may be exposed 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. Measurements have shown that atmospheric
concentrations of methyl chloroform are falling,
indicating that emissions have been greatly
reduced. Concentrations 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
currently peaking and are expected to slowly
decline in the years to come. 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 the second half of this century. All
nations that signed the Protocol must complete
implementation of ozone protection programs
if full repair of the ozone layer is to happen.
24
-------
Conclusions
The Clean Air Act has resulted in many improve-
ments 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 and state, local, and tribal agen-
cies. New data help 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 improve-
ments in air quality, especially because our lifestyles
create more pollution sources. Many of the strate-
gies 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.
25
-------
CFCs
CO2
CO
DU
EPA
FCCC
IMPROVE
IPCC
km
NAAQS
NAS
NCDC
NEI
NESDIS
NO2, NOX
NO
NOAA
03
Pb
PM10, PM2 5
ppm
SO2, SOX
VOCs
uv
chlorofluoro carbons
carbon dioxide
carbon monoxide
Dobson units
U.S. Environmental Protection Agency
Framework Convention on Climate Change
Interagency Monitoring of Protected Visual Environments
Intergovernmental Panel on Climate Change
kilometers
National Ambient Air Quality Standards
National Academy of Sciences
National Climatic Data Center
National Emissions Inventory
National Environmental Satellite Data and Information Service
nitrogen dioxide, nitrogen oxides
nitric oxide
National Oceanic and Atmospheric Administration
ozone
lead
particulate matter (10 |j,m or less, 2.5 |j,m or less in diameter)
parts per million
sulfur dioxide, sulfur oxides
volatile organic compounds
ultraviolet
26
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Detailed information on Air Pollution Trends: www.epa.gov/airtrends
Real-Time Air Quality Maps and Forecasts: www.epa.gov/airnow
On-line Air Quality Data: www.epa.gov/air/data/index.html
Office of Air and Radiation: www.epa.gov/oar
Office of Air Toxics: www.epa.gov/ttn/atw
Office of Air Quality Planning and Standards: www.epa.gov/oar/oaqps
Office of Transportation and Air Quality: www.epa.gov/otaq
Office of Atmospheric Programs: www.epa.gov/air/oap.html
Office of Radiation and Indoor Air: www.epa.gov/air/oria.html
Global Warming Emissions Information: www.epa.gov/globalwarming/index.html
Acid Rain Web site: www.epa.gov/airmarkets/arplindex.html
Acid Ram Hotline: (202) 564-9620
Energy Star (Climate Change) Hotline: (888) STAR-YES
Mobile Sources National Vehicles and Fuel Emissions Lab: (734) 214-4200
Ozone Depletion Web site: www.epa.gov/ozone/
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