&EPA
United States
Environmental Protection
Agency
Latest Findings on National
Air Quality
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Cover Photo of Deriali National Park, Alaska, by Kim Ferguson, Waynesville, North Carolina
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EPA 4547K-03-001
August 2003
2002 STATUS AND TRENDS
Contract No. 68-D-02-065
Work Assignment No. 1 -03
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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National Air Quality
A summary report highlighting our nation's air quality
status and trends.
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 going back
more than 30 years.
Highlights
• 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.
• Since 1970, aggregate emissions of the six
principal pollutants have been cut 48 percent.
During that same time, U.S. gross domestic
product increased 164 percent, energy con-
sumption increased 42 percent, and vehicle
miles traveled increased 155 percent.
• Despite this progress, about 160 million tons
of pollution are emitted into the air each year
in the United States. Approximately 146 mil-
lion people live in counties where monitored
air in 2002 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). Important efforts to control these
pollutants include implementing more protec-
tive National Ambient Air Quality Standards
(NAAQS) for ozone and PM and issuing rules
to reduce emissions from onroad transportation
and stationary combustion sources. These rules
•will bring reductions in emissions over the
next several years.
• Additional reductions will be needed to
provide clean air in the future. For example,
the Clear Skies legislation currently being
considered in Congress, would, if enacted,
mandate reductions of particle- and ozone-
forming compounds from power generators
by 70 percent from current levels through a
nationwide cap and trade program. This will
also reduce acid rain and improve visibility.
Also, in May 2003, EPA proposed nonroad
diesel engine regulations that would help
improve PM and ozone air quality. By 2030,
this program would reduce annual emissions of
PM by 95 percent, NOX by 90 percent, and
sulfur levels by 99 percent from these engines.
Of the six tracked pollutants, progress has been
slowest for ground-level ozone. Over the past
20 years, almost all geographic areas experi-
enced some progress in lowering ozone
concentrations. The Northeast and Pacific
Southwest exhibited the greatest improvement.
In particular, substantial progress seen in Los
Angeles has continued through 2002. How-
ever, the national average ozone (8-hour) levels
have been fairly constant in other metropolitan
areas. An analysis to adjust 8-hour ozone levels
in metropolitan areas to account for the influ-
ence of meteorological conditions shows the
10-year trend to be relatively unchanged. At the
same time, for many national parks, the 8-hour
ozone levels have increased somewhat.
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. Emissions of
VOCs have decreased about 40 percent over
the past 20 years. However, regional-scale
NOX reductions over the same period are only
15 percent. More NOX reductions will be
necessary before more substantial ozone air
quality improvements are realized. Some of
these additional reductions will result from
existing and recently enacted NOX emission
reduction programs and also, potentially, from
the Clear Skies legislation, if enacted.
The improvement in overall emissions since
1970 included in this year's findings reflect
more accurate estimates of VOC, NOX, PM,
and carbon monoxide (CO) releases from
highway vehicles and nonroad engines.
Previous years' findings underreported
emissions for cars and trucks in the 1970s
and 1980s. This year's findings incorporate
improvements in EPA's mobile source emission
models, which are based on actual emissions
measurements from thousands of motor vehi-
cles and have been peer-reviewed. The new
mobile model better represents average U.S.
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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)
driving habits, such as more rapid accelerations
and faster highway speeds.
Sulfates formed primarily from SO2 emissions
from coal-fired power plants are a major
component of fine particles (known as PM25)
in the eastern United States. SO2 emissions
decreased approximately 33 percent from 1983
to 2002. Nationally, average SO2 ambient
concentrations have been cut approximately
54 percent over the same period. Reductions
in SO2 concentrations and emissions since
1990 are primarily due to controls imple-
mented under EPA's Acid Rain Program.
Sulfate reductions since 1999 are partly
responsible for some improvement in ambient
fine particle concentrations, particularly in the
southeastern United States.
In many locations, EPA now has 4 years of
air quality monitoring data for fine particles
Comparison of 1970 and 2002 Emissions
250
200
150 -
100 -
50 -
._
p
(-98
i
3
>/o)b
a Based
;d on 1985 emission estimates. Emission estimates prior to 1985 are
uncertain.
b Values for lead are based on 2001 data; 2002 data for lead are not yet available.
(known as PM2 5). Areas across the Southeast,
Mid-Atlantic, Midwest regions, and California
have air quality that is unhealthy due to
particle pollution. Region-wide emissions
from power plants and motor vehicles are
among the largest contributors to the high
PM2 5 concentrations.
• Since 1990, many actions have been taken that
will significantly reduce air toxics across the
country. Specifically, regulations for facilities
such as chemical plants, dry cleaners, coke
ovens, and incinerators will reduce emissions
of toxic air pollution by 1.5 million tons from
1990 levels. In addition, recent actions to
address emissions of toxic air pollutants from
motor vehicles as well as stringent standards
for heavy-duty trucks, buses, and diesel fuel
will eliminate 95 percent of emissions of diesel
particulate matter.
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 chlorofluorocarbons
(CFCs), are also beginning to decrease.
Air Pollution
The Concern
Exposure to air pollution is associated with numer-
ous 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 out-
doors 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
associated with reductions of agricultural and
commercial forest yields, and airborne releases of
NOX are one of the largest sources of nitrogen
pollution in certain waterbodies, such as the
Chesapeake Bay.
The Causes
Air pollution comes from many different sources.
These include large 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 older adults.
EPA also sets limits to protect public •welfare. This
includes protecting ecosystems, including plants
and animals, from harm, as well as protecting
against decreased visibility and damage to crops,
vegetation, and buildings.
Percent Change in Air Quality
1983-2002 " 1993-2002
NO2
03 1-h
8-h
SO2
-21
-22
-14
-54
-11
-2a
+4"
-39
PMi0 — -13
PM2.5
CO
Pb
—
-65
-94
-8b
-42
-57
Percent Change in Emissions
1983-2002 1993-2002
NOX
voc
SO2
PMi0<=
PM2.5<=
CO
Pbe
-15
-40
-33
-34d
—
-41
-93
-12
-25
-31
-22
-17
-21
-5
—Trend data not available.
a Not statistically significant.
bBased on percentage change from 1999.
c Includes only directly emitted particles.
BBased on percentage change from 1985. Emission esti-
mates prior to 1985 are uncertain.
eLead emissions are included in the toxic air pollutant
emissions inventory and are presented for 1982-2001.
Negative numbers indicate improvements in air quality
or reductions in emissions. Positive numbers show where
emissions have increased or air quality has gotten worse.
Changes in air quality concentrations do not always match changes in
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.
Fourth, emissions from some sources are estimated rather than measured.
Finally, weather conditions 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.
EPA has set national air quality standards for six
principal air pollutants (also called the criteria
pollutants): nitrogen dioxide (NO2), ozone (O3),
sulfur dioxide (SO2), participate matter (PM),
carbon monoxide (CO), and lead (Pb). Four of
these pollutants (CO, Pb, NO2, and SO2) are emit-
ted directly from a variety of sources. Ozone is not
directly emitted, but is formed when NOX and
volatile organic compounds (VOCs) react in the
presence of sunlight. PM can be directly emitted,
or it can be formed when emissions of nitrogen
oxides (NOJ, sulfur oxides (SOJ, ammonia,
organic compounds, and other gases react in
the atmosphere.
Each year EPA looks at the levels of these pollut-
ants in the air and the amounts of emissions from
various sources to see how both have changed
over time and to summarize the current status
of air quality.
Reporting Air Quality and Emissions Trends
Each year, air quality trends are created using
measurements from monitors located across the
country. The table to the left shows that the air
quality based on concentrations of the principal
pollutants has improved nationally over the past 20
years (1983-2002).
EPA estimates nationwide emissions of ambient air
pollutants and the pollutants they are formed from
(their precursors). These estimates are based on
actual monitored readings or engineering calcula-
tions of the amounts and types of pollutants emit-
ted by vehicles, factories, and other sources.
Emission estimates are based on many factors,
including levels of industrial activity, technological
developments, fuel consumption, vehicle miles
traveled, and other activities that cause air pollution.
Methods for estimating emissions continue to
improve. Today's estimates are different from last
year's estimates. One reason is because this year
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Comparison of Growth Areas and Emissions
200%
150%
100%
50%
Gross Domestic Product
Energy Consumption
Population
-50%
Aggregate Emissions
(Six Principal Pollutants)
70 80 90 95 96 97 98 99 00 01 02
Between i970 and 2002,gross domestic product increased i 64 percent, vehicle miles traveled increased 155 percent, energy
consumption increased 42 percent, and U.S. population increased 38 percent. At the same time, total emissions of the six principal
air pollutants decreased 48 percent.
EPA used updated, peer-reviewed models that
estimate VOC, NOX, CO, and PM emissions from
highway vehicles and nonroad engines and and
better represent real-world conditions, such as
more rapid accelerations and faster highway speeds.
The emissions estimates generated by the new
highway vehicle model are derived from actual
tailpipe measurements from thousands of vehicles.
Another change in the reporting of emissions
trends is that emissions from •wildfires and pre-
scribed burning are not considered in the estimates
of emission change. This is due to the large vari-
ability in the year-to-year levels of these emissions
and the relatively small impact these distant emis-
sions have on most monitoring locations. Because
of the high degree of uncertainty in predicting
emissions for these fires, their emissions have not
been projected for 2002 for PM,CO, andVOCs.
These emissions will be estimated when 2002
acres-burned data become available. However, fire
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emissions are included in the emission graphics
through 2001. As a result of these reporting
changes, some emissions trends have changed
significantly. For example, rather than describing
no change in the 20-year emission trend for CO,
EPA now estimates a 41 percent decrease in CO
emissions from 1983 to 2002. This estimated
change in emissions is supported by the trend
in CO air quality.
Emissions of air pollutants continue to play an
important role in a number of air quality issues.
About 160 million tons of pollution are emitted
into the atmosphere each year in the United
States. These emissions mostly contribute to the
formation of ozone and particles, the deposition
of acids, and visibility impairment.
Despite great progress in air quality improvement,
approximately 146 million people nationwide
lived in counties with pollution levels above the
NAAQS in 2002. Out of the 230 nonattamment
areas identified during the 1990 Clean Air Act
Amendments designation process, 124 areas
remain. In these nonattainment areas, however, the
severity of air pollution episodes has decreased.
Number of People Living in Counties
with Air Quality Concentrations above
the Level of the NAAQS in 2002
NO2
136.4 (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. Improvements in air quality are
the result of effective implementation of clean air
laws and regulations, as well as efficient industrial
technologies. Under the Clean Air Act, EPA has
a number of responsibilities, including
Conducting periodic reviews of the 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, which can reduce visibility across
large regional areas, including many of the
nation's most treasured parks and wilderness
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.
u Limiting the use of chemicals that damage the
stratospheric ozone layer in order to prevent
increased levels of harmful ultraviolet radiation.
0.7
Pb
Any NAAQS
C
0.2
i
50 100
Millions of People
Il46.2
i
150
C/3
HP
B'
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o
Multiple years of data are generally used to determine if an area
attains the NAAQS.
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NITROGEN DIOXIDE
N O-
Nature and Sources of Nitrogen Oxides
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 generic term for a group of
highly reactive gases that contain nitrogen and
oxygen in varying amounts, play a major role in
the formation of ozone, PM, haze, and acid rain.
While EPA tracks national emissions of NOX, the
national monitoring network measures ambient
concentrations of NO2 for comparison to national
air quality standards. The major sources of
NO2 Air Quality, 1983-2002
Based on Annual Arithmetic Average
0.06
0.05
0.04
0.03
0.02
0.01
0.0
125 Sites
90% of sites have concentrations below this line
NAAQS
10% of sites have concentrations below this line
83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02
1983-02: 21% decrease
1993-02: 11% decrease
NOX Emissions, 1983-2002
c
£ 20,000
•e
o
£ 15,000
c
o 10,000
H
5,000
n
F — *"
'
-
'
• Fuel Combustion D Industrial Processes
D Transportation D Miscellaneous
^^ In 1985, EPA refined its methods for estimating emissions.
^^^^
=^^==^^
83 85
93 94 95 96 97 98 99 00 01 02
man-made NOX emissions are high-temperature
combustion processes such as those that occur in
automobiles and power 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. These exposures
may also increase respiratory illnesses in children.
Long-term exposures to NO2 may lead to increased
susceptibility to respiratory infection and may cause
irreversible alterations in lung structure. NOX react
in the air to form ground-level ozone and fine
particle pollution, which are associated with adverse
health effects.
NOX contribute to a wide range of environmental
effects directly and when combined with other
precursors in acid rain and ozone. Increased nitro-
gen inputs to terrestrial and wetland systems can
lead to changes in plant species 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 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. NOX also contribute to visibility
impairment.
1983-02: 15% decrease
1993-02: 12% decrease
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Trends in NO2 Levels and NOX Emissions
Since 1983, monitored levels of NO2 have
decreased 21 percent. These downward trends in
national NO2 levels are reflected in all regions of
the country. Nationally, average NO2 concentra-
tions are well below the NAAQS and are currently
at the lowest levels recorded in the past 20 years.
All areas of the country that once violated the
NAAQS for NO2 now meet that standard. Over
the past 20 years, national emissions of NOX have
declined by almost 15 percent. The reduction in
emissions for NOX presented here differs from the
increase in NOX emissions reported in previous
editions of this report. In particular, this report's
higher estimate of NOX emissions in the 1980s
and early 1990s reflects an improved understanding
of emissions from real-world driving. While overall
NOX emissions are declining, emissions from some
sources such as nonroad engines have actually
increased since 1983.These increases are of
concern given the significant role NOX emissions
play in the formation of ground-level ozone
(smog) as well as other environmental problems
like acid rain and nitrogen loadings to waterbodies
described above. In response, EPA has proposed
regulations that will significantly control NOX
emissions from nonroad diesel engines.
HP
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fl
GROUND-LEVEL OZONE
u
Nature and Sources of Ozone
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
Ozone Air Quality, 1983-2002
Based on Annual 2nd Maximum 1-Hour Average
0.20
0.15
ffi 0.10
•£.
0.05
0.00
90% of sites have concentrations below this line
370 Sites
Average
T
NAAQS
10% of sites have concentrations below this line
83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02
1983-02: 22% decrease
1993-02: 2% decrease
Ozone Air Quality, 1983-2002
Based on Annual 4th Maximum 8-Hour Average
0.20
0.15
.3
•5 0.10
o
O
0.05
0.00
370 Sites
90% of sites have concentrations below this line
Average f
NAAQS
10% of sites have concentrations below this line
83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02
1983-02: 14% decrease
1993-02: 4% increase
Ozone occurs naturally in the strato-
sphere and provides a protective layer
high above the Earth. See page 26 for
more information on the stratospheric
ozone layer.
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.
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
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 evi-
dent 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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30,000
25,000
20,000
15,000
10,000
5,000
0
Trends in Ozone Levels, Related Emissions
In 1997, EPA revised the NAAQS for ozone by
setting an 8-hour standard at 0.08 ppm. Currently,
EPA is tracking trends based on 1-hour and
8-hour data. Over the past 20 years, national
ambient ozone levels decreased 22 percent based
on 1-hour data and 14 percent based on 8-hour
data. Between 1983 and 2002, emissions of VOCs
(excluding wildfires and prescribed burning)
decreased 40 percent. During that same time,
emissions of NOX decreased 15 percent. Additional
NOX reductions will be necessary before more
substantial ozone air quality improvements are
realized. For example, future emission reductions
from existing and recently enacted NOX control
programs such as the NOX SIP Call,Tier 2, Heavy
Duty Diesel, Non-road Proposal, and, potentially,
Clear Skies legislation will result in millions of
fewer tons of NOX emissions.
For the period 1983 to 2002, a downward national
trend in 1-hour and 8-hour ozone levels occurred
in most geographic areas in the country. The
Northeast and Pacific Southwest exhibited the
most substantial improvement for 1-hour and
8-hour ozone levels. The Mid-Atlantic and North
Central regions experienced minimal decreases in
8-hour ozone levels. In contrast, the Pacific North-
west region showed a slight increase in the 8-hour
ozone over the period 1983 to 2002.
For the 10-year period 1993-2002, the national
trend in 8-hour ozone shows a 4 percent increase
and the national trend in 1-hour ozone shows a
VOC Emissions, 1983-2002
• Fuel Combustion
D Transportation
D Industrial Processes
D Miscellaneous D Fires
In 1985 and 1996, EPA refined its methods
for estimating emissions. -*^\
Fire emissions not available for 2002.
83 85 93 94 95 96 97 98 99 00 01 02
1983-02: 40% decrease
1993-02: 25% decrease
2 percent decrease. However, standard statistical
tests show that these trends are not statistically
significant. Ozone concentrations varied over this
10-year period from year to year but did not
change overall.
Regional trends can provide additional informa-
tion to understand progress on ozone levels. For
example, the trend in 8-hour ozone for the Pacific
Southwest shows the 20-year trend (1983-2002) as
a 29 percent decrease. When considering the Los
Angeles area separately, the trend for Los Angeles
shows a 49 percent decrease for the 20-year period
and a 15 percent decrease for the other locations
in the Pacific Southwest. For the 10-year period
1993-2002, the Pacific Southwest has an overall
13 percent decrease in 8-hour ozone. However,
when considering Los Angeles separately, the
Los Angeles area has a 28 percent decrease for
the 10-year period while the Pacific Southwest
without Los Angeles has a 5 percent decrease.
This illustrates that national assessments for ozone
do not describe trends completely, particularly
where control measures such as those implemented
in Los Angeles have had a significant effect in
reducing ozone concentrations.
It is important to note that year-to-year changes in
ambient ozone trends are influenced by meteoro-
logical conditions, population growth, and changes
in emission levels of ozone precursors (i.e.,VOCs
and NOJ resulting from ongoing control mea-
sures. For example, to further evaluate the 10-year
a?
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fl
Trend in 1-Hour Ozone Levels, 1983-2002, Averaged across EPA Regional Office Boundaries*
Based on Annual 2nd Highest Daily Maximum
.175
u
10
.083 .083
1983 2002
^ 0%
.168
1 983 2002
f 39%
.J19 .0 95
1983 2002
f 20%
8
7
.109 .092
1983 ~~2002
f 12%
1983
.146 .119
1983
.128 .107
2002
2002
16%
f 18% 2
- 25%
.135
.120
1983 2002
1 1 %
The National Trend
138 .108
1983 2002
f> 22%
6 .130
.108
1983 2002
f 17%
120 .102
1983 2002
A t15%
*EPA Regional Office contacts
can be found at www.epa.gov/
epahome/locate2. htm.
Trend in 8-Hour Ozone Levels, 1983-2002, Averaged across EPA Regional Office Boundaries
Based on Annual 4th Maximum 8-Hour Average
.124 .098
^,
10
.058 .059
1983 2002
-fr 2%
.111 .079
1983 ^2002
f 29%
1983 2002
.111 .099
.083 075
1983 2002
f- 10%
1983 2002
.1
>*.
.096 .090 >*. *21°/
fn%2
1983 2002
f6%
8 .083 ,_°j°,
1983 2002
f-4%
.105 .097
1983 2002
8%
The National Trend
.100 .086
1983 ' 2002"
f 14%
.092 082
1983 "~2002
f-11%
.092 .083
1983 2002
A flO%
Concentrations are in
parts per million (ppm).
10
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C/3
8-hour ozone trends, EPA applied a model to the
annual rate of change in ozone based on measure-
ments in 53 metropolitan areas. This model
adjusted the ozone data in these areas to account
for the influence of local meteorological condi-
tions, including surface temperature and wind-
speed. The figure below shows the aggregated
trend in 8-hour ozone for these 53 areas adjusted
for meteorological conditions for the 10-year
period 1993-2002. The figure also shows the
aggregated trend for these areas unadjusted for
meteorology and the national average in 8-hour
ozone. From this figure, the meteorologically
adjusted trend for this 10-year period can be
seen as relatively flat.
Comparison of Actual and Meteorological
Adjusted 8-Hour O3 Trends, 1993-2002
0.1
Q.
°: 0.08
.2
2 0.06
0.04
0.02
93
94
95
96
97 98
Year
99
00
01
02
Selected Area Trend in Average Daily Maximum 8-Hour Concentrations
Meteorologically Adjusted Trend in Average Daily Maximum 8-Hour Concentrations
National Trend in Annual 4th Maximum 8-Hour Concentrations
In 2002, meteorological conditions were favorable
for relatively high ozone concentrations primarily
in the eastern half of the nation as evidenced by
the higher observed 8-hour ozone compared to
meteorologically adjusted levels. On average, the
June through August period in 2002 was the third
warmest year on record. A preliminary review of
these meteorological conditions indicates that they
were similar to conditions experienced in 1988 in
the eastern United States—another high-ozone
year and the fourth warmest summer period on
record. By way of comparison, the average daily
maximum 4th-highest 8-hour ozone concentra-
tions throughout the Eastern United States showed
decreases of approximately 15 to 20 percent
between 1988 and 2002.This indicates regional
improvements in 8-hour ozone concentrations.
Furthermore, preliminary examination of meteoro-
logically adjusted 8-hour ozone on a subregional
basis in the Eastern United States reveals a pattern
of increasing ozone through 1998 followed by a
period of generally improving ozone air quality.
This reversal appears to correspond to the imple-
mentation of regional NOX reductions from power
plants (see Acid Rain section).
Twenty-eight of our national parks had ozone
trend data for the 10-year period 1993-2002.
Seven 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), Denali (Alaska), and Acadia
(Maine). Monitoring data for one park showed
statistically significant improvements over the same
time period: Saguaro (Arizona). For the remaining
22 parks with ozone trends data, the 8-hour ozone
levels at 13 increased only slightly between 1993
and 2002, while 5 showed decreasing levels and
4 were unchanged.
Although the recent national trends in 1-hour
and 8-hour ozone are relatively unchanged,
important regional decreases have occurred. EPA
is continuing to investigate these regional assess-
ments to further evaluate the trends in 1-hour
and 8-hour ozone.
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SULFUR DIOXIDE
S O-
Nature and Sources of Sulfur Dioxide
Sulfur dioxide belongs to the family of SOX gases.
These gases are formed when fuel containing
sulfur (mainly coal and oil) is burned at power
plants and during metal smelting and other indus-
trial processes. Most SO2 monitoring stations are
located in urban areas. The highest monitored
concentrations of SO2 are recorded near large
industrial facilities. Fuel combustion, largely from
electricity generation, accounts for most of the
total SO? emissions.
SO2 Air Quality, 1983-2002
Based on Annual Arithmetic Average
0.04
I
0.03
0.02
I
o
O
0.01
0.00
244 Sites
NAAQS
90% of sites have concentrations below this line
• 10% of sites have concentrations below this line
83 84 85 86 87
i 89 90 91 92 93 94 95 96 97 98 99 00 01 02
1983-02: 54% decrease
1993-02: 39% decrease
SO2 Emissions, 1983-2002
30,000
25,000
20,000
15,000
• Fuel Combustion D Industrial Processes
D Transportation D Miscellaneous
1
i
| 10,000
H
5,000
In 1985, EPA refined its methods for estimating emissions.
83 85
93 94 95 96 97 98 99 00 01 02
1983-02: 33% decrease
1993-02: 31% decrease
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
alterations 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, and 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 54 percent from 1983 to 2002 and
39 percent over the more recent 10-year period
1993 to 2002. SO2 emissions decreased 33 percent
from 1983 to 2002 and 31 percent from 1993 to
2002. Reductions in SO2 concentrations and emis-
sions since 1990 are due, in large part, to controls
implemented under EPA's Acid Rain Program,
•which began in 1995. In addition, in 2001 and
2002, energy consumption for electricity genera-
tion and industrial power leveled off; therefore,
SO2 and NOX emissions from this sector did not
increase as much as expected.
12
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PARTICULATE MATTER
P M
C/3
Nature and Sources of Particulate Matter
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 |_im in diameter. "Coarse fraction"
particles are greater than 2.5 |_im, but less than or
equal to 10 |_im in diameter. PM10 refers to all
particles less than or equal to 10 |_im in diameter
(about one-seventh the diameter of a human hair).
PM can be emitted directly or formed in the
atmosphere. "Primary" particles, such as dust from
roads or black carbon (soot) from combustion
sources, are emitted directly into the atmosphere.
PM10 Air Quality, 1993-2002
Based on Seasonally Weighted Annual Average
60
50
40
1 30
20
10
804 Sites
NAAQS
90% of sites have concentrations below this line
10% of sites have concentrations below this line
93
94
95 96 97 98 99 00
1993-02: 13% decrease
01
02
4,000
m 3,000
I
c
o
-C
03 2,000
PM10 Emissions, 1993-2002
• Fuel Combustion D Industrial Processes
D Transportation
1,000
In 1996, EPA refined its methods
. for estimating emissions.
94
95 96 97 98 99 00
1993-02: 22% decrease
01
02
"Secondary" particles are formed in the atmos-
phere from primary gaseous emissions. Examples
include sulfates formed from SO2 emissions from
power plants and industrial facilities; nitrates
formed from NOX emissions from power plants,
automobiles, and other combustion sources; and
carbon formed from organic gas emissions from
automobiles and industrial facilities. 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
diameter) can cause numerous health problems
and have been linked with illness and death from
heart and lung disease.Various health problems
have been associated with long-term (e.g., multi-
year) exposures as well as daily and, potentially,
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 sections on
Acid Ram, NO2, and SO2.)
Trends in PM1O Levels and Direct Emissions
Between 1993 and 2002, average PM10 concentra-
tions decreased 13 percent, while direct PM10
emissions decreased 22 percent.
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PM2.s Emissions, 1993-2002
C/5
-4-J
fl
2,500
2,000
S
£
? 1,500
.c
03
• Fuel Combustion D Industrial Processes
D Transportation
U
In 1996, EPA refined its methods
^ for estimating emissions.
93 94 95 96 97 98 99 00 01
1993-02: 17% decrease
Annual Average PM2.s Concentrations
and Particle Type in Rural Areas, 2002
02
O
O 5ng/m3
Sulfate
Ammonium
U—i Nitrate
15ng/m3 1=1 Total Carbon
^ Crustal
Source: Interagency Monitoring of Protected
Visual Environments Network, 2002.
Note: Direct comparisons of the information in these two maps should take into
consideration the fact that one is a rural network and the other is an urban net-
work and that there are differences in instruments and measurement methods.
Annual Average PM2.s Concentrations
and Particle Type in Urban Areas, 2002
f) 10ng/m3
C J 15ng/m3
i Sulfate
i Ammonium
i Nitrate
i Total Carbon
i Crustal
Source: EPA Speciation Network, 2002.
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 5 Levels and Direct Emissions
The chart at lidf shows that direct PM2 5 emissions
from man-made sources decreased 17 percent
nationally between 1993 and 2002.This chart
tracks only directly emitted particles and does
not account for secondary particles, which typi-
cally account for a large percentage of PM2 5. As
discussed previously, the principal secondary parti-
cles are sulfates, nitrates, and organic carbon.
The maps at left show how sulfates, nitrates, and
total carbon (black carbon and organic carbon)
along with other components, contribute to PM2 5
concentrations. The first map represents the most
recent year of data (September 2001—August 2002)
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 PM25.The second map
represents the most recent year of data (September
2001-August 2002) from EPA's urban Speciation
network, which was established in 1999. All of
these sites are located in urban areas.
The IMPROVE data show that PM2 5 levels in
rural areas are highest in the eastern United States
and southern California, as shown by the larger
circles. Sulfates and associated ammonium domi-
nate the East, with carbon as the next most preva-
lent component. Sulfate concentrations in the East
largely result from SO2 emissions from coal-fired
power plants. In California and other areas of the
West, carbon and nitrates make up most of the
PM2 5 measured.
The urban Speciation data show that 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. Urban sites
in the East include a large percentage of carbon
and sulfates (and ammonium). Urban sites in the
Midwest and far West (and especially in California)
include a large percentage of carbon and nitrates.
14
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Urban Increments of PM2 5 Mass
and Major Chemical Species, 2002
0 I—
\ \ V
"$ "^
^ ~& O Q- *£.
v%V«\Y\
Sulfate •+• Nitrate -A- Ammonium
Total Carbonaceous Mass -0- Crustal
Source: Interagency Monitoring of Protected Visual Environments
Network and EPA Speciation Network, 2002.
The lines in the figure above display West-to-East
urban increments of PM25 levels and the major
chemical constituents. EPA compared the annual
average PM2 5 concentration at each of these
13 sites with measurements from a nearby rural
site. The urban excess shown above illustrates the
difference in concentrations from these paired sites.
In general, the single largest component of urban
excess is total carbonaceous material. There is little
or no excess of sulfates (confirming the regional
nature of this pollutant) and only moderate urban
PM2 5 Air Quality, 1993-2002
Based on Seasonally Weighted Annual Average
25
0) 20
a.
Concentration,
m o 01 o 01
858 Sites
-
90% of sites have concentrations below this line
- Trends monitoring data for
PM26 not available.
10% of sites have cone
3 94 95 96 97 98 9
NAAQS
^Average
A
jntrations below this line
9 00 01 0
excess of nitrate at some locations. The compo-
nents of PM2 5 showing urban excesses come from
sources local to the urban area.This illustrates the
importance of local, metropolitan area controls
in addition to regional control programs.
In 1999, EPA and its state, tribal, and local air
pollution control partners deployed a monitoring
network to begin measuring PM2 5 concentrations
nationwide. Now that there are several years of
monitoring data available, EPA has begun to
examine trends at the national level. Annual
average PM2 5 concentrations decreased 8 percent
nationally from 1999 to 2002. Much of that
reduction occurred in the Southeast where the
monitored levels of PM25 decreased 18 percent
from 1999 to 2002. Lower annual average concen-
trations in the Southeast can be attributed, in part,
to decreases in sulfates, which largely result from
power plant emissions of SO2.
PM2 5 concentrations vary regionally. Based on the
monitoring data, parts of California and many areas
in the eastern United States have annual average
PM25 concentrations above the level of the annual
PM25 standard. With few exceptions, the rest of
the country generally has annual average concen-
trations below the level of the annual PM2 5
health standard.
Because of health effects associated with short-
term exposure to PM2 5, daily levels are also of
concern. Actual and forecasted daily air quality
is assessed and reported using EPA's Air Quality
Index (AQI).The forecasted AQI is typically
featured in USA Today and on The Weather Channel,
as well as in local media. In the summertime,
ozone is usually the pollutant of concern on days
•when the air is unhealthy. But PM2 5 also plays a
role in unhealthy air quality in the summertime in
some regions, even on days when the ozone levels
are not high. PM2 5 is also responsible for days with
unhealthy air in cooler months. Because of its
complex chemical makeup, PM2 5 levels can be
in the unhealthy range any time during the year
(sulfates are usually higher in the summer; carbon
and nitrates, in the winter). Many major metropoli-
tan areas are beginning year-round reporting and
forecasting of AQI values through the incorpora-
tion of daily PM2 5 information.
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CARBON MONOXIDE
C O
Nature and Sources of Carbon Monoxide
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, 1983-2002
Based on Annual 2nd Maximum 8-hour Average
90% of sites have concentrations below this line
10% of sites have concentrations be ow this me
0
83 84 85 86 87
89 90 91 92 93 94 95 96 97 98 99 00 01 02
1983-02: 65% decrease
1993-02: 42% decrease
CO Emissions, 1983-2002
200,000
180,000
160,000
w
I 140,000
fe 120,000
% 100,000
§ 80,000
D
I 60,000
40,000
20,000
0
• Fuel Combustion
D Transportation
D Industrial Processes
D Miscellaneous D Fires
In 1985, EPA refined its methods for estimating emissions.
Fire emissions not available for 2002.
\
83
85
93 94 95 96 97 98 99 00 01 02
1983-02: 41% decrease
1993-02: 21% decrease
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 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 2002 ambient average CO concen-
tration is almost 65 percent lower than that for
1983 and is the lowest level recorded during the
past 20 years. CO emissions from transportation
sources, the major contributor to ambient CO
concentration, decreased dramatically during this
period as indicated by EPA's improved new model
of highway vehicle emissions. In particular, this
report's higher estimate of CO emissions in the
1980s and early 1990s reflects an improved under-
standing of emissions from real-world driving.
Between 1993 and 2002, ambient CO concentra-
tions decreased 42 percent. Total CO emissions
decreased 21 percent (excluding wildfires and
prescribed burning) for the same period. This
improvement in air quality occurred despite a 23
percent increase in vehicle miles traveled during
the 10-year period.
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LEAD ( P b )
C/3
Nature and Sources of Lead
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 con-
tribution of air emissions of lead from the trans-
portation sector, and particularly the automotive
sector, has greatly declined over the past two
decades. Today, industrial processes, primarily metals
processing, are the major source of lead emissions
to the atmosphere. The highest air concentrations
of lead are usually found in the vicinity of smelters
and battery manufacturers.
Lead Air Quality, 1983-2002
Based on Annual Maximum Quarterly Average
90% of sites have concentrations below this line
10% of sites have concentrations below this line
0.0
89 90 91 92 93 94 95 96 97 98 99 00 01 02
1983-02: 94% decrease
1993-02: 57% decrease
Lead Emissions, 1982-20023
I Fuel Combustion IZl Industrial Processes
D Transportation
60,000
20,000
In 1985, EPA refined its methods for estimating emissions.
82
85
92 93 94 95 96 97 98 99 00 01 02
1982-02: 93% decrease
1993-02: 5% decrease
a As of 2002, lead emissions are included in the Toxic National Emissions
Inventory.
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 2002
average air quality concentration for lead is
94 percent lower than in 1983. Emissions of lead
decreased 93 percent over the 21-year period
1982-2002.These large reductions in long-term
lead emissions from transportation sources have
changed the nature of the ambient lead problem
in the United States. Because industrial processes
are now responsible for all violations of the lead
NAAQS, the lead monitoring strategy currently
focuses on emissions from these point sources.
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.
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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 Ram Formation
Coal-fired electric utilities and other sources that burn
fossil fuels emit SO2 and NOX.
SO2 Emissions Covered under
the Acid Rain Program
12.46
11.20
10.63
10.19
10.19
1980 1985 1990 1995
Phase I Sources
Phase II Sources
1997 1998 1999 2000 2001 2002
D All Sources
• • • • Allowances Allocated for that Year
NOX Emissions Covered under
the Acid Rain Program
1 — 6.66
-
. 5.53
6.09
5.44
5.91
5.44
6.04
5.49
5.97
5.29
5.49
4.82
4.48
4.69
4.10
447
4.02
1990 1995 1996 1997 1998 1999 2000 2001 2002
CH NOx Program Affected Sources d Title IV Sources Not Affected for NOX
• • • • Projected Emissions Without Title IV
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 63 percent of annual
SO2 emissions and 22 percent of NOX emissions
are produced by burning fossil fuels for electricity
generation.
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 contrib-
utes 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 expo-
sure 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.
Program Structure
The goal of EPA s Acid Rain Program 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.
Approximately 3,000 units are now affected by the
Acid Rain Program.
By 2010, the Acid Rain Program will reduce
annual SO2 emissions by half from 1980 levels. 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. It employs an
emissions trading program to achieve emission
reductions more efficiently and cost-effectively
Sources are allocated allowances each year (one
allowance equals 1 ton of SO2 emissions), which
can be bought or sold or banked for future use.
This approach gives sources the flexibility and
incentive to reduce emissions at the lowest cost
18
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Change in Sulfate Deposition from Precipitation
Source: U.S. EPA analysis of National Atmospheric
Deposition Program data.
and the cap ensures that emission reductions are
maintained over time.
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
1990 levels by 2001. There is no cap on total NOX
emissions, but under this program a source can
choose to overcontrol 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 were significant in the
first 6 years of EPA's Acid Rain Program. In 2002,
sources in the Acid Rain Program emitted 10.2
million tons, down from 15.7 million tons in 1990.
Emissions of SO2 in 2002 were 400,000 tons less
than in 2001. As in 2001, sources again drew down
the bank of unused allowances in 2002, resulting in
emission levels greater than the allowances allocated
in 2002 but still lower than emissions during any
previous year.
NOX emissions from all Acid Rain Program
sources have also declined since 1990. NOX
emissions have decreased steadily from 6 million
tons in 1997 to 4.5 million tons in 2002.The more
than 1,000 sources affected by the Acid Rain NOX
Program emitted 4.1 million tons in 2000, approx-
imately 1.5 million tons (25 percent) less than they
did in 1990. NOX emissions from these sources in
2001 were 3.6 million tons (over 40 percent)
below what emissions were projected to have been
in 2000 without the Acid Rain Program.
For all years from 1995 through 2001, wet sulfate
deposition exhibited dramatic and unprecedented
reductions over a large area of the eastern United
States. Average sulfate deposition in 1999-2001 has
decreased more than 8 kg/ha from 30-40 kg/ha in
1989-1991 in much of the mid-Appalachian and
the northeastern United States. Similarly, sulfate air
concentrations, which contribute to human health
and visibility problems, were reduced significantly
in the East. Wet nitrogen deposition decreased
slightly in some places between 1989-1991 and
1999-2001, but increased in others up to 3 kg/ha
in areas with significant agricultural activity and
areas where vehicles are the predominant source
of NOX emissions.
These reductions in acid deposition and improve-
ments in air quality are directly related to the large
regional decreases in SO2 and NOX emissions
resulting from the Acid Rain Program. The largest
reductions in wet sulfate deposition occurred
across the Ohio River Valley and in the Northeast.
The largest reductions in sulfate concentrations
also occurred along the Ohio River Valley and
in states downwind. Reductions in the East in
hydrogen ion concentrations, the primary indicator
of precipitation acidity, were similar to those of
sulfate concentrations, both in magnitude and
location. The largest reductions in wet nitrate
deposition were in the northeastern United States,
Michigan, and Texas. The states immediately west
of the Mississippi River and in the eastern Plains,
parts of the Southeast, and California showed the
highest increases in nitrogen deposition even
though emissions from acid rain sources have
not increased substantially there. Acid rain sources
account for only 22 percent of nationwide nitro-
gen emissions, so emissions trends in other source
categories, especially agriculture and mobile
sources, also affect air concentrations and deposi-
tion of nitrogen.
>
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Visibility
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,
Shenandoah, and the Great Smoky Mountains
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
East
West
Sulfates
60%-86%
Organic Carbon
Nitrates
Elemental Carbon (soot)
5%-8%
Crustal Material (soil dust)
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.
Class I Areas
The Clean Air Act provides for the protection of visibility
in our national parks and wilderness areas, also known as
Class I areas. There are 156 Class I areas across the
United States as shown. (See http://www2.nature.
nps.gov/ard/parks/ClassIAreas.jpg)
elemental carbon (soot) from wood combustion.
In other cases, particles are formed in the atmos-
phere from primary gaseous emissions such as
sulfates formed from SO2 emissions from power
plants and other industrial facilities and nitrates
formed from NOX emissions from power plants,
automobiles, and other types of combustion
sources. These types of particles are referred to
as secondarily formed particles. In the eastern
United States, reduced visibility is mainly attrib-
utable to secondarily formed sulfates. Although
these secondarily formed particles still account for
a major portion of particulate loading in the West,
primary emissions from sources like wood smoke
contribute a larger percentage of the total particu-
late 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 with 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.
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.
In 1987, the IMPROVE 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 pollutants primarily
responsible for reduced visibility 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
20
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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.
In 2000, the IMPROVE Monitoring Network
started an expansion from 30 to 110 monitoring
sites. The expansion work was completed in the
fall of 2001. States, tribes, and federal land manage-
ment agencies support more than 50 additional
sites. Collectively, these will be used to track
future progress in accordance with the regional
haze program.
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
that visibility impairment for the worst visibility
in the West is similar to days with the best visibility
in the East. In 2001, mean visual range for the
•worst days in the East was only 29 km (48.3 miles)
compared to 117 km (195 miles) for the best
visibility. In the West, visibility impairment for the
•worst days remained relatively unchanged over the
10-year period, with the mean visual range for 2001
(103 km) nearly the same as the 1992 level (98 km).
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.
National Park
under bad and
good visibility
conditions. The
visual range in
the top photo is
iii km while
the visual range
in the bottom
photo is greater
than 208 km.
Visibility Trends for Eastern
U.S. Class I Areas, 1992-2001
^ou
_| 200
0)
D) 150
c
CO
01 100
•3
.— 50
0
_
-
Best Visibility
Mid-Range
Worst Visibility
I I I I I I I I
Best visibility
range is 105-117 km
Mid-range visibility
is 56-65 km
range is 24-30 km
92 93 94 95 96 97 98 99 00 01
Year
Visibility Trends for Western
U.S. Class I Areas, 1992-2001
_! 200
S) 150
CO
CO
.£ 50
0
9
_
1 • •"
1 1
2 93 94
Best Visibility
Mid-Range
i i
95 96
.Worst Visibility A
1 1 1 1
97 98 99 00 0
Best visibility
range is 21 1-234 km
Mid-range visibility
is 144-155 km
i Worst visibility
range is 93-1 03 km
1
Year
Extinction (Mnr1) 10
Deciviews (dv)
H •
Visual Range (km) 400
40 50 70 100
300 400 500 700 1000
I I I Mil
14 16 19 23
I I I Mil
130 100 80 60 40
I
30
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.
21
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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 identified
21 pollutants as mobile source air toxics, including
diesel particulate matter and diesel exhaust organic
gases. In addition, EPA has listed 33 urban hazard-
ous air pollutants that pose the greatest threats to
public health in urban areas.
Health and Environmental Effects
People exposed to toxic air pollutants at sufficient
concentrations may experience various health
effects, including cancer and damage to the
immune system, as well as neurological, reproduc-
tive (e.g., reduced fertility), developmental, respira-
tory, 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. Although 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. Currently,
there are about 300 air toxics monitoring sites in
operation. The available monitoring data help air
pollution control agencies track toxic air pollutant
levels in various locations around the country. EPA
is working with its regulatory partners to build on
the existing monitoring sites to create a national
monitoring network for a number of toxic air
pollutants. The goal is to ensure that those com-
pounds that pose the greatest risk are measured.
EPA initiated a 12-month pilot monitoring project
in 2001 in four urban areas and six small city/rural
areas (see map below). The pilot program was
developed to help answer several important
national network design questions (e.g., sampling
and analysis precision, sources of variability, mini-
mal detection levels). A National Air Toxic Trend
Site (NATTS) network was launched in early
2003. The central goal of the NATTS network is
to detect trends in high-risk air toxics such as
benzene, formaldehyde, 1,3-butadiene, acrolein,
and chromium. By early 2004, 22 NATT sites
(16 urban and 6 rural) will be operating (see map).
For the latest information on national air toxics
monitoring, see www.epa.gov/ttn/amtic/
airtxfil.html.
EPA also compiles an air toxics inventory as part
of the National Emissions Inventory (NEI, former-
ly the National Toxics Inventory) to estimate 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: (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 aircraft, locomotives,
and construction equipment.
22
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Recent National Air Toxics Monitoring Initiatives
A Pilot Program
38 sites in 10 cities
Barcelenta/San Juan, PR
Providence, Rl
Keeney Knob, WV
Tampa, FL
Detroit, Ml
Rio Rancho, NM
Cedar Rapids, IA
San Jacinto, CA
Grand Junction, CO
Seattle, WA
NATTS Sites
22 'areas'
Jan/03 Startup (13)
Providence, Rl
Roxbury, MA
New York, NY
Washington DC
Decatur (Atlanta), GA
Hazard, KY (Rural)
Detroit, Ml
Deer Park (Houston), TX
St. Louis, MO
Bountiful, UT
Grand Junction, CO (Rural)
San Jose, CA
Seattle, WA
I Jan/04 Startup (9)
Chittenden County, VT (Rural)
Rochester, NY
Tampa, FL
Chesterfield, SC (Rural)
Chicago, IL
Mayville, Wl
Harrison County, TX (Rural)
Phoenix, AZ
La Grande, OR (Rural)
o
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National Air Toxics Emissions, 1996
4.7 million tons
Nonroad
20%
Area/Other
25%
National Air Toxics Emissions
Total for 188 Toxic Air Pollutants
Baseline 1996
(1990-1993)
As shown in this pie chart, based on 1996 estimates
(the most recent year of available data), the emis-
sions of toxic air pollutants are relatively equally
divided between the four types of sources. How-
ever, this distribution varies from city to city.
Based on the data in the NEI, estimates of nation-
wide air toxics emissions decreased by approxi-
mately 24 percent between baseline (1990-1993)
and 1996. Thirty-three of these air toxics that pose
the greatest threat to public health in urban areas
have similarly decreased 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.
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 trends for benzene at 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
23
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fl
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 benzene
emissions from all sources dropped 20 percent
nationwide from 1990 to 1996. In the 2001 toxics
pilot monitoring project, city averages of benzene
ranged from about 0.9 to 2.5 |_ig/m3.
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
Benzene Levels in 2001
Pilot Monitoring Project
•*'
'\
Ambient Benzene, Annual Average Urban
Concentrations, Nationwide, 1994-2000
90% of sites nave concentrations below this line
10% of sites have concentrations below this line
95
96 97 98
1994-00: 47% decrease
99
00
inhalation exposure to toxic air pollutants from
outdoor sources. It will help EPA and states
prioritize 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 is expected to be released by the
end of 2003.
The map on page 23 shows a pattern of the distri-
bution 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. population. Three
air toxics (chromium, benzene, and formaldehyde)
appear to pose the greatest nationwide carcino-
genic 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 sug-
gests pose the greatest relative risk. One air toxic,
acrolein, is estimated to pose the highest potential
nationwide risk for significant chronic adverse
effects other than cancer. For more information,
visit www.epa.gov/ttn/atw/nata.
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 and combustion sources
(e.g., chemical plants, oil refineries, dry cleaners,
and municipal waste combustors) 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. Of this
total reduction, dioxin emissions from municipal
•waste combustors and municipal waste incinerator
units •will have been reduced by approximately
24
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County Risk Comparison
Estimated by National-Scale Assessment
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Median County Risk
• Highest
•
D
•
D Lowest
99 percent and mercury emissions by 95 percent.
Additional reductions are expected by 2005. EPA
has also put into place important controls for
motor vehicles and their fuels, including introduc-
tion of reformulated gasoline and low sulfur diesel
fuel, and is taking additional 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 emis-
sions of a number of air toxics (benzene, formalde-
hyde, acetaldehyde, and 1,3-butadiene) from
highway motor vehicles by about 75 percent and
diesel PM by over 90 percent from 1990 levels.
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 reduc-
tions. 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.
25
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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-
B radiation (UV-B) from the Sun. Over the past
3 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 and 2002 Scientific
Assessments of Stratospheric Ozone firmly estab-
lished 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 chlorofluorocarbons (CPCs), halons, carbon
tetrachloride, methyl bromide, and methyl chloro-
form. These chemicals are emitted from commer-
cial air conditioners, refrigerators, insulating foam,
Total Ozone 1979-2002
90 92 94 96 98 00 02 04
Year
Data courtesy of the National Oceanic and Atmospheric
Administration (NOAA), 2003. Monthly average total
ozone measured in Dobson units (DU) at four mid-
latitude stations across the United States from i979 to
2002. Total ozone measurements from four midlatitude
U. S. stations show a decline during the period. The large
annual variation shown in each of the four cities is a
result of ozone transport processes that cause increased
levels in the unnter and spring and lower ozone levels
in the summer and fall at these latitudes.
and some industrial processes. Strong winds carry
them through the lower part of the atmosphere,
called the troposphere, and into the stratosphere.
Once there, strong solar radiation reacts with the
emitted chemicals to release 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
Ozone depletion allows for additional UV-B radia-
tion to pass through the stratosphere and reach the
Earth's surface, leading to increases in UV-related
health and environmental effects. In humans, UV-B
radiation is linked to skin cancer, including mela-
noma, the form of skin cancer with the highest
mortality rate. It also contributes to 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 plants can be slowed by excessive
UV-B radiation. In addition, some scientists suggest
that marine phytoplankton, which are the base of
the ocean food chain, are already under stress from
UV-B radiation. This stress could have adverse
consequences for human food supplies from the
oceans.
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-deplet-
ing substances. Today, more than 180 nations have
signed the Protocol, which has been strengthened
over time 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 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,
26
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Equator -
153:2.3%'
25S:2.6%-
35S:2.9%-
45S:5.5%-
55S:9.9%-
65S: 11.0%-
Source: National Oceanic and Atmospheric Administration (NOAA), 1998.
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.
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the transition away from ozone-depleting sub-
stances has already been completed.
EPA is also emphasizing 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 over-
exposure to UV radiation and the steps they can
take to reduce those risks. To educate the public
about UV radiation levels and the associated health
risks, EPA promotes the UV Index, a daily forecast
of the strength of UV radiation, and its national
Sun Wise School for grades K through 8. Sun Wise
Partner Schools sponsor classroom and school-wide
activities to raise children's awareness of stratos-
pheric ozone depletion, UV radiation, and simple
sun safety practices. For more information on
Sun Wise, visit http://www.epa.gov/sunwise.
Trends in Stratospheric Ozone Depletion
Scientific evidence shows that the approach taken
under the Montreal Protocol has been effective
to date. The latest 2002 Scientific Assessment of
Ozone Depletion indicates that the rate of ozone
depletion is slowing. Measurements have shown
that atmospheric concentrations of methyl chloro-
form 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 decreasing.
It takes several years for these substances to reach
the stratosphere and release chlorine and bromine.
For this reason, stratospheric chlorine levels are
near their peak and are expected to slowly decline
in the years to come. Because of the stability of
most ozone-depleting substances, 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
be accomplished.
For more information on Stratospheric Ozone,
visit http://www.epa.gov/air/ozone/
index.html.
27
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International Issues
and U.S. Air Quality
The transboundary flow of air pollution affecting
the United States and its neighboring countries is
now well known and documented. Under bilateral
agreements with Mexico and Canada, EPA is
pursuing policies and technical efforts to better
understand and reduce the transport of air pollu-
tion back and forth across our borders, particularly
in areas where this transport threatens public health
and attainment of ambient air quality standards.
Also, there is increasing evidence of interconti-
nental pollution transport from Central America
and Asia to the United States. Recent studies and
satellite images illustrate the degree of transport
(see sidebar). EPA participates with other agencies
in various treaties and international cooperative
efforts to characterize and address the interconti-
nental transport of air pollution. For example, EPA,
in conjunction with other research organizations,
is currently conducting a modeling study of inter-
continental pollution transport from Asia and its
potential effects on regional air quality. This model-
ing analysis will also study the intercontinental
transport of air pollution from the United States
to Europe.
Under a bilateral agreement with Mexico signed
in 1983, also known as the La Paz Agreement, the
United States and Mexico have developed and
implemented a series of strategies to address air
quality along our shared border. The United States
and Mexico currently operate coordinated air
monitoring networks, compile emission invento-
ries, and conduct modeling analyses designed to
support reasonable pollution control strategies to
achieve national air quality standards on both sides
of the border. One example resulting from this
cooperative agreement is the US.-Mexico Border
Information Center on Air Pollution. Additional
information on the Border Information Center is
available at the EPA Technology Transfer Network
Web site, www.epa.gov/ttn/catc/cica.
Canada and the United States made a historic
commitment to address transboundary air pollu-
tion with the signing of the U.S.-Canada Air
Quality Agreement in 1991. Addressing acid
rain and transboundary flows of ozone have
been the primary focus of cooperation under
Air Pollution Transport
Modeling studies and satellite images show
evidence of significant air pollution transport
from Central America and southern Mexico. In
addition, analysis of weather patterns reveals
that upper air winds in summer months favor
transport of airborne pollutants northward to
the United States. With no mountain ranges to
modify or impede them, air masses from Central
America have an unobstructed path northward.
Pollution from Fires
In May 1998, smoke from Central American and
southern Mexican forest fires moved as far north
as the Great Lakes and north-central Ontario. EPA
and its many partners tracked the aerosol plumes,
evaluating and publicizing the threats to public
health as the plumes moved through the United
States. In Texas, visibility was typically down to
less than 1 mile in many large cities. A satellite
image (courtesy of NASA) illustrating the extent
of this aerosol plume transport is shown here.
Earth Probe TOMS
Smoke/Dust over North America for May 15, 1998
28
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3
ct
n>
Ozone Concentrations in the Eastern Regions of the U.S. and Canada
(Average Annual 4th Highest Daily Maximum 8-hour Ozone, 1999-2001
Ozone concentrations are based on monitoring data from ozone sites
located within approximately 500 km of the U.S.—Canadian border.
Ozone Concentrations in the Western Regions of the U.S. and Canada
(Average Annual 4th Highest Daily Maximum 8-hour Ozone, 1999-2001
the Agreement, and work to better understand
the transboundary flows of fine particulate matter
is under way. The Ozone Annex to this Agreement
includes specific monitoring and reporting require-
ments of the two nations including (1) reporting
ambient air quality within 500 km of the
U.S.—Canadian border, (2) reporting annual
emissions from major source categories beginning
in 2004, and (3) developing joint analyses on
ground-level ozone and precursors. The figures
below illustrate the ozone concentration measure-
ments within 500 km of the border in the eastern
and western regions of the United States and
Canada, respectively. These measurements repre-
sent the average annual fourth-highest daily
maximum 8-hour ozone for 1999-2001 (see
http://www.epa.gov/airmarkets/usca/). The
annual fourth-highest daily maximum 8-hour
ozone is illustrative of the ambient air quality
standard for 8-hour ozone.
The Convention on Long-Range Transboundary
Air Pollution (LRTAP), under the United Nations
Economic Commission for Europe, establishes a
broad framework for cooperative action on air
pollution in North America and Europe. The
Convention establishes a process for negotiating
specific measures to control air pollution through
legally binding protocols. LRTAP initially focused
on reducing the effects of acid rain through
control of sulfur emissions. Later protocols have
addressed the formation of ground-level ozone,
persistent organic pollutants (POPs), and heavy
metals. These multilateral efforts have established
a foundation of international cooperation and
understanding that has significantly advanced our
ability to understand and address transboundary air
pollution (see http://www.unece.org/env/
Irtap/).
The United States is also actively leading, with
other countries, global efforts to address POPs
and mercury, pollutants that persist and are readily
transported via air pollution pathways across
borders and oceans. In 2001, the United States
joined 151 other countries in signing the
Stockholm Convention on Persistent Organic
Pollutants. This treaty •will help reduce the public
health and environmental effects of pollutants
such as DDT, chlordane, dioxins, and PCBs (see
http://www.pops.int). Also in 2003, the United
States joined the international community in
endorsing a global effort to address mercury.
55
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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.
Acronyms
AQI
CFCs
C02
CO
DU
dv
EPA
FCCC
ha
IMPROVE
IQ
kg
km
LRTAP
NAAQS
NATTS
NEI
N02, NOX
NO
NOAA
OAQPS
Pb
PM10,PM25
POPs
ppm
S02, SOX
VOCs
uv
Air Quality Index
chlorofluorocarbons
carbon dioxide
carbon monoxide
Dobson units
deciviews
U.S. Environmental Protection
Agency
Framework Convention on
Climate Change
hectare
Interagency Monitoring of
ProtectedVisual Environments
intelligence quotient
kilograms
kilometers
Long-Range Transboundary
Air Pollutants
National Ambient Air Quality
Standards
National Air Toxic Trend Site
National Emissions Inventory
nitrogen dioxide, nitrogen
oxides
nitric oxide
National Oceanic and
Atmospheric Administration
ozone
Office of Air Quality Planning
and Standards
lead
particulate matter (10 |_im or
less, 2.5 |j,m or less in
diameter)
persistent organic pollutants
parts per million
sulfur dioxide, sulfur oxides
volatile organic compounds
ultraviolet
30
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For Further Information
Web sites:
Office of Air and Radiation: www.epa.gov/oar
Detailed information on Air Pollution Trends: wivw.epa.gov/airtrends
Real-Time Air Quality Maps arid Forecasts: www.epa.gov/airnow
On-line Air Quality Data: ivww.epa.gov/air/data/index.html
Air Toxics Information: vrww.epa.gov/ttri/atw
Ozone Depletion Web site: www.epa.gov/ozotie/
Global Warming Emissions Information: vrww.epa.gov/globalwarming/index.html
Acid Rain Web site: www.epa.gov/airiiiarkets/arplindex.htnil
Office of Air Quality Planning and Standards: ivww.epa.gov/oar/oaqps
Office of Transportation and Air Quality: vrww.epa.gov/otaq
Office of Atmospheric Programs: www.epa.gov/air/oap.html
Office of Radiation arid Indoor Air: www.epa.gov/air/oria.html
Hotlines:
Acid Ram Hotline: (202) 564-9620
Energy Star (Climate Change) Hotline: (888) STAR-YES
Mobile Sources National Vehicles and Fuel Emissions Fab: (734) 214-4200
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