United States
Environmental Protection
Agency
Office of Air Quality September 2001
Planning and Standards
Research Triangle Park NC 27711 EPA454/K-01-002
Air
EPA Latest Findings on National Air
Quality: 2000 Status and Trends
www.epa.gov/airtrends
Recycled/Recyclable Printed with Vegetable Oil Based Inks on Recycled Paper (Minimum 30% Postconsumer)
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EPA Latest Findings on National Air
Quality: 2000 Status and Trends
National Air Quality 2
Six Principal Pollutants 4
Acid Rain 16
Visibility 18
Toxic Air Pollutants 20
Stratospheric Ozone 22
Global Warming & Climate Change 24
Conclusion 26
Acronyms 26
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National Air Quality
Six Principal Air Pollutants Tracked
Nationally
Nitrogen Dioxide
Ozone (O3) - formed by volatile organic
compounds (VOCs) and nitrogen oxides
Sulfur Dioxide
Particulate Matter (PM) - formed by
SO2, A/OX, ammonia, VOCs, and
direct particle emissions
Carbon Monoxide (CO)
Lead(Pb)
EPA tracks air pollution in two ways:
Emissions from all sources going
back 30 years.
Air quality measured from monitoring
stations around the country going
back 20 years.
More detailed information on air pollution
trends is available at www.epa.gov/airtrends.
This summary report highlights the U.S. Environmental Protection Agency's
(EPA) most recent evaluation of status and trends in our nation's air quality.
Highlights
Since 1970, aggregate emissions of six principal pollutants tracked nationally
have been cut 29 percent. During that same time period, U.S. Gross Domestic
Product increased 158 percent, energy consumption increased 45 percent, and
vehicle miles traveled have increased 143 percent.
National air quality levels measured at thousands of monitoring stations across
the country have shown improvements over the past 20 years for all six
principal pollutants.
Despite this progress, over 1 60 million tons of pollution are emitted into the air
each year in the United States, and approximately 121 million people live in
areas where monitored air was unhealthy because of high levels of the six
principal air pollutants.
EPAis increasingly focusing its efforts on tracking and controlling two of these
pollutants: ground-level ozone and fine particles, key components of smog
and haze.
Of the six tracked pollutants, progress has been slowest for ground-level
ozone. In the southern and north central regions of the United States ozone
levels have actually worsened in the past 10 years. Similarly, over the last 10
years, the average ozone levels in 29 of our national parks increased over 4
percent.
Much of this ozone trend is due to increased emissions in nitrogen oxides
x), a family of chemicals that can spread ozone hundreds of miles down-
wind. Between 1970 and 2000 NOX emissions in the United States have
increased almost 20 percent (and 3 percent increase in the last 10 years) . The
majority of this increase is attributed to growth in emissions from non-road
engines (like construction and recreation equipment), diesel vehicles, and
power plants. Emissions of NOX also contribute to acid rain, haze, particulate
matter, and damage to water bodies, like the Chesapeake Bay.
EPA, states and tribes have only recently begun to measure fine particles
(known as PM/? 5) in the air on abroad national basis. EPA will require three
years worth of air quality monitoring data before determining whether areas
meet the health-based standards for PM/j.s. However, based on up to two
years of data available in most of the country, many areas across the Southeast,
Midwest, and Mid- Atlantic regions, and California may have air quality that is
unhealthful due to fine particles.
In late 2001, EPA will release the first in a series of national-scale assessments of
the risks associated with 32 toxic air pollutants and diesel PM. Details about this
effort conducted under the National Air Toxics Assessment (NATA) program
are available at http://www.epa.gov/ttn/atw/nata.
Sulfates formed primarily from SC>2 emissions from coal-fired power plants are
the dominant source of fine particles in the eastern United States. SC>2 emis-
sions also contribute to the formation of acid rain. EPA's market-based
emissions trading program to reduce acid rain has successfully reduced these
air pollutants from 16 million tons in 1990 to 11 .2 million tons in 2000. One of
the many benefits resulting from this reduction is that visibility has improved
in the eastern United States. However, measurements show that visibility for
the best days in the eastern United States is about the same as the worst days in
the West.
Improvements are being made in the fight to protect the stratospheric ozone
layer. Most recent measurements showed that concentrations of the ozone-
depleting substance, methyl chloroform, have started to fall, indicating that
emissions have been greatly reduced. Concentrations in the upper atmo-
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sphere of other ozone-depleting substances, like chlorofluorocarbons, are also
beginning to decrease.
EPAcontinues to work closely with thousands of companies and other organiza-
tions to voluntarily reduce greenhouse gases associated with global climate
change. In 2000 alone, EPA's voluntary programs reduced greenhouse gas
emissions by 57 million metric tons of carbon equivalent (equal to removing 40
million cars from the road). By investing in products that use energy more
efficiently, consumers and businesses have reduced energy consumption by some
75 billion kilowatt hours and saved more than $5 billion on their 2000 energy bills.
Air Pollution
The Concern
Exposure to air pollution is associated with numerous effects on human health,
including respiratory problems, hospitalization for heart or lung diseases, and
even premature death. The average person breathes 3,400 gallons of air each
day. 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, such as ground-level ozone, and air toxics, can also significantly
affect ecosystems. For example, ground-level ozone has been estimated to
cause over $500 million in annual reductions of agricultural and commercial forest
yields, and airborne releases of NOX are one of the largest sources of nitrogen
pollution in certain water bodies such as the Chesapeake Bay.
The Causes
Air pollution comes from many different sources. 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 wind-
blown dust and wildfires. Comparison of 1970 and 2000 Emissions
Million tons
140
120
100
80
60
40
20
The Law
The Clean Air Act provides the principal framework for national,
state, tribal, and local efforts to protect air quality. Under the
Clean Air Act, EPA has a number of responsibilities, including:
Setting national ambient air quality standards (NAAQS) for the six
principal pollutants that are considered harmful to public health
and the environment.
Ensuring that these air quality standards are met (in cooperation
with the state, tribal, and local governments) through national
standards and strategies to control air pollutant emissions from
vehicles, factories, and other sources.
Reducing emissions of sulfur dioxide and nitrogen oxides that
cause acid rain.
Reducing air pollutants such as particulate matter, sulfur oxides,
and nitrogen oxides that can cause visibility impairment across large regional
areas, including many of the nation's most treasured parks and wilderness areas.
Ensuring that sources of toxic air pollutants that cause or may cause cancer and
other adverse human health and environmental effects are well controlled, and
that risks to public health and the environment are substantially reduced.
Limiting the use of chemicals that damage the stratospheric ozone layer in order
to prevent increased levels of harmful ultraviolet radiation.
While the focus of this report is on national air pollution, globed air pollution issues
such as destruction of the stratospheric ozone layer and the effect of global
warming on the Earth's climate are major concerns and are also discussed.
Thousand tons 1
1
I
n
CO NOX VOC
(-25%) (+20%) (-43%)
~~i
t
SO2
(-44%)
1970
D2000
I ,
PM
(-88%)
200
150
100
50
Pb
(-98%)
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Six Principal Pollutants
Percent Change in Air Quality
1981-2000 1991-2000
NO2
O31-hr
8-hr
SO2
PM10
PMZ5
CO
Pb
-14
-21
-12
-50
Trend
-61
-10
data not available
-41
Percent Change in Emissions
1981-2000 1991-2000
NOX
voc
SO2
PM10*
+4
-32
-31
-47
PMZ5* -
CO
Pb
-18
-94
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 trends are more likely to track
changes in urban emissions rather than changes
in total national 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
conditions often control the formation and buildup
of pollutants in the ambient air. For example, peak
ozone concentrations typically occur during hot,
dry, stagnant summertime conditions.
* Includes only directly emitted particles.
Under the Clean Air Act, EPA
establishes air quality standards to
protect public health, including the
health of "sensitive" populations such
as asthmatics, children, and the
elderly. EPA also sets limits to protect
public welfare, including protection
against decreased visibility and damage to animals, crops, vegetation, and
buildings.
EPA has set national air quality standards for six principal air pollutants (also
referred to as criteria pollutants): carbon monoxide (CO), lead (Pb), nitrogen
dioxide (NO2), ozone (O3), particulate matter (PM), and sulfur dioxide (SO2).
Four of these pollutants (CO, Pb, NO^ and SO2) result solely from direct
emissions from a variety of sources. PM can result from direct emissions also,
but is commonly formed when emissions of nitrogen oxides (NOJ, SO^
ammonia, and other gases react in the atmosphere. Ozone is not directly
emitted, but is formed when NOX and volatile organic compounds (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 govern-
ment 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 at left show that the air quality based on concentra-
tions of the principal pollutants has improved nationally over the last 20 years
(1981-2000).
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 developments, fuel consumption, vehicle miles
traveled, and other activities that cause air pollution. Emissions estimates also
reflect changes in air pollution regulations and installation of emissions
controls. The 2000 emissions reported in this summary report are projected
numbers based on available 1999 information and historical trends. EPA's
emission estimation methods continue to change and improve. As a result,
comparisons of the estimates for a given year in this summary to the same
year in previous summaries may not be appropriate. Check http://
www.epa.gov/ttn/chief for updated emissions information. Emissions of the
principal pollutants have decreased over the last 20 years (1981-2000), with the
exception of NOX. While NOX emissions have increased, air quality measure-
ments for NO2 across the country are below the national air quality standards.
It is important to note that oxides of nitrogen, including NO^ contribute to the
formation of ozone, particulate matter, and acid rain. NOX also add to poor
visibility.
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Comparison of Growth Areas and Emission Trends
U.S. Gross Domestic Product Increased 158%
Vehicle Miles Traveled Increased 143%
Energy Consumption Increased 45%
U.S. Population Increased 36%
Aggregate Emissions Decreased 29%
(Six Principal Pollutants)
1970
1980
1990
2000
Between 1970 and 2000, gross domestic product increased 158 percent, energy consumption increased 45 percent, vehicle miles
traveled increased 143 percent, and U.S. population increased 36 percent. At the same time, total emissions of the six principal air
pollutants decreased 29 percent.
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
121 million people nationwide still lived in counties with pollution
levels above the national air quality standards in 2000.
Status of Ozone and Particulate Matter Standards
In 1997, EPA revised the national ambient air quality
standards for ozone and particulate matter. The
standards were challenged by several business and
state groups who claimed that EPA misinterpreted the
Clean Air Act to give itself unlimited discretion to set
air standards. On February 27, 2001, the U.S.
Supreme Court unanimously upheld the
constitutionality of the Clean Air Act as EPA had Any NAAQS
interpreted it in setting those health-protective air
quality standards. The Supreme Court also reaffirmed
ERA's long-standing interpretation that it must set
these standards based solely on public health
considerations without consideration of costs. The
case is now back in the U. S. Court of Appeals to
decide issues not addressed in their initial opinion.
Updates on this action can be found at http://
www.epa.gov/airlinks.
Number of People Living in Counties
with Air Quality Concentrations Above
the Level of the NAAQS in 2000
NO2
03
S02
PM10
PM2.5
CO
0
H34.7 (1-hour)
81.5 (8-hour)
0
8.3
75.0*
9.7
Pb 1.5
121.4
50 100
Millions of People
150
*TMs number is based on PM2 5 monitors with
complete data. Because the national PM2 5
monitoring network was still being deployed in
2000, some counties with PM2 5 monitors have
incomplete data for 2000. Since it is likely that
more monitors will have complete data as time goes \
by, this number may increase as this information
becomes available.
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1
Nitrogen Dioxide (NO2)
NOX Emissions, 1981-2000
Thousand Short Tons Per Year
30,000
D Fuel Combustion D Industrial Processing
D Transportation D Miscellaneous
25,000
20,000
15,000
10,000
5,000
In 1985, EPA refined its methods for estimating emissions.
81
97 98 99 00
1981-00:
1991-00:
4% increase
3% increase
Air quality concentrations do not always track
nationwide emissions. For a detailed explanation, see
the caption on page 4.
NO2 Air Quality, 1981-2000
(Based on Annual Arithmetic Average)
Concentration, ppm
0.06
0.05
0.04
0.03
0.02
0.01
10% of sites have concentrations below this line
81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00
1981-00:
1991-00:
14%
11%
decrease
decrease
Nature and Sources of the Pollutant
Nitrogen dioxide (NC>2) is a reddish brown, highly reactive gas that
is formed in the ambient air through the oxidation of nitric oxide
(NO). Nitrogen oxides (NOX), the term used to describe the sum of
NO, NO2 and other oxides of nitrogen, play a major role in the
formation of ozone, particulate matter, haze and acid rain. The major
sources of man-made NOX emissions are high-temperature combus-
tion processes, such as those occurring in automobiles and power
plants. Home heaters and gas stoves also produce substantial
amounts of NO2 in indoor settings.
Health and Environmental Effects
Short-term exposures (e.g., less than 3 hours) to low levels of nitrogen
dioxide (NO2) may lead to changes in airway responsiveness and
lung function in individuals with pre-existing respiratory illnesses
and increases in respiratory illnesses in children (5-12 years old).
Long-term exposures to NO2 may lead to increased susceptibility to
respiratory infection and may cause permanent alterations in the
lung. Nitrogen oxides react in the air to form ground-level ozone and
fine particle pollution which are both associated with adverse health
effects.
Nitrogen oxides contribute to a wide range of environmental effects,
including the formation of acid rain and potential changes in the
composition and competition of some species of vegetation in
wetland and terrestrial systems, visibility impairment, acidification
of freshwater bodies, eutrophication (i.e., excessive algae growth
leading to a depletion of oxygen in the water) of estuarine and
coastal waters (e.g., Chesapeake Bay), and increases in levels of
toxins harmful to fish and other aquatic life.
Trends in NO2 Levels
Over the past 20 years, monitored levels of NO2 have decreased 14
percent. All areas of the country that once violated the national air
quality standard for NO2 now meet that standard. While levels
around urban monitors have fallen, national emissions of nitrogen
oxides have actually increased over the past 20 years by 4 percent.
This increase is the result of a number of factors, the largest being an
increase in nitrogen oxides emissions from diesel vehicles. This
increase is of concern because NOX emissions contribute to the
formation of ground-level
ozone (smog), but also to
other environmental
problems, like acid rain
and nitrogen loadings to
water bodies.
Because few sites have 20 years of data, EPA used two
consecutive 10-year periods to construct this 20-year
trend.
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Ground-Level Ozone (O3)
Nature and
Sources of
the Pollutant
Ground-level
ozone (the
primary con-
stituent of smog)
continues to be a
pollution problem throughout many areas of the United
States.
Ozone occurs naturally in the stratosphere and
provides a protective layer high above the Earth. See
page 22 for more information on the stratospheric
ozone layer.
Ozone is not emitted directly into the air but is formed by
the reaction of VOCs and NOX in the presence of heat and
sunlight. Ground-level ozone forms readily in the atmo-
sphere, usually during hot summer weather. VOCs are
emitted from a variety of sources, including motor vehicles,
chemical plants, refineries, factories, consumer and
commercial products, and other industrial sources.
Nitrogen oxides are emitted from motor vehicles, power
plants, and other sources of combustion. Changing
weather patterns contribute to yearly differences in ozone
concentrations from region to region. Ozone and the
precursor pollutants that form ozone also can be trans-
ported into an area from pollution sources found hundreds
of miles upwind.
Health and Environmental Effects
Short-term (1-3 hours) and prolonged (6-8 hours) expo-
sures to ambient ozone have been linked to a number of
health effects of concern. For example, increased hospital
admissions and emergency room visits for respiratory
problems have been associated with ambient ozone
exposures. Exposures to ozone can make people more
susceptible to respiratory infection, result in lung inflam-
mation, and aggravate pre-existing respiratory diseases
such as asthma. Other health effects attributed to ozone
exposures include significant decreases in lung function
and increased respiratory symptoms such as chest pain
and cough. These effects generally occur while individuals
are 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 individu-
VOC Emissions, 1981-2000
Thousand Short Tons Per Year
D Fuel Combustion Industrial Processing
DTransportatlon Miscellaneous
In 1985, EPA refined its methods for estimating emissions.
91 92 93 94 95 96 97 98 99 00
1981-00: 32% decrease
1991-00: 16% decrease
Air quality concentrations do not always track
nationwide emissions. For a detailed explanation,
see the caption on page 4.
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Ozone Air Quality, 1981-2000
als with pre-existing respiratory disease such as asthma and chronic
Concentration, ppm
0.2
0.15
0.1
0.05
90% of sites have concentrations below this line
(Based on Annual 4th Highest Daily Maximum 8-Hour Average) lung 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
worsen chronic respiratory illnesses.
Ozone also affects vegetation and ecosystems, leading to reductions
in agricultural and commercial forest yields, reduced growth and
survivability of tree seedlings, and increased plant susceptibility to
disease, pests, and other environmental stresses (e.g., harsh weather).
In long-lived species, these effects may become evident only after
several years or even decades, thus having the potential for long-term
effects on forest ecosystems. Ground-level ozone damage to the
foliage of trees and other plants also can decrease the aesthetic value
of ornamental species as well as the natural beauty of our national
parks and recreation areas.
Trends in Ozone Levels
In 1997, EPA revised the national ambient air quality standards for
ozone by setting new 8-hour 0.08 ppm standards. Currently, EPA is
tracking trends based on both the 1-hour and 8-hour data.
NatieflaLStandafd
468 Sites A
10% of sites have concentrations below this line
81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00
1981-00:
1991-00:
12%
7%
decrease
decrease
Because few sties have 20 years of data, EPA used
two consecutive 10-year periods to construct this 20-
year trend.
Over the past 20 years, national ambient ozone levels decreased 21
percent based on 1-hour data, and 10 percent based on 8-hour data.
Between 1981 and 2000, emissions of VOCs have decreased 32
Ozone Air Quality, 1981-2000
(Based on Annual 2nd Highest Daily Maximum 1-Hour)
Concentration, ppm
0.2
0.15
0.1
0.05
90% of sites have concentrations below this line
471 Sites
National Standard
738 Sites
10% of sites have concentrations below this line
Comparison of Actual and Meteorologically
Adjusted 1-hour Ozone Trends, 1981-2000
0.15
0.14
0.13
0.12
0.11
0.10
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0.00
National Trend in Annual 2nd Maximum 1-Hour Concentrations
/*
(1981-1990: 471 sites; 1991-2000: 738 sites)
Selected Area Trend In Average Dally Maximum 1-Hour Concentrations
Areas)
Meteorolically Adjusted Trend in Average Daily Maximum 1 -Hour Concentrations
(52 Metropolitan Areas)
81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00
81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00
1981-00: 21% decrease
1991-00: 10% decrease
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percent. During that same time period, emissions of NOX
increased 4 percent.
Because sunlight and heat play a major role in ozone forma-
tion, changing weather patterns contribute to yearly differ-
ences in ozone concentrations. To better reflect the changes
that emissions have on measured air quality concentrations,
EPA is able to make analytical adjustments to account for this
annual variability in meteorology. For 52 metropolitan areas,
the adjusted trend for 1-hour ozone levels shows improve-
ment over the 20-year period from 1981-2000. However,
beginning in 1994, the rate of improvement appears to level off
and the trend in the last 10 years is relatively flat.
For the period 1981-2000, the downward trend in 1-hour
ozone levels seen nationally is reflected in every broad
geographic area in the country. The Northeast and West
exhibit the most substantial improvement while the South and
Southwest have experienced the least rapid progress in lower-
ing ozone concentrations. Over the last 10 years, this down-
ward trend continues for the Northeast, Midwest and West
coast; however, in the South and North Central regions of the
country, ozone levels have actually increased.
Across the country, the highest ambient ozone concentrations
are typically found at suburban sites, consistent with the
downwind transport of emissions from urban centers.
During the past 20 years, ozone concentrations decreased
more than 24 percent at urban sites and declined by 21
percent at suburban sites. For the more recent 10-year
period, urban sites show decreases of approximately 12
percent and suburban sites show 11 percent decreases.
However, at rural monitoring locations national improve-
ments have been slower. One-hour ozone levels for 2000
are 15 percent lower than those in 1981 but only 6 percent
below 1991 levels. In 2000, for the third consecutive year,
rural 1-hour ozone levels are greater than the levels
observed for the urban sites, but they are still lower than
levels observed at suburban sites.
Trend in 1-Hour Ozone Levels, 1981-2000
Averaged Across EPA Regions
(Based on Annual Second Highest Daily Maximum)
f-23%
.101
.^wV-» l
f 14%
f7%
f24%
»1«
t4%
The National Trend
Alaska is in EPA Region 10; Hawaii, EPA Region 9; and
Puerto Rico, EPA Region 2. Concentrations are ppm.
Trend in 1-Hour Ozone Levels, 1981-2000
by Location of Site
(Based on Annual Second Highest Daily Maximum)
Concentration, ppm
0.14
0.12
0.10
0.08
0.06
0.04
0.02
Over the last 10 years, 8-hour ozone levels in 29 of our o.oo
national parks increased over 4 percent. Thirteen monitor-
ing sites in eleven of these parks experienced statistically
significant upward trends in 8-hour ozone levels: Great Smoky
Mountains (TN), Cape Remain (SC), Cowpens (SC), Congaree
Swamp (SC), Everglades (FL), Mammoth Cave (KY), Voyageurs
(MN), Yellowstone (WY), Yosemite (CA), Canyonlands (UT) and
Craters of the Moon (ID). For the remaining 18 parks, the 8-hour
ozone levels at ten increased only slightly between 1991 and
2000, while seven showed decreasing levels, and one was
unchanged.
National Standard
Rural Suburban Urban
81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00
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3
Sulfur Dioxide (SO2)
SO2 Emissions, 1981-2000
Thousand Short Tons Per \tear
30,000
15,000
10,000
5,000
D Fuel Combustion D Industrial Processing
D Transportation D Miscellaneous
In 1985, EPA refined its methods Kir estimating emissions.
1981-00:
1991-00:
31%
24%
decrease
decrease
Air quality concentrations do not always track
nationwide emissions. For a detailed explanation, see
the caption on
SO2 Air Quality, 1981-2000
(Based on Annual Arithmetic Mean)
Concentration, ppm
0.04
0.03
0.02
0.01
National Standard
90% of sites have concentrations below this line
Nature and Sources of the Pollutant
Sulfur dioxide belongs to the family of sulfur oxide gases. These
gases are formed when fuel containing sulfur (mainly coal and oil)
is burned and during metal smelting and other industrial pro-
cesses. Most SC>2 monitoring stations are located in urban areas.
The highest monitored concentrations of SC>2 are recorded in the
vicinity of large industrial facilities. Fuel combustion, largely from
coal-fired power plants, accounts for most of the total SC>2 emis-
sions.
Health and Environmental Effects
High concentrations of SC>2 can result in temporary breathing
impairment for asthmatic children and adults who are active
outdoors. Short-term exposures of asthmatic individuals to
elevated SC>2 levels while at moderate exertion may result in
breathing difficulties that may be accompanied by such symptoms
as wheezing, chest tightness, or shortness of breath. Other effects
that have been associated with longer-term exposures to high
concentrations of SC>2, in conjunction with high levels of PM,
include respiratory illness, alterations in the lungs' defenses, and
aggravation of existing cardiovascular disease. The subgroups of
the population that may be affected under these conditions
include individuals with cardiovascular disease or chronic lung
disease, as well as children and the elderly.
Together, SC>2 and NOX are the major precursors to acidic deposi-
tion (acid rain), which is associated with the acidification of soils,
lakes, and streams, accelerated corrosion of buildings and monu-
ments. Sulfur dioxide also is a major precursor to PM2.s, which is
a significant health concern as well as a main pollutant that
impairs visibility.
Trends in SO2 Levels
Nationally average SC>2 ambient concentrations have decreased
50 percent from 1981-2000 and 37 percent over the more recent 10-
year period 1991-2000. SC>2 emissions decreased 31 percent from
1981 to 2000 and 24 percent from 1991-
2000. Reductions in SO2 concentrations
and emissions since 1994 are due, in
large part, to controls implemented
under EPA's Acid Rain Program begin-
ning in 1995.
81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00
1981-00: 50% decrease
1991-00: 37% decrease
Because few sites have 20 years of data, EPA used two
consecutive 10-year periods to construct this 20-year
trend.
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Particulate Matter
Nature and Sources
of the Pollutant
Particulate matter (PM)
is the general term used
for a mixture of solid
particles and liquid
droplets found in the
air. Some particles are large or dark enough to be seen as
soot or smoke. Others are so small they can be detected only
with an electron microscope. PM^s describes the "fine"
particles that are less than or equal to 2.5 micrometers in
diameter. "Coarse" particles are greater than 2.5, but less
than or equal to 10 micrometers in diameter. PMjo refers to
all particles less than or equal to 10 micrometers in diameter.
A particle 10 micrometers in diameter is about one-seventh
the diameter of a human hair. PM can be emitted directly or form
secondarily 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 sulfate, formed from SC>2 emissions 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, fine
PM is composed mostly of secondary particles, and coarse PM is
composed largely of primary particles.
Direct PM10 Emissions from Man-Made
Sources, 1981-2000
In 19S5, EPA refined its
methods for estimating emissions.
Thousand Short Tons PerYrar
7,000
6,000
4,000
3,000
1,000
1981-00:
1991-00:
47%
6%
decrease
decrease
Starting in 1999, PM emissions from certain open
burning sources in the "Industrial Processing"
category were estimated differently than in previous
years. The apparent increase in PM emissions from
this category between 1998 and 1999 is the result of
this change in estimation methodology.
Air quality concentrations do not always track
nationwide emissions. For a detailed explanation, see
the caption on page 4.
Health and Environmental Effects
Particulate matter includes both fine and coarse particles.
When breathed, particles can accumulate in the respiratory
system and are associated with numerous health effects.
Exposure to coarse particles is primarily associated with
the aggravation of respiratory conditions, such as asthma.
Fine particles are most closely associated with such health
effects as increased hospital admissions and emergency
room visits for heart and lung disease, increased respira-
tory disease and symptoms such as asthma, decreased
lung function, and even premature death. Sensitive groups
that appear to be at greatest risk to such effects include the
elderly, individuals with cardiopulmonary disease such as
asthma, and children. In addition to health problems, PM
is the major cause of reduced visibility in many parts of the
United States. Airborne particles also can impact vegeta-
tion and ecosystems and can cause damage to paints and
building materials.
Trends in PM10 Levels
Between 1991 and 2000, average PMjo concentrations de-
creased 19 percent, while direct PMjo emissions decreased 6
percent.
PM10 Air Quality, 1991-2000
(Based on Annual Arithmetic Mean)
Concentration, |jg/m3
60-
50
40
30
20-
10
National Standard
90% of sites have concentrations below this line
Ten-year trend
not available
before 1990.
10% of sites have concentrations below this line
81 82 83 84 85 86 87 88
90 91 92 93 94 95 96 97 98 99 00
1991-00: 19% decrease
-------
Particulate Matter
Direct PM,. Emissions from Man-Made Sources
Thousand Short Tons Per Year
3,000
D Fuel Combustion Industrial Processing
D Transportation
92
93 94 95 96 97
1991-00: 5% decrease
98
00
Starting in 1999, PM emissions from certain open
burning sources in the "Industrial Processing"
category were estimated differently than in previous
years. The apparent increase in PM emissions from
this category between 1998 and 1999 is the result of
this change in estimation methodology.
1999 Annual Average PM25 Concentrations (ug/m3)
in Rural Areas
\| I Sulfate Predominately from coaMred power plants.
H Nitrate Predomlnatelyfrom automobiles and utility and Industrial boilers.
^^ Onjanic Caibon From sources such as automobiles, fcucks and industrial processes.
^| Elemental Carbon (Soot) From diesel, wood, end other combustion.
H Cmstal Material (Soil dust) From roads, construction, and agricultural activities.
Source: Interagency Monitoring of Protected
Visual Environments Network, 1999.
Trends in PM2.5 Levels
The chart to the left shows that direct PM^.s emissions
from man-made sources decreased 5 percent nation-
ally between 1991 and 2000. This chart tracks only
directly-emitted particles and does not account for
secondary particles formed when emissions of
nitrogen oxides (NOX), SO2, ammonia, and other gases
react in the atmosphere. The principal types of second-
ary particles are sulfates and nitrates, which are formed
when SC>2 and NOX react with ammonia.
The map (bottom left) shows how sulfates and
nitrates, along with three other components (organic
carbon, elemental carbon, and crustal material)
contribute to PM2.s concentrations. This map
represents the most recent year of data available from
the IMPROVE (Interagency Monitoring of Protected
Visual Environments) network. The IMPROVE
network was established in 1987 to track trends in
visibility and the pollutants, such as PM2.s, that
contribute to visibility impairment. Because the
monitoring sites are located in rural areas throughout
the country, the network is a good source for assess-
ing regional differences in PM2.5-
Sites in the East typically have higher annual average
PM2.5 concentrations. Most of the regional difference
is attributable to higher sulfate concentrations in the
eastern United States. Sulfate concentrations in the
eastern sites are 4 to 5 times greater than those in the
western sites. Sulfate concentrations in the East
largely result from sulfur dioxide emissions from
coal-fired power plants. EPA's Acid Rain Program,
discussed in more detail in the Acid Rain section of
this brochure, sets restrictions on these power plants.
Within the East, rural PM2.s levels are higher in the
Southeastern and Mid-Atlantic states. In the West,
rural PM2.s levels are generally less than one-half of
Eastern levels.
In 1999, EPA and its state, tribal, and local air
pollution control partners deployed a monitoring
network to begin measuring PM2.s concentrations
nationwide. The map (top right of page 13) shows
annual average PM2.s concentrations at the various
monitoring locations. Data completeness is illus-
trated by the size of the circles on the map, with larger
circles indicating relatively complete data for the year.
This map also indicates that PM2.s concentrations
vary regionally. Based on the 2000 monitoring data,
12
-------
California and much of the eastern United States
have annual average PM^.s concentrations above the
level of the annual PM^.s standard, as indicated by
the yellow and red on the map. With few exceptions,
the rest of the country generally have annual average
concentrations below the level of the annual PM2.s
health standard.
PM2.5 Trends in Rural Areas
Because the national monitoring network started in
1999, there is not enough data to show a national
long-term trend in urban PM2.s air quality concentra-
tions. However, 36 sites in the IMPROVE network
(10 in the East, and 26 in the West) have enough data
to assess trends in average rural PM2.s concentra-
tions from 1992-1999. In the East, where sulfates
contribute most to PM2.s, the annual average across
the 10 sites decreased 5 percent from 1992-1999.
The peak in 1998 is associated with increases in
sulfates and organic carbon. Average PM2.s concen-
trations across the 26 sites in the West from 1992-
1999, were about one-half of the levels measured at
Eastern sites.
2000 Annual Average PM2.5 Concentrations
f*k
O < 4 quarters £ >20
O one or more quarters with < 11 samples Q 15-20
O All quarters with at least 11 samples 10-15
O All quarters 75% or more complete 0 0-10
Source: US EPA AIRS Data base as of 7/10/01.
Note: PM^, 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.
Average PM25 Concentrations, Average PM25 Concentrations,
1992-1999 at Rural Western U.S. Sites 1992-1999 at Rural Eastern U.S. Sites
Con
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
sentration, (jg/mS
26 Sites
_.--
92 93 94 95 96 97 98 99
Con
15
14
13
12
11
10
9
8
7
6
Measured PM2.5
4
3
Organic Carbon
Sulfate 2
Crustal Material <
Nitrate
Elemental Carbon Q
centration, |jg/m3
10 Sites
' «^ ________.. ' .
^^^
92 93 94 95 96 97 98 99
Measured PM2.5
Sulfate
Organic Carbon
Nitrate
Crustal Material
Elemental Carbon
Source: Interagency Monitoring of Protected Visual Environments Network, 1999.
13
-------
5
Carbon Monoxide (CO)
CO Emissions, 1981-2000
Thousand Short Tons Per Year
Fuel Combustion!Industrial Processing
D Transportation Miscellaneous
In H85, EfM refined Us methods for estimating emissions.
94 95 96 97 98 99 00
1981-00: 18% decrease
1991-00: 5% decrease
Air quality concentrations do not always track
nationwide emissions. For a detailed explanation, see
the caption on page 4.
CO Air Quality, 1981-2000
(Based on Annual 2nd Maximum 8-hour Average)
Concentration, ppm
14
12
10
8
6
4
2
90% of sites have concentrations below this line
National Standard
10% of sites have concentrations below this line
Nature and Sources of the Pollutant
Carbon monoxide (CO) is a colorless and odorless gas, formed when
carbon in fuel is not burned completely. It is a component of motor
vehicle exhaust, which contributes about 60 percent of all CO
emissions nationwide. Non-road vehicles account for the remaining
CO emissions from transportation 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 automo-
bile exhaust. Other sources of CO emissions include industrial
processes, non-transportation fuel combustion, and natural sources
such as wildfires. Peak CO concentrations typically occur during the
colder months of the year when CO automotive emissions are greater
and nighttime inversion conditions (where air pollutants are trapped
near the ground beneath a layer of warm air) are more frequent.
Health and Environmental Effects
Carbon monoxide enters the bloodstream through the lungs and
reduces oxygen delivery to the body's organs and tissues. The health
threat from levels of CO sometimes found in the ambient air is most
serious for those who suffer from cardiovascular disease, such as
angina pectoris. At much higher levels of exposure, CO can be
poisonous, and even healthy individuals may be affected. Visual
impairment, reduced work capacity, reduced manual dexterity, poor
learning ability, and difficulty in performing complex tasks are all
associated with exposure to elevated CO levels.
Trends in CO Levels
Nationally the 2000 ambient average CO concentration is 61 percent
lower than that for 1981 and is the lowest level recorded during the
past 20 years. CO emissions levels decreased 18 percent over the
same period. Between 1991 and 2000, ambient CO concentrations
decreased 41 percent, and the estimated number of exceedances of
the national standard decreased 95 percent while CO emissions fell 5
percent. This improvement occurred despite a 24 percent increase in
vehicle miles traveled in the United States during this 10-year period.
81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00
1981-00: 61% decrease
1991-00: 41% decrease
Because few sites have 20 years of data, EPA used two
consecutive 10-year periods to construct this 20-year
trend.
-------
Lead (Pb)
50,000
40,000
20,000
^ '^ Nature and Sources of the
^l Pollutant
f ^H In the past, automotive sources
were the major contributor of
^J fcj leac^ emissi°ns to the atmo-
sphere. As a result of EPA's
A ^1 HI regulatory efforts to reduce the
^£_ ^1 [l content of lead in gasoline, air
emissions of lead from the
transportation sector have
declined over the past decade.
Today, industrial processes, primarily metals processing,
are the major source of lead emissions to the atmosphere.
The highest air concentrations of lead are found in the
vicinity of smelters, and battery manufacturers.
Health and Environmental Effects
Exposure to lead occurs mainly through inhalation of air and
ingestion of lead in food, water, soil, or dust. It accumulates in
the blood, bones, and soft tissues. Lead can adversely affect the
kidneys, liver, nervous system, and other organs. Excessive
exposure to lead may cause neurological impairments such as
seizures, mental retardation, and behavioral disorders. Even at
low doses, lead exposure is associated with damage to the
nervous systems of fetuses and young children, resulting in
learning deficits and lowered IQ. Recent studies also show that
lead may be a factor in high blood pressure and subsequent heart
disease. Lead can also be deposited on the leaves of plants,
presenting a hazard to grazing animals.
Trends in Lead Levels
Because of the phase-out of leaded gasoline, lead emis-
sions and concentrations decreased sharply during the
1980s and early 1990s. The 2000 average air quality
concentration for lead is 93 percent lower than in 1981.
Emissions of lead decreased 94 percent over that same 20-
year period. Today, the only violations of the lead national
air quality standard occur near large industrial sources
such as lead smelters.
0.5
Lead Emissions, 1981-2000
Short Tons Per Year
80,000 i
D Fuel Combustion I
D Transportation
Industrial Processing
In 19S5, ERA refined its methods for estimating emissions.
94 95 96 97 98 99 00
1981-00:
1991-00:
94%
4%
decrease
decrease
Air quality concentrations do not always track
nationwide emissions. For a detailed explanation, see
the caption on page 4.
Lead Air Quality, 1981-2000
(Based on Annual Maximum Quarterly Average)
Concentration, |jg/m3
1.5
National Standard
90% of sites have concentrations below this line
130 Sites
rations below this line
81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00
1981-00: 93% decrease
1991-00: 50% decrease
Because few sites have 20 years of data, EPA used two
consecutive 10-year periods to construct this 20-year]
trend.
-------
Acid Rain
Acid Rain Formation
Coal-fired electric utilities and other sources that
burn fossil fuels emit sulfur dioxide and nitrogen
oxides.
SO2 Emissions Covered Under
the Acid Rain Program
- 17.30
-
;
- 9.40
-
1R09
9.30
8.70
11.87
D Phase I Sources D Phese II Sources
D All Affected Sources, 2000
12.51
12.51
12.98
12.98
13.13
13.13
1745
12.45
11.20
1995-1999: Allowances issued for 263 Phase I units.
2000: Allowances issued for all affected sources.
NOX Emissions Covered Under
the Acid Rain Program
6.7
5.53
--
6.09
5.44
5.91
5.44
6.04
5.49
5.97
5.29
5.49
4.82
..V
5.11
4.48
1990
1995
1996
1997
1999
2000
D Phase II units not affected for NOx
D Phase II NOx affected units (1,046)
' Projected NOx without the Acid Rain Program
Nature and Source of the Problem
Acidic deposition or "acid rain" occurs when emissions of sulfur
dioxide (802) and oxides of nitrogen (NOX) in the atmosphere react with
water, oxygen, and oxidants to form acidic compounds. These com-
pounds fall to the Earth in either dry form (gas and particles) or wet form
(rain, snow, and fog). Some are carried by the wind, sometimes hundreds
of miles, across state and national borders. In the United States, about 64
percent of annual SC>2 emissions and 26 percent of NOX emissions are
produced by electric utility plants that burn fossil fuels.
Health and Environmental Effects
In the environment, acid deposition causes soils and water bodies to
acidify (making the water unsuitable for some fish and other wild-
life), 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
contributes 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 appears to increase the rate that bacteria living at the
bottom of rivers and lakes can convert elemental mercury and mercury
salts to highly toxic methyl mercury. The availability of methyl mercury
may increase human exposure to mercury from eating contaminated
fish. Reductions in SC>2 and NOX have begun to reduce some of these
negative environmental effects and are leading to significant improve-
ments 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 SC>2 and NOX. The program is being implemented in two
phases: Phase I for SC>2 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.
The Acid Rain Program will reduce annual SC>2 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 SC>2 that may be
emitted by power plants nationwide, about half of the amount
emitted in 1980. It employs an emissions trading program to achieve
that emissions cap more cost-effectively Sources are allocated
allowances each year (one allowance equals one ton of SC>2 emis-
sions) 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 while ensuring that the emissions limit 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 reduc-
tion from 1980 levels by 2000. There is no cap on total NOX emis-
sions, but under this program a source can choose to overcontrol at
units where it is technically easier to control emissions, average these
emissions with those at their other units, and thereby achieve overall
emissions reductions at lower cost.
-------
Emissions and Atmospheric Trends
SC>2 emissions reductions have been significant in the first 6
years of compliance with EPA's Acid Rain Program. 2000
was the first year of compliance with Phase II of the Acid
Rain Program. Over two thousand sources are now affected
by the program. Sources in the Acid Rain Program emitted
11.2 million tons in 2000, down from 16 million tons in
1990. Emissions of SC>2 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 year of Phase I.
Actual NOX emissions, as shown in the graph to the bottom
left of page 16, have also declined since 1990. NOX emis-
sions decreased steadily from 6 tons in 1997 to just over 5
tons in 2000. The more than 1000 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 are projected to have been in 2000
without the Acid Rain Program.
For all years from 1995 through 2000, both deposition and
concentrations of sulfates in precipitation exhibited dra-
matic and unprecedented reductions over a large area of the
eastern United States. Average sulfate deposition in 1996-
2000 is 10 percent lower than in 1990-1994 nationwide, and
15 percent lower in the east. Similarly, sulfate air concentrations,
which contribute to human health and visibility problems, were
reduced significantly, especially in the east. There was a small
decrease in nitrate deposition in some places but in others there were
increases, 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 SC>2 and NOX emissions resulting from the Acid
Rain Program. The largest reductions in sulfate concentrations
occurred along the Ohio River Valley and in states immediately
downwind. The largest reductions in wet sulfate 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 reduc-
tions 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 nationwide nitrogen
emissions, so emissions trends in other source categories, especially
agriculture and mobile sources, impact air concentrations and
deposition.
Sulfate Deposition in Precipitation
Sulfate
Nitrate
Source: USEPA analysis of National
Atmospheric Deposition Program data.
Deposition vs. Concentration
Think of putting the same amount of salt
into two different glasses of water (one
full and one half-full). The total amount
(deposition) is the same, but the
solution in the half-full glass has a
greater concentration.
17
-------
Visibility
Shenandoah National Park under bad and good
visibility conditions. The visual range in the top
photo is 25 km (28 deciviews) while the visual range
in the bottom photo is 180 km (8 deciviews).
A view across the Potomac River at the Lincoln
Memorial and the Washington Monument, an
urban setting, under bad and good visibility
conditions. The visual range in the top photo is 8 km
(38 deciviews) while the visual range in the bottom
photo is > 150 km (10 deciviews).
Nature and Sources of the Problem
Visibility impairment is one of the most obvious effects of air pollu-
tion and occurs at many of the best known and most treasured
natural areas such as the Grand Canyon, Yosemite, Yellowstone,
Mount Rainer, Shenandoah, and the Great Smokies as well as in
urban areas. Visibility impairment occurs as a result of the scattering
and absorption of light by air pollution, including particles and
gases. In addition to limiting the distance that we can see, the
scattering and absorption of light caused by air pollution can also
degrade the color, clarity, and contrast of scenes. The same fine particles
that are linked to serious health effects and premature death can also
significantly affect our ability to see.
Both primary emissions and secondary formation of particles
contribute to visibility impairment. "Primary" particles, such as dust
from roads or elemental carbon (soot) from wood combustion, are
emitted directly into the atmosphere. "Secondary" particles are
formed in the atmosphere from primary gaseous emissions. Ex-
amples include sulfate, formed from sulfur dioxide (802) emissions
from power plants and other industrial facilities; and nitrates,
formed from nitrogen oxides (NOX) emissions from power plants,
automobiles, and other types of combustion sources. In the eastern
United States, reduced visibility is mainly attributable to secondarily-
formed sulfates. While these secondarily-formed particles still account
for a significant amount in the West, primary emissions from sources
like wood smoke contribute a larger percentage of the total particle
loading than in the East.
Humidity can significantly increase the effect of pollution on visibil-
ity. Some particles, such as sulfates, accumulate water and grow in
size, becoming more efficient at scattering light and causing visibility
impairment. Annual average relative humidity levels are 70-80
percent in the East as compared to 50-60 percent in the West. Poor
summer visibility in the eastern United States is primarily the result
of high sulfate concentrations combined with high humidity levels.
Visibility conditions are commonly expressed in terms of three
mathematically related metrics: light extinction, deciviews, and
visual range. The graphic at the bottom of the page shows the
relationship among the three metrics.
Program Structure
The Clean Air Act provides for the protection of visibility in national
parks and wilderness areas, also known as Class I areas. There are
Eattoctkm {MiT1) ID
Drolvkm M»)
Vlwid Rwi|J» Ikm.i .IfMl
14 tt
I I I .III
It IS £
Ml
300
i.ii- \ff-. ?t. sn an
roe LL'HU
Visibility Metrics Comparisons of
extinction (Mm1), deciviews (dv), and
visual range (km). Notice the difference in
the three scales; 10 Mm1 corresponds to
about 400 km visual range and 0.0 dv,
while WOO Mm'1 is about 4 km visual
range and 46 dv.
18
-------
156 Class I areas across the United States. The Clean Air
Act's national goal calls for remedying existing visibility
impairment and preventing future impairment in these
Class I areas.
In 1987, EPA, states, tribes, the National Park Service, the
U.S. Forest Service, the Bureau of Land Management, and
the U.S. Fish and Wildlife Service cooperatively estab-
lished the Interagency Monitoring of Protected Visual
Environments (IMPROVE) visibility network. In 2000 the
IMPROVE network expanded from 30 to 110 sites to collect
data and track progress at all federal Class I areas.
In April 1999, EPA initiated a new regional haze program.
The program addresses visibility impairment in national
parks and wilderness areas caused by numerous sources
located over broad regions. Because fine particles are
frequently transported hundreds of miles, pollution that
occurs in one state may contribute to the visibility impair-
ment in another state. For this reason, EPA is working with
states and tribes to coordinate efforts through regional
planning organizations, to develop regional strategies to
improve visibility, and to reduce pollutants that contribute
to fine particles and ground-level ozone.
Other air quality programs focussing on vehicles, fuels,
woodstoves and other sources of pollution, are expected to
lead to emission reductions that will improve visibility in
certain regions of the country. For example, EPA's acid rain
program is designed to achieve significant reductions in
SOX emissions, which is expected to reduce sulfate haze,
particularly in the eastern United States. Additional control
programs on sources of NOX to reduce the formation of
ground-level ozone can also improve regional visibility
conditions.
Recent Trends
Data collected by the IMPROVE network show visibility for
the worst days in the West is similar to days with the best
visibility days in the East. In the East, visibility on the worst
days has improved by 1.5 deciviews, but visibility remains
significantly impaired. In 1999, mean visual range in the East
was only 24 km (14.4 miles) compared to 84 km (50.4 miles) for
the best visibility days. Without man-made air pollution,
visibility in the East would be about 75-150 km (45-90 miles).
In the West, visibility impairment for the worst days remains
relatively unchanged over the 1990s with the mean visual
range for 1999 (80 km/48 miles) nearly the same as the 1990
level (86 km/52 miles). Natural visibility in the West is 200-300
(120-180 miles).
Visibility Trends For Eastern
U.S. Class 1 Areas, 1992-1999
30
g 25
Q)
8 n
Q '°
10
5
0
9
J/Vorst Visibility
A A -A ± >
Mid-Range
Best Visibility
1 range is 20-24 km
Mid-Range visibility
Is 44-50 km
Best visibility
range is 83-94 km
2 93 94 95 96 97 98 99
Year
Visibility Trends For Western
U.S. Class 1 Areas, 1990-1999
JO
30
25
20
b
n
Worst Visibility
I t t A , _i_L_ . A 1
Mid-Range
Best Visibility
Worst visibility
range is 80-92 km
Mid-Range visibility
Is124-140km
Best visibility
Range is 180-2 10 km
90 91 92 93 94 95 96 97 98 99
Year
East
West
Sulfates
60-86% 25-50%
Organic Carbon 10-18% 25-40%
Nitrates
7-16% 5-45%
Elemental Carbon 5-8% 5-15%
(soot)
Crustal Material 5-15% 5-25%
(soil dust)
Pollutants that contribute to visibility impairment
in the eastern and western parts of the United
States. Sulfates are generally the largest
contributor in both the East and the West.
km
-------
Toxic Air Pollutants
1996 National Air Toxics Emissions
188 Toxic Air Pollutants
(4.6M tons)
Nonroad
20%
Major
25%
Onroad
30%
Area/Other
25%
Note: These emissions are from outdoor
sources. Also, mobile source emissions do
not include diesel paniculate matter.
National Air Toxics Emissions
(Total for 188 Toxic Air Pollutants)
7.0
6.0
SB 5-°
fc
CD 4.0
D.
1 3.0
C
o
! 2-°
1.0
0.0
6.0
4.6
Baseline
(1990-1993)
1996
D 33 urban air toxics
D Other 155 Air Toxics
Nature and Sources
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. EPA is required to reduce air emissions of 188 air toxics listed in the
Clean Air Act. 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.
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, reproductive (e.g., reduced fertility), develop-
mental, 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 a nationwide monitoring network for air toxics
as they do for many of the other pollutants discussed in this report. Although
such a network is under development, EPA has compiled a National Toxics
Inventory (NTI) to estimate and track national emissions trends for the 188
toxic air pollutants regulated under the Clean Air Act. In the NTI, EPA divides
emissions into four types of sectors: 1) major (large industrial) sources; 2) area
and other sources, which include smaller industrial sources, like small 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.
As shown in the 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.
While EPA, states and tribes 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. Together with the emissions data from the
NTI, the available monitoring data help air pollution control agencies track
trends in toxic air pollutants in various locations around the country. EPA is
working with states, tribes and local air monitoring agencies to build upon
these monitoring sites to create a national monitoring network for a number
of toxic air pollutants.
Based on the data in the NTI, estimates of nationwide air toxics emissions have
dropped approximately 23 percent between baseline (1990-1993) and 1996.
Although changes in how EPA compiled the national inventory over time may
account for some differences, EPA and state regulations, as well as voluntary
reductions by industry, have clearly achieved large reductions in overall air
toxic emissions.
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Trends for individual air toxics vary from pollutant to pollutant. For
example, data taken from California's monitoring network for 39 urban
sites show an average reduction of 60 percent in measured levels of
perchloroethylene for the period 1990-1999. Perchloroethylene is a
chemical widely used in the dry cleaning industry. Based on the
NTI, EPA estimates that nationwide perchloroethylene emissions
dropped 67 percent from 1990-1996. These reductions reflect state
and federal efforts to regulate emissions of this pollutant, and
industry efforts to move to other processes using less toxic
chemicals.
4.5
3.5
Ambient Perchloroethylene
Annual Average Urban Concentrations
in California
(60-percent reduction, 1990-1999)
Concentration, |jg/m3
\
39 Sites
A 90% of the sites have concentrations below this line.
Benzene is another widely monitored toxic air pollutant. It is
emitted from cars, trucks, oil refineries, and chemical processes.
The graph at the lower right shows measurements of benzene
taken from 87 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 40-percent drop in benzene levels from 1994-1999.
During this period, EPA phased in new (so-called "tier 1") car
emission standards; required many cities to begin using cleaner
burning gasoline; and set standards that required significant reductions in
benzene and other pollutants emitted from oil refineries and chemical
processes. EPA estimates that nationwide benzene emissions from all sources
dropped 25 percent from 1990-19%.
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 emissions of toxic air
pollutants by nearly 1.5 million tons per year from 1990 levels. EPA
has also put into place important controls for motor vehicles and
their fuels and is continuing to take additional steps to reduce air
toxics from vehicles. This includes stringent standards for heavy-
duty trucks and buses and diesel fuel that will lead to a reduction in
emissions of diesel particulate matter by over 90 percent between
1996 and 2020.
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 construc-
tion equipment. In addition, by 2004, EPA plans to regulate air toxic
emissions, including mercury from power plants.
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 water bodies from air
toxics deposition (e.g., the Great Waters program which includes the Great
Lakes, Lake Champlain, Chesapeake Bay, and many coastal estuaries) and
Agency initiatives concerning mercury and other persistent and bioaccumula-
tive 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/pubs/index.html.
In late 2001, EPA will release the first in a series of national-scale assessments of
the risks associated with 32 toxic air pollutants and diesel PM. Details about this
effort conducted under the National Air Toxics Assessment (NATA) program
are available at http://www.epa.gov/ttn/atw/nata. EPA, states, and others are
continuing to gather data to improve knowledge about the risks from air
toxics both nationally and locally. 21
1990 1991 1992 1993 1994 1995 1996 1997 1998 19991
Ambient Benzene Annual Average Urban
Concentrations, Nationwide
(40-percent reduction, 1994-1999)
Concentration, ug/m
A 90% of the sites have concentrations below this line.
10% of the sites have concentrations below this line.
1994
1995
1996
1997
1998
For more information about EPA's air
toxics program, visit the Agency's website
at http://www.epa.gov/ttn/atw.
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Stratospheric Ozone
£
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Programs to Restore the Stratospheric
Ozone Layer
In 1987, 27 countries signed the Montreal Protocol, a
treaty that recognized the international nature of
ozone depletion and committed the world to limiting
the production of ozone-depleting substances. Today,
more than 175 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 stratospheric
ozone layer. In January 1996, U.S. production of
many ozone-depleting substances virtually ended,
including CFCs, carbon tetrachloride, and methyl
chloroform. Production of halons ended in January 1994. Many new
products that either do not affect or are less damaging to the ozone
layer are now gaining popularity. For example, computer-makers are
using ozone-safe solvents to clean circuit boards, and automobile
manufacturers are using HFC-134a, an ozone-safe refrigerant, in new
motor vehicle air conditioners. In some industries, the transition
away from ozone-depleting substances has already been completed.
EPA is also emphasizing new efforts like the UV Index, a daily
forecast of the strength of UV radiation people may be exposed to
outdoors, to educate the public about the health risks of overexposure
to UV radiation and the steps they can take to reduce those risks.
Trends in Stratospheric Ozone Depletion
Scientific evidence shows that the approach taken under the
Montreal Protocol has been effective to date. In 1996, measurements
showed that the concentrations of methyl chloroform had started to
fall, indicating that emissions had been greatly reduced. Concentra-
tions of other ozone-depleting substances in the upper layers of the
atmosphere, like CFCs, are also beginning to decrease. It takes
several years for these substances to reach the stratosphere and
release chlorine and bromine. For this reason, stratospheric chlorine
levels are 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 around 2050. All
nations that signed the Protocol must complete implementation of ozone
protection programs if full repair of the ozone layer is to happen.
In 1996, scientists developed a new technique allowing them to draw
conclusions about UV-b radiation at ground level. According to
satellite-based trend analyses, major populated areas have experi-
enced increasing UV-b levels over the past 15 years. As shown by the
figure above, at latitudes that cover the United States, UV-b levels are
4-5 percent higher than they were in 1986.
UV-b Radiation Increases by Latitude
A 1996 study using satellite-base 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 1986-1996. UV-b
incidence is strongly dependent on latitude. At
latitudes that cover the United States, UV-b levels
are 45 percent higher than they were in 1986.
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Global Warming & Climate Change
The Greenhouse Effect
Some solar radiation
is reflected by the Earth
and the atmosphere.
Nature and Sources
The Earth's climate is fueled by the Sun. Most of the Sun's energy,
called solar radiation, is absorbed by the Earth, but some is reflected
back into space. Clouds and a natural layer of atmospheric gases
absorb a portion of Earth's heat and prevent it from escaping to
space. This keeps our planet warm enough for life and is known as
the natural "greenhouse effect," as illustrated in the diagram below.
Without the natural greenhouse effect, the Earth's average tempera-
ture would be much colder, and the planet would be uninhabitable.
Recent scientific evidence shows that the greenhouse effect is being
increased by release of certain gases to the atmosphere that cause the
Earth's temperature to rise. This is called "global warming." Carbon
dioxide, methane, particulate matter (especially black carbon or soot),
nitrous oxide, fluorinated compounds, and ozone, are some of the
compounds contributing to global warming. Carbon dioxide
accounts for about 81 percent of greenhouse gases released in the
United States. Carbon dioxide emissions are largely due to the
combustion of fossil fuels in electric power generation, motor ve-
hicles, and industries. Methane emissions,
which result from agricultural activities,
landfills, and other sources, are the next
largest contributors to greenhouse gas
emissions in the United States and world-
wide.
Solar
radiation
passes
through
the clear
atmosphere.
Some of the infrared
radiation passes through
the atmosphere, and
some is absorbed and
re-emitted in all directions
by greenhouse gas molecules.
The effect of this is to
warm the Earth's surface and
the lower atmosphere.
The greenhouse effect is being accelerated by releases
of certain gases to the atmosphere that are causing the
Earth's temperature to rise.
Industrial processes such as foam produc-
tion, refrigeration, dry cleaning, chemical
manufacturing, and semiconductor
manufacturing produce other greenhouse
gas emissions, such as hydrofluoro-
carbons. Smelting of aluminum produces
another greenhouse gas called
perfluorinated compounds. Emissions of
NOX and VOCs from automobile exhaust
and industrial processes contribute to the
formation of ground-level ozone or smog,
also a greenhouse gas.
Health and Environmental Effects
In 1988, the Intergovernmental Panel on
Climate Change (IPCC) was formed to
assess the available scientific and eco-
nomic information on climate change.
IPCC recently published its Third Assess-
ment Report representing the work of more than 2,000 of the world's
leading scientists. The IPCC concluded that humans are changing
the Earth's climate, and that "there is new and stronger evidence that
24
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most of the warming observed over the last 50 years is attributable to
human activities."
According to the IPCC, continued emissions of greenhouse gases
could cause a 2.5° to 10° Fahrenheit rise in temperature during the
next century. Although this change may appear small, it would be
an unprecedented temperature change relative to the past 10,000
years. This could lead to more extreme weather events such as
droughts and floods, threaten coastal resources and wetlands by
raising sea level, and increase the risk of certain diseases by produc-
ing new breeding sites for pests and pathogens. Agricultural regions
and woodlands are also susceptible to changes in climate that could
result in increased insect populations and plant disease. This
degradation of natural ecosystems could lead to reduced biological
diversity.
International Developments
In 1992, over 150 countries signed the Framework Convention on
Climate Change (FCCC), which has the objective of stabilizing the
concentration of greenhouse gases in the atmosphere at levels that
would prevent dangerous interference with the climate system.
Under the FCCC, industrialized countries agreed to aim to reduce
greenhouse gas emissions to 1990 levels by the year 2000. Most
industrialized countries, including the United States, have not been
able to meet this target. In light of this, the United States and the rest
of the international community continue to work towards ways of
achieving the FCCC's ultimate objective.
U.S. Programs to Mitigate Climate Change
The United States implemented a Climate Change Action Plan in
1993 to reduce greenhouse gas emissions and help achieve the goals
of the FCCC. Thousands of companies and other organizations are
working in partnership with the Federal government to effectively
reduce their emissions. The Plan involves more than 40 programs
implemented by EPA, the Department of Energy, the Department of
Agriculture, and other government agencies. In 2000 alone, EPA's
voluntary climate protection programs reduced greenhouse gas
emissions by 58.5 million metric tons of carbon equivalent (MMTCE),
the same as eliminating the greenhouse gas emissions from about 40
million cars. By investing in products that use energy more effi-
ciently, consumers and businesses have also reduced energy con-
sumption by an estimated 75 billion kilowatt hours and netted
savings of more than $5 billion on their 2000 energy bills while
achieving these environmental benefits.
1998 Greenhouse Gas Emissions
in the United States
Carbon Dioxide
81%
Fluorinated Compounds
2%
Nitrous Oxide
7%
Methane
10%
1998 total greenhouse gas emissions rose 11
percent from 1990 baseline levels. The major
contributor to these emissions is carbon
dioxide from fossil fuel combustion. Other
contributors include methane gas from
landfills, fermentation, natural gas systems,
and coal mining; nitrous oxide from
agricultural management and mobile
sources, and fluorinated compounds from
such processes as aluminum and magnesium
production and electrical transmission and
distribution systems.
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Conclusion
The Clean Air Act has resulted in many improvements in
the quality of the air in the United States. Scientific and
international developments continue to have an effect on
the air pollution programs that are implemented by the
U.S. Environmental Protection Agency and state, local,
and tribal agencies. New data help identify sources of
pollutants and the properties of these pollutants. Al-
though much progress has been made to clean up our air,
work must continue to ensure steady improvements in air
quality, especially because our lifestyles create more
pollution sources. Many of the strategies for air quality
improvement will continue to be developed through
coordinated efforts with EPA, state, local and tribal
governments, as well as industry and other environmen-
tal organizations.
Acronyms
CO Carbon Monoxide
For Further Information Pb Lead
Detailed information on Air Pollution Trends: NO2> N°x Nitrogen Dioxide,
http://www.epa.gov/airtrends Nitr°9en Oxides
03 Ozone
Real-Time Air Quality Maps and Forecasts: ^ Particulate Matter
http://www.epa.gov/airnow (10 micrometers in
On-line Air Quality Data: diameter or less)
http://www.epa.gov/air/data/index.html PM25 Particulate Matter
(2.5 micrometers
Office of Air and Radiation: in diameter or less)
http://www.epa.gov/oar SO2, SOX Sulfur Dioxide,
,,. , .. _ Sulfur Oxides
Office of Air Toxics:
http://www.epa.gov/ttn/atw Other Pollutants
Office of Air Quality Planning and Standards: CFCs Chlorofluorocarbons
http://www.epa.gov/oar/oaqps CH4 Methane
~cf. r^ ,.. CO2 Carbon Dioxide
Office of Transportation and Air Quality:
http://www.epa.gov/otaq HFCs Hydrofluorocarbons
N2O Nitrous Oxide
Office of Atmospheric Programs: RCBs Polychlorinated Biphenyls
http://www.epa.gov/air/oap.html ppCs Perfluorinated Carbons
Office of Radiation and Indoor Air: VOCs Volatile Organic Compounds
http://www.epa.gov/air/oria.html
Other Acronyms
Global Warming Emissions Information: CCAp c|imate change Actjon p|an
http://www.epa.gov/globalwarming/emissions/ D|J Dobson Unit(s)
national/index.html
EPA Environmental
Acid Rain Website: http://www.epa.gov/airmarkets/ Protection Agency
Acid Rain Hotline: (202) 564-9620 FCCC Framework Convention
on Climate Change
Energy Star (Climate Change) Hotline: IPCC Intergovernmental Panel
(888) STAR-YES on Climate Change
A/r , ., c T.-T .. i w u- i j -n i NAAQS... ... National Ambient Air Quality
Mobile Sources National Vehicles and Fuel
Emissions Lab: (734) 214-4200
NTI National Toxics Inventory
Stratospheric Ozone Hotline: (800) 296-1996
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