United States
Environmental Protection
Agency
Air and Radiation
(6204J)
EPA430-R-99-011
November 1999
www. epa.gov/acid rai n
Progress Report on the EPA Acid Rain Program
Printed on paper that contains at least 30 percent postconsumer fiber.
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Table of Contents
1 Introduction
2 The Acid Rain Program
5 What Has the Program Achieved so Far?
11 Acid Deposition and the Environment
20 Summary of Accomplishments and Next Steps
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Progress Report on the EPA Acid Rain Program 1
Introduction
The Acid Rain Program: A success in reducing emissions and costs. How is the environment responding?
In 1990, Congress established the Acid Rain Program under the Clean Air Act. The principal goal of the program is to achieve reductions
of 10 million tons of sulfur dioxide (S02) and 2 million tons of nitrogen oxides (NOX), the primary components of acid rain. These pollu-
tants, in their various forms, lead to the acidification of lakes and streams rendering some of them incapable of supporting aquatic life.
In addition, they impair visibility in our national parks, create respiratory problems in people, weaken forests, and degrade monuments
and buildings.
These environmental and public health problems caused by acid rain have affected us for several decades. We have, however, started on
the path to recovery. Through efforts made by the United States Environmental Protection Agency's (EPA's) Acid Rain Program, emissions
of S02 and NOX are declining. The centerpiece of the Acid Rain Program is a creative, market-based approach for bringing about signifi-
cant, cost-effective reductions in S02. As a result of the program and its innovative approaches, we will enjoy multiple environmental and
health benefits in a cost-effective manner.
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Progress Report on the EPA Acid Rain Program
The Acid Rain Program
To address the problem of acid rain— more accurately known as
acid deposition— Congress established the National Acid
Precipitation Assessment Program (NAPAP) in 1980 to study the
causes and impacts of acid deposition. This research revealed acid
deposition's broad environmental and health effects and also docu-
mented that the pollution causing acid deposition can travel hundreds
of miles, crossing state and national boundaries. In addition, these
studies identified electric power generation as responsible for two-
thirds of S02 emissions and one-third of NOX emissions.
With NAPAP's scientific underpinning, Congress created the Acid Rain
Program under Title IV (Acid Deposition Control) of the 1990 Clean Air
Act Amendments. The long-range transport of acid deposition and the
amount of emissions linked to electric power generation led Congress
to require significant reductions of S02 and NOX emissions from elec-
tric utilities. By 2010, utilities would need to lower their emissions by
8.5 million tons compared to their 1980 levels. In addition, they would
need to reduce their NOX emissions by 2 million tons each year com-
pared to levels before the Clean Air Act Amendments.
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Progress Report on the EPA Acid Rain Program
Marketing Emission Reductions:
The Cap and Trade Program
For S02, the Acid Rain Program places a mandatory ceiling, or cap, on
emissions nationwide from electric utilities, and allocates emissions
to these pollution sources in the form of allowances. An allowance is
an authorization to emit 1 ton of S02. At the end of the year, sources
must hold an allowance for each ton of S02 they emitted. Extra
allowances may be banked (or carried over) for future use or sold to
other companies. This system of emissions trading, known as "cap
and trade," is innovative in its use of the market to achieve greater
environmental results for a given cost than are possible through tradi-
tional approaches. Traditional approaches might include requirements
to install specific pollution control equipment. In addition to providing
an economic incentive to reduce S02, this system allows utilities the
flexibility to decide how they will achieve the necessary emission
reductions. For example, they could install pollution control equipment
such as "scrubbers," switch to less polluting fuel, conserve energy,
rely more on renewable energy, trade S02 allowances, or use any com-
bination of these options. Furthermore, utilities can change their
approach as new opportunities arise, without needing government
approval. This freedom allows them to determine for themselves the
most cost-effective timing and method of emission reductions.
In return, sources must continuously measure and report their emis-
sions, providing emissions information unprecedented in its accuracy and
completeness. Detailed measurement ensures that emission goals are
attained and that sources are in compliance. Since the start of the pro-
gram in 1995, no company in the trading program has failed to comply.
NOX is treated differently. Rather than using a cap and trade program,
the Acid Rain Program reduces NOX emissions by designating an emis-
sion rate for each source. The program gives utilities the opportunity
to find cost efficiencies while ensuring that overall emission reduc-
tions are achieved by allowing emission rates to be averaged across a
utility's boilers. The primary difference between the NOX and S02
What Is Acid Rain?
Acid rain, more accurately known as acid deposition, begins
with the burning of fossil fuels, such as coal, gas, or oil, for
energy. The resulting air pollution contains S02 and NOX.
These gases react in the atmosphere with water, oxygen, and
oxidants to form various acidic compounds, most often
tracked as sulfate, nitrate, and hydrogen ions. Often carried by
winds for hundreds of miles, these compounds may be
deposited on earth as dry deposition, a process where acidic
particles or gases settle on or are absorbed by plants, land,
water, or building materials. The acidic compounds may also
be deposited through rain, snow, and cloud water, which is
known as wet deposition. In other words, there are many path-
ways by which acid "rain" reaches the earth.
(Fig'
ure 1.
Origins of Acid Rain
Gaseous
Pollutants in
Atmosphere
Paniculate
Pollutants in
Atmosphere
SOURCES
voc
NOY
Pollutants in
Cloud Water
and
Precip:tation
NOV
Wet
Deposition
,J 4i******m*
— Natural RFHFPTDR.S
Anthropogenic
A combination of natural and manmade activities result in the deposition of acidic compounds.
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Progress Report on the EPA Acid Rain Program
Predicted costs for reducing acid rain continue to
decline...
In 1990, EPA estimated that complying with the program's S02 emis-
sions reduction goals would cost utilities approximately $4.6 billion
per year by 2010 (the date when the annual 10 million ton emis-
sions reduction is expected to be reached). In 1994, the cost was
reevaluated by the General Accounting Office and the estimate was
lowered to about $2 billion by 2010. Based on recent compliance
cost information, a 1998 Resources for the Future report estimated
costs of S02 emissions reductions to be less than $1 billion by
2010. These independent studies show that real-life experiences
with the program reveal greater cost savings than initially expected.
programs is that the S02 cap and trade approach ensures total
power plant emissions never exceed the mandated ceiling.
The program's ultimate objective is to protect the environment and
improve human health by reducing both S02 and NOX emissions.
EPA believes these reductions will benefit the nation by:
Restoring acidified lakes and streams so they can once again
support native aquatic life.
Protecting air quality and public health.
Improving visibility, especially at scenic vistas in national parks.
Reducing the damage to forests along the mountain ranges of the
East Coast.
Protecting our historic buildings and monuments from degradation.
Figure 2. Estimated Cost of the Acid Rain Program at Full
Implementation (2010)
15
cT ,_
CD
V 9
c
^o
^ 6
O
o
1989*
1990 1994
Year
1998
Key
CH Edison Electric Institute I I General Accounting Office
I I EPA I I Resources for the Future
'Estimate assumes no trading program and the associated cost savings.
Cost estimates of implementing the Acid Rain Program have declined.
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Progress Report on the EPA Acid Rain Program
What Has the Program Achieved so Far?
Emission Trends
The first step in protecting the environment and human health
from acid rain is reducing emissions. The Acid Rain Program
is proving to be extremely effective in this regard. In 1995,
the first year of compliance under the program, S02 emissions
dropped dramatically, by 3 million tons, reducing total S02 emitted
nationally as shown in Figure 3. Over the first 4 years of the pro-
gram, emissions from the largest, highest emitting utility units were
about 5 million tons below their 1980 levels, as shown in Figure 4.
These deep cuts in emission levels include reductions of about 30
percent below the allowable emission levels made in advance of
future limits. These early reductions mean environmental benefits
can begin sooner. Figure 5 presents another encouraging sign: the
largest emission reductions are occurring in the heaviest emitting
areas, particularly the Midwest.
While overall NOX emissions have remained constant since the 1980s
(see Figure 6), the average emission rate of utilities participating in
Phase I of the NOX program has decreased by 42 percent since 1996.
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Progress Report on the EPA Acid Rain Program
/'Figure 3. Trend in Sulfur Oxide Emissions for Six Principal
Source Categories, 1987 to 1997
1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
Year
DComb-Util D Comb-Industry D Comb-Other • Metals DAII Other BOn-Road • Non-Road
National emissions of S02 have been decreasing over the past decade, punctuated by a
significant decrease attributable to the start of the Acid Rain Program in 1995. Utilities
account for about 67 percent of the total estimated S02 emissions. Other contributors
include industrial sources and metallurgical processes as well as cars, trucks, and con-
struction equipment.
Source: EPA, 1998, National Air Quality and Emission Trends Report.
Figure 4 SO2 Emissions From 263 Large Utility Units
IT12
o
•^ 10
g
1,
E 6
o
' 4
tn
E
O
oo
1980
1998
Emission reductions have been substantial since the program began in 1995.
Ultimately, the program will result in a 10 million ton reduction in S02 from 1980
levels in 2010.
This reduction translates to a 35 percent drop in actual NOX emissions
from electric utilities currently affected by the Acid Rain Program.
Starting in 2000, additional utility units will be affected with more
stringent S02 emissions limitations nationwide. NOX rates (i.e., the
amount of NOX emitted per unit of coal used) will be reduced to
between 0.40 and 0.86 Ibs/mmBtu, depending on the boiler type.
Air Quality
Emission reductions from the Acid Rain Program are contributing to
improved air quality. Data collected for the past 10 years, shown in
Figure 7, indicate that ambient S02 concentrations are declining, as
are ambient S04, or sulfate, concentrations. Sulfates are com-
pounds formed from S02 emissions and are transported long
Figure 6. Trend in Nitrogen Oxide Emissions for Five
Principal Source Categories, 1987 to 1997
1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997
Year
National NOX emissions have not declined. They have remained at around 23 million
tons per year since the 1980s. Electric utilities generate about 30 percent of the total
tribute significantly. Although NOX emission rates have declined and cleaner technolo-
gies are being used, total NOX emissions have not decreased significantly because
electricity generation and vehicle use-and, therefore, fuel combustion-have increased.
Source: EPA, 1998, National Air Quality and Emission Trends Report,
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Progress Report on the EPA Acid Rain Program
Figure 5 1980 to 1997 SO2 Emissions From Utilities
Emission reductions are occurring where they are needed- in some of the highest emitting areas of the country. For example, electric
utilities affected by the Acid Rain Program in 1997 in both Ohio and Indiana reduced S02 emissions by about 44 percent and 50 per-
cent, respectively, from 1990 levels. This decrease is important environmentally, but it also supports an economic premise of the Acid
Rain Program's market-based approach: the highest emitting plants have more incentive to make substantial emission reductions
because they can achieve these reductions at a lower cost per ton. Experience is validating this expectation, and concerns that the
biggest emitters of S02 would simply buy allowances and continue to emit at their historical levels have proved unwarranted thus far.
199?
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Progress Report on the EPA Acid Rain Program
distances. These fine particles aggravate respiratory health, can
lead to premature mortality, and degrade visibility, resulting in a hazy
view of the horizon.
Downward trends in S02 emissions lead to decreases in airborne sul-
fate particles and improved air quality in areas distant from the origi-
nal source of air pollution. The relationship between regional S02
emissions and sulfate concentrations in air quality in the Northeast
is illustrated in Figure 8. This graph compares long-term trends
(1978 through 1996) in annual mean aerosol sulfate concentrations
at two rural locations in New York State (Mayville and Whiteface
Mountain) with upwind S02 emissions for the Midwest (Minnesota,
Wisconsin, Illinois, Michigan, Indiana, Ohio, West Virginia, Kentucky,
and western Pennsylvania). The underlying trend in sulfate concentra-
tions parallels S02 emissions, with both trends decreasing. Sulfates
declined sharply in 1995, corresponding to a 36 percent reduction in
regional S02 emissions. Air quality improved by approximately 30 per-
cent for Mayville, New York, and an impressive 47 percent for the
more distant Whiteface Mountain, New York, location.
Figure 7 Regional SO2 Trends 1988 to 1997
Figure 8. Relationship Between Emissions and
Air Quality
Alaska is in EPA Region 10; Hawaii, EPA Region 9; and Puerto Rico, EPA Region 2. Concentrations are PPM.
Percentage is the percent drop in S02 concentration in that Region. Trend line shows changes in S02 concentration
from 1988 on the left side to 1997 on the right side. Trends are decreasing in all Regions, with most prominent
trends occurring in the Northeast and Mid-Atlantic states.
Source: EPA
11
S fl
o
o>
nE 7
% 5
5
01
df 3
1
'
o
x^ Midwest Emissions
-000
o
o
n n
Mayville (— -'
0 o DD
Whiteface Mt. Op)
I II IE
978 1981 1984 1987 1990 1993 1996
Declining emissions in the Midwest correlate to improved air quality in
Mayville and Whiteface Mountain, New York. Ambient sulfates dropped
significantly in 1995, the first year of Title IV implementation.
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Progress Report on the EPA Acid Rain Program 9
Figure 9 Wet Sulfate Deposition in Acid Rain Reduced (kg/ha)
1989 to 1991 1995 to 1997
Figure 10. Nitrate Concentration in
Acid Rain Unchanged ((ieq/L)
20 23 26 29 32 >35
These maps represent snapshots of wet sulfate deposition over time. As illustrated in the 1995 to 1997 map, following the 1995
implementation of the Acid Rain Program, total sulfate deposition fell in a dramatic and unprecedented reduction of up to 25 per-
cent over a large area of the Eastern United States. The greatest reductions occur in the Northeastern United States, where many
of the most acid sensitive ecosystems are located. (Units are in kilograms per hectare).
-6.0 -4.5 -3.0 -1.5 0 1.5
4.5 6.0
As compared to the 1983 to 1994 trend, in both 1995 and 1996,
nitrate concentrations have been estimated to be about the same as
levels expected. White crosses indicate locations of NADP/NTN sites
used in this analysis. (Units are in microequivalents per liter (neq/L).)
Lower Emissions Mean Less Acid Deposition
Declining emissions from fossil fuel combustion will bring about
decreases in concentration of acidic compounds and total acid deposi-
tion. Measured as sulfate, nitrate, and hydrogen ions, acid deposition
is tracked by scientists and EPA with the use of data from several
monitoring networks.
Field data collected by the National Atmospheric Deposition
Program/National Trends Network (NADP/NTN), a network of more than
200 monitoring stations, show that sulfate levels in precipitation have
declined sharply since the Acid Rain Program began requiring emission
reductions in 1995. As shown in Figure 9, sulfate deposition levels have
fallen by about 25 percent in the Northeast and Mid-Atlantic regions,
where ecosystems have proven more sensitive to acidic deposition.
Figure 10 shows that no dramatic regional changes in nitrate concentra-
tion levels have been recorded due to steady NOX emissions levels.
The Clean Air Status and Trends Network (CASTNet) measures dry depo-
sition1 of sulfur and nitrogen, among other pollutants, at approximately
70 sites. CASTNet data show that dry deposition sulfate concentration
levels also have declined by up to 30 percent in the Northeast and the
Mid-Atlantic (see Figure 11). As anticipated, no statistically significant
regional trends have been measured for nitrate concentration levels.
'Actual measurement of dry deposition (acid deposition in the form of particles or gases) is very complex. CASTNet measures concentration levels and meteorology and then estimates what is deposited on the surface.
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10 Progress Report on the EPA Acid Rain Program
Figure 11. Widespread Reductions in Sulfate Concentrations at CASTNet Sites Between 1989 and 1995 ((ig/m3)
Percent Increases
10% o%
Allegheny Front
Allegheny Plateau
Mid-Appalachians
Midwest
Ohio River Valley
South
Unique Sites
-10%
Percent Reductions
-20% -30% -40% -50%
-60%
Key
_
SO 42~ (Sulfate
)
~ Laurel Hill
~~ M K Goddard
Cedar Creek
—
Ann Arbor
_ Unionville
— n r
—
_ Coffeeville
Edgar Evins
Georgia State
_ Pisgah
_ Prince Edward
_ Sand Mountain
_ Shenandoah
_ Speedwell
_ Virginia Tech
—
_ Ashland
_ Caddo Valley
_ Coweeta
Sumatra
10%
0%
-10%
-20%
-30%
-40%
-50%
-60%
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Progress Report on the EPA Acid Rain Program
11
Acid Deposition and the Environment
The ultimate consequence of acid deposition is its impact on
the environment and public health. In both wet and dry forms,
acid rain has multiple effects, sometimes through mecha-
nisms that scientists are still trying to understand. In general, the
chemical composition of rainwater varies from place to place, often
due to air pollution and other chemicals found in a particular area.
Figure 12 presents the pH, a measure of acidity, of precipitation
measured by the NADP network in 1997.
The following sections discuss areas that will benefit from the Acid
Rain Program's emission reductions: surface water, visibility, forests,
human health, and materials and structures.
Surface Water: Lakes and Streams
In a national surface water survey conducted under NAPAP in the
mid-1980s, acid rain was the dominant cause of acidification in 75
percent of the acidic lakes and about 50 percent of the acidic
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12
Progress Report on the EPA Acid Rain Program
1997 Estimated Acidity (pH) of Precipitation at NADP Sites
^
A
*.. « -*w _n ,
V5'Q t?
. ^ -5'1
Okm
Estimated pH of precipitation sampled at more than 200 sites nationwide. Most acidic precipitation is found in the
Midwest and Northeast. Normal pH for rainfall is about 5.5.
streams (NAPAR 1991). Acid deposition can deplete the ability of
lakes and streams to sustain some fish and other aquatic species'
capability to grow, reproduce, or survive. Although the diversity and
abundance offish species present in a body of water is related to
many factors, in some cases, the types of species able to survive
can be directly correlated to surface water acidity. Figure 13 shows
critical pH levels below which various species offish cannot survive.
The loss offish occurs primarily in surface waters resting atop shallow
soils that are not able to buffer, or counteract, acidity, most commonly
in the Northeast and Mid-Atlantic regions (see Figure 14). Furthermore,
as acidity increases, aluminum is leached from the soil causing
concentrations in lakes and streams to increase.
Aluminum, particularly inorganic aluminum, is
highly toxic to aquatic life. The Adirondack
Mountains in New York and the Mid-Appalachian
highlands contain many of the U.S. waters most
sensitive to acidification. Other sensitive areas
include Florida, the upper Midwest, and the high-
elevation West. In eastern Canada, where the
soil is similar to that found in the Adirondacks,
the Canadian government estimates that about
14,000 lakes are acidic.
Acidification can be chronic or episodic. Lakes
and streams suffering from chronic acidifica-
tion have a constantly low capacity to buffer
acids over a long period of time. The NAPAP
survey found that more than 500 streams in
the Mid-Atlantic Coastal Plain and more than
1,000 streams in the Mid-Atlantic Highlands
are chronically acidic, primarily due to acidic
deposition. In the New Jersey Pine Barrens
area, more than 90 percent of streams are
acidic, the highest rate in the nation. Many
streams in that area have already experienced
trout losses due to the high level of acidity. Hundreds of lakes in
the Adirondacks have acidity levels unsuitable for the survival of
sensitive fish species [see inset on Adirondacks]. In some sensitive
lakes and streams further south, acidification has severely depleted
even the hardiest species, such as the brook trout [see inset on
streams in the southern Appalachians].
Episodic acidification is the rapid increase in surface water acidity,
resulting from large surges of nitrate and/or sulfate, which typically
occur during snowmelt or the heavy rains of early spring. Preventing
these surges in winter and early spring is critical because fish and
other aquatic organisms are in their vulnerable, early life stages.
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Progress Report on the EPA Acid Rain Program
13
Though temporary, episodic acidification can affect aquatic life signifi-
cantly and has the potential to cause "fish kills."
Episodic acidification increases the number of lakes and streams
that are susceptible to acid rain. Approximately 70 percent of sensi-
tive lakes in the Adirondacks may be at risk of episodic acidification.
This amount is more than three times the number of chronically
acidic lakes. About 30 percent of sensitive streams in the mid-
Appalachians are likely to become acidic during an episode. This level
is seven times the number of chronically acidic streams in that area.
High-elevation lakes in the Western United States also are at risk.
Acid Neutralizing Capacity
Whether surface waters can resist acidification depends on the ability
of the water and watershed soil to neutralize the acid deposition it
receives. The best measure of this ability is acid neutralizing capacity
(ANC), which is determined by the amount of dissolved compounds
that will counteract acidity. Surface water with an ANC of 200 micro
equivalents per liter is normal. ANC less than 50 micro equivalents
Figure 13 Critical pH for Selected Fish in Lakes and Streams
6.5
5.5
5.0
1
Yellow Perch
Brook Trout
Lake Trout
Smallmouth Bass
Rainbow Trout
Common Shiner
*£=>
PH is a measure of acidity. The lower the pH, the more acidic the water. Fish species have different
abilities to withstand excess acidity.
Solid symbols for each type of organism are placed in favorable pH ranges; empty symbols are
placed in less favorable ranges. No symbol is placed in pH ranges that generally do not support
populations of a particular type of organism.
Source: National Acid Precipitation Assessment Program. 1991. 1990 Integrated Assessment Report
NAPAP Office of Director, Washington, DC.
Adirondacks: Slow to Recover
In spite of declining emissions and even declining surface water sulfate
concentrations in the Adirondacks, lakes in this region are not showin;
any measurable increase in acid neutralizing capacity. Why have other
Northeastern lakes, such as those in New England, begun to recover, but
not Adirondack lakes?
Recovery of Adirondack surface waters may be affected by several factors:
relatively constant deposition and presence of nitrate in surface waters,
loss of soil's ability to neutralize excess acidity ("base cation depletion"),
naturally occurring acid sources, underestimated dry deposition, and
lengthy lag time between deposition reduction and ecosystem recovery.
Recent research and modeling efforts suggest that although conditions
would likely have been substantially worse without the Acid Ram
Program, full recovery of the Adirondack ecosystems may require reduc-
tions in sulfur and nitrogen beyond those currently expected. Watershed
dynamics are proving to be complex, highlighting the need for continued
environmental monitoring in order to fully evaluate the effects of control-
; atmospheric sulfur and nitrogen depositii
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14 Progress Report on the EPA Acid Rain Program
Fresh Water Fish and Rising
Acidification
Compared to the Adirondacks, streams
in Shenandoah National Park are in the
early stages of acidification. Recent
declines in fish population and species
diversity indicate, however, that episodic
acidification is taking its toll. In a
University of Virginia study on trout
reproduction in the Southern
Appalachian Mountains, researchers
found nearly 100 percent death in the
trout eggs and newly hatched fish after
a severely acidic rainfall and steep
increase in stream water acidity. This
sharp acidic surge, due to acidic rainfall,
altered stream chemistry, resulting in
conditions fatal to fish at young and vul-
nerable stages. [Trout Unlimited, 1998.]
Percentage of Acidic Surface Waters in Surveyed Regions
West
New
England
Source: NAPAP. 1991. 1990 Integrated Assessment Report.
per liter is considered highly sensitive to
acidification. An ANC of zero or less is acidic.
Surface water pH is another direct measure
of the balance of acid and base ions in a
lake or stream. However, pH does not indi-
cate whether the cause of the acidity is acid
deposition or other sources, like organic
soils or drainage from mining activities.
ANC depends largely on the surrounding
watershed's physical characteristics such as
geology, soils, and size. Waters that are
acidic tend to be located in small water-
sheds that have few alkaline minerals and
shallow soils. Conversely, watersheds that
contain alkaline minerals, such as lime-
stone, tend to have waters with a high ANC.
Deposition reductions from the Acid Rain
Program are expected to benefit surface
water chemistry. Recently, many acidic sur-
face waters have shown declines in sulfate
concentrations consistent with the program's
emissions reductions.
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Progress Report on the EPA Acid Rain Program 15
Recovery In New
England
The Acid Rain Program has led
to significant emissions cuts
from Northeastern and
Midwestern utilities. These
reductions can be expected to
spur the recovery of lakes and
streams in the Northeast, partic-
ularly in New England. Some
acidified ecosystems are already
showing signs of improvement
as emissions and acid deposi-
tion decline. A recent study
examining acidified lakes in the
Northeast found that lakes atop
thin gravel soils (and thus sensi-
tive to acid rain) in New England
have shown statistical decreases
in surface water sulfate concen-
trations and concurrent increas-
es in ANC. These trends (as
shown in Figure 15) are signifi-
cant because ANC indicates an
ecosystem's long-term ability to
resist acidification.
The study of New England lakes
used surface water data from
EPA's Environmental Monitoring
and Assessment Program's Long-
Term Monitoring Project, which
provides estimates of the recov-
ery of lakes and streams
exposed to large-scale emissions
reductions. Ecosystem recovery
speed depends heavily on at
least three factors: 1) emissions
and acid deposition reduction
rates; 2) ANC; and 3) time delay
for ecosystem response.
Figure 15. Improvements in Surface Water Acidity
For Bourn Pond, Vermont
Bourn Pond, Vermont
f ! !
82 83 84 85 86 87
90 91 92 93 94 95
Surface-water chemistry data indicated that acidic conditions are
improving in this New England lake. Acidic compounds are
decreasing while acid neutralizing capacity is increasing.
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16
Progress Report on the EPA Acid Rain Program
Chesapeake Bay
Nitrogen plays a significant role in both short-and long-term
acidification of surface waters. In addition, new research reveals
that atmospheric nitrogen deposition may have significant
adverse impacts on estuaries (where the ocean meets fresh
water), other coastal waters, and large river basins. Nitrogen is a
key cause of the eutrophication (oxygen depletion) of water bod-
ies, which occurs when excess nutrients enter an estuary and
cause excess algae growth. This additional growth limits the
amount of light and oxygen available to other organisms in the
estuary, making it difficult to survive. Further losses in available
oxygen occur once the algae begins to die off.
Figure 16.
Chesapeake Bay Airshed
and Watershed
0
Key
• Watershed
• Airshed
Most of the excess nutri-
^^^^^m ents entering the
Chesapeake Bay and its
tributaries come from drainage waters,
such as pollutant discharge and run-off
from farms. Still, scientists estimate
that up to 25 percent of the nitrogen
in the Chesapeake Bay comes from
atmospheric deposition. Long-range
transport of atmospheric nitrogen deposition
is also an important factor. The Acid Rain
Program will help reduce these airborne
sources that contribute to eutrophication.
Good visibility day in Great Smoky Mountains.
Visual range is 100 miles.
Visibility
The pollutants associated with
acid deposition also reduce
visibility. Visibility impairment
occurs when particles and
gases in the atmosphere,
including sulfates and
nitrates, scatter and absorb
light. Visibility tends to vary by
season and geography
because it also is affected by
the angle of sunlight and
humidity. High relative humidi-
ty heightens pollution's effect
on visibility because particles,
such as sulfates, accumulate
water and grow to sizes at
which they scatter more light,
creating haze.
Sulfate particles from S02
emissions account for more
than 50 percent of the impaired visibility in the Eastern United
States, particularly in combination with high summertime humidity.
In the West, nitrogen and carbon also impair visibility, and sulfur has
been implicated as a major cause of visibility impairment in many of
the Colorado River Plateau national parks, including the Grand
Canyon, Canyonlands, and Bryce Canyon.
The Interagency Monitoring of Protected Visual Environments
(IMPROVE) network monitors visibility primarily in the nation's nation-
al parks. Reductions in particulate sulfate, usually correlated to visi-
bility improvements, have been measured at 13 eastern IMPROVE
sites (see Figure 17). It is too soon to tell how much of these
improvements can be attributed to the Acid Rain Program.
Bad visibility day at same location. Visual range
is 20 miles.
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Progress Report on the EPA Acid Rain Program 17
Figure 17. Visibility Improvements in National Parks
Boundary Waters Canoe Area
Lye Brook
Wilderness
Dolly Sods Wilderness Area
Shenandoah National Park
Improvements in visibility at our national parks correspond to
i National Park reductions in the seasonal averaged sulfate concentrations.
Percent reduction in particulate sulfate concentrations is
calculated by comparing 1995 data to the 1993 to 1994 mean
of the IMPROVE network sites.
Mammoth Cave National Park
Upper Buffalo Wilderness Area Great Smoky Mountains
Sipsey Wilderness Area
Edmond B. Forsythe
* National Wildlife Refuge
Washington, DC
Source: NAPAP, 1998, NAPAPBiennial Report to Congress: An Integrated Assessment,
National Park
^f-rw^m— Okefenokee National
yWildlife Refuge
~^ ^^^
Chassahowitzka National,
Wildlife Refuge
Key
Spring
Summer
Fall
Winter
Annual
Boundary Waters
Acadia
Lye Brook
E. B. Forsythe
Upper Buffalo
Shenandoah
Great Smoky Mts.
i
I
Mammoth Cave
Eft
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18 Progress Report on the EPA Acid Rain Program
Figure 18 Relationship Between Soil Acidity and Nutrients
As soil and deposition
acidity increases, nutri-
ents, such as base
cations, are leached
from the soil and are
not available for plant
growth.
Increasing Soil Acidity
Figure 19. Sensitive Forest Ecosystems
CD
Identified as a sensitive ecosystem
and subject to high deposition rates.
Four major forest types assessed by NAPAP.
Acid deposition, combined with other pollutant and natural stress
factors, can damage forest ecosystems. Damage could include
increased death and decline of Northeastern red spruce at high ele-
vations and decreased growth of red spruce in the southern
Appalachians. In some cases, acid deposition is implicated in
impairing a tree's winter hardening process, making it susceptible to
winter injury. In other cases, acid deposition seems to impair tree
health beginning with the roots. As acid rain moves through soils, it
also can strip nutrients from the soil and increase the presence of
aluminum ions, which are toxic to plants.
Long-term changes in the chemistry of some sensitive soils may
have already occurred. In some regions, nitrogen deposition in
forests can lead to nitrogen saturation, which occurs when the forest
soil has taken up as much nitrogen as possible. Saturated, the soil
can no longer retain nutrients and they are leached away (shown in
Figure 18). Nitrogen saturation has been observed in a number of
regions including Northeastern forests, the Colorado Front Range
and mountain ranges near Los Angeles, California. Effects also have
been seen in Canada and Europe. This phenomenon can create
nutrient imbalances in the soils and roots of trees, leaving them
more vulnerable to the effects of air pollutants such as ozone, cli-
matic extremes such as drought and cold weather, or pest invasion.
Figure 19 shows the location of forests sensitive to acid deposition.
The Acid Rain Program can be expected to reduce the stress to for-
est ecosystem health.
Human Health Effects
In the atmosphere, S02 and NOX gases are transformed into fine
particles of sulfates and nitrates. These particles— the same that
impair visibility— have serious health effects as well. Particulate mat-
ter (PM) is the term used for the mix of particles that, when air-
borne, may appear as haze, dust, or soot. Within that mix, particles
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Progress Report on the EPA Acid Rain Program
19
are divided by size; coarse PM is less than 10 microns in diameter,
while fine PM is less than 2.5 microns. Although both fine and
coarse particles are of health concern, fine particles are particularly
important because they easily penetrate the deepest portions of the
lungs. Recent studies have found an association between exposure
to fine PM and increased health problems, including premature
death, cardiac and respiratory-related hospital admissions and emer-
gency room visits, aggravated asthma, acute respiratory symptoms
such as aggravated coughing and difficult or painful breathing, new
cases of chronic bronchitis, and work and school absences.
The Acid Rain Program's reductions of S02 and NOX, especially from
coal-burning utilities, have brought about significant drops in air-
borne concentrations of fine PM. The estimated mean value in 1994
dollars of the health benefits associated with decreased sulfate lev-
els and associated fine PM reductions in the Eastern United States
is $10 billion for 1997 and $40 billion per year by 2010.
suggests the same is true for car paints. Ultimately, cultural preser-
vation as well as significant monetary benefits from avoided damage
will accompany reductions in S02 and NOX.
Materials and Structures
Sulfur dioxide, sulfates, and, to a lesser degree, nitrates, are corro-
sive to most materials, and thus can severely damage manmade
objects exposed to the atmosphere. NAPAP found evidence that acid
deposition degrades materials beyond natural weathering. The \
Eastern United States, with its high concentration of historic build-
ings and outdoor monuments, also has some of the nation's highest
levels of acid deposition.
Materials potentially damaged include monuments and historic build-
ings; outdoor structures such as bridges and buildings; and automo-
tive paints and finishes. For some materials, such as carbonate,
steel, or nickel, the effects are apparent after about 1 year of expo-
sure; for others, including copper and paints, effects may appear
after about 4 years. Research suggests that materials containing
calcium carbonate, such as limestone and marble, are more dam-
aged by dry acid deposition than wet deposition. Anecdotal evidence
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20
Progress Report on the EPA Acid Rain Program
Summary of Accomplishments and Next Steps
Progress in Solving the Acid Rain Problem...
Phase I of the Acid Rain Program began achieving significant reduc-
tions of S02 emissions from large electric power generators in
1995. The emissions trading program has proven to be an extremely
cost-effective mechanism, and is facilitating 100 percent compliance
by affected sources and stimulating early emissions reductions.
Phase II of the Acid Rain Program begins in the year 2000.
Emission reductions will be achieved for a greater number of
smaller plants, and emissions from larger plants will be further
reduced. By 2010, we will attain a S02 emissions cap on electric
utilities of 8.95 million tons (a level approximately one half of the
industrywide emissions in 1980).
About 350,000 tons of NOX emissions have been eliminated. In
2000, these reductions are expected to exceed 2 million tons
compared to levels without EPA controls. Absent an emissions
cap, however, NOX emissions could be expected to rise in the
future as electrical production increases.
The Environment's Response to Date...
In the Northeast and Mid-Atlantic regions of the United States,
where ecosystems are most sensitive to acidic deposition, sulfate
levels in precipitation (wet deposition) have declined by up to 25
percent, mirroring the reductions in S02
emissions achieved through the implemen-
tation of the Acid Rain Program. No distinct
regional trends in wet deposition of nitrate
have been detected. This is consistent with
NOX emission trends, which have remained
fairly constant over the past decade. Trends
in dry deposition of sulfur and nitrogen are
comparable.
• While in most cases it is too early to assess the ecological benefits
of the Acid Rain Program, some surface water chemistry trends in
New England are showing signs of recovery, as indicated by a rise
in acid neutralizing capacity in some lakes.
Ecosystems most severely impacted by acid deposition, such as
the Adirondacks, have not yet shown signs of recovery. Some sci-
entists believe that further reductions in S02 and NOX may be
necessary for full recovery of these sensitive ecosystems.
Where Do We Go From Here?
Efforts are under way to better coordinate research, monitoring,
and assessment activities to further our understanding of the envi-
ronmental response to the Acid Rain Program and other air quality
control efforts. In addition, these activities will enable better pre-
dictions of the environmental benefits from future policies under
consideration such as the implementation of the new ozone and
particulate matter standards.
Due to the Acid Rain S02 trading program's success in cost sav-
ings and unprecedented levels of emission reductions, other air
quality efforts include cap and trade programs. For example, EPA
is administering a NOX cap and trade program for large stationary
sources in 12 Northeastern states and has offered to administer
a similar program for 23 states and the District of Columbia EPA
also is working with these states to reduce NOX during summer
months to reduce regionwide ozone (smog) levels in the Midwest
and Eastern United States. These NOX reductions and expected
reductions from the transportation sector may also provide some
benefits for a number of other nitrogen-related environmental con-
cerns (e.g., acid rain and eutrophication of coastal waters). A
trading program also has been discussed as a possible approach
to facilitate future greenhouse gas emissions reductions.
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For more information contact...
EPA's Acid Rain Division:
www.epa.gov/acidrain
National Acid Precipitation Assessment Program:
www.nnic.noaa.gov/CENR/ NAPAP/NAPAP_96.htm
National Atmospheric Deposition Program:
nadp.sws.uiuc.edu
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