Environmental Protection
Agency
(6204J)
October 1992
&EPA Acid Rain Program
Environmental Benefits
In order to reduce acid rain in the United States and Canada, Title IV
of the Clean Air Act Amendments of 1990 established the Acid Rain
Program. The program will cut sulfur dioxide emissions in half and
substantially reduce nitrogen oxides emissions from electric utility
plants. This fact sheet discusses the environmental effects of acid rain
and the benefits that will accrue as a result of the required emissions
reductions, and is one of a series containing information about the
program.
Acidic deposition, or acid rain as
it is commonly known, occurs
when chemically laden emissions re-
act in the atmosphere with water,
oxygen, and oxidants to form vari-
ous acidic compounds. These com-
pounds then fall to the earth in either
dry form (such as gas and particles)
or wet form (such as rain, snow, and
fog).
Sulfur dioxide (SO2), which is
emitted primarily by coal-buming
electric power plants, is the domi-
nant precursor of acid rain in the
United States. Emissions of nitrogen
oxides (NOx) also play a role in the
formation of acid rain and are signi-
ficant in the formation of ground-
level ozone.
Electric utility plants account for
about 70 percent of annual SO2
emissions and 30 percent of NOx
emissions in the United States.
Over 20 million tons of each of
these two pollutants are emitted
into the atmosphere each year.
Acid rain causes surface water
acidification and damages trees at
high elevations (for example, red
spruce trees above 2,000 feet in ele-
vation). Air concentrations of sulfur
and nitrogen species degrade visibil-
ity in large parts of the country, in-
cluding our national parks.
In addition, acid rain accelerates
the decay of building materials and
Eaints, including irreplaceable
uildings, statues, and sculptures
that are part of our nation's cultural
heritage. Finally, air concentrations
of acidic aerosols (tiny droplets of
sulfuric acid derived from SO2 emis-
sions) may pose a risk to public
health.
Implementation of the acid rain
provisions will confer significant
benefits on the nation. Acid rain con-
trol will allow acidified lakes and
streams to recover so that they can
or.ee again support fish life. Visibility
will improve, allowing for increased
enjoyment of scenic vistas across our
country. Acid rain control will im-
Erove the health of forests, particu-
rly red sprace forests that populate
the ridges of mountains from Maine
to Georgia. I: will provide new safe-
guards for our nation's cultural
heritage through protection of his-
toric buildings and monuments,
and it will provide an insurance
policy against the potential threat
to public health posed by acidic
aerosols.
Surface Waters
Acid rain primarily affects sensi-
tive bodies of waters, that is,
those that rest atop soil with a limit-
ed ability to neutralize acidic
compounds (called "buffering capac-
ity"). Many lakes and streams exam-
ined in a National Surface Water
Survey (NSWS) suffer from chronic
acidity, a condition in which water
has a constant low pH level. The
NSWS investigated the effects of
acidic deposition in over 1,000 lakes
larger than 10 acres and in thousands
of miles of streams thought especially
sensitive to acidification. Of tne lakes
and streams surveyed in the NSWS,
acid rain has been determined to
cause acidity in 75 percent of the
acidic lakes and about 50 percent of
the acidic streams.
In some sensitive lakes and
streams, acidification has completely
eradicated fish species, such as the
brook trout, leaving these bodies of
water barren. In fact, hundreds of the
lakes in the Adirondacks surveyed in
the NSWS have acidity levels indica-
tive of chemical conditions unsuit-
able for the survival of sensitive fish
species.
Emissions from U.S. sources con-
tribute to acidic deposition in
Canada. The soil in eastern Canada
is very similar to the soil of the
Adirondack Mountains. Lakes in
eastern Canada are consequently ex-
tremely vulnerable to chronic acidifi-
cation problems. The Canadian
government has estimated that
14,000 lakes in eastern Canada are
acidic.
Streams flowing over soil with
low buffering capacity are equally
as susceptible to damage from acid
rain as lakes are. Approximately
580 of the streams in the Mid-
Atlantic Coastal Plain* are acidic
primarily due to acidic deposition.
The New Jersey Pine Barrens area
endures the highest rate of acidic
streams in the nation with over
90 percent of the streams acidic.
Over 1,350 of the streams in the
The Mid-Atlantic Coastal Plain encompasses parts of the Piedmont and coastal plain in New Jersey, Delaware, Pennsylvania,
Maryland, Virginia, and North Carolina. The Nlid-Atlantic Highlands extend from southeastern New York through most of
Pennsylvania and include portions of Maryland. West Virginia, ana Virginia. The Mid-Appalachians include Virginia, West Virginia,
Maryland, Pennsylvania, and North Carolina.
Printed on paper that contains at least 50% recycled fiber.

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Mid-Atlantic Highlands are
acidic, primarily due to acidic
deposition, while streams in the
Mid-Appalachians are also under-
going increasing acidification.
Many streams in that area have
already experienced trout losses
due to the rising acidity
Acidification is also a problem in
areas that were not surveyed in
federal research projects. For exam-
ple, although lakes smaller than 10
acres were not included in the
NSWS, there are from one to four
times as many of these small lakes
as there are larger lakes. In the Adi-
rondacks, the percent of acidic
lakes is significantly higher when
it includes smaller lakes (26 per-
cent) than when it includes only the
NSWS target size lakes (14 percent).
The acidification problem in
both the United States and Canada
grows in magnitude if "episodic
acidification" (brief periods of low
pH levels from snowmelt or heavy
downpours, which can result in
fish lulls) is taken into account.
Lakes and streams throughout the
United States, including western
lakes, are sensitive to episodic
acidification. In the Mid-Atlantic
Highlands, the Mid-Atlantic Coastal
Plain, and the Adirondack Moun-
tains, about three times as many
lakes and streams become tempo-
rarily acidic during storms and
snowmelt.
Acid rain control will produce
significant benefits in terms of low-
ered surface water acidity. If acidic
deposition levels were to remain
constant over the next 50 years (the
timeframe used for projection
models), the acidification rate of
lakes in the Adirondacks that are
larger than 10 acres would rise by
50 percent or more. Scientists pre-
dict, however, that the decrease in
SO2 emissions required by the Acid
Rain Program wul virtually elimi-
nate emission-caused acidification
in that area.
Forests
Acid rain contributes to forest
degradation, especially in high-
elevation spruce trees that populate
the ridges of the Appalachian
Mountains from Maine to Georgia,
including national park areas such
as the Shenandoah and Great
Smokey Mountains national parks.
Acidic deposition seems to impair
the trees' growth in several ways; for
example, acidic cloudwater at high
elevations increases the susceptibil-
ity of the red spruce to winter injury.
There also is a concern about the
impact of acid rain on forest soils.
There is good reason to believe that
long-term changes in the chemistry
of some sensitive soils may have al-
ready occurred as a result of acid
rain. As acid rain moves through the
soils, it can strip away vital plant
nutrients through chemical reac-
tions, thus posing a threat to future
forest productivity.
Visibility
Sulfur dioxide emissions lead to
the formation of sulfate parti-
cles in the atmosphere. Sulfate
particles account for more than 50
percent of the visibility reduction
in the eastern part of the United
States, affecting enjoyment at
many of our national parks. The
legislated reduction in SO2 emis-
sions is expected to result in a 30-
percent increase in visual range in
the eastern part of the country. In
the western part of the United
States, nitrogen and carbon also
play roles, but sulfur has been im-
plicated as an important source of
visibility impairment in many of
the Colorado River Plateau na-
tional parks, including the Grand
Canyon, Canyonlands, and Bryce
Canyon.
Building Materials
Acid rain is known to contribute
to the corrosion of metals and
deterioration of stone and paint in
buildings, statues, and other struc-
tures of cultural significance. The
damage inflicted on cultural objects,
such as statues or historic monu-
ments, proves especially costly since
a loss of detail caused by the corro-
sive potential of acid nun seriously
depreciates the objects' value to soci-
ety. Dry deposition of acidic
compounds can also dirty buildings #
and other structures, leading to *
increased maintenance costs. Given
the very large number of buildings
affected by wet and dry deposition,
even a small impact on maintenance
costs could translate into a very large
savings to society.
Health
High levels of SO2 have been
proven to cause or aggravate
various types of lung disorders.
These lune disorders, which affect a
person's ability to breathe, have led
to both increased morbidity (sick-
ness) and mortality. Based on these
concerns, SO2 has historically been
regulated under the Clean Air Act.
Additionally, studies at Harvard
University have suggested a rela-
tionship between acidic sulfate (a
type of acidic aerosol) levels and
increased levels of morbidity and
mortality. While EPA continues to
study the problem, SO2 emission
reductions under the Acid Rain
Program will reduce sulfate levels
in the atmosphere, thereby pro-
viding an insurance policy against
this threat to public health.
Clean Air for
a Better Life
By reducing SO2 emissions by
such a significant amount, the
Clean Air Act promises to confer
numerous benefits on the nation.
Scientists project that the 10 mil-
lion-ton reduction in SO2 emissions
should significantly decrease the
acidification of water bodies and
damage to forests and even allow
these processes to be reversed. In
addition, visibility will be signifi-
cantly improved due to the cut-
backs, ana the lifespan of building
materials and structures of cultural
importance should lengthen. Fi-
nally, the reductions in emissions
will help to protect public health.
For More Information
Write to:
U.S.EPA
Acid Rain Division (6204J)
401 M Street, SW.
Washington, DC 20460
If you would like to receive other
fact sheets on the Acid Rain
Program, call the Acid Rain Hotline
at 617-674-7377 or the EPA Public
Information Center (PIC) at 202-
260-2080.
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