United States
Environmental Protection
Agency
Air and Radiation
(ANR-445)
400/1-91/039
December 1991
Environmental
Benefits
On November 15, 1990, President Bush signed into law the Clean Air Act
Amendments of 1990. Title IV of the Act, which deals with acid rain control,
contains provisions for a 10-million-ton reduction in sulfur dioxide emis-
sions and for controls on nitrogen oxide 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.
Acidic deposition, or acid rain as
it is commonly known, occurs
when chemically laden emissions
react in the atmosphere with water,
oxygen, and oxidants to form
various acidic compounds. These
compounds then fall to the earth in
either dry form (such as gas and par-
ticles) or wet form (such as rain,
snow, and fog).
Sulfur dioxide, which is emitted
primarily by coal-burning electric
power plants, is the dominant
precursor of acid rain in the United
States. Nitrogen oxide emissions also
^lay a role in the formation of acid
rain and are significant in the forma-
tion of ground-level ozone.
Electric utility plants account for
about 70 percent of annual sulfur
dioxide emissions and 30 percent of
nitrogen oxide emissions in the
United States. Over 20 million tons of
each of these two pollutants are
emitted into the atmosphere each
/ear.
Acid rain causes surface water
acidification and damages trees at
high elevations (for example, red
spruce trees above 2,000 feet in eleva-
tion). Air concentrations of sulfur
and nitrogen species degrade
visibility in large parts of the country,
including our national parks.
In addition, acid rain accelerates
the decay of building materials and
paints, including irreplaceable build-
ings, statues, and sculptures that are
part of our nation's cultural heritage.
Finally, air concentrations of acid
aerosols (tiny droplets of sulfuric
acid derived from sulfur dioxide
Emissions) may pose a risk to public
Aealth.
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
once again support fish life.
Visibility will improve, allowing for
increased enjoyment of scenic vistas
across our country. Acid rain control
will improve the health of forests,
particularly red spruce forests that
populate the ridges of mountains,
from Maine to Georgia. It will
provide new safeguards for our
nation's cultural heritage through
protection of historic buildings and
monuments and it will provide an
insurance policy against the poten-
tial threat to public health posed by
acid aerosols.
Surface Waters
Acid rain primarily affects sensi-
tive bodies of waters, that is,
those that rest atop soil with a limited
ability to neutralize acidic
compounds (called "buffering
capacity"). Many lakes and streams
examined 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 especial-
ly sensitive to acidification. Of the
lakes and streams surveyed in the
NSWS, acid rain has been deter-
mined to cause acidity in 75 percent
of the acidic lakes and about 50 per-
cent of the acidic streams.
In some sensitive lakes and
streams, acidification has completely
eradicated fish species, such as the
brook trout, leaving the 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 un-
suitable for the survival of sensitive
fish species.
The soil in Eastern Canada is very
similar to the soil of the Adirondack
Mountains and lakes in that area are
consequently extremely vulnerable
to chronic acidification 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 (about 60 percent) of which
over 90 percent is attributed to acidic
deposition. Over 1,350 of the streams
in the 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 ex-
ample, lakes smaller than 10 acres
"The Mid -Atlantic Coastal Plain encompasses parts of
the Piedmont and coastal plain in New Jersey,
Delaware, Pennsylvania, Maryland, Virginia, and
North Carolina. The Mid- Atlantic Highlands extend
from southeastern New York through most of Pennsyl-
vania and include portions of Maryland, West Virginia,
and Virginia. The Mid- Appalachians include Southern
Virginia, North Carolina, and Georgia.
Printed on Recycled Paper.
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were not included in the NSWS, and
there are from one to four times as
many of these small lakes as there are
larger lakes. In the Adirondacks, the
percent of acidic lakes is sig-
nificantly higher when it includes
smaller lakes (26 percent) 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
kills—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 Mountains, about three
times as many lakes and streams be-
come temporarily acidic during
storms and snowmelt.
Acid rain control will produce sig-
nificant benefits in terms of lowered
surface water acidity. If acidic
deposition levels were to remain con-
stant 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 predict,
however, that the decrease in sulfur
dioxide emissions required by the
acid rain provisions will virtually
eliminate emission-caused acidifica-
tion in that area.
A cid 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 suscep-
tibility 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.
Sulfur dioxide emissions lead to
the formation of sulfate particles
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 sulfur dioxide 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 national
parks, including the Grand
Canyon, Canyonlands, and Bryce
Canyon.
cid Rain is known to contribute
the corrosion of metals and
deterioration of stone and paint in
buildings, statues, and other struc-
tures or 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 cor-
rosive potential of acid rain seriously
depreciates the objects' value to
society. 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.
TTigh levels of sulfur dioxide have
JOLbeen proven to cause or ag-
gravate various types of lung disor-
ders. These lung disorders, which
affect a person's ability to breathe,
have led to both increased mor-
bidity (sickness) and mortality.
Based on these concerns, sulfur
dioxide has historically been regu-
lated under the Clean Air Act.
Additionally, studies at Harvard
University nave suggested a
relationship between acidic sulfate
(a type of acid aerosol) levels and
increased levels of morbidity and
mortality. While EPA continues to
study the problem, sulfur dioxide
emission reductions called for!
under the acid rain provisions
reduce sulfate levels in the atmos-
phere, thereby providing an in-
surance policy against the threat
to public health.
Si l@l@r Luff©
By reducing sulfur dioxide emis-
sions by such a significant
amount, the Clean Air Act promises
to confer numerous benefits on the
nation. Scientists project that the 10-
million-ton decrease in sulfur
dioxide emissions should stop the
worsening acidification of water
bodies and damage to forests and
even allow these processes to be
reversed. In addition, visibility will
be significantly improved due to the
cutbacks, and the lifespan of build-
ing materials and structures of cul-
tural importance should lengthen.
Finally, the reduction in emissions
will provide the additional assurance
that the public's health will not bq|
put at risk.
F©IT uwj©IT@
Wrote too
U.S. EPA Office of Air and
Radiation
Acid Rain Division
(ANR-445)
Washington, DC 20460
If you would like to receive other
fact sheets in this series, call the Acid
Rain Hotline at (617) 641-5377 or the
EPA Public Information Center (PIC)
at 202-260-2080.
Fact sheets are available on the fol-
lowing subjects:
o Allowance System
° Continuous Emission
Monitoring
° Excess Emissions
o Permits
° Proposed Acid Rain Rules
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