Acid Rain
The effects of acid rain are evident in New York's Adirondack Mountains, in Germany's Black Forest
and industrial urban areas around the world. The picture is not a pretty one. It includes stands of dying
trees, lakes uninhabitable by fish and weathered and damaged historic architecture.
Acid rain has not caused such severe problems in Wisconsin as in the places mentioned above.
However, it is still an air pollution issue that generates concern among our residents. Frequently asked
questions are: How bad is the problem in the state? What are the causes? What is being done to protect
Wisconsin's resources?
Kinds of Acid Rain
"Acid rain" is a broad term used to describe several ways that acids fall out of the atmosphere. A more
precise term is acid deposition, which has two parts: wet and dry.
Wet deposition refers to acidic rain, fog, hail, dew and snow. Acidic water affects a variety of plants
and animals as it flows over and through the ground. The strength of the effects depend on many
factors, including how acidic the water is, the chemistry and buffering capacity of the soils involved.
Buffering capacity is the soils ability to resist chemical change. Affects also depends on the types of
fish, trees, and other living things that rely on the water.
Dry deposition refers to acidic gases and particles. About half of the acidity in the atmosphere falls
back to earth through dry deposition. The wind blows these acidic particles and gases onto buildings,
cars, homes and trees. Dry deposited gases and particles can also be washed from trees and other
surfaces by rainstorms. When that happens, the runoff water adds those acids to the acid rain making
the combination more acidic than the falling rain alone.
Prevailing winds blow the compounds that cause both wet and dry acid deposition across state and
national borders, and sometimes over hundreds of miles. Acid rain can affect us here in Baraboo.
What is Acid Rain? Where Does It Come From?
Pure rain is naturally slightly acidic. The slight natural acidity of pure rain is the result of carbon
dioxide in the air dissolving in water to produce a weak carbonic acid solution. This natural acid in
rainfall and snowmelt is partly responsible for the slow weathering of soil and rocks.
Acid rain, however, is the result of sulfur dioxide and nitrogen oxides entering the atmosphere. These
two pollutants are mainly produced by human activities. Sulfur dioxide is most commonly produced by
coal-fired power plants and factories. Scientists have also confirmed that about 2/3 of all sulfur dioxide
(SO2) and 1/4 of all nitrogen oxides (NOx) comes from electric power generation that relies on burning
fossil fuels like coal. Nitrogen oxides are products of motor vehicles and off-road engines, coal-fired
power plants and factories (such as pulp and paper mills in Wisconsin) and home furnaces.
Acid rain is formed when these gases react in the atmosphere with water, oxygen, and other chemicals
to form various acidic compounds. Sunlight increases the rate of most of these reactions. The result is a
mild solution of sulfuric acid (H2SO4) and nitric acid (HNO3). Once these chemicals are released into
the atmosphere they combine with moisture, change chemically, and return to earth in the form of
acidic deposition. Acidic deposition also may occur in a dry form when acidic compounds attach to
particulates (dust) and return to earth. These acids can overwhelm the neutralizing capacity of some
soils and lake water. Simply stated, the environment is sometimes unable to defend itself against the
effects of these acids.
The pH of Acid Rain
Chemists use pH (potential of Hydrogen) to measure the concentration of hydrogen ions in a chemical
solution to determine how acidic or basic the solution is. The pH scale measures how acidic or basic a
substance is. It ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic, and a pH greater
than 7 is basic. Each whole pH value below 7 is ten times more acidic than the next higher value. For
example, a pH of 4 is ten times more acidic than a pH of 5 and 100 times (10 times 10) more acidic
than a pH of 6. The same holds true for pH values above 7, each of which is ten times more basic than
the next lower whole value. For example, a pH of 10 is ten times more basic than a pH of 9.
Chemicals that are very basic or very acidic are called "reactive." These chemicals can cause severe
burns. Automobile battery acid is an acidic chemical that is reactive. Automobile batteries contain a
stronger form of some of the same acid that is in acid rain. Household drain cleaners often contain lye,
a strong base that is reactive.
Acidic and basic
are two extremes
that describe
chemicals just
like hot and cold
are two extremes
that describe
temperature.
Mixing acids and
bases can cancel
out their effects
much like mixing
hot and cold
water can even out the water temperature. When equal strength bases and acids are mixed they
neutralize each other. The resulting solution is water and a salt. Remember, a salt is defined as a metal
combined with a non-metal so chances are that it will not be sodium chloride (table salt). A substance
that is neither acidic nor basic is neutral.
Normal rain is slightly acidic because carbon dioxide dissolves into it so it has a pH of about 5.5. As
the rain (H2O) falls through the atmosphere and combines with the carbon dioxide (CO2) it creates mild
carbonic acid (H2CO3). Wisconsin Department of Natural Resources investigators consider rain with
pH less than 5.0 to be "acid rain." As of the year 2000, the most acidic rain falling in the US has a pH
of about 4.3.
What Do We Know About the Effects of Acid Rain in Wisconsin?
Acid rain has been studied in Wisconsin for more than ten years, and more than $7 million has been
spent to assess the impact of this environmental problem, making the state a leader in research. Below
are some general conclusions regarding the impact of acid deposition in the state.
Forests
Research has determined that while acid rain has been linked to declines in forest health in many
regions of the world, no major forest declines due to these causes have been identified in Wisconsin.
Acid rain can leach nutrients from forest soils making trees vulnerable to other pollutants, climatic
extremes and pest attacks. Research that looks at possible causes of forest decline in Wisconsin is
relatively new. More needs to be done to understand the complex interactions of environmental and
human factors that affect the health of the state's forests.
Aquatic Resources
Many factors affect whether acidification, due to acid rain, occurs in bodies of water. Bodies of water
that are low in acid neutralizing capacity (ANC) are considered especially vulnerable to the effects of
acid rain. Soils in Northern Wisconsin are derived from granite bedrock so they have low acid
neutralizing capacity due to the lack of carbonates. Carbonates are basic so they neutralize the acid.
Parts of Wisconsin that have primarily sandstone and limestone bedrock based soils have a high acid
neutralizing capacity because the limestone bedrock is a carbonate.
A body of water is more likely to become acidic if it does not have any acid neutralizing capacity. That
does not, however, mean that it is already devoid of fish and other aquatic life. As a body of water
becomes more acidic, it loses some of its biodiversity as the more acid-sensitive species of plant and
animal life die off or experience a decrease in reproductive success. The degree of threat from acid rain
depends on the vulnerability of plant and animal species in that body of water to an acidic environment.
According to the DNR's Surface Water Resources Data Base, approximately 2 percent of the state's
lakes are acidic. An additional 10 percent are "extremely sensitive" to acid rain, 25 percent are
"moderately sensitive" and 60 percent are not sensitive. This will remain true only if present patterns of
groundwater flow continue. Surveys done in northern parts of Wisconsin, however, where most of the
state's lakes are located, show that these areas have an even greater incidence of acidic lakes. A survey
done in 1984 by the U.S. Environmental Protection Agency showed that up to 9 percent of lakes in the
northeast and north central region were acidic. On the other hand, Wisconsin's streams are not
considered to be sensitive to the effects of acid rain.
Health Effects
A direct effect of acid deposition on human health results from exposure to acid aerosols inhaled from
the surrounding air. Acid aerosols are mixtures of several different pollutants including particles (large
and small), strong acids (e.g. sulfuric acid), weak acids and vapors (e.g. nitric acid). Long-term
exposure to acid aerosols is known to damage lung tissue and contribute to the development of
respiratory diseases such as asthma and chronic bronchitis, especially in children and the elderly.
Acid deposition also has been connected to elevated mercury concentrations in fish and fish-eating
wildlife such as the common loon, mink, otter, and eagles. Researchers believe that acidification of
bodies of water increases the formation and movement of methylmercury, a toxic form of mercury, into
the aquatic food chain. This also endangers the health of people, especially infants, children, and
fetuses carried by women who eat contaminated fish.
Exposure of humans to mercury may result in damage to the kidneys, brain and central nervous system.
It may also cause developmental defects. Recent research indicates that prenatal exposure to mercury
concentrations much lower than the current "safe" levels established by the World Health Organization
may result in subtle neurological defects in children, such as abnormal reflexes and delayed motor skill
development. Arsenic is another heavy metal that is released by acidic water flowing through the
ground. Arsenic is commonly used as rat poison.
Visibility
Pollutants associated with acid rain interfere with light transmission in the atmosphere resulting in
reduced visibility. A trend analysis was conducted for the years 1950 through 1987, using visibility
observations at two National Weather Service locations in Milwaukee and Green Bay. Results for both
locations showed a decrease in the number of days reporting good visibility and an increase in
moderate visibility reported. The highest frequencies of reduced visibility for both locations in recent
years occurred during the summer, probably due to the chemical processes which result in summertime
"smog" (ozone) and haze. An additional study is currently underway using photographs to see if
changes in visual range are taking place.
Materials damage
Although no materials research has been done in Wisconsin, research done elsewhere indicates that the
pH levels of rain in the state have been low enough to cause damage to building materials such as paint,
stone, mortar and metals. An example of this is when marble changes to gypsum when exposed to acid
rain. The gypsum molecule is much larger and softer than the original marble molecule resulting in
weakened building stones and flaking of building materials. In addition to damaging building materials,
acid rain can also cause increased weathering of historic structures and outdoor art objects, such as the
Bradley Sculpture Garden in Milwaukee.
What legislative action has been taken?
Wisconsin passed one of the first and strongest state acid rain control laws in the nation in 1986,
making the state a leader in acid rain policy. The law required Wisconsin's major electric utility
companies to reduce their sulfur dioxide emissions by 50 percent from 1980 emission levels by 1993.
By 1990, overall annual sulfur dioxide emissions from electric utility companies had fallen 46 percent.
In 1992, these companies filed compliance plans indicating that they would easily meet the
requirements of the law.
Meanwhile, Congress passed the Clean Air Act Amendments of 1990. They also contained strong acid
rain control measures. The federal law required electric utility companies nationwide to reduce their
collective sulfur dioxide emissions by 10 million tons per year from 1980 emission levels by the year
2000. This represented a 40 percent reduction in nationwide sulfur dioxide emissions. Utility sulfur
dioxide emissions were capped at about nine million tons per year in the year 2000 and thereafter. The
law also resulted in a reduction in nitrogen oxide emissions of about two million tons per year.
These measures--especially the state law--are credited with a reduction in emissions that has been
associated with a noticeable decrease in the acidity of rainfall in the state. The most recent analysis of
wet acid precipitation data (1990) indicated that the annual average pH in Wisconsin ranged from 4.59
in the southeast to 5.06 in the northwest. In contrast, the annual average pH in the early 1980s ranged
from 4.4 in southeastern Wisconsin to 4.8 in the northwestern part of the state. The goal established in
the state law is to raise the pH of the state's rain to 4.7 or greater across the state.
What Can You Do to Help?
Because a substantial amount of the acid rain that falls in Wisconsin results from pollution sources
within the state, there are a number of things Wisconsin residents can do to combat the acid rain
problem. Using electrical energy wisely could have a significant impact because a lot of the emissions
that contribute to acid rain originate from coal-burning electric power plants. You can reduce electrical
energy use in a number of ways:
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Insulate your home so it is more energy efficient during the winter and the summer.
Replace your heating system if it is over 25 years old.
Keep the thermostat down in the winter.
Open windows and use fans instead of the air conditioner during the summer.
Use energy-efficient compact fluorescent bulbs instead of incandescent ones and turn off lights
when not in use.
Purchase energy efficient appliances, especially those that use large amounts of electricity such as
hot water heaters, ranges, dryers and refrigerators.
Turn off electric appliances, such as computers, when you aren't using them and make sure that
they run as efficiently as possible.
Driving a fuel-efficient vehicle and driving less overall both help because motor vehicle exhaust is a
significant source of nitrogen oxide emissions.
With a combination of education and action, Wisconsin residents can continue to reduce acid rain and
help preserve the natural beauty of the state for generations to come.
Secondary Pollutants
Another form of air pollution is formed when smoke and fog are combined to make smog. The two
common types of smog are photochemical smog and sulfurous smog. Secondary pollutants are
damaging to humans and plant life. Large cities often have hazy blankets of smog covering them.
Some cities have “smog alert” days where they recommend being outside for only very short periods of
time. Mexico City, Milwaukee, Denver, Los Angeles, New York and Phoenix all have smog alert days.
What we typically call smog is primarily made up of ground-level ozone (O3) mixed with other
chemicals. Ground-level ozone is the main harmful ingredient in smog. Ozone causes breathing
difficulties, headaches, fatigue and can aggravate respiratory problems.
Photochemical smog forms when sunlight reacts with nitrogen and oxygen in the air. Burning fossil
fuels, such as, oil, natural gas and gasoline in automobiles, factories and airplanes release nitrogen and
oxygen into the air. The nitrogen and oxygen reacts with the sunlight to chemically combine forming
NOx which creates a brown haze in the air. The NOx can attach to water molecules to form mild nitric
acid (HNO3) that slowly erodes buildings and other structures.
Catalytic converters in automobiles reduce air pollution by oxidizing hydrocarbons to CO2 and H2O.
They also convert nitrogen oxides to N2 and O2 to prevent the formation of smog.
Sulfurous smog forms when sunlight reacts with sulfur and oxygen in the air forming sulfur
compounds (SOx). Burning coal to generate electricity releases sulfur compounds, dust and smoke
particles into the air forming a gray haze in the air. When the air is stagnant, not moving, over an area
the sulfurous smog develops. Mixing sulfurous smog with water molecules creates a weak sulfuric
acid (H2SO4) that eats away at buildings and other structures.
Write all answers in your notebook.
Acid Rain Questions
Use the words to fill in the blanks. Write the correct answers in your notebook.
acidic
basic
cars
nitrogen gases
factories
wind
soil
sulfur
Midwest
The amount of acid rain in an area depends on the number of __1__ and __2__ in the area. This is because they
are the sources of __3__ and __4__ that become acid rain. Does acid rain fall where the pollution starts? It
depends on the __5__, which sometimes carries the pollution away.
When acid rain does fall, the damage it does depends partly on the kind of __6__ in the area. Some soils are
already __7__, and plants that grow in them can't survive when more acid is added. Other soils are __8__, and
the damage is less when acid rain falls on these. As a rule, soils in the __9__ are basic and soils in the
northeastern states are acidic.
Use the words to fill in the blanks. Write the correct answers in your notebook.
sulfur
car exhaust
cost
coal-burning
public transportation
scrubber
jobs
car pooling
coal
Acid rain is created when moisture in the air combines with nitrogen oxide to form nitric acid.
Do you know what the main source of nitrogen oxide is? It comes from __10__. Two ways people can help to
reduce nitric acid are by __11__ and using __12__.
Another source of acid rain comes from __13__ power plants that release __14__ into the air. Power plants can
help this situation in two ways. They can wash the __15__, and they can run the smoke through
a __16__.
Why don't people insist that the power plants make their exhaust cleaner? Because the __17__ of electricity
would increase and because many people could lose their __18__.
Fill in the blank:
Use the reading to find the term(s) to complete the sentences. Write the correct answers in your notebook.
"Acid rain" is a broad term used to describe several ways that acids fall out of the atmosphere. A more precise
term is __19__, which has two parts: __20__ and __21__.
Wet deposition refers to acidic rain, fog, __22__, dew and __23__.
Acid rain, however, is the result of __24__ and __25__ entering the atmosphere.
Scientists have also confirmed that about 2/3 of all __26__ (SO2) and 1/4 of all __27__ (NOx) comes from
__28__ power generation that relies on burning fossil fuels like coal.
Acid rain is formed when these gases react in the atmosphere with __29__, oxygen, and other chemicals to form
various acidic compounds. __30__ increases the rate of most of these reactions. The result is a mild solution of
__31__ (H2SO4) and __32__ (HNO3).
Normal rain is slightly __33__ because carbon dioxide dissolves into it, so it has a pH of about __34__.
Wisconsin Department of Natural Resources investigators consider rain with pH less than __35__ to be "acid
rain." As of the year 2000, the most acidic rain falling in the US has a pH of about __36__.
A substance that is neither acidic nor basic is __37__.
The pH scale measures how __38__ or __39__ a substance is. It ranges from __40__ to __41__. A pH of
__42__ is neutral. A pH less than 7 is __43__, and a pH greater than 7 is __44__
Wisconsin passed one of the first and strongest state acid rain control laws in the nation in __45__, making the
state a leader in acid rain policy. The law required Wisconsin's major electric utility companies to reduce their
sulfur dioxide emissions by __46__ percent from 1980 emission levels by 1993.
The most recent analysis of wet acid precipitation data (1990) indicates that the annual average pH in Wisconsin
ranged from __47__ in the southeast to __48__ in the northwest. In contrast, the annual average pH in the early
1980s ranged from __49__ in southeastern Wisconsin to __50__ in the northwestern part of the state. The goal
established in the state law is to raise the pH of the state's rain to __51__ or greater across the state.
Short Answer:
Answer these questions in your notebook
52. What is acid rain?
53. Why should Baraboo be concerned about acid rain when we have so little air pollution?
54. How can acid rain have a negative impact on tourism and fishing in Wisconsin?
55. Why is acid rain considered to be an international problem?