Acid Rain Experiments
Experiment 1: Measuring pH
This experiment will illustrate how to measure the approximate pH of chemicals in water using a pH indicator. A pH
indicator is a chemical that changes color when it comes in contact with acids or bases.
Materials
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pH paper and color chart (pH range 3 to 12) or garden soil pH testing kit
distilled water (available at grocery stores and drug stores)
white vinegar
household ammonia (or baking soda)
3 small, clear cups or glasses
3 stirring spoons
measuring cups and spoons (1/2 cup, 1/4 and 1 teaspoon)
notebook and pencil
Instructions
1. Rinse each cup with distilled water, shake out excess water, and label one cup vinegar, the second cup
ammonia, and the third cup water.
2. Pour 1/2 cup distilled water into each of the 3 cups.
3. Add 1/2 teaspoon white vinegar to the vinegar cup and stir with a clean spoon.
4. Add 1/2 teaspoon ammonia to the ammonia cup and stir with a clean spoon.
5. Do not add anything to the water cup.
6. Dip an unused, clean strip of pH paper in the vinegar cup for about 2 seconds and immediately compare with
the color chart. Write down the approximate pH value and set the cup aside. (If using a garden soil pH tester
kit, pour 1/4 teaspoon of the contents of the vinegar cup into the test container, and add 1/4 teaspoon of the
test solution. Cover the test tube and shake once or twice to mix, or stir if necessary. Compare with the color
chart provided in the kit, and record the result.)
7. Dip an unused, clean strip of pH paper in the ammonia cup for about 2 seconds and immediately compare with
the color chart. Write down the approximate pH value and set the cup aside. (If using a garden soil pH tester
kit, repeat the same process in step 6 using the contents of the ammonia cup instead of the vinegar cup.)
8. Dip an unused, clean strip of pH paper into the water cup for about 2 seconds and immediately compare with
the color chart. Write down the approximate pH value. (If using a garden soil pH tester kit, repeat the same
process above using the contents of the water cup instead of the ammonia cup.)
Questions and Answers
Is vinegar an acid or a base?
Vinegar is an acid, and in this experiment it will display a pH of about 4. Vinegar at pH 4 turns pH paper yellow and
most other pH indicators red.
Is ammonia an acid or a base?
Ammonia is a base and in this experiment it will display a pH of about 12. Bases turn most pH indicators blue.
Were you surprised to find that the distilled water did not have a neutral pH?
PURE distilled water would have tested neutral, but pure distilled water is not easily obtained because carbon dioxide
in the air around us mixes, or dissolves, in the water, making it somewhat acidic. The pH of distilled water is between
5.6 and 7. To neutralize distilled water, add about 1/8 teaspoon baking soda, or a drop of ammonia, stir well, and
check the pH of the water with a pH indicator. If the water is still acidic, repeat the process until pH 7 is reached.
Should you accidentally add too much baking soda or ammonia, either start over or add a drop or two of vinegar, stir,
and recheck the pH.
Acid Rain Experiments
Experiment 2: Determining the pH of Common Substances
In this experiment you will use a pH indicator to measure the pH of some fruits, common beverages, and borax. Borax
is a cleaning agent that some people add to their laundry detergent. It is available at grocery stores. Many foods and
household cleaners are either acids or bases. Acids usually taste sour, and bases bitter. Household cleaners are
poisons so you should never taste them.
Materials
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pH paper and color chart (range pH 2 to 12) or garden soil pH testing kit
3 fresh whole fruits (lemon, lime, orange, or melon)
3 beverages (cola, carbonated non-cola, milk)
1/8 teaspoon borax
measuring spoons (1/4 and 1/8 teaspoons)
4 small, clear cups or glasses
1 clean stirring spoon
notebook and pencil
paring knife
Instructions
1. Cut each fruit in half, drying off the knife after each cut.
2. Place an unused strip of pH paper half-on and half-off the inside of the cut fruit. Leave until wet (about 2
seconds). Immediately compare with the color chart. Write down the approximate pH value of the fruit. (If using
a garden soil pH tester kit, squeeze 1/4 teaspoon of juice from the cut fruit into the test container, and add 1/4
teaspoon of the test solution. Cover the test container and shake once or twice to mix, or stir if necessary.
Compare with the color chart provided in the kit, and record the result.)
3. Repeat the same process for the other 2 fruits.
4. Label the 3 cups: one cola, another non-cola, and the third milk.
5. Pour each liquid into an appropriately labeled cup.
6. Dip an unused strip of pH paper into the cola, compare with the color chart, and record the result. Repeat the
same process for the remaining beverages. Be sure to use a clean, unused strip of pH paper for each one. (If
using a garden soil pH tester kit, pour 1/4 teaspoon of cola into the test container, and add 1/4 teaspoon of the
test solution. Tightly press your finger over the top of the test container and shake once or twice to mix, or stir
if necessary. Compare with the color chart provided in the kit, and record the result.)
7. Add 1/8 teaspoon borax to 1/4 cup distilled water and stir for about 2 minutes. Dip an unused strip of pH paper
in the borax mixture, compare with the color chart, and record the result. (If using a garden soil pH tester kit,
pour 1/4 teaspoon of the borax/water mixture into the test container, and add 1/4 teaspoon of the test solution.
Tightly press your finger over the top of the test container and gently shake, or stir if necessary. Compare with
the color chart provided in the kit and record the result.)
Questions and Answers
Are lemons, limes and oranges acids or bases?
These fruits all contain acids and taste sour. Lemons and limes have pH values near 2. Oranges may be slightly less
acidic than lemons and limes, but your pH indicator may not be accurate enough to show the difference.
Are colas and non-colas acids or bases?
They are both acidic, primarily becasue they both contain carbon dioxide to make them fizz, and carbon dioxide and
water produce carbonic acid. The pH of these beverages varies with the amount of carbon dioxide and other
ingredients in them, but it is usually below 4.
Was the milk acidic or basic?
Milk can be slightly basic or slightly acidic depending on its age and how it was processed at the dairy.
Was the borax/water mixture acidic or basic?
Borax contains a strong base and will turn most pH indicators blue. The approximate pH of the borax/water mixture is
9. Its alkaline properties make it an excellent cleaning agent, which is why some people use it to wash clothes.
Acid Rain Experiments
Experiment 3: Making a Natural pH Indicator
In this experiment you will make your own pH indicator from red cabbage. Red cabbage contains a chemical that turns
from its natural deep purple color to red in acids and blue in bases. Litmus paper, another natural pH indicator, also
turns red in acids and blue in bases. The red cabbage pH indicator can be obtained by boiling the cabbage.
Materials
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sliced red cabbage
stainless steel or enamel pan or microwave casserole dish
1 quart water
stove, microwave, or hotplate
white vinegar
ammonia or baking soda
clear, non-cola beverage
3 glass cups (preferably clear)
measuring spoons
3 clean teaspoons for stirring
measuring cup (1/4 cup)
notebook and pencil
Instructions
1.
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Boil cabbage in a covered pan for 30 minutes or microwave for 10 minutes. (Don't let water boil away.)
Let cool before removing the cabbage.
Pour about 1/4 cup of cabbage juice into each cup.
Add 1/2 teaspoon ammonia or baking soda to one cup and stir with a clean spoon.
Add 1/2 teaspoon vinegar to second cup, stir with a clean spoon.
Add about 1 teaspoon clear non-cola to the last cup and stir with a clean spoon.
After answering the first two questions for this experiment, pour the contents of the vinegar cup into the
ammonia cup.
Related Experiment: Neutralizing Acids or Bases Using a Garden Soil pH Tester Kit
Pour 1/4 teaspoon of the contents of the vinegar cup into the test container, and add 1/4 teaspoon of the test solution.
Seal the top of the test container with your finger, shake once or twice, or stir if necessary, and compare with the color
chart. Then pour about 1/4 teaspoon of the contents of the ammonia cup into the test container. Mix it and compare
with the color chart. What happens to the pH ? What would happen if you added more of the ammonia mixture? (For
answers: see questions 3 and 4.)
Questions and Answers
What color change took place when you added vinegar to the cabbage juice? Why?
The vinegar and cabbage juice mixture should change from deep purple to red, indicating that vinegar is an acid.
Did the ammonia turn the cabbage juice pH indicator red or blue? Why?
The ammonia and cabbage juice mixture should change from deep purple to blue, because ammonia, like baking
soda, is a base, which reacts chemically with the pH indicator, turning it blue.
What happens to the color if you pour the contents of the vinegar cup into the ammonia cup?
You should find that the acid and base are neutralized, changing the color from blue or red to purple, which is the
original, neutral color of the cabbage juice
If you were to gradually add vinegar to the cup containing the baking soda (or ammonia) and cabbage juice,
what do you think would happen to the color of the indicator? Try it, stirring constantly.
As you add more vinegar, the acid level increases and the color becomes red.
Is the non-cola soft drink acidic or basic?
It is acidic and turns the cabbage juice pH indicator red.
Acid Rain Experiments
Experiment 4: Measuring the pH of Natural Water
In this experiment, you will measure the pH of natural water located near your home or school.
Materials
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pH paper and color chart (range pH 2 to 7) or garden soil pH testing kit
clean paper cups
notebook and pencil
Instructions
1. Locate a stream, river, lake, or pond. Go with an adult.
2. Scoop some of the surface water into a cup.
3. Measure the pH of the water using either pH paper or a garden soil pH testing kit and record the result.
Questions and Answers
How acidic is the water?
Based on where you live and what you have learned about acid rain, are you surprised by the result? Discuss the
findings with your parents or teacher.
How does the measured pH compare to the pH levels that affect plants and animals in aquatic habitats?
See the chart explaining how acid rain affects animals living in the water.
Acid Rain Experiments
Experiment 5: Measuring Soil pH
In this experiment you will collect soil and measure its pH. Soil pH is one of several important conditions that affect the
health of plants and animals. In addition, you will also be asked to survey the plants and animals that live in the area
where you collected the soil. Area surveys provide information about how well plants and animals can live under
different conditions.
For this experiment, you will need an inexpensive garden soil pH test kit, which may be obtained from lawn and garden
stores or nurseries.
Materials
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garden soil pH test kit
distilled water
2 cups soil from each of two or three different locations (some of the soil will be needed for the "Soil Buffering"
experiment)
measuring spoons
digging tool
self-sealing plastic bags
notebook and pencil
Instructions
1. Pick two or three different soil locations, such as a garden, wooded area, city park, or meadow. Ask an adult to
go with you.
2. At each location, observe the plants and animals living in or rooted on these soils, especially those that are in
greatest numbers. Write down as much as you can about what you find. Dig down about 2 inches, scoop out 2
cups of soil, and seal it in a plastic bag for later use. Label each plastic bag. Be sure to clean your digging tool
after collecting soil samples at each location.
3. Measure the pH of each soil sample following the directions provided in the garden soil pH test kit, and record
the approximate pH of each soil sample. Save the excess soil from each site for use in the "Soil Buffering"
experiment.
Questions and Answers
Were there any big differences between the plant and animal life at each location?
Some types of plants and animals are able to live in acid soils, while others are not. Be aware, however, that many
factors, not just the soil acidity, determine the types of plants and animals that occur at a particular site.
Were any of your soil samples acidic?
Some plants require acid soils to grow and thrive. For example, pine trees, azaleas, rhododendrons, cranberries,
blueberries, potatoes, and tomatoes prefer acid soils. However, most plants thrive only in soils of pH 6 to 7.
Were any of your soil samples basic?
Some soils, such as in many midwestern United States, contain a lot of limestone and are alkaline. In those locations,
people often add sulfate, such as ammonium bisulfate to soil to make it less basic.
Acid Rain Experiments
Experiment 6: Soil Buffering
Soil sometimes contains substances, like limestone, that buffer acids or bases. Some salts in soil may also act as
buffers. In this experiment you will find out if soil from your lawn, garden, or school can buffer acids. You will observe
the pH change of an acid mixture poured over soil in a filter. If the water collected from the filter is less acidic than the
original mixture, then the soil is buffering some of the acid. If it does not change, then the soil may not be capable of
buffering acids. Since the buffering capability of soils differs, you may want to do this experiment with several different
soil types including those collected for the "Soil pH" experiment.
Materials
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pH paper and color chart (pH range 2 to 10) or garden soil pH test kit
about 2 cups of soil from a garden, wooded area, lawn, or school yard
distilled water
white vinegar
measuring cups and spoons
stirring spoon
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large funnel
3 coffee filters
paper cup
notebook and pencil
Instructions
1. Pour 1 teaspoon of vinegar into 2 cups of distilled water, stir well, and check the pH with either pH paper or a
garden soil pH testing kit. The pH of the vinegar/water mixture should be about 4. If it is below that, add a
sprinkle of baking soda, stir well, and recheck the pH; but if it is above pH 4, add a drop or two of vinegar and
again recheck the pH.
2. Put 1 coffee filter into the funnel, and fill the filter with soil from one location. Do not pack the soil down.
3. Hold the filter over a paper cup and slowly pour the vinegar/water mixture over the soil until some water
collects in the paper cup (the filter may clog quickly, but you need only a small amount of water).
4. Check the pH of the collected water using either pH paper or a garden soil pH testing kit and record the
results.
5. Repeat the experiment with other soil samples, using a new coffee filter for each sample.
Questions and Answers
Did the pH of the collected water stay the same as the original mixture, increase, or decrease?
If the pH stayed the same, the soil did not buffer the acid. Each pH value above 4 indicates that the soil buffered
increasing amounts of the acid. Even soil capable of buffering acids can be overpowered if enough acid is added. As
more acid is added to the soil, the buffering capability decreases, and the water from the filter becomes more acidic.
What can you add to the soil to increase its buffering capability?
Limestone can be added, but it takes weeks to months for the limestone to work into the soil.
Acid Rain Experiments
Experiment 7: Observing the Influence of Acid Rain on Plant Growth
Acid rain most often damages plants by washing away nutrients and by poisoning the plants with toxic metals. It can,
however, have direct effects on plants as well. In this experiment you will observe one of the direct effects of acid
water on plant growth. The experiment will take about 2 weeks.
Materials
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4 cups or jars
distilled water
white vinegar
measuring cups
stirring spoon
2 cuttings of a philodendron plant (1 leaf and small amount of stem)
2 cuttings of a begonia or coleus plant (1 leaf and small amount of stem)
notebook and pencil
Instructions
1. Pour 1 teaspoon of vinegar into 2 cups of distilled water, stir well, and check the pH with either pH paper or a
garden soil pH testing kit. The pH of the vinegar/water mixture should be about 4. If it is below pH 4, add a
sprinkle of baking soda, or a drop of ammonia, stir well, and recheck the pH. If it is above pH 4, add a drop or
two of vinegar and again recheck the pH.
2. Measure the pH of the distilled water using either pH paper or a garden soil pH testing kit. If the pH is below 7,
add about 1/8 teaspoon baking soda, or a drop of ammonia, stir well, and check the pH of the water with the
pH indicator. If the water is still acidic, repeat the process until pH 7 is reached. Should you accidentally add
too much baking soda or ammonia, either start over again or add a drop or two of vinegar, stir, and recheck
the pH.
3. Put one of the following labels on each cup or jar:
-- water philodendron
-- acid philodendron
-- water begonia (or coleus)
-- acid begonia (or coleus)
4. Pour about a cup of distilled water into the water-philodendron and water-begonia cups.
5. Pour about a cup of the vinegar/water mixture into the acid-philodendron and acid-begonia cups.
6. Put one philodendron cutting into each philodendron labeled cup, covering the stem and part of the leaf with
the liquid.
7. Put one begonia cutting into each begonia-labeled cup, covering the stem and part of the leaf with the liquid.
8. Set the cups where they are not likely to be spilled and where they will receive some daylight.
9. About every 2 days, check to be sure that the plant cuttings are still in the water or vinegar/water. You may
need to add more liquid if the cups become dry.
10. After 1 week, compare the new root growth of each plant in distilled water with the new root growth of its
corresponding plant in acid water. Record the results.
11. After 2 weeks, again observe the plant cuttings for new root growth, and record the results.
Questions and Answers
Which plant cuttings had the fastest root growth, those in distilled water or those in acid water?
The plants grown in distilled water should grow faster than plants grown in acid water. Acid water, like acid rain, can
directly damage plants and slow or stop new growth.
Acid Rain Experiments
Experiment 8: Observing Buffers in Lakes, Ponds, and Streams
In this experiment you will observe the effects of limestone on the acidity of water. Some areas of the nation have a lot
of limestone in lake bottoms and in soil, which helps neutralize the effects of acid rain. Crushed limestone is
sometimes added to lakes, ponds, and other aquatic areas to help neutralize the effects of acid rain, thus preserving
important aquatic systems until the source of acid rain can be reduced. Crushed limestone is easily obtained from local
lawn and garden stores or nurseries.
Materials
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pH paper and color chart (pH range 2 to 7) or garden soil pH testing kit
white vinegar
distilled water
measuring cup and spoon
2 stirring spoons
1/2 cup crushed hydrated limestone or spray limestone
2 cereal bowls (about 2 cup size)
plastic wrap
notebook and pencil
Instructions
1. Label one bowl vinegar; the other one vinegar plus limestone.
2. Pour 1/4 cup crushed limestone into one bowl.
3. Pour 1 teaspoon of vinegar into 2 cups of distilled water, stir well, and check the pH with either pH paper or a
garden soil pH testing kit. The pH of the vinegar/water mixture should be about 4. If it is below pH 4, add a
4.
5.
6.
7.
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sprinkle of baking soda, stir well, and recheck the pH; but if it is above pH 4, add a drop or two of vinegar and
again recheck the pH.
Pour about 1 cup of the vinegar/water mixture over the limestone in the cereal bowl and stir with a clean, dry
spoon.
Pour the remaining vinegar/water mixture into the other cereal bowl.
Check the pH of the vinegar/water mixture over the limestone and record it.
Cover each bowl with plastic wrap to prevent evaporation.
Every day for 6 days, stir the contents of each bowl with a clean, dry spoon and about 4 or more hours later
(after the limestone has settled), test the pH of the water mixture in each bowl and record the result.
Questions and Answers
Did the pH of the vinegar/water mixture over the limestone become more or less acidic during the 6-day
period? Why?
The water mixture should have become less acidic, changing from about pH 4 to as much as pH 6, depending on the
water content of the limestone you used.
Does crushed limestone buffer the acid?
Yes, by neutralizing it.
Did the pH of the vinegar/water mixture in the other bowl (without limestone) change during the 6-day period?
The pH of the bowl without limestone should not have changed.
Acid Rain Experiments
Experiment 9: Looking at Acid's Effects on Metals
When acids and metals come in contact with each other, the metal is gradually dissolved away in a chemical reaction.
In this experiment you will observe this reaction for yourself, but you will need patience. The chemical effect of acids
on metals may take at least five days for the human eye to see, even though the reaction starts as soon as the acid
contacts the metal.
Materials
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pH paper and color chart (pH range 2 to 7) or garden soil pH testing kit
2 small, clear glasses (nonmetal)
2 clean copper pennies (use pennies minted before 1983)
white vinegar or fresh-squeezed lemon juice
distilled water
plastic wrap
notebook and pencil
Instructions
1. Label one glass water and the other vinegar or lemon juice depending on which acid you use.
2. Place one penny in each glass. Be sure to use pennies minted before 1983 because pennies minted after that
time have a different chemical composition.
3. Barely cover one of the pennies with either vinegar or lemon juice.
4. Dip a strip of pH paper into the vinegar, or lemon juice, for about 2 seconds, compare with the color chart, and
record the result. Or use a garden soil pH test kit.
5. Add enough distilled water to the glass labeled water to barely cover the other penny.
6. Dip a strip of pH paper into the distilled water for about 2 seconds and compare with the color chart. Or use a
garden soil pH test kit. If the pH is below 6, add a tiny amount (less than 1/8 teaspoon) of baking soda, or a
7.
8.
9.
10.
drop of ammonia, and recheck the pH. Repeat this process until the pH is between 6 and 7. Record the pH of
the water.
Seal the top of each glass with plastic wrap to prevent evaporation.
Place in a safe, dry place for about 5 days.
After about 5 days, observe the changes that occurred in each glass.
At the end of the experiment, wash off the pennies with water, and pour the contents of the glasses down the
sink (do not drink).
Questions and Answers
What change, if any, took place in the water glass after 5 days?
There should be no change
What change, if any, took place in the vinegar (or lemon juice) glass after 5 days?
The liquid should be bluish-green. The bluish-green substance in the vinegar, or lemon juice, comes from the copper in
the penny. It is a byproduct of the chemical reaction in which the acid in the vinegar, or lemon juice, very gradually eats
away the penny.
When you rinsed off the pennies, were you surprised that they both looked about the same as they did at the
beginning of the experiment (assuming you used clean pennies)?
The chemical reaction between the acid and the copper penny is so slow that you cannot see any difference in the
shape of the metal in just 5 days, at least not with your eye alone. You may see some changes after about two weeks,
especially at the edge of the penny.
Effects of Acid Rain: Lakes & Streams
The ecological effects of acid rain are most clearly seen in the aquatic, or water, environments, such as streams,
lakes, and marshes. Acid rain flows to streams, lakes, and marshes after falling on forests, fields, buildings, and roads.
Acid rain also falls directly on aquatic habitats. Most lakes and streams have a pH between 6 and 8, although some
lakes are naturally acidic even without the effects of acid rain. Acid rain primarily affects sensitive bodies of water,
which are located in watersheds whose soils have a limited ability to neutralize acidic compounds (called "buffering
capacity"). Lakes and streams become acidic (pH value goes down) when the water itself and its surrounding soil
cannot buffer the acid rain enough to neutralize it. In areas where buffering capacity is low, acid rain also releases
aluminum from soils into lakes and streams; aluminum is highly toxic to many species of aquatic organisms.
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Where Does Acid Rain Affect Lakes and Streams?
How Does Acid Rain Affect Fish and Other Aquatic Organisms?
How Does Acid Rain Affect Ecosystems?
What is the Role of Nitrogen in Acid Rain and other Environmental Problems?
How is the Acid Rain Program Addressing These Issues?
Where Does Acid Rain Affect Lakes and Streams?
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 survey investigated the effects of acidic deposition in over 1,000 lakes
larger than 10 acres and in thousands of miles of streams believed to be sensitive to acidification. Of the lakes and
streams surveyed, acid rain caused acidity in 75 percent of the acidic lakes and about 50 percent of the acidic
streams. Several regions in the U.S. were identified as containing many of the surface waters sensitive to acidification.
They include the Adirondacks and Catskill Mountains in New York state, the mid-Appalachian highlands along the east
coast, the upper Midwest, and mountainous areas of the Western United States. In areas like the Northeastern United
States, where soil buffering capacity is poor, some lakes now have a pH value of less than 5. One of the most acidic
lakes reported is Little Echo Pond in Franklin, New York. Little Echo Pond has a pH of 4.2.
Acidification is also a problem in lakes that were not surveyed in federal research projects. For example, 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 Adirondacks, the percentage of acidic lakes is significantly higher when it
includes smaller lakes.
Streams flowing over soil with low buffering capacity are as susceptible to damage from acid rain as lakes.
Approximately 580 of the streams in the Mid-Atlantic Coastal Plain are acidic primarily due to acidic deposition. In the
New Jersey Pine Barrens, for example, over 90 percent of the streams are acidic, which is the highest rate of acidic
streams in the nation. Over 1,350 of the streams in the Mid-Atlantic Highlands (mid-Appalachia) are acidic, primarily
due to acidic deposition.
The acidification problem in both the United States and Canada grows in magnitude if "episodic acidification" is taken
into account. Episodic acidification refers to brief periods during which pH levels decrease due to runoff from melting
snow or heavy downpours. Lakes and streams in many areas throughout the United States are sensitive to episodic
acidification. In the Mid-Appalachians, the Mid-Atlantic Coastal Plain, and the Adirondack Mountains, many additional
lakes and streams become temporarily acidic during storms and spring snowmelt. For example, approximately 70
percent of sensitive lakes in the Adirondacks are at risk of episodic acidification. This amount is over three times the
amount of chronically acidic lakes. In the mid-Appalachians, approximately 30 percent of sensitive streams are likely to
become acidic during an episode. This level is seven times the number of chronically acidic streams in that area.
Episodic acidification can cause "fish kills."
Emissions from U.S. sources also contribute to acidic deposition in eastern Canada, where the soil is very similar to
the soil of the Adirondack Mountains, and the lakes are consequently extremely vulnerable to chronic acidification
problems. The Canadian government has estimated that 14,000 lakes in eastern Canada are acidic.
How Does Acid Rain Affect Fish and Other Aquatic Organisms?
Acid rain causes a cascade of effects that harm or kill individual fish, reduce fish population numbers, completely
eliminate fish species from a waterbody, and decrease biodiversity. As acid rain flows through soils in a watershed,
aluminum is released from soils into the lakes and streams located in that watershed. So, as pH in a lake or stream
decreases, aluminum levels increase. Both low pH and increased aluminum levels are directly toxic to fish. In addition,
low pH and increased aluminum levels cause chronic stress that may not kill individual fish, but leads to lower body
weight and smaller size and makes fish less able to compete for food and habitat.
Some types of plants and animals are able to tolerate acidic waters. Others, however, are acid-sensitive and will be
lost as the pH declines. Generally, the young of most species are more sensitive to environmental conditions than
adults. At pH 5, most fish eggs cannot hatch. At lower pH levels, some adult fish die. Some acid lakes have no fish.
The chart below shows that not all fish, shellfish, or the insects that they eat can tolerate the same amount of acid; for
example, frogs can tolerate water that is more acidic (has lower pH) than trout.
How Does Acid Rain Affect Ecosystems?
Together, biological organisms and the environment in which they live are called an ecosystem. The plants and
animals living within an ecosystem are highly interdependent. For example, frogs may tolerate relatively high levels of
acidity, but if they eat insects like the mayfly, they may be affected because part of their food supply may disappear.
Because of the connections between the many fish, plants, and other organisms living in an aquatic ecosystem,
changes in pH or aluminum levels affect biodiversity as well. Thus, as lakes and streams become more acidic, the
numbers and types of fish and other aquatic plants and animals that live in these waters decrease.
What is the Role of Nitrogen in Acid Rain and other Environmental Problems?
The impact of nitrogen on surface waters is also critical. Nitrogen plays a significant role in episodic acidification and
new research recognizes the importance of nitrogen in long-term chronic acidification as well. Furthermore, the
adverse impact of atmospheric nitrogen deposition on estuaries and near-coastal water bodies is significant. Scientists
estimate that from 10-45 percent of the nitrogen produced by various human activities that reaches estuaries and
coastal ecosystems is transported and deposited via the atmosphere. For example, about 30 percent of the nitrogen in
the Chesapeake Bay comes from atmospheric deposition. Nitrogen is an important factor in causing eutrophication
(oxygen depletion) of water bodies. The symptoms of eutrophication include blooms of algae (both toxic and nontoxic), declines in the health of fish and shellfish, loss of seagrass beds and coral reefs, and ecological changes in food
webs. According to the National Oceanic and Atmospheric Administration, these conditions are common in many of
our nation's coastal ecosystems. These ecological changes impact human populations by changing the availability of
seafood and creating a risk of consuming contaminated fish or shellfish, reducing our ability to use and enjoy our
coastal ecosystems, and causing economic impact on people who rely on healthy coastal ecosystems, such as
fishermen and those who cater to tourists.
How is the Acid Rain Program Addressing These Issues?
Acid rain control will produce significant benefits in terms of lowered surface water acidity. If acidic deposition levels
were to remain constant over the next 50 years (the time frame used for projection models), the acidification rate of
lakes in the Adirondack Mountains that are larger than 10 acres would rise by 50 percent or more. Scientists predict,
however, that the decrease in SO2 emissions required by the Acid Rain Program will significantly reduce acidification
due to atmospheric sulfur. Without the reductions in SO2 emissions, the proportions of acidic aquatic ecosystems
would remain high or dramatically worsen.
Effects of Acid Rain: Forests
Over the years, scientists, foresters, and others have watched some forests grow more slowly without knowing why.
The trees in these forests do not grow as quickly at a healthy pace. Leaves and needles turn brown and fall off when
they should be green and healthy. In extreme cases, individual trees or entire areas of the forest simply die off without
an obvious reason.
Researchers now know that acid rain causes slower growth, injury, or death of forests. Acid rain has been implicated in
forest and soil degradation in many areas of the eastern United States, particularly high elevation forests of the
Appalachian Mountains from Maine to Georgia that include areas such as the Shenandoah and Great Smoky
Mountain National Parks. Of course, acid rain is not the only cause of such conditions. Other things that add stress,
such as air pollutants, insects, disease, drought, or very cold weather also harm trees and plants. In most cases, in
fact, the impacts of acid rain on trees occur due to the combined effects of acid rain and these other environmental
stressors. After many years of collecting information on the chemistry and biology of forests, researchers are beginning
to understand how acid rain works on the forest soil, trees, and other plants.
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Acid Rain on the Forest Floor
How Acid Rain Harms Trees
How Acid Rain Affects Other Plants
Acid Rain on the Forest Floor
A spring shower in the forest washes leaves and falls through the trees to the forest floor below. Some trickles over the
ground and runs into a stream, river, or lake, and some of the water soaks into the soil. That soil may neutralize some
or all of the acidity of the acid rainwater. This ability is called buffering capacity, and without it, soils become more
acidic. Differences in soil buffering capacity are an important reason why some areas that receive acid rain show a lot
of damage, while other areas that receive about the same amount of acid rain do not appear to be harmed at all. The
ability of forest soils to resist, or buffer, acidity depends on the thickness and composition of the soil, as well as the
type of bedrock beneath the forest floor. Midwestern states like Nebraska and Indiana have soils that are well buffered.
Places in the mountainous northeast, like New York's Adirondack and Catskill Mountains, have thin soils with low
buffering capacity.
How Acid Rain Harms Trees
Acid rain does not usually kill trees directly. Instead, it is more likely to weaken trees by damaging their leaves, limiting
the nutrients available to them, or exposing them to toxic substances slowly released from the soil. Quite often, injury
or death of trees is a result of these effects of acid rain in combination with one or more additional threats.
Scientists know that acidic water dissolves the nutrients and helpful minerals in the soil and then washes them away
before trees and other plants can use them to grow. At the same time, acid rain causes the release of substances that
are toxic to trees and plants, such as aluminum, into the soil. Scientists believe that this combination of loss of soil
nutrients and increase of toxic aluminum may be one way that acid rain harms trees. Such substances also wash away
in the runoff and are carried into streams, rivers, and lakes. More of these substances are released from the soil when
the rainfall is more acidic.
However, trees can be damaged by acid rain even if the soil is well buffered. Forests in high mountain regions often
are exposed to greater amounts of acid than other forests because they tend to be surrounded by acidic clouds and
fog that are more acidic than rainfall. Scientists believe that when leaves are frequently bathed in this acid fog,
essential nutrients in their leaves and needles are stripped away. This loss of nutrients in their foliage makes trees
more susceptible to damage by other environmental factors, particularly cold winter weather.
How Acid Rain Affects Other Plants
Acid rain can harm other plants in the same way it harms trees. Although damaged by other air pollutants such as
ground level ozone, food crops are not usually seriously affected because farmers frequently add fertilizers to the soil
to replace nutrients that have washed away. They may also add crushed limestone to the soil. Limestone is an alkaline
material and increases the ability of the soil to act as a buffer against acidity.
The Effects of Acid Rain on Automotive Coatings
Over the past two decades, there have been numerous reports of damage to automotive paints and other coatings.
The reported damage typically occurs on horizontal surfaces and appears as irregularly shaped, permanently etched
areas. The damage can best be detected under fluorescent lamps, can be most easily observed on dark colored
vehicles, and appears to occur after evaporation of a moisture droplet. In addition, some evidence suggests damage
occurs most frequently on freshly painted vehicles. Usually the damage is permanent; once it has occurred, the only
solution is to repaint.
The general consensus within the auto industry is that the damage is caused by some form of environmental fallout.
"Environmental fallout," a term widely used in the auto and coatings industries, refers to damage caused by air
pollution (e.g., acid rain), decaying insects, bird droppings, pollen, and tree sap. The results of laboratory experiments
and at least one field study have demonstrated that acid rain can scar automotive coatings. Furthermore, chemical
analyses of the damaged areas of some exposed test panels showed elevated levels of sulfate, implicating acid rain.
The popular term "acid rain" refers to both wet and dry deposition of acidic pollutants that may damage material
surfaces, including auto finishes. These pollutants, which are released when coal and other fossil fuels are burned,
react with water vapor and oxidants in the atmosphere and are chemically transformed into sulfuric and nitric acids.
The acidic compounds then may fall to earth as rain, snow, fog, or may join dry particles and fall as dry deposition.
Automotive coatings may be damaged by all forms of acid rain, including dry deposition, especially when dry acidic
deposition is mixed with dew or rain. However, it has been difficult to quantify the specific contribution of acid rain to
paint finish damage relative to damage caused by other forms of environmental fallout, by the improper application of
paint or by deficient paint formulations. According to coating experts, trained specialists can differentiate between the
various forms of damage, but the best way of determining the cause of chemically induced damage is to conduct a
detailed, chemical analysis of the damaged area.
Because evaporation of acidic moisture appears to be a key element in the damage, any steps taken to eliminate its
occurrence on freshly painted vehicles may alleviate the problem. The steps include frequent washing followed by
hand drying, covering the vehicle during precipitation events, and use of one of the protective coatings currently on the
market that claim to protect the original finish. (However, data on the performance of these coatings are not yet
sufficient.)
The auto and coatings industries are fully aware of the potential damage and are actively pursuing the development of
coatings that are more resistant to environmental fallout, including acid rain. The problem is not a universal one-- it
does not affect all coatings or all vehicles even in geographic areas known to be subject to acid rain-- which suggests
that technology exists to protect against this damage. Until that technology is implemented to protect all vehicles or
until acid deposition is adequately reduced, frequent washing and drying and covering the vehicle appear to be the
best methods for consumers who wish to minimize acid rain damage.
Effects of Acid Rain: Materials
Acid rain and the dry deposition of acidic particles contribute to the corrosion of metals (such as bronze) and the
deterioration of paint and stone (such as marble and limestone). These effects seriously reduce the value to society of
buildings, bridges, cultural objects (such as statues, monuments, and tombstones), and cars.
Dry deposition of acidic compounds can also dirty buildings and other structures, leading to increased maintenance
costs. To reduce damage to automotive paint caused by acid rain and acidic dry deposition, some manufacturers use
acid-resistant paints, at an average cost of $5 for each new vehicle (or a total of $61 million per year for all new cars
and trucks sold in the U.S.) The Acid Rain Program will reduce damage to materials by limiting SO2 emissions. The
benefits of the Acid Rain Program are measured, in part, by the costs now paid to repair or prevent damage--the costs
of repairing buildings and bridges, using acid-resistant paints on new vehicles, plus the value that society places on the
details of a statue lost forever to acid rain.
To observe the effects of acid rain on marble and limestone, two building materials commonly used in monuments,
ancient buildings, and in many modern structures:
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Place a piece of chalk in a bowl with white vinegar.
Place another piece in a bowl of tap water.
Leave the dishes overnight.
The next day, see if you can tell which piece of chalk is more worn away.
This experiment with chalk allows you to see the effect of acid rain on marble and limestone because chalk is made of
calcium carbonate, a compound occurring in rocks, such as marble and limestone, and in animal bones, shells, and
teeth.
Effects of Acid Rain: Visibility Reduction
Sulfates and nitrates that form in the atmosphere from sulfur dioxide (SO2) and nitrogen oxides (NOx) emissions
contribute to visibility impairment, meaning we can't see as far or as clearly through the air. Sulfate particles account
for 50 to 70 percent of the visibility reduction in the eastern part of the United States, affecting our enjoyment of
national parks, such as the Shenandoah and the Great Smoky Mountains. The Acid Rain Program is expected to
improve the visual range in the eastern U.S. by 30 percent. Based on a study of the value national park visitors place
on visibility, the visual range improvements expected at national parks of the eastern United States due to the Acid
Rain Program's SO2 reductions will be worth over a billion dollars annually by the year 2010. In the western part of the
United States, nitrates and carbon also play roles, but sulfates have been implicated as an important source of visibility
impairment in many of the Colorado River Plateau national parks, including the Grand Canyon, Canyonlands, and
Bryce Canyon.
Effects of Acid Rain: Human Health
Acid rain looks, feels, and tastes just like clean rain. The harm to people from acid rain is not direct. Walking in acid
rain, or even swimming in an acid lake, is no more dangerous than walking or swimming in clean water. However, the
pollutants that cause acid rain (sulfur dioxide (SO2) and nitrogen oxides (NOx)) also damage human health. These
gases interact in the atmosphere to form fine sulfate and nitrate particles that can be transported long distances by
winds and inhaled deep into people's lungs. Fine particles can also penetrate indoors. Many scientific studies have
identified a relationship between elevated levels of fine particles and increased illness and premature death from heart
and lung disorders, such as asthma and bronchitis.
Based on health concerns, SO2 and NOx have historically been regulated under the Clean Air Act, including the Acid
Rain Program. In the eastern United States, sulfate aerosols make up about 25 percent of fine particles.By lowering
SO2 and NOx emissions from power generation, the Acid Rain Program will reduce the levels of fine sulfate and
nitrate particles and so reduce the incidence and the severity of these health problems.asthma and bronchitis. When
fully implemented by the year 2010, the public health benefits of the Acid Rain Program are estimated to be valued at
$50 billion annually, due to decreased mortality, hospital admissions, and emergency room visits.
Decreases in nitrogen oxide emissions are also expected to have a beneficial impact on human health by reducing the
nitrogen oxides available to react with volatile organic compounds and form ozone. Ozone impacts on human health
include a number of morbidity and mortality risks associated with lung inflammation, including asthma and
emphysema.
A
acid deposition
The process by which acidic particles, gases, and precipitation leave the atmosphere. More commonly
referred to as acid rain, acid deposition has two components: wet and dry deposition.
acid rain
The result of sulfur dioxide (SO2) and nitrogen oxides (NOx) reacting in the atmosphere with water and
returning to earth as rain, fog, or snow. Broadly used to include both wet and dry deposition. The acid rain
page provides a great deal of information about this issue.
Al
Aluminum; a metal that is toxic to trees and fish
allowance
A tradeable permit to emit a specific amount of a pollutant. For example, under the Acid Rain Program, one
allowance permits the emissions of one ton of sulfur dioxide (SO2).
anions
Negatively charged molecule such as sulfate (SO4(2-)) and nitrate (NO3-). In combination with hydrogen (H+),
these molecules act as strong acids.
acid neutralizing capacity (ANC)
A measure of the ability for water or soil to neutralize added acids. This is done by the reaction of hydrogen
ions with inorganic or organic bases such as bicarbonate (HCO3-) or organic ions.
acidification
Refers to reducing something's pH, making it more acidic; also means the loss of ANC.
adsorb
To take up and hold (a gas, liquid, or dissolved substance) in a thin layer of molecules on the surface of a solid
substance.
B
buffering capacity
The resistance of water or soil to changes in pH.
base cations
Positively charged ions such as magnesium, sodium, potassium, and calcium that increase pH of water (make
it less acidic) when released to solution through mineral weathering and exchange reactions.
C
Ca(2+)
Calcium; a base cation that helps to reduce acidification
chronic acidification
Generally refers to surface waters that remain acidified (ANC<0) regardless of variations in hydrologic
conditions (precipitation, stream flow, etc.).
D
deposition
The processes by which chemical constituents move from the atmosphere to the earth's surface. These
processes include precipitation (wet deposition, such as rain or cloud fog), as well as particle and gas
deposition (dry deposition).
dose response functions
The relationship between the effects (response) on an organism or system and the amount (dose) of some
material to which the organism/system is exposed.
dry deposition
The settling of gases and particles out of the atmosphere. Dry deposition is a component of acid deposition,
more commonly referred to as acid rain.
E
eutrophication
A reduction in the amount of oxygen dissolved in water. The symptoms of eutrophication include blooms of
algae (both toxic and non-toxic), declines in the health of fish and shellfish, loss of seagrass beds and coral
reefs, and ecological changes in food webs.
L
leaching
Process by which water removes chemicals from soil through chemical reactions and the downward
movement of water.
M
Mg(2+)
Magnesium; a base cation that helps to reduce acidification
mineral weathering
The physical and chemical breakdown of rocks that releases ions such as calcium and aluminum.
MW
Megawatt; a unit for describing how much electricity a power plant can generate. The Acid Rain Program
includes virtually all units in the US that can generate over 25 MW.
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N
nitrogen fixation
The process in which bacteria convert biologically unusable nitrogen gas (N2) into biologically usable
ammonia (NH3) and nitrates (NO3-).
nitrogen oxides (NOx)
A group of gases that cause acid rain and other environmental problems, such as smog and eutrophication of
coastal waters. Burning fossil fuels, such as coal and gasoline, releases NOx into the atmosphere. Various
programs are reducing NOx emissions, including the Acid Rain Program and NOx cap and trade programs.
P
pH
A scale that denotes how acidic or basic a substance is. Pure water has a pH of 7.0 and is neither acidic nor
basic. For more information, see the pH page.
precipitation
Water in the form of rain, sleet, or snow (wet deposition).
S
sulfur dioxide (SO2)
A gas that causes acid rain. Burning fossil fuels, such as coal, releases SO2 into the atmosphere. Various
EPA programs are reducing SO2 emissions, including the Acid Rain Program.
W
wet deposition
The process by which chemicals are removed from the atmosphere and deposited on the Earth's surface via
rain, sleet, snow, cloudwater, and fog.