acid rain.doc

7/27/2019 acid rain.doc

1/5

Introduction

Acid rain is rain consisting of water droplets that are unusually acidic because of atmosphericpollution - most notably the excessive amounts of sulfur and nitrogen released by cars and

industrial processes. Acid rain is also called acid deposition because this term includes other

forms of acidic precipitation such as snow.

Acidic deposition occurs in two ways: wet and dry. Wet deposition is any form of precipitationthat removes acids from the atmosphere and deposits them on the Earths surface. Dry deposition

polluting particles and gases stick to the ground via dust and smoke in the absence of

precipitation. This form of deposition is dangerous however because precipitation can eventuallywash pollutants into streams, lakes, and rivers.

Acidity itself is determined based on the pH level of the water droplets. PH is the scale

measuring the amount of acid in the water and liquid. ThepH scale ranges from 0 to 14 with

lower pH being more acidic while a high pH is alkaline; seven is neutral. Normal rain water is

slightly acidic and has a pH range of 5.3-6.0. Acid deposition is anything below that scale. It isalso important to note that the pH scale is logarithmic and each whole number on the scale

represents a 10-fold change.

Today, acid deposition is present in the northeastern United States, southeastern Canada, andmuch of Europe including portions of Sweden, Norway, and Germany. In addition, parts of

South Asia, South Africa, Sri Lanka, and Southern India are all in danger of being impacted by

acid deposition in the future.

Causes and History of Acid Rain

Acid deposition can occur via natural sources like volcanoes but it is mainly caused by therelease of sulfur dioxide and nitrogen oxide during fossil fuel combustion. When these gases are

discharged into the atmosphere they react with the water, oxygen, and other gases already

present there to form sulfuric acid, ammonium nitrate, and nitric acid. These acids then disperseover large areas because of wind patterns and fall back to the ground as acid rain or other forms

of precipitation.

The gases responsible for acid deposition are normally a byproduct of electric power generation

and the burning of coal. As such, it began entering the atmosphere in large amounts during theIndustrial Revolution and was first discovered by a Scottish chemist, Robert Angus Smith, in

1852. In that year, he discovered the relationship between acid rain and atmospheric pollution in

Manchester, England.

Although it was discovered in the 1800s, acid deposition did not gain significant public attentionuntil the 1960s and the term acid rain was coined in 1972. Public attention further increased in

the 1970s when the New York Times published reports about problems occurring in the Hubbard

Brook Experimental Forest in New Hampshire.
http://staff.jccc.net/PDECELL/chemistry/phscale.htmlhttp://www.hubbardbrook.org/http://www.hubbardbrook.org/http://www.hubbardbrook.org/http://www.hubbardbrook.org/http://www.hubbardbrook.org/http://staff.jccc.net/PDECELL/chemistry/phscale.html


2/5

Effects of Acid Rain

After studying the Hubbard Brook Forest and other areas today, there are several important

impacts of acid deposition on both natural and man-made environments. Aquatic settings are the

most clearly impacted by acid deposition though because acidic precipitation falls directly into

them. Both dry and wet deposition also runs off of forests, fields, and roads and flows into lakes,rivers, and streams.

As this acidic liquid flows into larger bodies of water, it is diluted but over time, acids can accrue

and lower the overall pH of the body. Acid deposition also causes clay soils to release aluminumand magnesium further lowering the pH in some areas. If the pH of a lake drops below 4.8, its

plants and animals risk death and it is estimated that around 50,000 lakes in the United States and

Canada have a pH below normal (about 5.3 for water). Several hundred of these have a pH toolow to support any aquatic life.

Aside from aquatic bodies, acid deposition can significantly impact forests. As acid rain falls on

trees, it can make them lose their leaves, damage their bark, and stunt their growth. By damagingthese parts of the tree, it makes them vulnerable to disease, extreme weather, and insects. Acidfalling on a forests soil is also harmful because it disrupts soil nutrients, kills microorganisms in

the soil, and can sometimes cause a calcium deficiency. Trees at high altitudes are also

susceptible to problems induced by acidic cloud cover as the moisture in the clouds blankets

them.

Damage to forests by acid rain is seen all over the world, but the most advanced cases are in

Eastern Europe. Its estimated that in Germany and Poland, half of the forests are damaged,

while 30% in Switzerland have been affected.

Finally, acid deposition also has an impact on architecture and art because of its ability tocorrode certain materials. As acid lands on buildings (especially those constructed with

limestone) it reacts with minerals in the stones sometimes causing it to disintegrate and wash

away. Acid deposition can also corrode modern buildings, cars, railroad tracks, airplanes, steelbridges, and pipes above and below ground.

What's Being Done?

Because of these problems and the adverse effects air pollution has on human health, a numberof steps are being taken to reduce sulfur and nitrogen emissions. Most notably, many

governments are now requiring energy producers to clean smoke stacks by using scrubbers

which trap pollutants before they are released into the atmosphere and catalytic converters in carsto reduce their emissions. Additionally, alternative energy sources are gaining more prominence

today and funding is being given to the restoration of ecosystems damaged by acid rain

worldwide.


3/5

Are SO2 and NOx the causes of acid rain?

Indirectly, yes. When SO2 and NOx enter the atmosphere, they react with water vapor, oxygen

and other compounds to form sulfuric acid and nitric acid. This process may take place locally,

or -- when winds blow emissions hundreds of miles away -- across international or state

boundaries. These acids lower the pH of water condensation in the atmosphere, and when thatcondensation falls as rain, fog or snow, the resulting acids can wreak havoc on plant and animal

life.

(Note: The more acids found in rain, the lower the pH. The pH scale goes from 0 to 14. Valuesfrom 0 to 6 are considered acid, 7 is considered neutral, and values from 8 to 14 are considered

alkaline. A pH of 1, for example, is far more acidic than a pH of 6.)

What are the effects of acid rain?

The effects of acid rain can vary depending on where it falls and what the local rock and soil is

composed of -- an alkaline soil can help buffer the effects of acid rain and reduce its impact onlocal lakes.

However, when acid rain falls on some soils, the acids can wipe out important microbes andinsects that live in soil and leaf litter. When acids from rain and snow enter rivers and lakes, it

can kill fish and their eggs -- many fish eggs can't survive at pH lower than 5. This has caused

the disappearance of some fish like brook trout from streams in the eastern U.S., where acid rainis more prevalent than in western states. Crayfish, clams, amphibians and other aquatic wildlife

are also killed off by acid rain.

What about the effect of acid rain on forests?

Trees are among the most visible victims of acid rain (see the photo above). When acid rain or

snow falls on forest floors, it leaches out valuable nutrients that are found in the soil, leavingbehind aluminum and other elements that can be toxic to plant life. Thus, the trees slowly die

from lack of food and from soil toxins -- eventually, an entire forest can be killed off by acid

rain.

Trees are especially vulnerable at higher altitude, since they receive more rain and snow, and areoften surrounded by acid fog and clouds. The effects of acid rain and snow have been widely

seen throughout Appalachian Mountains, including the Great Smoky Mountains, the Adirondack

Mountains and the Catskillsin New York. Many forests in Europe, including Germany's famous

Black Forest and the high-altitude forests throughout Scandinavia, are also in peril due to acidrain and snow.

Can acid rain affect humans?

The amount of acid in rain is too small to have a serious impact on human health, and

agricultural land is now amended with lime and other fertilizers to buffer the effect of acid rain.

However, the acid in rain and snow is strong enough to erode rock -- centuries-old buildings,
http://gonewengland.about.com/od/newyorkstate/a/aacatskillstour.htmhttp://gonewengland.about.com/od/newyorkstate/a/aacatskillstour.htmhttp://gonewengland.about.com/od/newyorkstate/a/aacatskillstour.htm


4/5

monuments and statues made of marble, limestone or other rock are slowly eroding away due to

the effects of acid rain.

What can we do about acid rain?

Though much has been done to reduce the impact of acid rain, much more needs to beaccomplished. Smokestack scrubbers that reduce emissions from coal-generated power plantshave helped, but with millions of sources like auto tailpipe emissions, sources of acid rain are

difficult to manage.

And though international treaties have been signed and implemented throughout Europe and

North America, their benefits have been limited, especially as rapidly developing countries inAsia and South America rely heavily on coal and oil for energy. Since the single largest source

of acid rain and snow is coal-powered electrical plants, developing alternative sources of energy

becomes more important than ever. Until that time, however, acid rain will continue to destroytrees, forests, wildlife and historical buildings and monuments.

People who are concerned about acid rain can start by saving electricityin their homes,

improving theirgas mileage and taking other steps to save energyand reduce our dependence on

the fossil fuels that cause acid rain.

Suggested Reading

Precipitation - Measuring Precipitation

The Hydrologic Cycle - The Water Goes Around and Around

Aquifers

Related Articles

Acid Rain

Acid Rain Our Struggling Lakes and Forests - The Environment for Ki...

acid rain - definition of the aquarium term acid rain

How Salicylic Acid Treats Acne Video

Acid Rain - Nature for Kids

Website refered

http://greenliving.about.com/od/scienceandtechnology/a/Acid-Rain.htm

https://sites.google.com/site/acidrain1project/
http://greenliving.about.com/od/greenathome/a/energy-efficient-air-conditioning.htmhttp://greenliving.about.com/od/greenathome/a/energy-efficient-air-conditioning.htmhttp://greenliving.about.com/od/travelinggreen/tp/Ten_Ways_to_Green_Your_Ride.htmhttp://greenliving.about.com/od/greenlivingbasics/tp/save-energy-conservation.htmhttp://greenliving.about.com/od/greenlivingbasics/tp/save-energy-conservation.htmhttp://geography.about.com/od/physicalgeography/a/precipitation.htmhttp://geography.about.com/od/physicalgeography/a/hydrologiccycle.htmhttp://geography.about.com/od/physicalgeography/a/aquifers.htmhttp://greenliving.about.com/od/scienceandtechnology/a/Acid-Rain.htmhttp://www.netplaces.com/kids-environment/the-air-and-water/acid-rain-our-struggling-lakes-and-forests.htmhttp://freshaquarium.about.com/od/termsandtables/g/acidrain.htmhttp://video.about.com/acne/How-Salicylic-Acid-Treats-Acne.htmhttp://www.netplaces.com/kids-nature/people-affecting-nature/acid-rain.htmhttp://greenliving.about.com/od/scienceandtechnology/a/Acid-Rain.htmhttps://sites.google.com/site/acidrain1project/http://greenliving.about.com/od/greenathome/a/energy-efficient-air-conditioning.htmhttp://greenliving.about.com/od/travelinggreen/tp/Ten_Ways_to_Green_Your_Ride.htmhttp://greenliving.about.com/od/greenlivingbasics/tp/save-energy-conservation.htmhttp://geography.about.com/od/physicalgeography/a/precipitation.htmhttp://geography.about.com/od/physicalgeography/a/hydrologiccycle.htmhttp://geography.about.com/od/physicalgeography/a/aquifers.htmhttp://greenliving.about.com/od/scienceandtechnology/a/Acid-Rain.htmhttp://www.netplaces.com/kids-environment/the-air-and-water/acid-rain-our-struggling-lakes-and-forests.htmhttp://freshaquarium.about.com/od/termsandtables/g/acidrain.htmhttp://video.about.com/acne/How-Salicylic-Acid-Treats-Acne.htmhttp://www.netplaces.com/kids-nature/people-affecting-nature/acid-rain.htmhttp://greenliving.about.com/od/scienceandtechnology/a/Acid-Rain.htmhttps://sites.google.com/site/acidrain1project/


5/5

http://www.epa.gov/acidrain/education/site_students/whatcauses.html

LEARNING OBJECTIVES

Students will be able to:

Define acid rainExplain the cause of acid rainExplain the effects of acid rain on vegetationExplain the effects of acid rain on waterExplain the effects of acid rain on man-made objectsExplain the effects of acid rain on humansDescribe what can be done to solve the acid rain problem

Effects of Acidity on Plants and Animals

As a first example of the effects of acid rain, we can examine a case which is not

obvious - effects on non-aquatic, tree nesting birds. This study was carried out in theNetherlands. It was observed that the proportion of birds laying defective eggs rosefrom roughly 10% in 1983-84 to 40% by 1987-88. The defective eggs had thin andhighly porous egg shells, which resulted in eggs failing to hatch because of shellbreakage and desiccation. As a result, there was also a high proportion of emptynests and clutch desertion. It was also observed that these effects were limited toareas of acid rain.

Since the birds did not appear to be directly affected by the acidity, the foodchain was examined (these birds are positioned at the upper part of the local foodchain). The difference between areas of normal soil pH (buffered by high calcium

content due to limestone and marble outcrops and bedrock) and those with acidic soilappeared to be the presence of snails. The snails depend on the soil as their calciumsource as they secrete their shells. With much of the CaCO3 leached out of the soil bythe acid precipitation, the snails could not survive in the area. The birds did not, atfirst, appear to be affected, because they continued to eat spiders and insects which,while supplying a sufficiently nutritious diet for the birds, where a poor source ofcalcium.

To test the hypothesis that the lack of calcium was the cause of the bird's layingdefective eggs, ecologists "salted" the area with chicken egg shell fragments. Thebirds began to eat the chicken egg shells, and those that did laid normal eggs.

In this case, acid precipitation had affects that passed on up the food chain.
http://www.epa.gov/acidrain/education/site_students/whatcauses.htmlhttp://www.epa.gov/acidrain/education/site_students/whatcauses.html

acid rain.doc

Documents