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Definition of Acid Rain

Precipitation that has a pH of less than thatof natural rainwater (which is about 5.6 due

to dissolved carbon dioxide). It is formed when sulphur dioxides and

nitrogen oxides, as gases or fine particles inthe atmosphere, combine with water vapour

and precipitate as sulphuric acid or nitric acidin rain, snow, or fog.

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Acidic particles and vapours are deposited via two processes -

wet and dry deposition.

Wet deposition is acid rain, the process by which acids with a

pH normally below 5.6 are removed from the atmosphere inrain, snow, sleet or hail.

Dry deposition takes place when particles such as fly ash,

sulphates, nitrates, and gases (such as SO2 and NO), are

deposited on, or absorbed onto, surfaces.

The gases can then be converted into acids when they contact

water.

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Causes of Acid Rain

Natural Sources

Emissions from volcanoes and from

biological processes that occur on the land,in wetlands, and in the oceans contributeacid-producing gases to the atmosphere

Effects of acidic deposits have beendetected in glacial ice thousands of yearsold in remote parts of the globe

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Causes of Acid Rain

The principal cause of acid rain is fromhuman sources

Industrial factories, power-generatingplants and vehicles

Sulphur dioxide and oxides of nitrogen are

released during the fuel burning process(i.e. combustion)

MSNEncarta

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Formation of Acid Rain

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Formation of Acid Rain

When water vapour condeses, or as therain falls, they dissolve in the water to

form sulphuric acid (H2SO4) and nitricacid (HNO3).

While the air in cleaned of the

pollutants in this way, it also causesprecipitation to become acidic, formingacid rain

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When CO2

reacts with water, carbonic acid is formed.

CO2 (g)+H2O(l)-H2CO3(aq)

When SO2 reacts with water, sulfurous acid is formed

SO2 (g)+H2O(l)-H2SO3(aq)

When NO2 reacts with water, nitric acid is formed.

2NO2(g)+H2O(l)-HNO2(aq)+HNO3(aq)

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Formation of Acid Rain

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Affected Areas

CanadaAcid rain is a problem in Canada

Water and soil systems lack naturalalkalinity such as lime base Cannot neutralize acid

Canada consists of susceptible hard rock

such as graniteDo not have the capacity to effectively

neutralize acid rain

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Affected Areas

Industrial acid rain is a substantial problem inChina, Eastern Europe and Russia and areas

down-wind from them.Acid rain from power plants in the Midwest

United States has also harmed the forests ofupstate New York and New England.

This shows that the effects of acid rain canspread over a large area, far from the sourceof the pollution

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Effects of Acid Rain

Harmful to aquatic life

Increased acidity in water bodies

Stops hatching of eggs of certainorganisms (e.g. fish)

Changes population ratios

Affects the ecosystem

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Effects of Acid Rain

Harmful to vegetation Increased acidity in soil

Leeches nutrients from soil, slowing plantgrowth

Leeches toxins from soil, poisoning plants

Creates brown spots in leaves of trees,

impeding photosynthesisAllows organisms to infect through broken

leaves

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Effects of Acid Rain

MSNEncarta

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Effects of Acid Rain

Accelerates weathering inmetal and stone structures

Eg. Parthenon in Athens,Greece; Taj Mahal in Agra,India

http://www.lauraknauth.com/photos/france/thinker.jpgMSNEncarta

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Sandstone portal Fig

ure on Herten Castle

in Ruhr district of Ge

rmany. Sculpted 170

2; photographed in 1

908.

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Same sandstone por

tal figure photograp

hed in 1969.

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PreventiveMeasures

Reduce amount of sulphur dioxide andoxides of nitrogen released into the

atomosphere Use less energy (hence less fuel burnt)

Use cleaner fuels

Remove oxides of sulphur and oxides of

nitrogen before releasing Flue gas desulphurization

Catalytic Converters

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PreventiveMeasures

Use cleaner fuels

Coal that contains less sulphur

"Washing" the coal to reduce sulphurcontent

Natural Gas

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PreventiveMeasures

Flue Gas Desulphurisation (FGD)

Removes sulphur dioxide from flue gas (waste

gases) Consists of a wet scrubber and a reaction tower

equipped with a fan that extracts hot smoky stackgases from a power plant into the tower

Lime or limestone (calcium carbonate) in slurryform is injected into the tower to mix with thestack gases and reacts with the sulphur dioxidepresent

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PreventiveMeasures

(continued)

Produces pH-neutral

calcium sulphate that isphysically removed fromthe scrubber

Sulphates can be usedfor industrial purposes

Scrubber at workMSN

Encarta

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PreventiveMeasures

Use other sources of electricity (i.e.nuclear power, hydro-electricity, wind

energy, geothermal energy, and solarenergy)

Issue of cost

http://upload.wikimedia.org/wikipedia/commons/4/4e/Nuclear_Power_Plant_Cattenom.jpg

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Reducing the effects of Acid Rain

Liming

Powdered limestone/limewater

added to water and soil toneutralize acid

Used extensively in Norway andSweden

Expensive, short-term remedy

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Bibliography

MSN Encarta

http://en.wikipedia.org/wiki/Acid_rain

Marian Boderick. (1994). Weather andClimate. Hong Kong: Time Life Asia.

Katherine K. Rothschild. (1994). Matter

and Chemistry. Hong Kong: Time LifeAsia.

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Thank You

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Problem Scenario

Suppose you worked in the government.A company wants to set up a factory in

your country. It would bring jobs, but itwould also bring about pollution, whichwould lead to acid rain. Would you

allow it? Justify your answer.