Contents I.Review of pH II.Definition of acid rain III.Pollutants that create acid rain: a. sulfur dioxide b. nitrogen oxide c. ammonia IV.Acid rain.

Contents

I. Review of pH

II. Definition of acid rain

III. Pollutants that create acid rain:

a. sulfur dioxide

b. nitrogen oxide

c. ammonia

IV. Acid rain ecosystem impacts

V. Other impacts

VI. Legislation and technology

VII. Trends over time

• pH is a measure of the activity of hydrogen ions (H+) in a solution.

• pH is shorthand: - pH = -log10 [H+]

- a small p is used in place of writing -log10

- H represents the concentration of hydrogen ions ([H+])

I. Review of pHI. Review of pH

Acid Rain 101

• Water is converted into hydrogen and hydroxyl ions.

H2O H+ + OH-

water hydrogen ion hydroxyl ion

• When the activity of these ions is equal, water is neither acidic or alkaline and is said to be neutral, represented by a pH value of 7.

• When the activity of hydrogen ions is greater, a solution is said to be acidic and is represented by a range of pH values from 0-6.

• When the activity of hydroxyl ions is greater, a solution is said to b alkaline and is represented by a range of pH values from 7-14.

1.Review of pH

• Because pH is a logarithmic function, there are tenfold differences between each pH value.

• Examples:

- A pH value of 6 is ten times more acidic than a pH value of 7.

- A pH value of 5 is one hundred times more acidic than a pH value of 7.

1.Review of pH

From Acid Rain Revisited, page 5

In 1997, the pH of wet deposition at HBEF was 4.2; today it is 4.5.

1.Review of pH

Acid rain

Average pH of rain at Hubbard Brook Experimental Forest in 2007

< 5.2

4.5

pH levels found in precipitation

II. Definition of Acid RainII. Definition of Acid Rain

Acid Rain 101

Acid rain isn’t just RAIN-

It includes everything that falls from the atmosphere (with a pH < 5.2):

- Wet precipitation (rain, snow, etc.)

- Dry dust and gases (dry deposition)

- Clouds and fog

The terms “acid deposition” and “acid precipitation” are more descriptive, but “acid rain” is widely used and

accepted.

2. Definition of Acid Rain

What creates acid rain?- sulfur dioxide - nitrogen oxides

- ammonia

III. Pollutants that Cause Acid RainIII. Pollutants that Cause Acid Rain

Acid Rain 101

•Sulfur dioxide, emitted mainly from combustion of coal and oil in factories and powerplants.

3. Pollutants that cause acid rain

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Chemical reactions: sulfur dioxide

• Coal and oil contain sulfur. When burned in factories and powerplants, the sulfur combines with oxygen in the air and is emitted from smokestacks and chimneys.

S + O2 SO2 (sulfur dioxide)

• Processes found in chemical and petroleum industries also release sulfur into the air.

http://en.wikipedia.org/wiki/Image:Gavin_Plant.JPG

3. Pollutants that cause acid rain

SO2 + H2O → H2SO4

sulfur dioxide + water → sulfuric acid

H2SO4 ↔ H+ + HSO4- ↔ 2H+ + SO4

2-

sulfuric acid ↔ hydrogen ions + sulfate

Hydrogen ions make a solution acidic.

Sulfur dioxide reacts with water in the atmosphere to create sulfuric acid, which dissociates into sulfate and hydrogen ions.

Chemical reactions: sulfur dioxide

3. Pollutants that cause acid rain

Nitrogen oxides from

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electric utilities automobiles

Lightening (to a much smaller degree)

3. Pollutants that cause acid rain

Transportation ≈ 54% nationally

- Uses nitrogen found in atmosphere

Electric Utilities ≈ 30% nationally - Use nitrogen found in coal and oil

The high temperature of the internal combustion engine- used in autos, airplanes, electric utility boilers, etc.- releases energy that causes a reaction between nitrogen and oxygen.

Major sources of Nitrogen oxides:

3. Pollutants that cause acid rain

Acid Rain 101

Nitrogen oxides Energy + N2 + O2 2NO

Energy + 2NO + O2 2NO2

• The transportation sector (cars, trucks, etc..,) is the leading source of nitrogen oxides in the atmosphere.

• Electricity generation, which still largely relies on combustion, is the second leading source.

• The energy released by the lightning also creates a reaction between oxygen and nitrogen, so it is a natural source of nitrogen oxides to the atmosphere.

3. Pollutants that cause acid rain

Chemical reactions: nitrogen oxides

NOx + H2O → HNO3

nitrogen oxides + water → nitric acid

HNO3 ↔ H+ + NO3-

nitric acid ↔ hydrogen ion + nitrate

Nitrogen oxides react with water in the atmosphere to create nitric acid, which dissociates into nitrate and hydrogen ions.

Hydrogen ions make a solution acidic.

3. Pollutants that cause acid rain

Ammonia (NH3) is produced mainly through agriculture:• livestock and poultry• manure• fertilizer application

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3. Pollutants that cause acid rain

Chemical reactions: Ammonia• Ammonia gas reacts with sulfuric and nitric acids

to form ammonium aerosols.Example: NH4

+ + NO3- NH4NO3

ammonium nitrate ammonium nitrate

• When aerosols are deposited to the ground they react with oxygen in a process called nitrification.NH4NO3 + 2O2 2H+ + 2NO3

- + H2Oammonium nitrate oxygen hydrogen ions nitrate water

• This process releases H+ ions, which lowers the pH (creates more acidic conditions).

3. Pollutants that cause acid rain

From emissions to acid deposition:

From Acid Rain Revisited, pg. 4

1. Acid rain causes increased loss of base cations from soil

Decrease in acid neutralizing capacity (ANC) of soils

(reduced ability to buffer the incoming acids)

Lower fertility of soils

(base cations are nutrients necessary for tree growth)

this causes

IV. Acid rain ecosystem impactsIV. Acid rain ecosystem impacts

Acid Rain 101

How does acid rain affect soils?2. Inorganic aluminum is dissolved from

minerals and accumulates in the soil.

The presence of dissolved inorganic aluminum in soil is harmful to plants as it can damage root tips and affect the way plants take up nutrients.

Dissolved inorganic aluminum is also toxic to animals that live in the soil such as frogs, salamanders and larval stages of insects.

this causes

4.a. Impacts on terrestrial ecosystems

From Acid Rain Revisited, pg. 10

4.a. Impacts on terrestrial ecosystems

Is it a big problem in terrestrial

ecosystems?

It depends on the soil of the ecosystem. Soils with limestone bedrock, for example, are able to buffer incoming acids. Soils with a low acid neutralizing capacity (ANC), such as granitic

bedrock, are not and are called acid-sensitive soils.

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4.a. Impacts on terrestrial ecosystems

Changes in the calcium cycle at the Hubbard Brook Experimental Forest

between 1950-1995

From Acid Rain Revisited, pg. 10

The amount of available calcium in the soil at the HBEF appears to have declined more

than 50 percent between the years 1950 – 1995.

Inorganic aluminum dissolves out of minerals at acidic pH levels, and is toxic to living things.

Inorganic aluminum is 1,000 times more soluble in water with a pH of 4.6 than in water with a pH of 5.6.

1. Chemical effects on aquatic systems

4.b. Impacts on aquatic ecosystems

Acid Rain 101

• It can reduce the acid neutralizing capacity of water.

• Acidic waters are defined as having an ANC of less than zero (i.e., no buffering capacity in the water).

1. Chemical effects on aquatic systems

4.b. Impacts on aquatic ecosystems

• Animals all along the food chain are affected: zooplankton, invertebrates and fish can be harmed.

Aluminum clogs fish gills by forming lesions that obstruct a fish’s ability to take oxygen from water.

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2. Biological effects:

4.b. Impacts on aquatic ecosystems

Different organisms can tolerate different pH levels. For example, frogs are the only organisms included on this chart that can tolerate a pH of 4.0.

2. Biological effects on animals:

From http://www.epa.gov/acidrain/effects/surface_water.html

4.b. Impacts on aquatic ecosystems

Acid Rain 101

• ≈ 8% of lakes in Adirondacks • ≈ 15% of lakes in New England

and• ≈ 8.5% of streams in the northern

Appalachian Plateauare considered acidic, which means ANC

is less than zero.

4.b. Impacts on aquatic ecosystems

Acid Rain 101

•Causes damage to certain building materials, historical monuments, ancient statues and gravestones.

•Sulfuric acid in the rain chemically reacts with calcium compounds in the stones (limestone, sandstone, marble and granite) to create gypsum, which then flakes off.

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V. Other Impacts from acid rainV. Other Impacts from acid rain

• Visibility is reduced by sulfate and nitrate in the atmosphere.

• Causes an increased rate of oxidation for iron.

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5. Other impacts from acid rain

Acid Rain 101

What has been done to remedy the problem of acid rain?

In the past 30 years, the U.S. Congress has enacted several laws to promote clean air.

Two important laws were the Clean Air Act of 1970 and the

Clean Air Act Amendments of 1990.

VI. Legislation and technologyVI. Legislation and technology

The Clean Air Act of 1970

• Was not written to reduce acid rain, but to reduce pollutants in the air in general.

• Identified six major pollutants as harmful to human health and environment:

Carbon monoxide Sulfur dioxide

Ozone Nitrogen dioxide

Lead Particulate matter*

* With size of particle less than or equal to 10 micrometers

6. Legislation and technology

Title IV of the Clean Air Act Amendments of 1990

• Targeted the emissions of electric utilities, which accounted for 70% of sulfur and 30% of nitrogen emissions.

• Goals:

- reduce SO2 by 10 million tons, or 40%

- reduce NOx by 2 million tons, or 10%

compared to 1980 levels

6. Legislation and technology

Some strategies used to reduce sulfur and nitrogen oxides emissions:

• ‘cap,’ or limit, the amount of SO2 that can be emitted by electric utilities

• use of trade allowances for SO2

• use of catalytic converters in automobiles

6. Legislation and technology

Some strategies used to reduce sulfur and nitrogen oxides emissions:

• use of ‘clean coal technology’ (use of low sulfur coal in factories and electric utility plants)

• Installation of scrubbers in smokestacks

6. Legislation and technology

A type of scrubber called ‘Counter Current Packed Tower’, sold by Ceilcote Air Pollution Control

• Generally, a scrubber is tower equipped with a fan that extracts gases from the power plant into the tower.

• A limestone slurry is injected into tower to mix with these gases.

• Calcium carbonate of the limestone produces pH-neutral calcium sulfate that is physically removed from scrubber.

How do scrubbers work?

How do catalytic converters work?

Catalytic converters treat exhaust before it leaves the car and remove a lot of the pollution.

• US car manufacturers were required to reduce the amount of emissions coming from vehicles by

installing catalytic converters.

• ‘cap’ NOx emissions from electric utilities, which will likely increase as electric generation from power plants increases

• set standards for ammonia emissions.

To date there is no legislation to:

6. Legislation and technology

Have the CAA and CAAA helped to reduce SO2 and NOx pollution?

Acid Rain 101

Change in SO2 emissions in the U.S. over time

Total SO2 emissions (US)

•1940: 20 million tons•1970: 28 million tons•2002: 19 million tons

SO2 emissions from utilities (US)

•1980: 17.5 million tons•2002: 10.3 million tons

VI. Legislation and technologyVI. Legislation and technology

Sulfate

6. Trends over time

1994 2005

Concentration of Sulfate in Precipitation at the Hubbard Brook Experimental Forest

Data provided by G.E. Likens through funding from the National Science Foundation and The A.W. Mellon Foundation.

6. Trends over time

Change in NOx emissions in the U.S. over time

• 1990: 5.5 million tons• 2001: 4.7 million tons

NOx emissions from utilities (US)

6. Trends over time

Acid Rain 101

Nitrate

6. Trends over time

1994 2005

Concentration of Nitrate in Precipitation at the Hubbard Brook Experimental Forest

Data provided by G.E. Likens through funding from the National Science Foundation and The A.W. Mellon Foundation.

6. Trends over time

Ammonium

6. Trends over time

1994 2005

Concentration of Ammonium in Precipitation at the Hubbard Brook Experimental Forest

Data provided by G.E. Likens through funding from the National Science Foundation and The A.W. Mellon Foundation.

6. Trends over time

Have reductions in SO2 and NOX affected the acidity, or

pH of precipitation?

6. Trends over time

Acidity (pH)

6. Trends over time

1994 2005

pH of Stream Water and Precipitation at the Hubbard Brook Experimental Forest

Note: An increase in pH indicates a decrease in acidity.Data provided by G.E. Likens through funding from the National Science Foundation and The A.W. Mellon Foundation.

6. Trends over time

Overall…• Sulfur dioxide regulation has been fairly

successful. However, emissions remain high compared to background (pre-industrial) conditions.

• Although emissions of NOx and ammonia have not been fully addressed, nitrogen deposition has declined significantly over the past decade as electric utility regulations take effect.

6. Trends over time

A complex, tricky problem…• Sulfur and nitrogen compounds can travel thousands

of kilometers from their original source, therefore• Air pollution crosses state and national boundaries.

(ie: Pollutants from power plants in Michigan or New Jersey can travel to the forests of New Hampshire and Vermont.)

• Taller smokestacks have improved air quality in industrialized areas, but now pollutants are blown great distances by wind and affect much larger areas.

6. Trends over time

Clean Air Interstate Rule• Designed to reduce air pollution that moves

across state boundaries

• Will cap SO2 and NOx emissions across 28 eastern states and the District of Columbia.

• When fully implemented…

-will reduce SOx by 70% from 2003 levels

-will reduce NOx by 60% from 2003 levels

6. Trends over time

States

Covered by Clean

Air Interstate

Rule

States covered by Clean Air Interstate Rule

From www.epa.gov

6. Trends over time

A number of international treaties dealing with the long-range transport of atmospheric pollutants have been signed.

• Sulfur Emissions Reduction Protocol• Convention on Long-Range Transboundary Air Pollution

World-wideAcid rain is a substantial problem wherever there is concentrated industry, particularly in

-People’s Republic of China

-Eastern Europe

-Russia

6. Trends over time

The Hubbard Brook Acid Rain StoryPart 1: The Discovery

For more information on the role of the Hubbard Brook Ecosystem Study in acid rain research,

please view the next slideshow.