acid deposition - department of atmospheric and oceanic...

Acid Deposition

1

Acid Deposition

• Brief History

• Acids and Bases

• Chemical Processes and Sources

• Deposition Processes

• Acid Deposition Distribution

• Environmental Effects

Health Effects

Lakes and Forests

• Abatement

2

Early History of Acid Deposition

• 1200s: Coal combustion produces SOx and NOx

• 1750s: Industrial Revolution expands use of coal-fired steam engines

• Early 1800s: Alkali factories producing compounds for soap release hydrochloric acid (HCl), some sulfuric acid (H2SO4) and NOx

• 1863 Alkali Act in the UK

3

pH

• pH: index of acidity or alkalinity of a solution

Negative logarithm of the H+ ion concentration

Ex. H2SO4 → 2H+ + SO42–

• Difference of 1.0 in pH equivalent to 10x difference in acidity

pH = 7.0: neutral

pH < 7.0: acidic

pH > 7.0: basic

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Typical pH Values

1 2 3 4 5 6 7 8 9 10 11 12 13

Neutral

Distilled water LyeVinegar

Natural rain AmmoniaBattery

acidAcid rain

Tomato juice

Cola

beverage

Baking

soda

5

Sulfur ChemistryNatural SO2

SOx → … → SO3,g

Dissolve in

liquid water

Combustion

(oxidizes C, S,

N)

Fossil fuel

(C + S) Sulfuric acid

H2SO4,g/p

SO3,g + H2O,v

H2SO4,aq

SO2

6

Natural Sulfur Sources

Volcanoes

Organic Decay

SO2

H2S → … → SO2

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Anthropogenic Sulfur

Fossil

Fuels

(C + S)

Coal

1–6% S

Oil

1–2% S

Gas

0.5% S60%

33%

7%

ElectricityIndustrialOther

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Other Acids

Nitric acid (HNO3)

Organic acids

Hydrogen chloride (HCl)

NO2 + OH

Anthropogenic: Incineration of PVC plastic

Natural: Volcanic emission

Methyl chloride (CH3Cl) from ocean

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Acid Deposition Processes

• Wet deposition

Acidicgases

Rain, snow scavenging

Runoff

Washout RainoutAcidic gases

Cloud or fog droplets

Acidic gasesWater

coating

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• Dry deposition

Acidic gases

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pH of Rain

CO2,g

SOx

H2CO3,aq

Unpolluted

rain

pH ~ 5.6

from carbonic acid

Acid rain

pH < 5

from sulfuric acidH2SO4,aq

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Regional Transport of AcidsAdirondack Mts.

SW to

NE flow

SO2 source regions

SO2

receptor

region

Local

NOx in

So. Cal.

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Precipitation pH

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Precipitation pH

Hydrogen ion concentration as pH from measurements made at the Central Analytical Laboratory, 2009

National Atmospheric Deposition Program/National Trends Network http://nadp.sws.uiuc.edu

Lab pH

5.2 - 5.3 5.1 - 5.2 5.0 - 5.1 4.9 - 5.0 4.8 - 4.9 4.7 - 4.8 4.6 - 4.7 4.5 - 4.6 4.4 - 4.5 4.3 - 4.4 < 4.3

5.3

Sites not pictured:AK01 5.1 AK03 5.1 PR20 5.1 VI01 5.1

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5.7

5.0

5.9

5.5

5.45.6

5.3 5.3

5.4 5.5

5.6

5.3 5.0

4.9

4.8

4.9

4.8

4.9

4.7

5.6

4.84.7 5.9

4.7

4.8

5.65.4

5.4 5.5

5.4

5.7

5.3 5.4

4.9

5.7

5.0 4.9

5.0

4.9

5.0

4.8

5.3

5.1

5.5

4.8

4.7

4.9

6.3 5.8

5.3

5.1

5.4

5.4 5.6

5.3

4.8

5.0 5.4

5.0

4.9

4.9

5.4

5.0

4.7

6.1

6.0

5.0

4.9

5.1

5.8

4.8

4.9

5.0

4.8

5.7

5.0

5.7

5.4

5.0

5.1

5.4

5.5

5.3

5.3

5.7

5.45.4

4.8

4.9

5.0

4.9

4.8

4.7

4.9

4.8

5.1

5.4

5.4

5.5

5.8

5.5

5.4

5.4

5.2

6.0

5.2

4.9

4.9

5.1

5.0

5.0

4.8

4.9

5.0 5.1

5.0

5.6

5.7 4.9

5.1

5.0

5.0

5.5 4.9 4.9

4.9

5.4 5.6

4.9 4.9

4.8

5.1 5.1

5.05.0

4.9

5.5

5.25.4

5.7

6.0

5.5

5.1

5.1

5.0

5.3

5.3

5.4

5.6

4.9

5.0

5.0 4.8

5.6

5.86.1

4.8

4.7

5.4

6.0

4.8 4.8

4.8 4.8

4.9

4.8

4.7

4.7 4.6

4.8

5.4

5.5

6.1

5.3

5.4 5.4 5.5

4.7 4.74.6

4.7

4.7

5.8

6.1

4.9

5.0 5.0

5.0

5.5 5.0 5.4

5.4

4.8

5.0

5.0

4.9

4.9

5.2

5.6

5.1 5.2

5.3

5.2

5.4

5.3 5.1

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15

SOx Health Effects

• Effect of SO2 gas on respiratory system (ch. 7)

Taste

Odor

Slight bronchial constriction

Inflammation of mucous membranes

• SO2 + aerosol particles is worse than SO2 alone

16

Freshwater Acidification

High-altitude

Lakes

Low-altitude

Lakes

Water source =

direct precip.

and runoff

Little or

no soil

buffering

East: acidic

granite soil

West: alkaline

limestone soil

Water source

filters through

soil—buffered

17

Freshwater Acidification

High-altitude

Lakes

Low-altitude

Lakes

Water source =

direct precip.

and runoff

Little or

no soil

buffering

East: acidic

granite soil

West: alkaline

limestone soil

Water source

filters through

soil—buffered

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Effects

19

Effects

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Effects

21

Effects

• Aquatic plants and fish are stunted, reproduction impaired

• Metallic ions (e.g., aluminum, copper, lead) mobilize and leach from soils into nearby lakes

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Forest Decline

• Definition: suppression of growth/reproduction rates and death of trees

• Susceptible regions:

Downwind of sulfur sources

• Eastern regions of continents, due to west-to-east prevailing winds

High elevation

• Long-term contact with acidified clouds and fog

• Thinner soils, less buffering

Eastern Europe, Northeastern

U.S., Southeastern Canada

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24

Recent Regulatory Action

• Clean Air Act Amendments of 1970 (US)

• 1977: National Atmospheric Deposition Program (NADP, US)

• 1979: Geneva Convention ln Long-range Transboundary Air Pollution

1985: Sulfur Protocol

1988: Nitrogen Oxide Protocol

1994: Second Sulfur Protocol

• Clean Air Act Amendments of 1990 (US)

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AbatementLocate acid

sources downwind

of sensitive areas

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Abatement

DispersionTaller stacks

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Abatement

Use low-

sulfur fuels

Oil, gas

Low-sulfur coal

Coal gassification

Solvent-refined coal

Reduce emissions

Scrubbers

Modified

combustion

28

Abatement

Clean-up

Lake and soil buffers

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