Download 5.8 Acid Deposition

5.8 ACID DEPOSITION
pH Scale
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PRIMARY POLLUTANTS (sulfur dioxide & nitrogen
oxides) are emitted by combustion.
Primary pollutants can travel as far as 1,000 km.
As the primary pollutants react with H2O vapor and O2 and
become SECONDARY POLLUTANTS (nitric acid vapor,
droplets of sulfuric acid, and particles of acid-forming sulfate
and nitrate salts).
Acidic substances descend to the earth’s surface in two
forms:
1.
Wet deposition (as acid rain, snow, fog, and cloud
vapor).
2.
Dry deposition as acidic particles.
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Most dry deposition falls near the emission sources.
Most wet deposition falls in more distant downwind
areas.
Soils and lakes vary in their ability to buffer or remove
excess acidity.
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Wind
Transformation to
sulfuric acid (H2SO4)
and nitric acid (HNO3)
Windborne ammonia gas
and particles of cultivated soil
partially neutralize acids and
form dry sulfate and nitrate salts
Nitric oxide (NO)
Acid fog
Ocean
Sulfur dioxide (SO2)
and NO
Dry acid
deposition
(sulfur dioxide
gas and particles
of sulfate and
nitrate salts)
Wet acid deposition
(droplets of H2SO4 and
HNO3 dissolved in rain
and snow)
Farm
Lakes in
deep soil
high in limestone
are buffered
Lakes in shallow
soil low in
limestone
become
acidic
Buffering
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Soils that contain basic compounds such as calcium
carbonate (CaCO3) or limestone can neutralize or buffer
some inputs of acids.
Soils that don’t have basic compounds (granite & depleted
soils) are more sensitive to acid deposition.
Coral reefs contain CaCO3, pH in saltwater environments
doesn’t change much.
Freshwater ecosystems are more sensitive to acid
deposition.
Effects on Humans
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Contributes to human respiratory diseases.
Can leach toxic metals into drinking water.
Damage statues, buildings, metals and car finishes.
Decreases atmospheric visibility.
Can lower profits and causes job losses because of
lower productivity.
Effects on Aquatic Ecosystems
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Fish kills below pH 4.5.
Al3 from soil can stimulate production of excess mucus
which clogs gills.
Toxic shock is the damage caused sudden runoff of
large amounts of highly acidic water and Al3.
Water
boatman
Whirligig
Yellow perch
Fish and
other aquatic
organisms
vary in their
sensitivity to
acidity.
Lake trout
Brown trout
Salamander
(embryonic)
Mayfly
Smallmouth
bass
Mussel
6.5
6.0
5.5
5.0
pH
4.5
4.0
3.5
Effects of Plants & Soil Chemistry
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Can harm forests and crops (pH below 5.1).
Damage leaves directly.
Leaching reduces plant productivity and buffering abilities
of soil.
Al3 can hinder uptake and use of soil nutrients and water
by plants.
Dissolving insoluble soil compounds and ions of metals
are toxic to both plants & animals.
Promoting growth of acid resistant competing and
parasitic mosses.
Emission
Acid
deposition
SO2
H2O2
PANs
NOX
O3
Others
Direct damage
to leaves
and bark
Reduced
photosynthesis
and growth
Increased
Susceptibility
to drought,
extreme cold,
insects, mosses,
and disease
organisms
Soil acidification
Leaching of
soil
nutrients
Acid
Air
pollutants
are one of
several
interacting
stresses that
can
damage,
weaken or
kill trees.
Tree death
Release of
toxic
metal icons
Root
damage
Reduced
nutrient
and
water
uptake
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Prevention
Reduce air pollution
by improving energy
efficiency
Reduce coal use
Increase natural gas
use
Increase use of
renewable resources
Burn low-sulfur coal
Remove SO2
particulates, and NOx
from smokestack gases
Remove Nox from
motor vehicular exhaust
Tax emissions of SO2
Cleanup
Add lime to neutralize
acidified lakes
Add phosphate
fertilizer to neutralize
acidified lakes
Methods for
reducing
acid
deposition.
Reducing Primary Pollutants
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Sulfur dioxide emissions have been reduced by
installing smokestack scrubbers in coal-fired power
plants.
Using low-sulfur coal reduced sulfur dioxide, but
increased CO2 emissions.
Nitrogen oxide emissions have not declined due to
more motor vehicles traveling farther.
Using limestone to neutralize acids
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Temporary and expensive.
Limestone can kill some types of plankton.
Can harm wetland plants that need acidic water.
It is difficult to know how much lime to put where.