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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
4
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
7
Anthropogenic Sulfur
Fossil
Fuels
(C + S)
Coal
1–6% S
Oil
1–2% S
Gas
0.5% S60%
33%
7%
ElectricityIndustrialOther
8
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
9
Acid Deposition Processes
• Wet deposition
Acidicgases
Rain, snow scavenging
Runoff
Washout RainoutAcidic gases
Cloud or fog droplets
Acidic gasesWater
coating
10
• Dry deposition
Acidic gases
11
pH of Rain
CO2,g
SOx
H2CO3,aq
Unpolluted
rain
pH ~ 5.6
from carbonic acid
Acid rain
pH < 5
from sulfuric acidH2SO4,aq
12
Regional Transport of AcidsAdirondack Mts.
SW to
NE flow
SO2 source regions
SO2
receptor
region
Local
NOx in
So. Cal.
13
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
18
Effects
19
Effects
20
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
22
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
23
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)
25
AbatementLocate acid
sources downwind
of sensitive areas
26
Abatement
DispersionTaller stacks
27
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
29