1. Acid Rain Causes Regional Effects Treatment

2. Acid Formation and Deposition
Release of SO2 and NOX by anthropogenic activities can result in acid formation, deposition
SO2 reacts in the atmosphere to form H2SO4 (sulfuric acid)
NOX react in the atmosphere to form HNO3 (nitric acid)
oxidation
SO2
oxidation
NO, NO2, N2O
H2SO4
HNO3

3. Acid Rain: Source Fossil Fuel Burning
Sulfur: Coal
When burned, coal sulfur oxidizes to SO2(g)
Release of SO2
Atmospheric H2SO4
Dry acid particulates (sulfate aerosols)
Nitrogen: Combustion (any)
Any combustion process involving air will form NOX
Automotive exhaust
Power plant emissions
Forest fires

4. What is acidity of Natural Rain?
Carbonic acid
Dissolution of atmospheric CO2 into cloud droplets forms dissolved carbonic acid (H2CO3), giving some weak acidity (clean rainwater pH ~ 5.6)
CO2 + H2O = H2CO3
H2CO3 = HCO3- + H+ (H+ gives acidity)
Weak acids =
Carbonic acid, most organic acids

5. pH Scale
pH = -log[H+]

6. Acid Rain distribution in the US (1955 - 1999)
pH of clean rainfall ~5.6

8. Sources of Sulfur Pollution in the US
Data from 1998
Most emissions are from electric utilities
Coal burning
Fuel Combustion
(Heating) (3%)
Other (8%)
Transportation
(7%)
Industrial Sources
(15%)
Electric Utilities (67%)

9. Sources of Sulfur Pollution in the US
Transportation
(5%)
Data from 2002
Total emissions down 34% since 1990
Most emissions are from electric utilities
Coal burning
Other (3%)
Industrial Sources
(8%)
Fuel Combustion (84%) - 70% of this is electrical utilities

10. Sulfate Deposition Animation
National Atmospheric Deposition Program

11. Sources of NOX Pollution in the US
Data from 1998
Most emissions are from transportation
Nitrogen oxide emissions from automobiles
Electric Utilities
(25%)
Other (5%)
Fuel Combustion
(Heating) (5%)
Transportation
(53%)
Industrial Sources
(12%)

12. Sources of NOX Pollution in the US
Other (2%)
Fossil Fuel
Combustion*
(34%)
Data from 2002
Total: 16% decrease since 1990
Most emissions are from transportation
Nitrogen oxide emissions from automobiles
Transportation
(59%)
Industrial Sources
(5%)
*22% electrical; 12% heating fuels

13. NO3 and NH4 Atmospheric Deposition Animations

14. Results of Acid Rain Direct damage to surface materials
Stone monuments (especially limestone, marble)
Paint
Plastics
Ecological damage
Acidification of watersheds
Lakes
Rivers
Groundwater
Damage to soil nutrient capacity
Decline of forest growth, health

15. Geology and Acid Rain Effects
Natural buffering
Aquifer rock and surface exposed rock can naturally buffer acidity, depending on rock composition
Carbonate rock: strongly buffers pH, neutralizes acidity from rain
CaCO3 + H+ = Ca2+ + HCO3- (a tiny bit of limestone dissolves)
Limestone rock
Will neutralize acid rain, ameliorating the effects of acid deposition
Silicate rock
Does not react with acids as quickly, will not provide much buffering capacity, does not neutralize acid deposition

16. Areas Sensitive to Acid Rain in the US
Sensitive areas
Exposed silicate bedrock
No significant carbonates
Other areas
Carbonates (mostly limestone) exposed at surface

17. Effects of Acid Deposition: Soils
Nutrient Leaching
Acids mixing into soil solutions will be neutralized, at first…
Nutrient cations (Mg2+, Ca2+, K+, Na+,…..) will leach from soil organic matter and minerals
Cations are released into solution
H+ (acidity) is taken up by soil particles, organic acids in soil
Leached nutrients will be washed away in water as it drains down through soil layers into groundwater, or into surface water channels
Long term effects:
Leaching of mineral cations = starvation of soil, plants
Exhaustion of soil buffering capacity (ability to neutralize acid deposition)

18. Caused by soil exhaustion through acid leaching of nutrients
“Forest decline”
Caused by soil exhaustion through acid leaching of nutrients
Slow onset
Encroaches over decades
Will require decades to centuries to recover
Smoky Mtns in
Eastern USA
Black Forest,
Germany
China

19. Acidification of Lakes
Like soils, lakes can buffer pH
Depends on bedrock beneath lake
Limestone bedrock has greater buffering capacity
Sustained acidification can exhaust buffering capacity of lake water, surface sediments…
Lake pH drops once buffering capacity is used up
Dramatic declines in aquatic life (insects, molluscs, fish)
Requires decades to centuries to recover
Remediation
Expensive, only partially effective, must be repeated
Addition of lime (CaO) to lakes is a common method

20. Acidification of Lakes
Geochemical / Ecological Effects
Aluminum toxicity
Al is very insoluble at neutral pH
In low-pH lake water (<5), thouh, Al solubility increases
Toxic: dissolved Al interferes with gill function, O2 uptake
Shelled animals
At lower pH, more difficult to build chitinous shells, calcite tests
Crayfish shells soften below pH ~5.1

22. Acidification Effects on Lakes (Norway species)

24. Acid Mine Drainage (AMD)
Mining for base metal sulfide minerals
Cd, Cu, Pb, Zn, Ag, Au, Pt, others….
Economic ore minerals of these metals are often hosted in pyritic rock
Excavation and dumping of mine waste (spoil) at the surface
Produces large volumes of pyritic rock at surface
Opens passages into subsurface rock, allowing air, water flow
Long term effects:
Oxidation of sulfide minerals by bacteria
Flux of acidic drainage from discontinued mine sites

25. Yellow Dog Plains Sulfide Mine (Upper Peninsula, MI)
High grade nickel and copper deposits, hosted in sulfide
2006: Kennecott Minerals applies for air discharge, groundwater discharge, mining, land use lease and exploration lease permits from MDEQ
Permits granted in 2008, but US EPA must still approve underground injection control permit & National Wildlife Foundation is challenging the permitting

26. Thiobacillus ferrooxidans
Acidophilic bacterium (lives at pH < 2)
Fixes C by oxidizing Fe(II) and S(-II) in pyrite
Produces acidity
Very common

27. Biological Sulfur Transformations
Weathering of Pyrite (FeS2)
Environmental Effects…
The net reaction
4FeS2(pyrite) + 15CO2 + 23H2O =>
8SO Fe2O3(hematite) + 15”CH2O” + 16H+
Produces four moles of acid per mole of weathered pyrite.
In natural weathering, low-pyrite rocks are slowly weathered and thus do not yield significant acidification of soils, rivers
But mining for high-concentration pyrite rocks produces large amounts of exposed pyrite in one place
Pyrite weathering in air
Wholesale acid production (Acid Mine Drainage)

28. AMD Effects
Red or orange color is due to particulates of oxidized Fe compounds (rust) in the water

29. AMD Effects

30. Iron Mountain Mine, CA
Presently a Superfund site, former site of base metal mining… now a massive AMD problem
ca.water.usgs.gov/water_quality/acid/
Nordstrom and Alpers (1999)

31. Iron Mountain Mine, CA
Declared a Superfund site in 1983, former site of base metal mining… now a massive AMD problem
Runoff from mine
Inside the mine

32. Iron Mountain Mine, CA Waters draining from mine area are pH < 1
Lowest recorded pH values on Earth (-3.5)
Highest dissolved metal contents ever recorded (1000s ppm)
Mine drainage
Keswick Reservoir

33. Iron Mountain Mine, CA Highly contaminated mine runoff, sediment
Mine sediment (1% Cu by weight)
Keswick Reservoir

34. Photo from EPA Superfund 25th Anniversary
Water treatment plant was built in 1994
*>1.3 billion gallons of acid mine drainage have been treated so far