1. Chapter 9
Acid Rain

2. Rain Is Rain Water Hard or Soft? Is Rain Water Acidic or Basic?
SOFT, salts and minerals do not evaporate
Is Rain Water Acidic or Basic?
ACIDIC, carbon dioxide is soluble in water
pH of Pure Rain Water is ~5.6
CO2 + H2O H2CO3

3. Carbonic Acid CO2 + H2O H2CO3 H2CO3 + H2O H3O+ + HCO3-
Carbonic Acid is a weak acid
carbone dioxide is an anhydride
[H+] = 2.5 x 10-6 M
pH = 5.6
Dissociation is about 1%

4. Acid Rain What is Acid Rain? Pollutants rain with lower than normal pH
pollutants from industrial process, automobiles and energy generation lower the pH
combustion of fossil fuels
Pollutants
SO2 and SO3 called sulfoxides (SOx)
NO and NO2 called nitroxides (NOx)
Small amount of HCl and volatile organics
How are these pollutants formed and how are they do they form acid rain

5. Pollutants Sulfur Dioxide S(s) + O2(g)  SO2(g)
by-products from the combustion of coal
coal can contain up to 3-5% Sulfur
S(s) + O2(g)  SO2(g)
sulfur dioxide is released into the air
laws now regulate the release of SO2
Coal from the Midwest – Illinois, Indiana, Ohio and others have “hard coal”
with sulfur from 3-5%
Coal from Western State along the Rocky Mountains have “soft coal”
with sulfur from 0-1% Montana, Wyoming, Colorado, New Mexico
80% of all Sulfur dioxide emission come from electric utilities that burn fossil fuels.

6. Pollutants Sulfur Dioxide Cu2S(s) + 3 O2(g)  2 CuO(s) + 2 SO2(g)
the purification of sulfide ores
most common ores are of copper and iron
Cu2S(s) + 3 O2(g)  2 CuO(s) + 2 SO2(g)
2 CuO(s) + Cu2S(g)  6 Cu(s) + SO2(g)
coal also has some of these metal ores

7. Pollutants Sulfoxides 2 SO2(g) + O2(g)  2 SO3(g)
sulfur dioxide combines with oxygen to form sulfur trioxide
2 SO2(g) + O2(g)  2 SO3(g)
This is a more hazardous pollutant because it results in a stronger acid

8. Pollutants Nitroxides N2(g) + O2(g)  2 NO(g)
Primary from the high temperatures from the combustion of fossil fuels
N2(g) + O2(g)  2 NO(g)
2 NO(g) + O2(g)  2 NO2(g)
50% come from the utilities
40% come from automobiles

9. Acid Rain Pollutants react with water to form acids
SO2(g) + H2O(g)  H2SO3(aq)
SO3(g) + H2O(g)  H2SO4(aq)
Acids formed in the atmosphere collect in clouds and precipitate in rainfall
NO(g) + H2O(g)  HNO2(aq)
NO2(g) + H2O(g)  HNO3(aq)

10. Acid Rain

11. Damage by Acid Rain Lakes and streams Forest Buildings and statues
Corrosion of Metals

12. Lakes and Streams Aquatic Life prolific with pH 6.6-9.2
pH 6.0 fish begin to die off
pH 5.5 most species are affected
pH 5.0 most aquatic life is dead
pH 4.0 “dead” lake, can not support life
Some lake and streams are more resistant to change in pH called Acid Neutralization Capacity (ANC)
Many lakes in the northeast have acidity problems, some are “dead.”
Lakes near natural deposits of limestone (CaCO3) have a high ANC and are not as impacted by acid rain.

13. Lakes and Streams Another problem is Leaching 침출
Aluminum concentration increase 1000-fold with a pH change from 6.0 to 5.0
Lead, mercury, cadmium are trace metal ions that increase with decrease in pH
Harm fish and aquatic life, but also pollute water supplies
Many minerals become more soluble in acidic conditions and metals can be leached from soil and rocks into water sources
High concentration of aluminum cause a thick mucous to cover the gills of fish and they suffocate

14. Forests
Acid Rain is a contributing factor for destruction and death of trees
Other factors include
increase in ground-level ozone (O3)
increase in the use of nitrogen fertilizers
trace metals released by acid rain
natural causes

15. Urban Structure 탄산칼슘, Calcium Carbonate, CaCO3 Calcium Sulfate, CaSO4
2 H+(aq) + CaCO3(s)  Ca2+(aq) + CO2(g) + H2O(l)
H2SO4(aq) + CaCO3(s)  CaSO4(aq) + CO2(g) + H2O(l)
Calcium Sulfate, CaSO4
more soluble and can be washed away
Calcium carbonate is a component of building, statues, marble, limestone
Calcium carbonate can be dissolve in acid

16. Corrosion of Metals Metals are also susceptible to acid rain
Iron rusts when exposed to air and water
4 Fe(s) + 2 O2(g) + 8 H+(aq)  4 Fe2+(aq) + H2O(l)
4 Fe2+(aq) + O2(g) + 4 H2O(aq)  2 Fe2O3(s) + 8 H+(aq)
4 Fe(s) + 3 O2(g)  2 Fe2O3(s)

17. Solving the Problem
The problem is complicated but the solution is even more complex.
politics, economics and environment
Clean Air Act 1990
Control Strategies
Reducing Emission
Cleaner Energy Sources
Clean Air Act 1990, President Bush
Cut SO2 emission by 10million tons per year in 10 years, which would brings the US back to 1980 emission levels.
Permits were given to power companies and fines were imposed $25000/day for excess emissions.
Upgrading Cars

18. Control Strategies Upgrade Catalytic Converter
change NO back to N2 and O2
Burn cleaner coal (less sulfur)
Coal Cleaning
“Scrubbing” - SO2 removal
Burn clean coal from Western States, but that make states like Kentucky vulnerable.
Coal Cleaning involves crushing the coal and washing away the heavier metal ores, not very effective (~50%) and costly $ per ton of SO2 removed.
The gases are scrubbed with wet calcium carbonate, which makes calcium sulfate and carbon dioxide, efficient (~90%) and cost effective $ per ton of SO2 removed, but generate greenhouse gas carbon dioxide and generates waste