Chapter 9 Acid Rain

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

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%

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

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.

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

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

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

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)

Acid Rain

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

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.

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

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

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

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)

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

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 $500-1000 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 $400-600 per ton of SO2 removed, but generate greenhouse gas carbon dioxide and generates waste