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Understanding Acid Rain: Causes, Effects, and Solutions

Chapter 6 explores the phenomenon of acid rain, highlighting its sources, particularly sulfur oxides (SOx) and nitrogen oxides (NOx) from coal combustion and urban areas. It discusses the detrimental effects of acid rain on natural ecosystems, including lakes, forests, and historical monuments, emphasizing the importance of regulatory measures like the Clean Air Act. The chapter details statistical data on emissions, remediation strategies, and the economic impact of air quality management, illustrating the ongoing challenges in addressing acid rain globally.

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Understanding Acid Rain: Causes, Effects, and Solutions

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  1. Chapter 6 (CIC) • Read in CTCS • Problems in CTCS:

  2. Acid Rain • Natural rain is at pH = 5.6 • CO2 + H2O H+ + HCO3- • Acid is clearly in Eastern 1/3 of US (Ohio River Valley) • Must be due to more than just CO2 • SO2, SO3, NO, NO2 (SOx and NOx) • SOx is primarily from coal fired power plants, steel mills and heavy industry • NOx is found in large urban areas with heavy population densities – auto traffic

  3. Where’s the H+? • Just like with CO2, SOx and NOx are acid anhydrides • But where did the S come from in coal? • C135H96O9NS • Ca, Si, Na, Al, Ni, Cu, Zn, As, Pb, Hg can also be found in ash • amino acid cysteine

  4. Statistics • US is about 50:50 in NOx and SOx • 86% of SO2 is from coal fired electrical utilities • 46% of NOx is from coal fired electrical utilities • Twice as much SOx asNOx worldwide • Difficulties in getting global air treaty (Kyoto)

  5. What does Acid Rain Do? • Marble statues (Parthenon-Greece; Taj Mahal-India; Mayan ruins-Mexico; US Capitol; Stalagtites in Lincoln Memorial) • Rusting of Steel (bridges, buildings, railroads) • Coat metal with Zn or Cr • Visibility • Illness in elderly, asthma, bronchitis, and emphysema • EPA estimates saving $12-40 billion in health care because of 90’ Clean Air Act • Solubility of toxic metals (Pb, Cd, Hg)

  6. Visibility Great Smoky Mountain National Park… …on a hazy day

  7. Damage to Lakes and Streams • Healthy lakes have a pH of no less than 6.5 • A pH below 5.0 has few species surviving • A pH below 4.0 is essentially dead • CaCO3 buffers a lake • H+ can release Al3+ - mess up gills • Add lime, Ca(OH)2, to lakes

  8. Trees and Forests • 1993 – 25% of all European trees had lost 25% or more of their needles • Acid tends to make the trees more susceptible to: • Insects • Disease • Weather • drought

  9. Costs • 1990 Clean Air Act • Phase I – Reduce power plant SO2 emissions by 10 million tons below 1980 levels for 110 of 2000 dirtiest plants (from 10lbs/106 BTU to 2.5 lbs/106 BTU) • 2 million ton reduction of NOx • Starts in 1995 • Phase II – Reduce SO2 to 1.2 lbs/106 BTU • Includes other power plants • Starts in 2000

  10. Options 1. Move to clean coal (little S) • It’s nearly all gone in the east; transport from the west 2. Clean up coal to remove S • $750/ton SO2 3. Neutralize SO2 by scrubbing • $500/ton SO2 mostly for disposal of CaSO4 • SO2 + O2 + CaCO3 CaSO4 + CO2 • 59% have chosen option #1 (get less energy/g coal) • 28% have chosen option #3

  11. Estimated Costs • Congressional Office of Technology Assessment: $3-4 billion per year • Electric Power Companies: $4-23 billion/yr Actual Costs • $836 million in 1995 - $3/person in the US • Utility bills have remained nearly constant over the last decade

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