Air Pollution Special Cases

• Acid Rain


  Precipitation (rain, hail, freezing rain, sleet, snow) that is acidic (pH <7) and usually lower (pH <5)
• Acidic Deposition


  Deposition of acidic pollutants from atmosphere to land/water, may be dry (e.g. dust) or wet (e.g. precipitation)
• Sources and Formation of Acid Rain

  1. Burning fossil fuels release SO2 and NOx

  2. Compounds react with water forming sulfuric and nitric acids
• Many acidified regions downwind of major pollution sources
• Effects of Acid Rain

  • Negative effects on communities and ecosystems
  • Negative effects on populations of different species
  • Causes property damage (accelerated leaching of nutrients, erodes stone buildings, erases writing on tombstones, corrosion of metal containers and vehicles)
• Transboundary Pollution


  Pollutants originating in one region travel to other regions by crossing borders through air (wind) and water pathways
• Solutions to Acid Rain Problem

  1. Reduction in SO2 emissions from point sources (power plants, factories, smelters) has led to recovery of acidified ecosystems using new technologies (e.g. smokestack scrubbers)

  2. SO2 emissions reductions led to increased pH of precipitation (= recovery)

  3. NOx emissions remain high due to ongoing issues with vehicle emissions – more difficult to control non-point sources
• Ozone Layer


  Located in lower stratosphere (~10 km altitude), concentrations (average 12 ppm) effectively block incoming damaging ultraviolet radiation, protects living organisms from UV radiation from the sun that leads to damage to genetic material (e.g., DNA), causing mutations that can result in cancers (e.g., skin cancer)
• Ozone Hole results from Chemical Reactions with CFCs

  1. Chlorofluorocarbons (CFCs) produced and used in the 1970s as a refrigerant in air conditioners and refrigerators, used in fire extinguishers, propellants for aerosol spray cans, cleaners for electronics

  2. CFCs are very nonreactive so assumed to be safe for the environment

  3. Found to attack ozone molecules in stratosphere (good ozone)

  4. Primary ozone-depleting substances are halocarbons - synthetic compounds derived from hydrocarbons where hydrogen atoms are replaced by atoms of chlorine, fluorine, or bromine
• The "Hole" in the Ozone Layer


  In 1985, researchers detected an area of reduced ozone levels was forming every spring over Antarctica, referred to this thin layer of ozone as the ozone hole, further research showed similar ozone hole was forming over the Arctic and spreading globally, mechanism involves chemical reactions in high-altitude polar stratospheric clouds that break up CFCs into carbon atoms and chlorine atoms, which are released in the spring when the sun breaks up the clouds
• Synthetic Chemicals deplete Ozone Layer creating Ozone Hole
• Scientists were concerned that elevated UV levels resulting from ozone depletion would cause more skin cancer among humans and damage plant life affecting food production
• Research showed that ozone levels had declined by 40-60% over Antarctica between 1955 and 1995
• Solutions to the Problem of the Ozone Hole

  1. In 1987, an international treaty called the Montreal Protocol was signed by 180 countries who agreed to reduce CFC production in half by 1998

  2. Additional agreements were passed, adding more halocarbons to the restricted list which has led to even further reductions in the levels of ozone destroying chemicals entering the atmosphere

  3. Today, production and use of ozone-depleting chemicals has decreased 95% from pre-1987 levels

  4. Ozone depletion has stabilized with ozone layer showing recovery

  5. Ozone layer expected to recover fully sometime after the year 2060

  6. Challenge - CFCs will remain in the stratosphere for a long time slowing recovery

  7. The Montreal Protocol is considered a successful model for solving global environmental problems