Air Pollution

• Troposphere


  • Innermost layer (0 – 17 km)
  • 75% of Earth's air mass
  • 78% N2, 21% O2
  • Responsible for weather and climate

  
• Ozone layer


  • Stratosphere (17 – 48 km) similar composition to troposphere, except more O3 and less H2O
  • In the lower stratosphere, an ozone (O3) layer filters 95% of the sun's harmful UV radiation
  • "good" ozone protect us from sunburn, skin and eye cancer and damage to our immune systems

  
• Ozone formation


  3 O2 + UV → 2 O3

  
• Air pollution is a major cause of human death worldwide
• Air pollution


  • Presence of chemicals in the atmosphere in concentrations high enough to affect climate and harm organisms and materials
  • Heat and noise are also considered forms of air pollution

  
• Primary pollutant


  Chemicals directly to the air by natural events or human activities
• Secondary pollutant


  Harmful chemicals formed when a primary air pollutant reacts with natural air components and/or other pollutants

  
• Major types of air pollutants

  • Carbon monoxide (CO)
  • Nitrogen dioxide (NO2)
  • Sulphur dioxide (SO2)
  • Suspended particulate matter (SPM)
  • Lead (Pb)
  • Ozone (O3)

  
• Carbon monoxide (CO)

  • Colourless poison gas
  • Fossil fuel burning in motor vehicles (car exhaust)
  • Decrease ability of blood to carry oxygen
• Nitrogen dioxide (NO2)


  • Reddish-brown gas in smog
  • From fossil fuel burning in motor vehicles and industrial plants
  • Breathing problems, ecological damage (acid rain)

  
• Sulphur dioxide (SO2)


  • Colourless, irritating gas
  • Mostly from coal burning and industrial processes (e.g. smelting)
  • Breathing problems, ecological damage (acid rain)

  
• Suspended particulate matter (SPM)

  • Variety of aerosols
  • Mainly from coal and diesel burning
  • Breathing problems, ecological damage (acid rain)

  
• Lead (Pb)


  • Toxic metal emitted into the atmosphere as particulate matter
  • Paint, manufacturing, batteries
  • Accumulates in the brain and causes serious nervous system damages, can also harm wildlife
• Ozone (O3)


  • Highly reactive, irritating gas forms in troposphere
  • Made from chemical reactions between emitted compounds and nitrogen oxides (secondary pollutant)
  • Major component of photochemical smog

  
• Photochemical smog


  Mixture of air pollutants formed by the reaction of nitrogen oxides (NOx) and Volatile Organic Hydrocarbons (VOCs) under the influence of sunlight

  
• Industrial smog


  • Mixture of sulfur dioxide (SO2), droplets of sulphuric acid (H2SO4) and a variety of suspended solid particles emitted by burning coal and oil
  • London Smog (Dec 1952): High coal burning + temperature inversion (layer of warm air trapping cold air and pollutants on the ground)
  • 12,000 deaths (4,000 during the 5 days and 8,000 in the following months)
  • The Clean Air Act (1956) introduced a number of measures to reduce air pollution (e.g. smoke control areas)

  
• Harmful effects of smog

  • Harmful to both the respiratory (lungs) and cardiovascular (heart) systems
  • Affects climate (warming some areas, cooling others)
  • The cloud reduces the amount of solar energy hitting the Earth's surface by 2% - 15% (e.g. may reduce India's winter rice harvests by 3% to 10%)
  • Detrimental to ecosystems
  • Especially an issue in dense and industrial Asian countries
• Acid deposition

  • Precipitation with a pH < 5.6, commonly called acid rain
  • Sulphur dioxide and nitrogen oxides form secondary pollutants such as nitric acid vapour or sulphuric acid

  
• Harmful effects of acid rain

  • Contributes to human respiratory diseases such as bronchitis and asthma
  • Can leach toxic metals (e.g. lead) from water pipes into drinking water
  • Damage statues, national monuments, buildings, metals, and car finishes
  • Decrease atmospheric visibility
  • Decreased productivity and profitability of fisheries, forests, and farms (depletion of nutrients in soil and damages to plants)
  • When aquatic systems < 4.5, most fish die and toxic aluminum ions are dissolved into waters

  
• Wet sulphate deposition (kilograms/hectare/year) declined considerably from the early 1980s to the late 1990s
• 1980s: U.S. SO2 emissions acidifying Canadian lakes and forests


  • 1985: U.S. took no action; Canada reduced emissions
  • 1990: U.S. Clean Air Act amended to reduce SO2 emissions
  • 1991: Canada–U.S. Air Quality agreement
  • Present day: U.S. still produces 90% of transboundary emissions

  
• Some pollutants are generated from interactions with atmosphere; others are toxic on their own

  
• Air pollution affects human and ecosystem health
• We need to focus on prevention to reduce air pollution