ozone

  • ozone (O3) → pollutant in the troposphere; ground-level ozone originates from the lithosphere, results from secondary reactions of air pollutants and contributes to smog formation in urban centres
    • NOx and volatile organic compounds (VOCs) produce O3 in the presence of sunlight
    • NOx + VOC + heat and sunlight = ozone
  • ozone in the stratosphere → naturally occurring, shields the Earth’s surface from UV radiation and is vital for life on Earth
  • ozone in the troposphere → bad pollutant, “ground-level ozone”
  • effects of ozone depletion → thinning of the ozone allows more UV radiation to penetrate the Earth which has negative effects, including damage to ecosystems (i.e. dying trees) and human health problems (cataracts, skin cancer, weakened immunity)
  • causes of ozone thinning → Chlorofluorocarbons (CFCs), halons, and industrial solvents; CFCs were cheap and easy to produce, gained popularity in the ‘60s for industrial activities but leaked out into the atmosphere and caused the breakdown of the ozone in the stratosphere
  • Montréal protocol → 1987, agreement among countries globally to phase out CFCs with industry substitutes such as hydrofluorocarbons that don’t attack the ozone
    • however, these are potent greenhouse gases that trap more heat on the surface of the Earth
    • additionally, HCFCs have a long residence time of 70-100 years, meaning they can remain in the atmosphere for a long time