3.6.2 Ozone Depletion
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3.6.2 Ozone Depletion

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3.6.2 Ozone Depletion 3.6.2 Ozone Depletion Presentation Transcript

  • 3.6.2 Global Climatic Change IB Geography Climatic Hazards and Change Ozone depletion in the stratosphere
  • Syllabus Objective 1.Be aware of the factors responsible for the formation of stratospheric ozone and its depletion by atmospheric pollution and natural causes. 2.Understand the effects of ozone depletion on humans, animals and plants. Study local, national and international responses to ozone depletion.
  • What is Ozone? Ozone or trioxygen (O3) is a triatomic molecule, consisting of three oxygen atoms.
  • What is the Ozone Layer The ozone layer is a layer 15 - 30 kms up in Earth's atmosphere which contains relatively high concentrations of ozone (O3). ( somewhere in the neighborhood of 0.00006% of the atmosphere) This layer absorbs 93-99% of the sun's high frequency ultraviolet light, (UV-B) which is potentially damaging to life on earth.
  • Effects on marine ecosystems UV-B can penetrate clear water to a depth of 20 metres. There is recent evidence that exposure to enhanced UV-B is harmful to phytoplankton, plankton and the larvae of fish and shrimps.
  • Effects on plants Although plants can react to UV-B by changing their pigment or growing in shaded positions, prolonged exposure may cause serious damage. Resistance to disease could be reduced and so lead to lower crop yields. Some temperate crops such as peas and cabbage are particularly sensitive. Failure of crops or even reduced cover leaves soils more prone to erosion.
  • Effects on human health Although humans have natural defences against ultra-violet radiation, prolonged exposure to UV-B can have serious effects on human health. Skin, if not protected can experience sunburn. Prolonged exposure can lead to the immune defences of the skin breaking down. This may lead to an increased susceptibility to infection, premature ageing of skin, and skin disorders.
  • How is Ozone formed Ozone in the stratosphere is mostly produced from ultraviolet rays reacting with oxygen: O2 + photon(radiation< 240 nm) → 2 O O + O2 → O3
  • How is Ozone destroyed? It is destroyed by reaction with atomic oxygen: O3 + O → 2 O2 The latter reaction is catalysed by the presence of certain free radicals, of which the most important are hydroxyl (OH), nitric oxide (NO) and atomic chlorine (Cl) and bromine (Br).
  • Ozone depletion Ozone depletion describes two distinct, but related observations: • a slow, steady decline of about 4 percent per decade in the total amount of ozone in Earth's stratosphere since the late 1970s; • and a much larger, but seasonal, decrease in stratospheric ozone over Earth's polar regions during the same period. The latter phenomenon is commonly referred to as the ozone hole.
  • Human Contributions to Ozone destruction Scientists suspected that a range of man-made gases, such as chlorofluorocarbons (CFCs), might be responsible for ozone depletion. CFCs were used in fridges, air-conditioning units, plastic foams and aerosol sprays. These gases are transported high into the stratosphere where they are eventually broken down by UV radiation. This reaction releases free chlorine, which acts as a catalyst in the destruction of ozone. 
  • Antarctic Ozone Hole An area of the Antarctic stratosphere in which the recent ozone levels have dropped to as low as 33% of their pre-1975 values. The ozone hole occurs during the Antarctic spring, from September to early December, as strong westerly winds start to circulate around the continent and create an atmospheric container
  • Ozone depletion Ozone depletion describes two distinct, but related observations: • a slow, steady decline of about 4 percent per decade in the total amount of ozone in Earth's stratosphere since the late 1970s; • and a much larger, but seasonal, decrease in stratospheric ozone over Earth's polar regions during the same period. The latter phenomenon is commonly referred to as the ozone hole.
  • Study local responses to ozone depletion Ozone depletion describes two distinct, but related observations: a slow, steady decline of about 4 percent per decade in the total amount of ozone in Earth's stratosphere since the late 1970s; and a much larger, but seasonal, decrease in stratospheric ozone over Earth's polar regions during the same period. The latter phenomenon is commonly referred to as the ozone hole.
  • Study national responses to ozone depletion
  • Study national responses to ozone depletion banning or phasing out of
  • Study national responses to ozone depletion
  • Study national responses to ozone depletion Cooling technology that uses “freon” older fridges & A/C
  • Study national responses to ozone depletion Cooling technology that uses “freon” Hairspray older fridges & A/C that uses CFCs
  • Study national responses to ozone depletion Cooling technology that uses “freon” older fridges & A/C
  • Study national responses to ozone depletion Cooling technology that uses “freon” older fridges & A/C Not “Hairspray” the Musical
  • Study international responses to ozone depletion Montreal Protocol Kyoto Protocol
  • Study international responses to ozone depletion 1976 - U.S. National Academy of Sciences says credible evidence of ozone depletion, - Halocarbon Industry skeptical 1983 - New leadership in USA EPA pushes for an international approach to halocarbon regulations. 1985 - 20 nations, including most of the major CFC producers, signed the Vienna Convention which established a framework for negotiating international regulations on ozone-depleting substances. That same year, the discovery of the Antarctic ozone hole was announced, causing a revival in public attention to the issue. 1987 - Montreal Protocol signed. Meanwhile, the halocarbon industry shifted its position and started supporting a protocol to limit CFC production. The reasons for this '...the chemical industry supported the Montreal Protocol in 1987 because it set up a worldwide schedule for phasing out CFCs, which [were] no longer protected by patents. This provided companies with an equal opportunity to market new, more profitable compounds.'
  • The Montreal Protocol on Substances That Deplete the Ozone Layer An international treaty designed to protect the ozone layer by phasing out the production of a number of substances believed to be responsible for ozone depletion. It is believed that if the international agreement is adhered to, the ozone layer is expected to recover by 2050. Due to its widespread adoption and implementation it has been hailed as an example of exceptional international co-operation with Kofi Annan quoted as saying it is quot;Perhaps the single most successful international agreement to date has been the Montreal Protocolquot;.
  • Kyoto Treaty An international treaty designed to protect the ozone layer by phasing out the production of a number of substances believed to be responsible for
  • The highest levels of ozone in the atmosphere are in the stratosphere, in a region also known as the ozone layer between about 10 km and 50 km above the surface (or between 6.21 and 31.1 miles). Here it filters out photons with shorter wavelengths (less than 320 nm) of ultraviolet light, also called UV rays, (270 to 400 nm) from the Sun that would be harmful to most forms of life in large doses. These same wavelengths are also among those responsible for the production of vitamin D, which is essential for human health. Ozone in the stratosphere is mostly produced from ultraviolet rays reacting with oxygen