ESS Topic 5.6 - Depletion of Stratospheric Ozone
5.6 Depletion of Stratospheric Ozone
These notes correspond with pages 288-293 of the IBO ESS Course Companion.
5.6.1 Outline the overall structure and composition of the atmosphere.
• Layers within the atmosphere (from the ground up) and their characteristics
• Troposphere • 0-12km thick;
• 75% of all gases in atmosphere;
• all weather happens here;
• temperature falls with altitude
• Stratosphere • 12-50 km thick
• temperature increases with altitude (gets warmer!)
• horizontal winds (jet stream)
• contains ozone layer
• Mesosphere • 50-80km thick
• temperature falls with altitude
• meteor showers happen here
• Thermosphere • aurora borealis and aurora australis
• ionosphere here (reflects radio waves for communications)
• can be very very hot (2000 C+) !
• Exosphere • outermost layer of earth’s atmosphere
• 550km+ above earth’s surface
• satellites orbit here
5.6.2 Describe the role of ozone in the absorption of ultraviolet radiation.
• allows UVa and UVb through, but blocks UVc waves
• UVa - causes wrinkles
• UVb - causes skin cancer
• UVc - worst one because of damage to organisms/tissues
• O2 + O + UV → O3
• the energy provided by incoming UV light changes O2 → O3
5.6.3 Explain the interaction between ozone and halogenated organic gases.
• HOG’s are usually stable but break down into halogen atoms (F, Cl, Br, I, At) which
are highly reactive (CFC = chlorofluorocarbon; Cl and F are halogens; organic =
contains carbon, therefore CFC = halogenated organic compound)
• How ozone is depleted by CFC’s:
1. UV radiation breaks off a chlorine atom from a CFC molecule.
2. The chlorine atom attacks an ozone molecule (O3), breaking it apart and
destroying the ozone.
3. The result is an ordinary oxygen molecule (O2) and a chlorine monoxide
molecule (ClO).
International School of Tanganyika IBDP ESS 2010-2011
Instructor: Mr Brad Kremer
ESS Topic 5.6 - Depletion of Stratospheric Ozone
4. The chlorine monoxide molecule (ClO) is attacked by a free oxygen atom
releasing the chlorine atom and forming an ordinary oxygen molecule (O2).
5. The chlorine atom is now free to attack and destroy another ozone molecule
(O3). One chlorine atom can repeat this destructive cycle thousands of times.
• sources of HOG’s - fire extinguishers, refrigerators, AC units
5.6.4 State the effects of ultraviolet radiation on living tissues and biological
productivity.
•
•
•
•
•
reacts with melanin in skin to cause sunburn & skin cancer
overexposure degrades immune system (but how?)
required for production of vitamin D (a good thing)
interferes with photosynthesis in producers (esp. phytoplankton)
zooplankton then gain less energy from phytoplankton, and food chain suffers (i.e.
productivity decreases)
5.6.5 Describe three methods of reducing the manufacture and release of
ozone‑ depleting substances.
• Ozone-depleting substances: CFC’s, halogenated organic gases
• Reduce-Regulate-Restore model
• Reduce:
• replace gas-blown plastics because…
• replace CFC’s with CO2, propane, or air
• replace aerosol propellants
• replace methylbromide pesticides with something other than GHG’s
• don’t use aerosol hair products or deodorant - use alternatives (gel, mousse,
roll-ons etc)
• Regulate:
• recover and recycle CFC’s from refrigerators and AC units
• HCFC’s are better because they don’t persist as long in the atmosphere;
however, they are still harmful to the ozone layer (just less so than CFC’s)
• legislate to have refrigerators returned to the manufacturer in order to recover
materials used in building them
• capture CFC’s from scrap cars AC units
• Restore:
• remove chlorine from the stratosphere or add ozone (not exactly feasible!)
• ozone layer is slowly replenishing itself as long as we continue the ban (see
below)
5.6.6 Describe and evaluate the role of national and international organizations in
reducing the emissions of ozone‑ depleting substances.
• UNEP (United Nations Environment Programme) forges agreements on:
• ITIHC (International Trade in Harmful Chemicals)
• air pollution
• contamination of international waterways
• provide information to countries and public on disadvantages of pollution
• 1987 Montreal Protocol
• international agreement on the emission of ozone-depleting substances
International School of Tanganyika IBDP ESS 2010-2011
Instructor: Mr Brad Kremer
ESS Topic 5.6 - Depletion of Stratospheric Ozone
• froze production and consumption of CFC’s with goal of zero production by year
2000
• LEDC’s granted a longer time to implement the treaty
• China and India have not met their quotas under the MP because of their rapid
economic growth and high demand for refrigeration & AC’s
• good example of a successful international cooperative effort to alter human
impact on the environment
International School of Tanganyika IBDP ESS 2010-2011
Instructor: Mr Brad Kremer