5.6 depletion of stratospheric ozone. depletion of ozone
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5.6 Depletion of Stratospheric Ozone
Depletion of Ozone
Composition of Atmosphere
Troposphere• 0-12km • 75% of all
gases in atmosphere; • All weather
happens here; • Temperature
falls with altitude
Stratosphere• 12-50 km • Temperature
increases with altitude (gets warmer!)
• Horizontal winds (jet stream)
• Contains ozone layer
Mesosphere• 50-80km • Temperature falls with altitude •Meteor showers happen here
Thermosphere• 80-550km• Aurora borealis and
aurora australis • Ionosphere here
(reflects radio waves for communications)
• Very hot (2000 C+) !
Exosphere
• Outermost layer of earth’s atmosphere• 550km+ above
earth’s surface• Satellites orbit
here
Ozone3 oxygen molecules
UV (ultraviolet) radiation is absorbed during the formation and destruction of ozone into oxygen (O2)
Ozone and UV light
• Allows UVa and UVb through, but blocks UVc wavesUVa - causes wrinklesUVb - causes skin cancerUVc - worst one because of damage to
organisms/tissues• O2 + O + UV → O3 • The energy provided by incoming UV light
changes O2 → O3
Ozone and HOGS (Halogenated Organic Gases)
HOG’s are usually stable but break down into halogen atoms (F, Cl, Br, I, At) which are highly reactiveEx. (CFC = chlorofluorocarbon Cl and F are halogens Organic = contains carbon
Process of Ozone DepletionHow 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).
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
UV light and ozone
UV radiation on Life• Reacts with melanin in
skin to cause sunburn & skin cancer
• Overexposure degrades immune system (but how?)
UV radiation and life
• Required for production of vitamin D (GOOD!)• Interferes with
photosynthesis in producers (esp. phytoplankton)• Zooplankton then gain
less energy from phytoplankton, and food chain suffers (i.e. productivity decreases)
Methods of reducing HOGS
• Replace CFC’s with CO2, propane, or air
• Don’t use aerosol hair products or deodorant• Create laws to require refrigerators returned
to manufacturers to recover harmful materials inside
• Capture CFC’s from scrap cars AC units• Remove chlorine from the stratosphere or
add ozone (not exactly feasible!)• Ozone layer is slowly replenishing itself as
long as we continue the ban
National and International Policies UNEP (United Nations Environment Program) forges
agreements on: ITIHC (International Trade in Harmful Chemicals) air pollutioncontamination of international waterwaysprovide information to countries and public on disadvantages of
pollution 1987 Montreal Protocol
international agreement on the emission of ozone-depleting substances
froze production and consumption of CFC’s with goal of zero production by year 2000
LEDC’s granted a longer time to implement the treatyChina 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
Hair Bands Ruined the Ozone
Poison 1983…so much hairspray