5.6 depletion of stratospheric ozone. depletion of ozone

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5.6 Depletion of Stratospheric Ozone

5.6 Depletion of Stratospheric OzoneDepletion of Ozone

Composition of Atmosphere

Troposphere0-12km 75% of all gases in atmosphere; All weather happens here; Temperature falls with altitude

Stratosphere12-50 km Temperature increases with altitude (gets warmer!)Horizontal winds (jet stream)Contains ozone layer

Mesosphere50-80km Temperature falls with altitude Meteor showers happen here

Thermosphere80-550kmAurora borealis and aurora australis Ionosphere here (reflects radio waves for communications) Very hot (2000 C+) !

ExosphereOutermost layer of earths atmosphere550km+ above earths surfaceSatellites orbit here

Ozone3 oxygen moleculesUV (ultraviolet) radiation is absorbed during the formation and destruction of ozone into oxygen (O2)

Ozone and UV lightAllows UVa and UVb through, but blocks UVc wavesUVa - causes wrinklesUVb - causes skin cancerUVc - worst one because of damage to organisms/tissuesO2 + O + UV O3 The energy provided by incoming UV light changes O2 O3

Ozone and HOGS (Halogenated Organic Gases)HOGs 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 CFCs:UV radiation breaks off a chlorine atom from a CFC molecule.The chlorine atom attacks an ozone molecule (O3), breaking it apart and destroying the ozone.The result is an ordinary oxygen molecule (O2) and a chlorine monoxide molecule (ClO).The chlorine monoxide molecule (ClO) is attacked by a free oxygen atom releasing the chlorine atom and forming an ordinary oxygen molecule (O2).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 HOGs - fire extinguishers, refrigerators, AC unitsUV light and ozone

UV radiation on LifeReacts with melanin in skin to cause sunburn & skin cancerOverexposure degrades immune system (but how?)

UV radiation and lifeRequired 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 HOGSReplace CFCs with CO2, propane, or airDont use aerosol hair products or deodorantCreate laws to require refrigerators returned to manufacturers to recover harmful materials insideCapture CFCs from scrap cars AC unitsRemove 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 pollution1987 Montreal Protocol international agreement on the emission of ozone-depleting substancesfroze production and consumption of CFCs with goal of zero production by year 2000LEDCs 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 & ACsgood example of a successful international cooperative effort to alter human impact on the environment

Hair Bands Ruined the Ozone

Poison 1983so much hairspray


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