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 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 km 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

Ozone 3 oxygen molecules UV (ultraviolet) radiation is absorbed during the formation and destruction of ozone into oxygen (O 2 )

Ozone and UV light 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

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 reactive Ex. (CFC = chlorofluorocarbon Cl and F are halogens Organic = contains carbon

Process of Ozone Depletion 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 (O 3 ), breaking it apart and destroying the ozone. 3. The result is an ordinary oxygen molecule (O 2 ) 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 (O 2 ). 5. The chlorine atom is now free to attack and destroy another ozone molecule (O 3 ). One chlorine atom can repeat this destructive cycle thousands of times. S ources 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 CO 2, 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 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 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

Hair Bands Ruined the Ozone Poison 1983… so much hairspray