5.6 Depletion of Stratospheric Ozone

Depletion of Ozone

Composition of Atmosphere

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)

• Very hot (2000 C+) !

Exosphere• Outermost layer of earth’s atmosphere

• 550km+ above earth’s surface• Satellites orbit here

Ozone3 oxygen moleculesUV (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

Atmosphere

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

HOGS cont.How ozone is depleted by CFC’s:

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 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)

Pollution Management of CFC’s and HOGS• Reduce-Regulate-Restore model

Reduce: Replace CFC’s with CO2, propane, or airReplace aerosol propellants Replace methylbromide pesticides with

something other than GHG’sDon’t use aerosol hair products or deodorant

Regulate:Require a switch to HCFC’s because they don’t persist as long in the atmosphere; (They are still harmful to the ozone layer…just less so)

Create laws to require refrigerators returned to manufacturers to recover harmful materials inside

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

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

Policies Continued1987 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