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Harmful Ultra-Violent Radiation • Ultraviolet Light • Invisible (its wavelength is way shorter than visible light) • Constitutes 10% of sun’s energy.

• Facilitates the formation of vitamin D in all organisms. • There are 8 subtypes in the electromagnetic spectrum. • The damaging effects of UV radiation: • It increases mutation rates, by causing damage to DNA. • It can cause cancers, especially of the skin cancers. • It causes severe sunburn and cataracts of the eye. • It reduces photosynthesis rates in plants and algae and so affects food chain.

Ozone and Ozone Layer • The term “ozone” mainly refers to the compound trioxygen, O3. • Ozone absorbs shortwave radiation, such as ultra-violet radiation (wavelength: 100 nm to 400 nm).

• The term “ozone layer” is one of the earth’s atmosphere layers with relatively high O3 concentration (0.6 ppm, comparing to 0.01 ppm in other layers) . • Most portion of the ozone layer exists in the stratosphere (about 20 – 30 km /12 – 19 mi above Earth). • The thickness of the ozone layer varies in different locations and seasons. • Because of ozone’s radiation-absorption property, the ozone layer absorbs nearly 97% - 99 % of the ultraviolet light coming from the sun.

Atmosphere Layers

Ozone-Oxygen Cycle • Ozone regenerates itself through the Ozone-Oxygen Cycle: • How the ozone layer protects the Earth from UV radiation. • In the process, ultraviolet radiation is prevented to enter further into the atmosphere and converted into heat. • Major source of heat in the stratosphere • The ozone layer maintains a stabilized balance through the cycle. • Reaction Formulas: 1) O2 → 2 O· 2) Ozone-Oxygen Cycle 1) O2 + O· + Energy (heat) → O3 + Energy (heat) 2) O3 + UV Radition → O2 + O· 3) O3 + O· → 2 O2

Ozone Depletion (“The Hole”) • Steady overall decrease • 4% per decade reduction in the total volume of ozone since late 1970s. • “The Hole” • Ozone Hole: Since the 1980s, there has been a hole over the Antarctic between September and October every year. • The Ozzy Ozone Video (0:57 – 04:32) • Tropospheric Ozone Depletion Events • Tremendous amount of ozone layer reduction takes place every spring near polar regions. • Due to a unique springtime chemical process: • Inert salt ions (e.g. Br-) → reactive halogen substances (e.g. Br atoms and BrO) • Ozone layer in boundary layer is depleted near to 0.

Ozone Depletion (continued)

Causes for Ozone Depletion • ODS (Ozone Depleting Substances) • CFCs (chlorofluorocarbons) • Compounds that contains only carbon (C), chlorine (Cl), hydrogen (H), and fluorine (F). • Primarily used as refrigerants with the trademark Freon. • Also found in fire extinguishers and versatile industrial solvents. • First synthesized by a Belgian scientist Frédéric Swarts in the 1890s • Do not break down in the lower atmosphere from 20 to 120 years or more

• After CFCs is dissociated by UV radiation, they release free chlorine that damages the ozone layer (photodissociation): ◦ Cl + O3 → ClO + O2 ◦ ClO + O → Cl + O2

1) Energy (heat) →up O3to+ ThisOprocess be repeated 2 + O· +can Energy (heat) 100,000 times with a single chlorine 2) O + UV Radition → O2 + O· (Cl) atom. 3

• Contributing to global warming (green house gas).

Regulations and Solutions ◦ Vienna Convention for the Protection of the Ozone Layer ◦ A multinational agreement on protecting the ozone layer. ◦ It does not include legal binding reduction goals of ODS.

◦ Montreal Protocol (on Substances that Deplete the Ozone Layer) ◦ a protocol to the Vienna Convention ◦ Since then, it has undergone seven revisions, in 1990 (London), 1991 (Nairobi), 1992 (Copenhagen), 1993 (Bangkok), 1995 (Vienna), 1997 (Montreal), and 1999 (Beijing). ◦ 197 countries ratified it and it became effective on January 1st 1989 ◦ Required a gradual phase-out (reduction in production and emission) of CFCs in the ratified countries. ◦ At its 25-year celebration, Montreal Protocol has effective phased-out 98% of ODS.

Bibliography ◦ Wikipedia, Photodissociation.

◦ Wikipedia, Montreal Protocol.

◦ ◦ ation toco ◦ "Science: Ozone Basics.". Retrieved 2007-01-29. ◦ Wikipedia, Chlorofluorocarbon. ◦ Speth, J. G. 2004. Red Sky at Morning: America ◦ and the Crisis of the Global Environment New arbon Haven: Yale University Press, pp 95.

◦ Wikipedia, Vienna Convention.

◦ Wikipedia, Ozone.

◦ ◦ ention_for_the_Protection_of_the_Ozone_La ◦ Wikipedia, Ozone Layer. yer ◦

◦ Wikipedia, Tropospheric ozone depletion ◦ Oxford, IB Study Guide: Biology. events. ◦ ◦ Enviropedia, Causes of Ozone Depletion. _ozone_depletion_events

◦ Wikipedia, UV. ◦

◦ letion/Causes.php

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Ozone Depletion and Ultraviolet Radiation