OZONE LAYER & CFC’S

Understanding Stratospheric Ozone Discovered in 1839 by Christian Schonbein Pale blue, unstable, made up of 3 oxygen atoms Found in stratosphere naturally If found in troposphere considered a pollutant & major contributing factor to photochemical smog Important b/c it screens out harmful UV rays from sun A 1 % loss in ozone = 2% increase in UV reaching earth’s surface

How is Ozone Formed & Maintained? UV light splits O 2 into two free O atoms. One of these free O atoms bonds with another O 2 to make O 3. More UV light can split O 3 to make O and O 2 and the process repeats

The Ozone Hole First discovered in 1985 over Antarctica Why Antarctica? –Exceptionally cold air during long, dark winter months due to strong circumpolar vortex isolating Antarctic air. –Allows ice crystals to form at high altitudes –Chlorine containing cmpds (CFC’s) that destroy ozone are attached to ice crystals –When sun returns in spring, chlorine atoms are liberated & work quickly to destroy ozone

science.widener.edu/svb/ atmo_chem/oct15.html

Latest Data from NASA c.nasa.gov/ c.nasa.gov/ October 9, 2010

Chlorofluorocarbons (CFC’s) and halon gases First used in 1928 by General Motors as refrigerant Widely used in 1940’s & 50’s By 1988, 320,000 metric tons of CFC’s have been released Used as –propellants in aerosol cans –Refrigerants in air conditioning units –Making of Styrofoam –Fire retardants Last for years becuz very stable CFC’s are broken by UV radiation to release chlorine atom which is mostly responsible for breaking ozone molecules O 3 +Cl  ClO+ O 2 ClO+O  Cl+O 2

Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, such as CFCl 3, breaking off a chlorine atom and leaving CFCl 2. UV radiation Sun Once free, the chlorine atom is off to attack another ozone molecule and begin the cycle again. A free oxygen atom pulls the oxygen atom off the chlorine monoxide molecule to form O 2. The chlorine atom and the oxygen atom join to form a chlorine monoxide molecule (ClO) The chlorine atom attacks an ozone (O 3 ) molecule, pulling an oxygen atom off it and leaving an oxygen molecule (O 2 ). Cl C F O O O O O O O O O O

A single chlorine atom removes about 100,000 ozone molecules before it is taken out of operation by other substances

Harmful effects of UV radiation. Skin cancer (ultraviolet radiation can destroy acids in DNA) Cataracts and sun burning Suppression of immune systems Adverse impact on crops and animals Reduction in the growth of ocean phytoplankton Degradation of paints and plastic material

matrix.ucdavis.edu/tumors/tradition/ gallery-ssmm.html

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Ozone Legislation US, Canada, and some of Europe banned nonessential use of CFC’s Montreal Protocol –An international treaty designed to protect the ozone layer –phasing out production of number of substances believed to be responsible for ozone depletion –Effective January 1, 1989 –Five revisions 1990 (London) 1992 (Copenhagen) 1995 (Vienna) 1997 (Montreal) 1999 (Beijing) Sherwood Rowland, Mario Molina, and Paul Crutzen shared a Nobel Prize for their work on ozone. First Nobel Prize awarded for an environmental issue.