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 O2 into two free O atoms.

• One of these free O atoms bonds with another O2 to make O3.

• More UV light can split O3 to make O and O2 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

• http://ozonewatch.gsfc.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 10-100 years becuz very stable• CFC’s are broken by UV radiation to release chlorine

atom which is mostly responsible for breaking ozone molecules

• O3 +Cl ClO+ O2

• ClO+O Cl+O2

Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, such as CFCl3, breakingoff a chlorine atom and leaving CFCl2.

UV radiation

Sun

Once free, the chlorine atom is off to attack another ozone moleculeand begin the cycle again.

A free oxygen atom pulls the oxygen atom off the chlorine monoxide molecule to form O2.

The chlorine atom and the oxygen atom join to form a chlorine monoxide molecule (ClO)

The chlorine atom attacksan ozone (O3) molecule, pulling an oxygen atom off it and leaving an oxygen molecule (O2).

Cl

Cl

ClC

F

Cl

Cl

OO

Cl

OO

O

ClO

OO

ClO

O

A single chlorine atom A single chlorine atom removes about 100,000 removes about 100,000 ozone molecules before ozone molecules before

it is taken out of it is taken out of operation by other operation by other

substancessubstances

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

www.snec.com.sg/clinical_services/ cataract.asp

Ozone Legislation• 1978- 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.