Molecules such as CFCs (chlorofluorocarbons) generate free radicals which destroy atmospheric ozone. State the nature of the ozone-destroying free radicals, and write equations to help you to explain how these radicals destroy ozone?
Answers
Answer:
Chlorofluorocarbons and Ozone Depletion
At the University of California, Irvine, F. Sherwood Rowland and Mario J. Molina discovered that
chlorofluorocarbons (CFCs) could deplete Earth’s atmospheric ozone layer, which blocks the sun’s
damaging ultraviolet rays. When the scientists reported their findings in 1974, CFCs were in wide
use in refrigeration, air conditioning and aerosol spray cans. The research set off fierce debates,
yet the work of Rowland and Molina convinced skeptical industrialists, policymakers and the public
of the danger of CFCs.
The scientists’ advocacy — and the discovery by other researchers that the ozone layer over the
Antarctic was thinning — led to worldwide phaseout of CFCs and the development of safer
alternatives. For their work, Rowland and Molina shared the 1995 Nobel Prize in Chemistry with
another atmospheric chemist, Paul J. Crutzen.
Widespread Use of CFCs
In the 1920s, refrigeration and air
conditioning systems used
compounds such as ammonia,
chloromethane, propane and
sulfur dioxide as refrigerants.
Though effective, the compounds
were toxic and flammable, and
exposure to them could result in
serious injury or death. In the
1930s, chemists at Frigidaire led
by Thomas Midgely Jr. worked to
develop nontoxic, nonflammable
alternatives to the refrigerants.
The team focused their effort on
compounds containing carbon
along with halogens such as
fluorine and chlorine. Such
compounds were known to be
volatile and chemically inert,
desirable properties for their use
in refrigeration.
The first compound they
developed was dichlorodifluoro-
methane, which they dubbed
“Freon.” By the early 1970s,
CFCs were in widespread use,
and worldwide production of the
compounds had reached nearly
one million tons per year.
The Importance of Ozone
Ozone, a molecule made up of
three oxygen atoms, is a
confusing molecule from an
environmental standpoint. In the
troposphere, the region of the
atmosphere from Earth’s surface
up to about 6 miles, ozone is a
pollutant that is a component of
smog.
But in the stratosphere,
the region of the
atmosphere from 6 to 31
miles, ozone absorbs the
sun’s potentially
damaging ultraviolet (UV)
radiation. Without this
protective ozone layer in
the atmosphere, animals
and plants wouldn’t
survive on land.
Rowland’s interest in the
fate of CFCs in the
atmosphere was sparked
by a talk he heard at a
conference in 1972. The
speaker discussed a
British scientist’s findings
that practically all of a
particular CFC ever made
was still present in the
atmosphere.
Rowland, a chemistry professor,
decided to study the fate of CFCs
in the atmosphere. Although
CFCs are inert in the lower
troposphere, Rowland realized
that they can be broken down by
UV radiation once they drift up
into the stratosphere.
Courtesy UC