15) OZONE
Ozone (03) is a highly reactive, colourless gas, each molecule
of which is made up of three oxygen atoms. Oxygen is usually
found in the air and dissolved in water as O2, i.e. the two-atom
form of oxygen. Oxygen (O2) is essential for human and all other
life, except some bacteriological processes that are anaerobic.
High in the atmosphere, the three-oxygen-atom ozone forms the
ozone layer, which helps shield life on earth from the sun's
damaging UV (ultraviolet) radiation. At ground level, however,
ozone is a pollutant, irritating eyes, nose and throat, and
damaging the respiratory system. It is especially harmful to
people with cardiorespiratory problems. Ozone also corrodes some
metals.
THE OZONE 'LAYER'
This band of concentrated ozone is found in the stratosphere, an
upper layer of the atmosphere, 10 to 50 kilometres above the
earth's surface. Ozone shields life on earth from the sun's UV
radiation. Plants and animals living at different altitudes are
adapted to different amounts and wavelengths of UV radiation.
Some scientists believe that the evolution of life on earth has
been made possible by the existence of the protective ozone
shield.
OZONE DEPLETION
In 1982 a team from the British Antarctic Survey working in
Antarctica found that much of the ozone overhead had vanished.
Suspecting that their well-worn instruments might be faulty, the
team returned, with new equipment, in 1983 and 1984 - to find
even less ozone. The report of their findings caused a sensation,
as ozone depletion of this scale was totally unforseen. In
reaction to the British Antarctic Survey results, NASA (National
Aeronautics and Space Administration) scientists re-examined data
from their weather satellite, Nimbus 7. They found that the
satellite had indeed registered the same massive depletions, but
the computers had been programmed to reject such findings as
impossible!
It is now known that a depletion, often termed a hole, of the
ozone layer over Antarctica occurs each spring, and lasts for
approximately six weeks. It is as wide as the United States, and
up to 50% depletion can occur.
The ozone layer was first discovered by Professor Gordon Dobson
of Oxford University in 1957. Today ozone concentration is
measured in Dobson Units.
CAUSES OF OZONE DEPLETION
Ozone is destroyed mainly by chlorine-based compounds,
chlorofluorocarbons (CFCs), and chlorinated solvents such as
carbon tetrachloride, as well as the fire-extinguishing
chemicals, halons. Chlorine molecules are highly reactive and
readily break apart the three-atom ozone into the two-atom form
of oxygen. It is estimated that one chlorine atom can destroy
100 000 ozone molecules. Halons release bromine atoms which are
even more potent ozone destroyers.
CFCs
When they were discovered in 1928, CFCs appeared to be perfect
industrial chemicals: odourless, non-toxic, non-flammable and
chemically inert. This last property is particularly useful as
it means that CFCs do not react chemically with other materials,
such as the working parts of refrigerators, the contents of
aerosols or plastics. However, when CFCs are released into the
atmosphere, they slowly drift up to the ozone rich stratosphere
where they break down and release atoms of chlorine. Each
chlorine atom may react repeatedly to destroy many ozone
molecules. Unfortunately CFCs are very stable, i.e. they do not
easily break down or change form. Thus they can remain in the
atmosphere for more than 100 years.
USES OF CFCs
* Aerosols: CFCs used to be common aerosol propellants. Today,
however, all domestic aerosols made in South Africa are free of
CFCs. Certain medical aerosols, such as asthma pumps, contain
CFCs as a safe alternative has not yet been found. Fewer than 4%
of aerosols made in South Africa contain CFCs.
* Refrigeration and air-conditioning: Refrigerators, freezers
and air-conditioners rely on CFCs as refrigerants. A refrigerant
is a gas which, when compressed, becomes liquid. During
compression heat is taken up. Once the pressure is released, the
liquid changes to a gas and heat is released. During this process
the fridge is cooled.
* Foam: CFCs are used to create millions of air pockets in
plastic, thus forming foamed plastics such as polystyrene and
polyurethane foams. These provide insulation, cushioning and
packaging.
CONSEQUENCES OF OZONE DEPLETION
Ozone depletion will result in increased UV radiation,
specifically the biologically damaging UV-B, reaching the earth.
Consequences of this include:
* A higher incidence of cataracts and skin cancer. A 1% rise in
UV radiation is estimated to produce a 2 - 3% increase in the
frequency of skin cancer.
* Suppression of the immune system of both humans and animals
which could result in an increase in the spread of infectious
diseases.
* Inhibition of photosynthesis, and thus plant growth, would
reduce world food production.
* UV radiation penetrates water by up to 20 metres in clear
conditions. Phytoplankton and zooplankton, vulnerable to UV
radiation, form the base of the marine food web. Increased UV
radiation could damage the marine ecosystem. In addition,
phytoplankton play an important role in the uptake of carbon
dioxide, and reducing this would contribute to the greenhouse
effect (see Enviro Facts "Global Warming").
ACTION ON OZONE
Evidence of ozone depletion motivated growing international
efforts to phase out the use of ozone-depleting chemicals,
resulting in the Montreal Protocol. This international agreement
calls on signatory countries to phase-out CFC use by 1996.
Originally formulated in Montreal in 1987, the agreement was
amended in 1990 and 1992. South Africa signed the Protocol in
1990 and the amended version in 1992. South African industry has
reacted to the Montreal Protocol as follows.
Aerosol industry: By the end of 1992, all CFCs had been phased
out of use, other than those used for medical purposes.
Alternatives to CFCs are a butane-propane mix, or dimethylether.
Foam industry: Expect to have phased out CFC use by 1996.
Alternatives include carbon dioxide, hydrocarbons,
hydrofluorocarbons, partially-halogenated chlorofluorocarbons and
water vapour.
Refrigeration and air-conditioning industry: Faces the greatest
difficulty in phasing out CFCs by 1996. CFC refrigerants
recovered from old equipment can be reclaimed at AECI Midlands
factory, a practice that should reduce production requirements.
Fire fighting industry: Halons are used in many fire-fighting
systems. By the end of 1993, all signatories to the Montreal
Protocol will have stopped manufacturing halons, and new
installations will not be permitted to use halons.
WHAT YOU CAN DO
* The pipes of refrigerators and air-conditioners contain CFCs.
Avoid leakages from these appliances by following these tips:
- Don't scrape the ice from inside freezers using knives or other
hard objects which may puncture the inside-casing.
- If your refrigerator, freezer or air-conditioner (especially
in your car) needs a repair, go to a reputable dealer and ensure
that the service mechanic collects the gas so that it does not
escape into the atmosphere. Also ensure that a test for leaks
is carried out before re-gassing.
- When purchasing new air-conditioners or refrigerators, ensure
that they do not use CFCs.
* Do not buy halon based fire extinguishers (eg. total flood
systems used to protect computer equipment).
DID YOU KNOW?
* Most ozone depleting substances have a lifetime of about 100
years, so we can expect ozone depletion to continue well into the
next century.
Ozone depletion will reach its maximum in the next 10 years, and
recovery to pre-1960 levels will occur between 2050 and 2066.
* Assessment of the ozone problem is complicated by particulate
air pollution (e.g. particles of dust or ash) which has a light
scattering effect and reduces incoming UV radiation; and
increased ground level ozone, which like stratospheric ozone,
decreases UV radiation.
* Since 1978 ozone levels at Durban have dropped on average by
0,2% each year.
FURTHER READING
THE GAIA ATLAS OF PLANET MANAGEMENT.
N. Myers (ed). Pan Books, London, 1985.
ENVIRONMENTAL MANAGEMENT IN SOUTH AFRICA.
R. Fuggle and M. Rabie. Juta, Cape Town, 1992.
All books available from Russel Friedman Books, PO Box 73,
Halfway House 1685. Tel. 011-7022300/1.
USEFUL CONTACTS
Wildlife Society of Southern Africa.
PO Box 44344, Linden, 2104. Tel. 011-486 3294/5 or 0938.
Aerosol Manufacturers Association.
PO Box 483, Olifantsfontein, 1665. Tel. 011 - 884 6319.
AECI.
PO Box 1122, Johannesburg, 2000. Tel. 011 - 223 9113.
Fire Protection Association.
PO Box 61697, Marshalltown, 2107. Tel. 011 - 8366975
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