Ozone
is a chemical that is related to oxygen. Oxygen is usually
found as a stable particle, called a molecule, that is made
up of two atoms. However when another oxygen atom is added
the oxygen molecule becomes ozone. This happens when oxygen
is exposed to ultra-violet radiation. The oxygen molecule
completely changes, instead of being essential for breathing
life, it takes on quite different properties.
There is worldwide concern about the decrease in ozone. You
may have heard a lot of talk about "the ozone layer". This
is not a layer like a thick blanket, but is an area in the
outer atmosphere where you can expect to find rather more
ozone than elsewhere. These ozone molecules can be found anywhere,
but they are more concentrated about twenty kilometres above
the earth, in an area called the stratosphere. Here ultra-violet
radiation from the sun reaches the outer atmosphere and hits
oxygen molecules combining them to form ozone. Even so, the
concentration of ozone is only about one molecule in every
100,000.
The ozone layer, or ozonoshere, is this area where you would
expect to find this higher concentration of ozone. If all
the ozone was brought to earth and spread evenly it would
lie no thicker than a sunday newspaper.
Ozone screens out most (90%) of the harmful ultraviolet rays
from the sun. The ultra-violet radiation that penetrates through
the atmosphere has a number of effects both on plants and
people. UV radiation causes sun tanning, and eye irritation,
but also skin cancer. UNEP figures indicate that a 1% decrease
in world ozone would increase skin cancers worldwide by 6%.
The
ozone layer is threatened by a group of chemicals, originally
thought to be "miracle" chemicals, called Chloroflourocarbons.
They are used in all sorts of places, in refrigerators, as
solvents, to propel materials from aerosol cans, and to create
foams for creams. They easily evaporate and get up into the
stratosphere. There they attack the ozone breaking it back
down to oxygen.
People were alerted to what was happening in the mid 1970s.
UNEP launched a project in 1975 to identify hazards threatening
the ozone layer. In 1985 the ozone layer over the antarctic
region was found to be particularly thin. This thin layer
became known as "the hole"in the ozone layer.
The
'hole'in the ozone layer comes and goes each year. Each year,
the ozone layer is studied to see if the "hole"
is bigger or smaller. Tha annual spring thinning of the ozone
layer over Antacrtica was as serious in 2003 as in the record
year of 2000. It also lasted longer than ever, according to
the World Meteorological Organisation. The thinnest part of
the ozone layer was the largest on record. It seems the "small
hole" of 2002 was a one-off, and that it may be 2010
before there is evidence of healing and over 50 years for
full recovery.
In
1987 in Montreal a Protocol was adopted and signed by 62 countries
and the European Community. The agreement pledged to reduce
the use of CFCs to half and to freeze the use of halons.
There are a number of connections between the ozone layer
and the greenhouse effect.
-
CFCs
are greenhouse gases as well as ozone depleters.
-
Depletion
of the ozone layer allows more radiation on earth to hit
the earth increasing the input of heating
-
Some
CFC substitutes are greenhouse gases themselves eg hydrocarbons
-
CFCs
will contribute to both global warming and the ozone depletion
long after they have been banned.
CFCs
Chloroflurocarbons
(CFCs) are synthetic chemicals that contribute to the depletion
of the ozone layer found in the stratosphere. Ozone is made
up of three oxygen atoms and CFCs contain chlorine atoms,
chlorine chemistry is very complex. A chlorine atom can destroy
ozone catalytically.
After being released CFCs remain in the troposphere, the layer
of atmosphere above the earth where our weather is generated,
they eventually rise into the upper stratosphere, above the
ozone concentration. Once up there ultraviolet radiation from
the sun breaks the CFC molecules apart so freeing the chlorine
atoms, these attack ozone. A chlorine atom first steals one
of the oxygen atoms from ozone so breaking the molecule apart
to form chlorine monoxide and a stable oxygen molecule. These
atoms and molecules are not still but are constantly jostling
around in the stratosphere. When a chlorine monoxide molecule
bumps into another oxygen atom, the two oxygen atoms combine
easily, freeing the chlorine atom to continue destroying another
ozone molecule.
Some chemical processes interfere with this catalytic cycle.
Nitrogen dioxide (NO2) can bind to chlorine monoxide and form
a chlorine reservoir - whilst chlorine is bound in this way
it cannot react with ozone.
The unique climatic conditions at the south pole minimize
such interference, allowing the catalytic conversion of ozone
destruction to continue without interference so causing the
ozone hole.
Reduction in the use of CFC's will not reduce the effect that
chlorine atoms are now having on the ozone layer. In order
not to make the situation worse further emissions should be
halted if the ozone layer is to stand any chance of recovery.
OZONE
DEPLETION
History
The Vienna Convention for the Protection of the Ozone Layer
(1985)
The United Nations Environment Programme (UNEP) addressed
the issue of ozone depletion in 1977. Governments committed
themselves to protect the ozone layer and to co-operate with
each other in scientific research through the Vienna Convention
on the Protection of the Ozone Layer in 1985,
The Montreal Protocol on Substances
that Deplete the Ozone Layer (1987)
Since then there have been many changes, in particular the
Protocol in Montreal in 1987. Ozone Control is often referred
to as the "Montreal Protocol". The Protocol aims to reduce
and eventually eliminate the emissions of manufactured ozone
depleting substances. The Montreal Protocol on Substances
that Deplete the Ozone Layer was agreed by Governments in
1987. There have been a number of amendments since.
The London Amendment to the Montreal Protocol (1990)
The Copenhagen Amendment to the Montreal Protocol (1992)
Montreal Amendment to the Montreal Protocol (1997)
The
Montreal Amendment entered into force on 1 January 1999. This
version of the Montreal Protocol also includes the text of
the Amendment adopted by the Parties at the Ninth Conference
of the Parties in Montreal 1997.This laid down the following
schedule for the phase out of ozone depleting substances
Phase
Out Schedule
Control
measures that apply to:
1 January 1994 |
© Halons phased out |
1 January 1996 |
© HBFCs phased out
© Carbon tetrachloride phased out
© All CFCs phased out
© Methyl chloroform phased out |
1 January 1999 |
© Methyl bromide reduced by 25% from 1991 levels |
1 January 1999 |
* Freeze of Annex A CFCs at 1995-97 average levels |
1 January 2001 |
© Methyl bromide reduced by 50% from 1991 levels |
1 January 2002 |
* Freeze of halons at 1995-97 average levels
* Freeze of methyl bromide at 1995-1998 average levels
|
1 January 2003 |
© Methyl bromide reduced by 70% from 1991 levels
* Annex B CFCs reduced by 20% from 1998-2000 average
* Freeze in methyl chloroform at 1998-2000 average levels
|
1 January 2004 |
© HCFCs reduced by 35% below base levels |
1 January 2005 |
© Methyl bromide phased out
* Annex A CFCs reduced by 50% from 1995-97 average
* Halons reduced by 50% from 1995-97 average levels(7)
* Carbon tetrachloride reduced by 85% from 1998-2000
* Methyl chloroform reduced by 30% from 1998-2000 |
1 January 2007 |
* Annex A CFCs reduced by 85% from 1995-97 average
* Annex B CFCs reduced by 85% from 1998-2000 average |
1 January 2010 |
© HCFCs reduced by 65%
* CFCs, halons and carbon tetrachloride phased out
* Methyl chloroform reduced by 70% from 1998-2000 |
1 January 2015 |
© HCFCs reduced by 90%
* Methyl chloroform phased out
* Methyl bromide phased out |
1 January 2016 |
* Freeze of HCFCs at base line figure of year 2015 average
|
1 January 2020 |
© HCFCs phased out allowing for a service tail of up to
0.5% until 2030 for existing refrigeration and air-conditioning
equipment |
1 January 2040 |
* HCFCs phased out |
Outstanding
environmental issues:
-
Several
gases that are being used as ozone-safe replacements for
CFCs - notably hydrofluorocarbons (HFCs) and perfluorocarbons
(PFCs) - also contribute to global warming.
-
Global
warming may slow the ozone layer's healing process because
the warming of the atmosphere near the ground may cause
the stratosphere to become even colder.
-
There
is non-compliance with the Montreal Protocol on the part
of eight countries. Members of the former Soviet Union
have been unable to meet their phase-out schedules due
to their recent transition to market economies.
-
A
number of new substances (namely Chlorobromomethane, n-propylbromide
and Halon-1202) can be marketed as replacements for stronger
ozone-depleting substances controlled under the Protocol
even though they themselves have some ozone-depleting
potential.
-
Concentrations of halons have continued to increase due
to halons' long atmospheric lifetime and releases from
fire extinguishers.
Summary
CFC
Phaseout Schedules:
Allowed Production and Consumption for Developed Countries
(percent of baseline)
|
1987 |
1990 |
1992 |
1990 |
1994 |
|
Origonal Montreal Protocol |
London |
Copenhagen |
U.S Clean Air Act |
European Community |
1990 |
100% |
100% |
85% |
|
|
1991 |
100% |
100% |
80% |
|
|
1992 |
100% |
80% |
75% |
50% |
|
1993 |
80% |
80% |
25% |
25% |
15% |
1994 |
80% |
50% |
25% |
25% |
0% |
1995 |
80% |
50% |
0% |
0% |
|
1996 |
80% |
15% |
|
|
|
1997 |
80% |
15% |
|
|
|
1998 |
80% |
15% |
|
|
|
1999 |
50% |
0% |
|
|
|
2000 |
50% |
|
|
|
|
From 1 January 2002, discarded fridges need to have the insulation
foam removed before the fridge can be recycled or scrapped,
to prevent the release of CFCs into the environment.
For information about Fridges
and Ozone Depleting Substances Regulation
For
latest UN information visit: http://www.unep.org/ozone/
|