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The trouble with CFCs
A CFC (chlorofluorocarbon) is an organic compound which is used because of its
refrigerating effect. This refrigerating effect was first used by Thomas Midgley in 1928
and was used until the late 20th century when they were banned in most modern
countries as they were discovered to be a major cause of the depletion of the ozone
layer. The ozone layer is vital to living organisms on Earth as it protects us from the
sun’s ultra violet rays which can cause skin cancer and DNA mutations.
However when CFCs were first used scientists had no knowledge of the harmful effect
as they only saw the benefits which were a low boiling point, low toxic levels and low
reactivity levels. The low boiling point made it a good refrigerator as it turns to a vapour
quickly, so it can absorb any heat before it heats up the item which is being kept cool.
The low toxic level of CFC was a major plus point as previous refrigerators like
ammonia, chloromethane and sulphur dioxide were all toxic. Finally the low
reactiveness made sure the CFC wouldn’t react with other chemicals involved in
refrigeration systems.
As a result of the benefits of CFCs mentioned above they became extremely popular and
in 1991 it was reported that a massive 682 million kilograms of CFCs were used around
the globe. CFC’s had numerous uses apart from refrigerating as explained above, the
main uses were:
1. Blowing agents - CFCs were used as they produced cells which
helped harden or change the state of polymers, plastic and metal
2. Cleaning agents – CFCs were used to degrease solvents
3. Propellants – CFCs were used to decrease the pressure and
increase the content in a propellant
Despite all the positive traits of CFCs they had major problem which was later
discovered in the 1970s, this problem was that CFCs played a major part in the
depletion of the ozone layer which protects us from UV rays entering our atmosphere.
Scientists have proven that since 1970 4% of the ozone layer has been lost each year
which has been the cause of the infamous hole in the ozone layer above the arctic.
Although there are other contributing factors like barium CFCs are seen as one of the
main reasons for the hole and the overall decrease in the ozone layer. This is because
CFCs aren’t broken down on the Earth’s surface instead they rise up towards the upper
atmosphere where the ozone layer is. CFC is broken down and a chlorine atom is
released. The rest of the CFC is harmless however the chlorine atom isn’t; it reacts with
ozone molecules (o3) to form chlorine monoxide (Clo) and atmospheric oxygen o2. The
remaining Clo continues this process by reacting with ozone to form more chlorine
which starts the whole process again. This process reduces the amount of ozone
molecules in the ozone layer which causes the ozone layer to shrink.
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Following the discovery of the depletion of the ozone layer in the 1970s scientists have
long been searching for and developing an alternative for the harmful CFC compound.
The replacement for CFCs is HCFCs which doesn’t have the same breaking down effect
on the ozone layer (it has some effect but on a much lower scale.) HCFCs don’t affect the
ozone layer as much as CFCs do because they are less stable than CFCs so the chlorine is
easily reacted in rain before the HCFC reaches the ozone layer in the upper atmosphere,
whereas CFCs are more stable so they don’t react in the lower atmosphere and instead
reach the ozone layer and then react.
Although HCFCs have replaced CFCs since the Montreal Protocol in its main uses:
1.
2.
3.
4.
5.
Refrigerants
Solvents
Fire extinguishers
Plastic foam
Blowing agents
There are still some minor uses of CFCs such as asthma inhalers and Halon fire
suppression systems which HCFCs cannot replace instead CFCs are still allowed to be
used due to the minute amount of CFC needed.
As CFCs are no longer being used on a large scale due to the introduction of the much
safer HCFCs the ozone layer appears to be gradually repairing itself (although it is
predicted it won’t completely repair until 2060.) This is because the production and
destruction is a part of a natural equilibrium where ozone gas is naturally lost (broken
down in to O2 and O) when UV rays make contact with them. However an equal amount
of ozone is made in the following process:
1. UV rays hit an oxygen molecule
2. The molecules splits into two separate oxygen atoms
3. A free oxygen atom collides with an O2 molecule producing O3
As man’s cause of the depletion of the ozone layer is decreasing the equilibrium is
shifting so more ozone is being made then being destroyed, therefore the ozone is
essentially repairing itself.
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This image shows the stages of improvement although the final two images are a
prediction. However the first three images show an improvement in the concentration
of ozone which therefore proves that the ozone layer is repairing itself. The first three
images also show that there is a correlation between the amount of CFC used and the
amount of ozone. In 1974 (first image) CFCs were used the most as the connection
between the depletion of the ozone layer and the use of CFCs hadn’t been made.
Furthermore the next two images (1994 and 2009) show an increase in ozone whilst
the amount of CFCs used were dramatically decreased due to the emergence of HCFCs
and the agreements carried out during the Montreal protocol.
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Bibliography:
http://en.wikipedia.org/wiki/Ozone_depletion
http://www.epa.gov/ozone/science/sc_fact.html
http://en.wikipedia.org/wiki/Ozone_layer
http://yosemite.epa.gov/R10/airpage.nsf/webpage/Repairing+The+Ozone+Layer
http://en.wikipedia.org/wiki/Chlorofluorocarbon#Development_of_alternatives_for_CFCs
http://en.wikipedia.org/wiki/Montreal_Protocol#Hydrochlorofluorocarbons_.28HCFCs.29_Phaseout_Management_Plan_.28HPMP.29
http://www.watchyworld.com/alternatives-of-cfc-chlorofluorocarbon/
http://en.wikipedia.org/wiki/Chlorofluorocarbon
http://www.tetech.com/Cold-Plate-Coolers.html
http://zwhudson.myweb.uga.edu/chem8290/substitutes%20for%20CFCs.htm
http://www.epa.gov/ozone/science/process.html
http://www.theozonehole.com/cfc.htm
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