☁️🌎Ozone layer in atmosphere has significant impacts for human beings. Let's learn about it in A-Level Chemistry!
CFCs - chlorofluorocarbon
Refrigerants
CFCs are used as working fluids in refrigerators and air conditioners because they are gases at room temperature which can be easily liquefied by compression and because they are stable and non-toxic.
Foaming agents in plastics production
CFCs are used as foaming agents inthe production of polystyrene and foam plastics used for insulation and packing materials
Aerosol’s
CFCs are used as a propellant inspray cans for paint, insect repellents, deodorants
Ozone in the Lower Atmosphere (troposphere)
About 10% of all ozone (O3) in the atmosphere is found in the troposphere (up to 16km above the earth's surface).
Ozone in the troposphere has harmful effects on many living things because it is toxic. For humans, ozone causes eye irritation, compromised lung functions, aggravation of respiratory conditions like asthma, and increases the susceptibility to infection.
Ozone pollution in the troposphere is often linked to photochemical smog.
Ozone in the lower atmosphere is formed during electrical discharge from high voltage appliances as shown in the equations below:
O2(g) -----> 2O(g)
O2(g)+ O(g) -----> O3(g)
Gases are removed from the lower atmosphere in two general ways:
-They either dissolve in the clouds and are rained out,
-Or they react chemically to be converted into other substances.
Neither of these mechanisms are particularly relevant for CFCs. Chlorofluorocarbons are insoluble in water, and they are so stable that they can exist in the lower atmosphere for years.
Ozone in the Upper Atmosphere (stratosphere)
About 90% of all ozone (O3) in the atmosphere is found in the stratosphere (16 to 32 km above the earth's surface).
In the stratosphere ozone acts as the primary UV radiation shield, short wavelength UV radiation from the sun(<240nm) provides the energy to split oxygen molecules into oxygen atoms:
O2(g)(UV radiation) ------> 2O(g)
Oxygen atoms then react with oxygen molecules to form ozone:
O(g)+ O2(g)-------> O3(g)
Ozone can absorb harmful UV-B and UV-C radiation, preventing it from reaching the earth's surface:
O3(g)(UV radiation) ------> O2(g)+ O(g)
The constant formation and destruction of ozone maintains a balance over time. Human activities, such as the release of chlorofluorocarbons in to the atmosphere, have disturbed this balance.
During the life time in the atmosphere, the CFC molecules wander around moving wherever the air currents take them. They can eventually make their way up into the stratosphere where for the first time they come into contact with (UV) radiation of high enough energy to cause them to break down.
For example, energy of wavelength less than 215 nm will break the covalent bond between one of the chlorine atoms and the carbon atom in CF2Cl2.
Initiation: CF2Cl2 ----> Cl• + •CFCl
The breakdown of ozone takes place in two propagation steps:
Propagation Step1 Cl• + O----> ClO• + O
Propagation Step2 ClO• + O----> Cl• + O
The two propagation steps above repeat in a cycle, many thousands of times, with each cycle removing another ozone molecule.
Overall:O + O ----> 2O
Another radical that destroys ozone is nitrogen oxide, •NO.
As with the chlorine radicals,the breakdown of ozone proceeds in two propagation steps:
Propagation Step 1 •NO + O ---> •NO + O
Propagation Step 2 •NO + O ---> •NO + O
Overall: O + O ---> 2O
Montreal Protocol aimed at preserving the ozone layer
- Production of CFCs stopped by 2000
- Production of tetrachloromethane (used as a solvent) stopped by 2000
- Production of halons (used infire extinguishers) phased out by 2000
- Production of 1,1,1-trichloroethane (used as a solvent) phased out by 2005
- The use of HCFCs to replace CFCs in about 15% of applications.
If the amount of stratospheric ozone continues to decrease there are many consequences...
- Health implications because more dangerous UV radiation can get through, include: Cataracts, sunburn, skin cancer, weakens immune system.
- Global warming continues meaning more abrupt weather changes, more natural disasters, and rising water levels may overtake land inhabited by humans.
- Plants/Cropsdie – can’t adapt to climate/affected by UV.
- Danger to marine life and land animals.
Drafted by Eunice (Chemistry)
References:
http://www.dynamicscience.com.au/tester/solutions1/chemistry/greenhouse/cfc.htm
https://en.wikipedia.org/wiki/Ozone_depletion
https://scied.ucar.edu/learning-zone/atmosphere/ozone-layer