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6.2 - Stratospheric Ozone - Coggle Diagram
6.2 - Stratospheric Ozone
It is a key component of the atmospheric system as it protects living systems from negative effects of UV radiation from the sun.
Human activities have disturbed the dynamic equilibrium of stratospheric ozone formation. Pollution management strategies are being employed to conserve the stratospheric ozone.
The Ozone layer is in the stratosphere
. The concentration is very small - a few parts per million.
Importance
It absorbs biologically harmful UV radiation from the Sun
It is a form of O and also a GHG. They are three O atoms bonded together that is colourless and poisonous.
We breathe O2 present in the troposphere. In the higher stratosphere there are many O molecules.
Ozone creation
It is formed when the UV radiation is absorbed by the O2 atoms. The bonds break, splitting it into two O atoms
O atoms are very reactive, they bond with O2 molecules in the atmosphere to form O3 (Ozone).
This will break down again when absorbed by the UV radiation and plot back in to an O2 atom and O molecule. The O atom will then go through the process again leading to a dynamic equilibrium
Ozone depletion
Occurs when the equilibrium between the processes of the stratospheric ozone production and destruction (stated above) are disturbed = more ozone destroyed than produced...
Natural phenomena - volcanic eruptions = temporary loss of ozone. HOWEVER, human made compounds with bromine and chlorine are the main cause.
CFC's
DO NOT EXIST NATURALLY - man-made compounds with chlorine, fluorine and carbon. They account for 80% of the depletion
These were first used in firdges in the 1930s. After WWII it increased as they were used in
aerosol cans, hairspray, air conditioning
etc. They were first thought of as safe causing minimal environmental damage.
These are stable and remain 20 - 120 years in the atmosphere consistently depleting the ozone. The UV radiation breaks the bond with the Cl atom which then reacts with the O3 molecule. It takes one O atom forming chlorine monoxide. An O atom hits the ClO leading to O2 and a free Cl atom which repeats the process. THIS IS POSITIVE FEEDBACK, the change is magnified.
Methyl bromide, CFC, HCFC, HFC, Halon
= ozone depleters, act by removing one O atom from the Ozone molecule (O3) thus, it becomes an O2 molecule. HOWEVER, each atom of Cl or Br can break apart thousands of O3
There was a severe depletion over the Antarctic since 1979 and a general world decrease since early 1980s. Global levels declined by 3% annually from 1979 - 1991
Other
ODSs
HCFC:
Created to replace the CFC's. Deplete the ozone yet have a shorter lifespan so don't cause as much damage. They're powerful GHG's
HFC:
Replacement for CFCs. very little damage to ozone yet are powerful GHG's
Methyl Bromide:
A pesticide. Bromine if 75x as powerful as Cl when destroying the ozone. It destroys more ozone than CFCs
Halons:
Used in fire extinguishers. Same as CFCs but contain bromine rather than chlorine = powerful ozone depleter
Impact
Human
Damage to genetic material leading to mutations = skin cancer
Damage to the cornea of the eye = cataracts
Suppression of the immune system - impairs the ability to fight off disease
Aquatic species
Affects growth and reproduction of phytoplankton and their consumers, zooplankton = highly sensitive to UV - B radiation
Plankton is an important source of food for many organisms in the ocean. When ingested, this will have knock-of effects on the entire food chain hence, food web.
Plant species
Developmental processes of some plants are affected by UV-B, leading to possible reductions in crop yields
Montreal Protocol
An international agreement designed to control the amount of ODSs produced. First drawn up in 1987 and signed by 24 countries under the direction of the UNEP
Signatories agreed on freezing production and consumption of many ODSs by 2000s. Since many amendments have been reinforced and 120 countries have signed it.
It represented a landmark, for the first time countries were legally bound to reducing + phasing out ODSs. Failure to comply resulted in penalties.
Also, distinctions were made between MEDCs and LEDCs. LEDCs got more time to implement the treaty + an international fund was set up to help introduce new environmentally friendly tech and chemicals.
India still uses a lot of ODSs in refrigerators and air conditioning due to the fast economic growth.
Management
Recycle refrigerants
Develop new propellant alternatives and gas blown plastics, aerosols, halogenated pesticides etc.
The UNEP has had a key role in the management = instigated the Montreal Protocol
Illegal markets for trading ODSs have emerged. The alternatives are more expensive + less accessible. It is international, the trade flows across national boundaries.
Also, due to the long 120 year lifespan of the ODSs, the management efforts will not be seen directly. it is estimated that Cl will not return to normal levels in the atmosphere before 2050. Also, LEDCs may still be allowed to make or use CFCs (due to the flexible considerations).