Date post: | 13-Sep-2014 |
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INSTITUTE OF SCIENCE & TECHNOLOGY OF ADVANCE STUDIES & RESEARCH (ISTAR)A SEMINAR REPRESENT ON
OZONE DEPLATION BY :VADI NIKHIL.P :SAVALIYA PIYUS.B
KEY DEFINITIONSKEY DEFINITIONS
Ozone: an molecule with 3 oxygen atoms
Troposphere: the lowest layer of the Earth’s atmosphere, extending about 7km above the poles and 20km above the tropics.
Stratosphere: the second layer of the Earth’s atmosphere “containing” the ozone layer. It’s about 10-50km above the Earth’s surface
Dobsons: The unit in which ozone concentration is measured.
History of Ozone deplation
In 1974-nobel prize winners mario molina and sherwood Rowland discover that CFCs can break down stratospheric ozone.
Chemical Mechanism
Different chemicals are responsible for the destruction of the ozone layer
Topping the list :
chlorofluorocarbons (CFC’s)
man-made, non-toxic and inert in the troposphere
In the stratosphere are photolysed, releasing reactive chlorine atoms that catalytically destroy ozone
What are the causes of ozone depletion?
Presence of chlorofluorocarbons (CFCs)
Presence of oxides of nitrogen
Presence of halogens
Presence of bromine
The radicals would speed up the loss of ozone because they constantly re-emerge to trigger another reaction
Problem of Ozone Deplation
The problem of ozone depletion is caused by high levels of chlorine and bromine compounds in the stratosphere. The origins of these compounds are chlorofluorocarbons (CFC), used as cooling substances in air-conditioners and refrigerators, or as aerosol propellants, and bromofluorocarbons (halons), used in fire extinguishers.
Other Chemical break down ozone Hole
For over 50 years, chlorofluorocarbons (CFCs) were thought of as miracle substances. They are stable, nonflammable, low in toxicity, and inexpensive to produce. Over time, CFCs found uses as refrigerants, solvents, foam blowing agents, and in other smaller applications. Other chlorine-containing compounds include methyl chloroform, a solvent, and carbon tetrachloride, an industrial chemical. Halons, extremely effective fire extinguishing agents, and methyl Bromide, an effective produce and soil fumigant, contain bromine.
Future Evolution of ozone Remains unclear
Current models are unable to reproduce ozone variability accurately
Rates of future increases in greenhouse gases are not yet established
Interactions between ozone depletion and climate change not yet fully understood
Continued monitoring of ozone and ozone-depleting substances is essential
Ozone layer recovery expected by 2050
Hinges on the complete elimination of atmospheric ozone-depleting substances
Replacements for HCFCs, methyl bromide, and halons are still being sought, and studies of the new compounds must continue
Too mush Ultra-violet light can result in
Skin cancer
Eye damage such as cataracts
Immune system damage
Reduction in phytoplankton
Damage to the DNA in various life-forms
this has been as observed in Antarctic ice-fish that lack pigments to shield them from the ultra-violet light (they've never needed them before)
Possibly other things too that we don't know about at the moment
Use “cleaner energy”
Smart transportation and land use
Forestation
Watch less TV
Use less air conditioner
Turn off the light when leaving the room
Take public transport
Use less microwave oven
What can we do to solve the problems of global warming?
What can we do to solve the problems of ozone depletion?
Reduce emissions of ozone-depleting chemicals
Reduce the uses of aerosol sprays
Use the aerosol sprays that are free of CFC compounds instead
What can we do to solve the problems of global warming?
Use “cleaner energy”
Smart transportation and land use
Forestation
Watch less TV
Use less air conditioner
Turn off the light when leaving the room
Take public transport
Use less microwave oven
For society:
Understand acid deposition's causes and effects
Clean up smokestacks and exhaust pipes
Use alternative energy sources
Restore a damaged environment
Look to the future
What is Ozone Deplation?
Ozone is a highly reactive gas comprising triatomic oxygen
Ozone layer in the stratosphere protects the Earth’s surface from UV light
Ozone depletion refers to a lowered concentration of ozone in the upper atmosphere
“Holes” are formed
More UV radiation is reaching the Earth’s surface
What is the ozone layer?What is the ozone layer?
The ozone layer is found between the stratosphere and the troposphere. The ozone layer filters out and converts UV light into heat energy- this makes it a higher temperature than other parts of the upper atmosphere.
Keeping track of the Ozone Keeping track of the Ozone layer…layer…
Dobson set up a worldwide network of ozone monitoring stations which still operate today.
Ozone concentration is measured in units called Dobson's (in his honor).
What’s good and bad about What’s good and bad about the ozone layer?the ozone layer?
Bad: Ozone near the Earth’s surface in the troposphere is an air pollutant with harmful effects on animals and their respiratory systems.
Good: ozone in the stratosphere protects living organisms by preventing harmful UV from reaching the Earth’s surface, by converting it into heat.
UV radiation continually breaks down and creates the ozone layer as shown.
There are three types of UV radiation:
1. UV-a (320-400nm); it causes little damage with only 5% absorbed by the ozone
2. UV-b (280-320nm); causes sunburn, genetic damage and skin cancer over prolonged exposure. 95% absorbed by the ozone
3. UV-c (200-280nm); 100% absorption by the ozone
O₂ + (radiation < 240nm) 2O
High energy UV radiation breaks the oxygen into two oxygen atoms
O₂ + O O₃ + heat
The oxygen atom reacts with the oxygen to form the ozone
The heat is absorbed by the air molecules and raises the temperature of the stratosphere
The ozone is mainly formed on the upper reaches of the stratosphere
O₃ + (radiation < 310nm) O₂ + O
Ozone molecules absorb UV radiation (240-310nm)
This is, chemically, the reverse of the formation of the ozone layer
O₂ + O O₃ + heat
The cycle continues as the oxygen atom immediately reacts with O₂
Chemical energy released when oxygen and the oxygen atom combine is converted into kinetic energy of molecular motion (aka heat)
Overall, penetrating UV radiation is converted into heat without any net loss of the ozone
O₂ + O ↔ O₃
The cycle keeps the ozone in balance
The ozone is broken down and formed at the same steady rate
O₃ + O 2O₂
Luckily this reaction is very slow because the concentration of oxygen atoms is low
However, this balance can be affected by human activity
Ozone DepletionOzone Depletion
Chlorine radicals in the stratosphere mainly come from CFCs, which can only be broken down by the extremely energetic UV radiation found above most of the ozone layer
UV radiation strikes a CFC molecule, producing a chlorine radical Cl•
E.g. CFCl3 Cl• + • CFCl2
The breakdown of ozone takes place in 2 propagation steps
Step 1: Cl• + O3 ClO• + O2
Step 2: ClO• + O Cl• + O2
The propagation steps repeat in a cycle
Overall: O3 + O 2O2
A single CFC molecule can destroy 100,000 ozone molecules
Another radical that destroys ozone is nitrogen oxide (NO) from lightning or aircraft engines
Step 1: • NO + O3 • NO2 + O2
Step 2: • NO2 + O • NO + O2
Overall: O3 + O 2O2
Ozone levels over the northern hemisphere have been dropping by 4% per decade
Around the north and south poles, much larger and seasonal declines have been seen
These are the ozone holes
Regulation Regulation
Montreal Protocol
One of the most successful global envirnomental agreements to be signed.
Nations around the world realised that CFC emissions deplete the O-zone layer and they can damage both human health and the environment
The protocol contains restrictions which limit the use of products with CFC (unless there is no other alternative). At first 30 countries signed to this protocol and now (by 2006) 197 nations have signed the protocol.
The restrictions are:
CFCs - zero production by 2000
Tetra chloromethane (used in solvents) - zero production by 2000
Production of halons (used in fire extinguishers) - zero production by 2000 – if no alternative is found
1,1,1 – trichloroethane (used in solvents) - zero production by 2005
HCFCs and HFCs – To replace CFCs in about 15% of applications
However the problem with HCFCs and HFCs are that they are now thought to also contribute to global warming. Now the protocol wants to call out the use of HCFCs by 2030. There is also the risk that HCFCs are 10 000 times more potent than carbon dioxide. Although there may be enough time to find an alternative to CFCs.
On the other hand there is no restriction to the use of HFCs.