Nikhil

INSTITUTE OF SCIENCE & TECHNOLOGY OF ADVANCE STUDIES & RESEARCH ( ISTAR ) A SEMINAR REPRESENT ON OZONE DEPLATION BY :VADI NIKHIL.P :SAVALIYA PIYUS.B [email_address]

KEY 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? 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 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 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: UV-a (320-400nm); it causes little damage with only 5% absorbed by the ozone UV-b (280-320nm); causes sunburn, genetic damage and skin cancer over prolonged exposure. 95% absorbed by the ozone 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 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. CFCl 3  Cl • + • CFCl 2

The breakdown of ozone takes place in 2 propagation steps Step 1: Cl • + O 3  ClO • + O 2 Step 2: ClO • + O  Cl • + O 2 The propagation steps repeat in a cycle Overall: O 3 + O  2O 2 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 + O 3  • NO 2 + O 2 Step 2: • NO 2 + O  • NO + O 2 Overall: O 3 + O  2O 2

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 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.

THAKS TO ALL THE END E-mail:- [email_address] Contact:nikhil vadi(mob.:+919724611099)

Nikhil

More Related Content

What's hot (20)

Viewers also liked (7)

Similar to Nikhil (20)

Recently uploaded (20)

Nikhil