Ozone Layer Depletion
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OZONE LAYER DEPLETIONPRESENTED BY-AFSHA FATIMAFATIMA KHAN
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OZONE•O3
•a gas composed of three atoms of oxygen
•bluish gas that is harmful to breathe•Nearly 90% of the Earth's ozone is in the
stratosphere and is referred to as the ozone layer
•Ozone absorbs a band of ultraviolet radiation called UVB
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OZONE LAYER• Ozone is a triatomic form of oxygen (O3)
found in Earth’s upper and lower atmosphere.
• The ozone layer, situated in the stratosphere about 15 to 30 km above the earth's surface.
• Ozone protects living organisms by absorbing harmful ultraviolet radiation (UVB) from the sun.
• The ozone layer is being destroyed by CFCs and other substances.
• Ozone depletion progressing globally except in the tropical zone.
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Our atmosphere
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Ozone formation
Ozone (O3) Chemically forms when UV hits on stratosphere
Where Oxygen molecules dissociate into atomic oxygen.
• Atomic oxygen quickly combines with other oxygen molecules to form ozone
A pollutant on ground level– A component of photochemical smog
Important for our survival– Absorbs some of the potentially harmful UV radiation which can cause
skin cancer and damage to vegetation
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Split and regenerate repeatedly Highest concentration in the upper atmosphere Concentration decreases at lower altitudes Made up of three oxygen atoms Occurs naturally as a layer in the stratosphere The layer is thinnest around the equator and the
concentration increases towards the poles The amount of ozone above a point on the earth’s
surface is measured in Dobson units (DU)– ~ 260 DU near the Tropics– higher elsewhere
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Ground level Ozone Formation
•Secondary Pollutant•VOCs+ NOx Ozone•In presence of sunlight•Ozone + NOX + HCs Smog (haze)
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Smog Sources
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• Sources of Volatile Organic Carbons
• Sources of NOx
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Ozone depletion• Ozone depletion describes two distinct but
related phenomena observed since the late 1970s: a steady decline of about 4% in the total volume of ozone in Earth's stratosphere (the ozone layer), and a much larger springtime decrease in stratospheric ozone around Earth's polar regions. The latter phenomenon is referred to as the ozone hole. In addition to these well-known stratospheric phenomena, there are also springtime polar tropospheric ozone depletion events.
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•In 1985, using satellites, balloons, and surface stations, a team of researchers had discovered a balding patch of ozone in the upper stratosphere, the size of the United States, over Antarctica.
Team who discovered the hole 1985. From left: Joe Farman, Brian Gardiner, and Jonathan Shanklin
British Atlantic Survey Research station, Holly Bay, Antarctic coast
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Ozone-Depleting Substance(s)
•CFCs•HCFCs •halons •methyl bromide •carbon tetrachloride and •methyl chloroform
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Chlorofluorocarbons (CFCs)
Composed of elements chlorine, fluorine, and carbon
Developed in 1930 by DuPont CFCs were welcomed by industries:
– Low toxicity– Chemical stability– Cheap
Usage:– As refrigerants– As blowing agents– For making flexible foam– As cleaning agents– As propellants
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Effects on Human Health
• Over exposure may:▫ Increase risk of non-melanoma and
malignant melanoma skin cancer
Higher risks of malignant melanoma from severe sunburns – especially in childhood
Risk of malignant melanoma has increased 10%
Risk of nonmalignant melanoma has increased 26%
malignant
Non-malignant
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▫Suppress immune system▫Accelerate aging of skin due high exposure▫Cause an outbreak of rash in fair skinned
people due to photo allergy – can be severe
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Over Exposure to UV-B….
• Increases the risk of cataracts▫ Induces type of protein that provokes
cleaving (splitting) in the lens▫ Leading cause of blindness▫ The prevalence of cataract after age 30 is
doubling each decade
• Causes pterygium▫ A wedge-shaped growth over the central
cornea
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Impacts on other animals
Reduces plankton population Reduces penguin population Reduces the percentage of hatching of frog eggs
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IMPACTS ON PLANT
• Experiments were done to determine if increased UV-B is a threat to terrestrial vegetation:▫ Found
High UV-B exposure does induce some inhibition of photosynthesis
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What Is Being Done to Counter the Effects of Ozone Depletion?
•Montreal Protocol (adopted in 1987) – panel of experts was formed to investigate substances responsible for hole formation▫Established policies that prevent future use of certain
types of chemicals ▫Stipulated that the production and consumption of
compounds contributing towards depletion of ozone in the stratosphere were to be phased out by the year 2000 (2005 for methylchloroform)
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The Environmental Protection Agency (EPA)
•Responsible for enforcing the Montreal Protocol within the U.S.▫The EPA has several programs in place;
Regulating and enforcing on-road car and truck air-conditioning systems
Regulating most air-conditioning and refrigeration appliances
Technician certification Service equipment
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Signs of Recovery???
There have been some signs of recovery▫1997 satellite showed a decline of several known ozone-
depleting gases▫Satellite images show some slowing down of ozone loss
However….Recovery is slow.
Antarctica - Dec. 2012
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Efforts Need to Be Continued
•Create reliable models▫To gain a better understanding of the effects ozone depletion
has on organisms living within different ecosystems
•Enforcement of Montreal Protocol▫To reduce concentrations of chemicals responsible for ozone
depletion
•Monitoring chemicals being emitted
•Gain a better overall understanding on just how ozone depletion is affecting our planet