ozone depletion (preetamm iiserb)
TRANSCRIPT
PREETAM MEENA
2nd Semester(14117)Indian Institute of Science Education & Research , Bhopal
SUBMITTED TO :- Dr. SAMINA AZHAR(HSS DEPARTMENT)
1) The ozone layer sits in the stratosphere approximately
25km above the Earth.
2) It is made up of ozone gases that act like a blanket to stop
too much UV radiation from the sun entering the
atmosphere.
3) As UV radiation hits the Ozone layer the ozone gas
absorbs the radiation and turns it into oxygen.
4) The Ozone layer prevents the harmful UV radiation
entering the Earth, which is vital because too much of
these UV rays can cause cancer, cataracts and DNA
damage.
5) Small amounts of ozone are constantly being made by the
action of sunlight on oxygen. At the same time, ozone is
being broken down by natural and unnatural processes
that lead to ozone depletion. If this process is greater than
It protects the Earth from ultraviolet
rays emitted by the sun.
The wavelengths of ultraviolet
radiation are absorbed by the ozone
molecules.
Ozone Formation
Ozone (O3)
Chemically forms when UV hits on stratosphere
Oxygen molecules dissociate into atomic oxygen
Atomic oxygen quickly combines with other oxygen molecules to form ozone
O2 O + O
O + O2 O3
The ozone depletion is
the region over
Antarctica with total
ozone 220 Dobson
Units or lower. (The
avg total column ozone
in the atmosphere is
about 300 DU.)
Ozone hole in Sept 2005. Source: NASA
•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.
The ozone layer
• An increase in UV radiation has been linked to an increase in skin cancer which effects fair skinned individuals who are at a greater risk than darker skinned people.
• Scientists have proven that a 1% depletion in ozone causes a 5% increase in cases of skin cancer, the depletion rate has been 6% since 1970 and therefore the number of cancer cases has increased rapidly.
• UV radiation has also increased the number of cases of cataracts, which affects people’s vision.
• Immunity to diseases has also been effected due to the increase in UV radiation entering the atmosphere. The depletion of ozone and increase in UV rays can also lead to DNA damage, which can be catastrophic.
I. Linked to skin cancer – a deadly cancer
II.Linked to cataracts on the lens of the eye causing blindness
1) Skin cancer
2) Eye damage such as cataracts
3) Immune system damage
4) Reduction in phytoplankton
5) Damage to the DNA in various life-forms
1) 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)
6) Possibly other things too that we don't know
about at the moment
UV light and skin cancers– 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
• Disruption of plant
cycles and food
chains
– May limit plant growth
and change plant form,
how nutrients are
distributed,
• Lowers levels of
surface
phytoplankton in the
ocean
• Damages the base of
the ocean food chain
• Chlorofluoro carbons (CFC’s) and other halogenated hydrocarbons contribute to the destruction of stratospheric ozone.
• Just one chlorine and bromine atom can catalyze the destruction of 100,000 ozone molecules
• CFC’s (chlorofluorocarbons)
• Other harmful compounds include HCFCs, halons, methyl bromide, carbon tetrachloride, NO2, and methyl chloroform.
• CFCs were used in refrigerators, home insulation, aerosols, plastic foam, and throwaway food containers.
Note: Both chlorine and bromine from halogenated hydrocarbons deplete the ozone.
• Limiting the use of CFC’s is difficult
• Ban the production and use of CFC’s
• Use CFC substitutes such as HCFC’s and HFC’s
• Recycling refrigerants
• Alternatives to gas-blown plastics
• Alternative propellants
• Alternatives to methyl bromide, a fungicide
• Montreal Protocol (1987): 30 countries agreed to reduce CFC, also encouraging other countries.
– Effectiveness: As a result of the Protocol, ozone-depleting gases have been reduced in recent years. Expected to be completely reduced by 2050.
– Countries are required to report annually on their consumption and emission of ozone depleting substances to the UNEP
• London Convention (1990)
• Copenhagen (1992)
• Chlorine and bromine-containing compounds (CFC’s) are stable in the troposphere, but degraded under intense ultraviolet light in stratosphere.
• UV rays release the chlorine (Cl) from the CFCs, causing ozone (O3) to be depleted
• The chlorine and bromine atoms catalyze the destruction of stratospheric ozone.
The Antarctic Ozone Depletion
• The ozone depletion is defined as the area having less than 220 dobson units (DU) of ozone in the overhead column (i.e., between the ground and space).
25
Destruction of ozone layer
Chlorine atoms from CFCs attack the ozone, taking away ozone and forming chlorine monoxide (ClO).
O3 + Cl O2 + ClO
Chlorine monoxide then combines with another oxygen atom to form a new oxygen molecule and a chlorine atom.
ClO + O Cl + O2
The chlorine atom is free to destroy up to 100,000 ozone
molecules
What is CFCs? 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