Ozone depletion (preetamm iiserb)

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

Ozone is a molecule that contains three atoms of oxygen and thus has

the formula O3

Ozone was first

discovered in 1839

by German scientist

.

It protects the Earth from ultraviolet

rays emitted by the sun.

The wavelengths of ultraviolet

radiation are absorbed by the ozone

molecules.

There is a natural cycle of formation and depletion of ozone

O2 + sunlight O + O

O + O2 O3

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