ozone depletion in the atmosphere

1. OZONE
An Introduction

2. What is Ozone?
• Ozone is a colourless,
gaseous form of oxygen.
• Primarily in the upper
region of atmosphere-
stratosphere.
• The molecule of three
oxygen atom can be said
as ozone.
• 20-40km above earth’s
surface - ozone layer.

3. Ozone Cycle
• O2 + h v  O + O
• O2 + O + M  O3 + M
where M is a catalytic reagent
usually nitrogen.
The overall reaction can be given
as
3O2  2O3
O3 + hv  O2* + O*
Short wavelength UV light has
enough energy to impart it.

4. Cause of Ozone Depletion
• Ozone is mainly destroyed
by the chlorine
compounds(CFC’s) ,
chlorinated solvents(CCl4) as
well as fire extinguishing
chemicals (Halons).

5. Ozone Depletion
• CFC’s include freon-
11(CCl3F) and freon-
12(CCl2F2)
• CCl3F + hv  Cl + CCl2F
• Cl + O3  ClO + O2
• ClO + O  Cl + O2
1 molecule of CCl3F can kill
millions of O3 molecules.
1 Cl can kill 1,00,000 of O3
.

6. Sources of CFC’s
• Aerosols :- CFC is common
propellant.
• Refrigeration and air-
conditioning :- refrigerant is a
gas that becomes liquid when
compressed and during
compression heat is taken up
and it converts into gas.
• Foam :- CFC’s are used to
create air pockets in plastics
forming polystyrene and
polyurethane foams.

7. Consequences
Effects on Humans:-
- Basal and Squamous Cell Carcinomos :-
most common skin cancers in humans
due to UVB(290-300nm) radiations.
Generally mild n rarely fatal.
- Malignant Melanoma :- another type of
skin cancer. Due to UVA and UVB
radiations. Very fatal.
- Cortical Cataracts
- Depress human immune system- lowering
body’s resistance against tumors and
infectious diseases.

8. Continued…
• Effects on Crops :-
Cyanobacteria present in roots for retention of nitrogen is affected by
UV radiations.
Effects on Plankton :-
-Phytoplankton and Zooplankton,vulnerable to UV radiation, form the
basis of marine food web.
-It play an important role in uptake of carbon di-oxide and reducing
this would contribute to green house effect.

10. Prevention
• Avoid leakages in pipes of
refrigerants and air-
conditioners.
• Don’t scrap the ice from inside
freezers using knives,etc. to
puncture the inside casing.
• Do not buy halon based fire
extinguishers.

11. Ozone Recovery
The catalytic destruction of ozone can be
halted through injection of negative
charges.These charges first attach
themselves to the majority species of
oxygen and then transfer to Cl neutrals to
form inert negative Cl ions.The number of
charge carriers in a given volume is
approx. 20 times larger than the Cl
radicals, a significant recovery of ozone
concentration occurs.

12. BLOCK DIAGRAM

13. ANY QUERIES