The document discusses ozone depletion and the importance of the ozone layer. It explains that the ozone layer is found in the stratosphere between 10-50km above the Earth's surface and protects the surface from harmful UV radiation. It also discusses how CFCs released into the atmosphere were depleting the ozone layer by causing a chemical reaction that breaks down ozone molecules. As a result of the thinning ozone layer, more UV radiation reaches the Earth's surface, increasing risks of skin cancer, eye disease, and damage to food crops and marine life.

1. Subject: Elements of Mechanical
Engneering
Topic: OZONE DEPLETION

2. Ozone Depletion

4. Importance of the ozone layer
 Near ground level (trochosphere) - pollution
 Form photochemical smog and acid rain
 In the stratosphere (15 - 50 km) - ozone layer screen
out harmful Ultra-violet radiation from the sun.

5. Our atmosphere
 Troposphere:
 The lowest layer (about 15 km from the ground)
 Contains normal air composed of N2, O2, water vapour,
CO2, etc.
 Temperature decreases with altitude
 Stratosphere:
 Above the troposphere
 Temperature increases with altitude
 Contains a lot of ozone (ozone layer):
 Found in the stratosphere between 10 - 50km above the
ground
 Protects us from the harmful effects of UV of certain
wavelengths
 Decrease in ozone concentration  Increase in UV-B
radiation reaching the earth surface

6. Formation of ozone layer
O2 + sunlight  O + O
O + O2  O3

7. 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

8. Ozone formation
 Ozone (O3)
 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
 Split and regenerate repeatedly
 Highest concentration in the upper atmosphere
 Concentration decreases at lower altitudes

9. Ozone formation
 Ozone (O3)
 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

10. 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

11. Present situation
 Stratospheric ozone over Antarctica:
 Has been depleted over the last 15 years
 The ozone hole:
 enlarging
 large enough to cover most of the North America
 would take at least 50 years to restore

12. 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

13. Causes of ozone depletion
 Details are not fully understood
 Catalyzed by halocarbons (carbon compounds
containing fluorine, chlorine, bromine and iodine)
 Examples: CFCs and ClONO2
 Halogen atoms catalyze ozone layer depletion by
destroying ozone molecules and forming oxygen
molecules.
 Much more serious in Antarctica than other regions
on the planet

14. Consequences of less ozone
 Because CFCs has long life span and very stable, it
continuous to attack the ozone layer and more UV-B
reach our earth.
Health
 Sunburn, eye diseases (cataract), skin cancer.
 Reduce our immune system  other diseases

15. Food supply
 Reduce photosynthesis - crops affected.
 Kills plankton  fish ↓
Impacts on other animals
 Reduces plankton population
 Reduces penguin population
 Reduces the percentage of hatching of frog eggs

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