THE OZONE LAYERBy: Desiree Collins

History of the Ozone Discovery

Dramatic loss of ozone in the lower stratosphere over Antarctica was first noticed in the 1970s by a research group

from the British Antarctic Survey were monitoring the atmosphere above Antarctica.

What is the ozone hole?

News media confuses it with the problem of global warming

Ozone contributes to the greenhouse effect

Over Antarctica (and the Arctic), stratospheric ozone depleted over past 15 years at certain times of the year

Hole presently size Antarctica, 10km altitude - lower stratosphere

What is ozone?

Ozone forms a layer in the stratosphere, thinnest in the tropics (around the equator) and denser towards the poles

How is ozone formed?

UV radiation strikes the O2 molecule and splits it, atomic oxygen associates itself with another O2 molecule .

Hole Formation Based on Two different mechanisms:

Meteorological mechanism

Movement of air from one place to another in the upper stratosphere

Cold temperature in the upper atmosphere causes nitric acid to freeze into crystals forming wispy pink clouds

Forms a vortex of tightly twisted winds thus forming a hole in the upper atmosphere

Chemical Mechanism

Different chemicals are responsible for the destruction of the ozone layer

Topping the list : chlorofluorocarbons (CFC’s) man-made, non-toxic and inert in the troposphere In the stratosphere are photolysed, releasing

reactive chlorine atoms that catalytically destroy ozone

UV light & DNA

UV-B has a direct effect on DNA DNA absorbs UV light of 260nm The action of UV forms thymine

dimers This can cause a gene mutation

when the DNA replicates

Specific damage by UV light Sunburn Clouding of the cornea and formation

of cataract Skin cancer (melanoma) Reduced rates of photosynthesis

What are CFCs?

Used as propellants in aerosol spray cans

Used as refrigerants in fridges, freezers and air conditioning units

What can be done?

Reduce the use of CFCs They are already banned in aerosols

(1987) BUT they are still used as

refrigerants Recycle fridges and air conditioning

plants

The current situation

The holes developing over the pole suggest that they may be show an improvement

BUT CFC molecules take 30 years to rise up to the stratosphere

The chlorine radicals last a long time The peak ozone damage was

supposed to be in 2000 Damage could go on another 50

years