OZONE LAYER

The ozone layer  is a region of Earth‘s stratosphere that absorbs most of the Sun‘s ultraviolet radiation.

SCREENING OF UV BY OZONE

UV C: Entirely screened by ozone

UV B: Some radiation reaches the earth

UV A: Most radiation reaches the earth

OZONE LAYER FORMATION

O2———-à O + O   (in the presence of UV)

O+ O2—–à O3

The ozone thus formed is chemically unstable and breaks down into oxygen molecule and free oxygen

O3——à O+ O2  (in the presence of UV)

Thus in the stratosphere there is continuous formation and degeneration of ozone resulting in an equilibrium between oxygen and ozone.

OZONE LAYER DEPLETION

However ozone depleting substances which contain chlorine/ bromine eg: Chlorofluorocarbons(CF2Cl2) interfere in this equilibrium

CF2Cl2———à CF2Cl + Cl  (in the presence of UV)

The chlorine atom released from chlorofluorocarbon interferes with the natural ozone formation reaction in the following way

Cl+ O3——- > ClO + O2

ClO +O ——à Cl + O2

(Ozone is not getting formed whereas chlorine atom is getting regenerated in the reaction which can further degrade ozone. One chlorine atom can destroy upto 100, 000 ozone molecules).

OZONE DEPLETING SUBSTANCES

The ozone layer can be depleted by free radical catalysts, including nitric oxide (NO), nitrous oxide (N₂O), hydroxyl (OH), atomic chlorine (Cl), and atomic bromine (Br). 

 in recent decades because of the release of large quantities of man-made organohalogen compounds, especially chlorofluorocarbons (CFCs) and bromofluorocarbons. These highly stable compounds are capable of surviving the rise to the stratosphere, where Cl and Br radicals are liberated by the action of ultraviolet light. 

CONSEQUENCES OF OZONE DEPLETION

Increase in UV radiation which reaches the earth which can lead to

HUMANS AND ANIMALS:

Genetic damage, skin cancers, impaired immune system

PLANTS:

Affect their photosynthetic pathway, their metabolism and other physiological processes

AQUATIC ECOSYSTEM:

Death of phytoplankton affecting food chains, death of fish larvae, reduced reproductive capacity of fishes and marine animals

AIR QUALITY:

Increased photodissociation of gases in the troposphere resulting in release of harmful gases.