Erosion of Ozone Layer

Erosion of Ozone layer

Position of ozone layer : Ozone layer is mainly locate at height 20:40Km above sea level in the lower part of stratosphere layer.

Why ? Because it is the first layer of atmospheric envelope which faces ultraviolet radiations emitted from the sun, and also it contains suitable amount of oxygen gas.

Structure of Ozone layer : Ozone layer is composed of Ozone gas (O 3 ) which consists of three oxygen atoms.

How ? When ultraviolet rays pass from oxygen molecule it break the covalent bond and become one atom then it combine with anther molecule to make (O 3 ) molecule.

Ultraviolet rays UV O 2 O + O UV

O + O 2 O 3

Thickness of Ozone layer The English scientist DOBSON postulated that the thickness of the Ozone layer is compressed into 3mm. Only if it were under the normal pressure and 0 C temperature (STP).

The scientists took “ DOBSON ” as a measuring unit of degree for Ozone layer ( 100 DOBSON unit (DU) is defined as 1mm. Thickness ) so The thickness of Ozone layer=300DU.

The importance of Ozone layer: There are three types of UV rays that differ in wavelength and effect :

Types of UV rays Near UV Rays (UV-A) Medium UV Rays (UV-B) Far UV Rays (UV-C)

Harmful effectsLiving organisms Increase the rate of skin cancer cataract Human : Spoil eggs Amphibians : Death of plankton which is the main nutrient of small marine creature. Marine organisms : Upset the photosynthesis process Terrestrial plants :

Erosion in September ! Since 1978, scientists have noticed that there was erosion in Ozone layer above the South pole,and it increase in September : Why ?

Because all pollutants assemble as black cloud and are pushed by wind towards south pole making Ozone depletions increase from year to year.

Pollutant of Ozone layer : 1.Chlorofluorocarbon (CFC). 2.Methyl bromide gas. 3.Halons. 4.Nitrogen oxides.

Chlorofluorocarbon (CFC) They are compounds known as Freon, which used in: - Cooling substance in air condition sets. - propellant substance in aerosols. - flating substance in making foam backing. - solvent substance for cleaning electric circuits slides.

Methyl bromide gas : It is used as an insecticide to preserve stored agricultural crops.

Halons: They are used in fire extinguishers.

Nitrogen oxides : They are produced from the burning fuel of ultrasound planes (Concord).

The effect of (CFC) compound s on Ozone layer: CFC compounds erode ozone layer in three steps as the following:

The first step: CFCl 3 UV CFCl 2 + Cl

The second step : Cl + O 3 O 2 + ClO

The third step: ClO + O 3 2O 2 + Cl

Protecting the Ozone layer: - An international conference was held in “ CANADA" in to discuss how to protect Ozone layer and take all suitable measures to solve this problem.

- They reached a group recommendations called “MONTEREAL PROTOCOL” where it is signed by 191 nations:

Using of chlorofluorocarbon compounds must be reduced and find safer alternatives. Stop producing concord planes as their exhausts effect the Ozone layer. Some of these recommendations:

In 1990, Montreal Protocol in London has been modified in a way that all nations must ban: Production or handing CFC compounds otherwise they will be allowed to export their goods.

Amount of production In 1989 about 1010 m.t In 1990 about 700 m.t In 1991 about 600 m.t In 1992 about 500 m.t In 1993 about 400 m.t In 1994 about 200 m.t In 1995 less than 200 m.t In 1996 less than 200 m.t

The ministry of education Books

Made by: Rania Ramadan A.