English Class- Destruction of the ozone layer: Destruction of the Ozone Layer

The ozone layer is a layer in Earth’s atmosphere which contains relatively high concentrations of ozone (O3). This layer absorbs 93-99% of the sun's high frequency ultraviolet light, which is potentially damaging to life on earth.

Problem Description

Despite Ozone Layer is vitally important to life because it absorbs biologically harmful ultraviolet (UV) radiation emitted from the Sun, but it is being destroyed, forming a big hole in it that is commonly referred to as the ozone hole. It is particularly created over Antarctica where exists a special condition that accelerates the depletion of the ozone layer.

Every Arctic winter, a polar vortex (a swirling cold mass) forms over Antarctica. Since there is an absence of sun during Arctic winters, the air becomes incredibly cold and the formation of ice clouds occurs. When the sun returns in the spring, the light shining on the nitrogen oxide filled ice particles activates the formation of chlorine. This excess of ozone destroying chlorine rapidly accelerates the depletion of the ozone layer.

Causes

Chlorofluorocarbons (CFCs) contain fluorine, carbon and chlorine atoms. Besides this, they are considered to be the main cause of Ozone depletion.
CFCs are widely used as coolants in refrigeration and air conditioners, as solvents in cleaners, particularly for electronic circuit boards, as a blowing agents in the production of foam (for example fire extinguishers), and as propellants in aerosols.
It is calculated that a CFC molecule takes an average of 15 years to go from the ground level up to the upper atmosphere, and it has a lifetime in the atmosphere of about 20 to 100 years, and consequently one free chlorine atom from a CFC molecule can do a lot of damage, destroying ozone molecules for a long time.
The detailed mechanism by which the polar ozone holes form is different from that for the mid-latitude thinning, but the most important process in both trends is catalytic (the process in which the rate of a chemical reaction is increased by means of a chemical substance) destruction of ozone by atomic chlorine and bromine.

A chlorine atom reacts with an ozone molecule, taking an oxygen atom with it (forming ClO) and leaving a normal oxygen molecule. The chlorine monoxide (i.e., the ClO) can react with a second molecule of ozone (i.e., O3) to yield another chlorine atom and two molecules of oxygen.

Mechanism of ozone layer destruction by CFCs

Effects

The ozone layer naturally shields Earth's life from the harmful effects of the Sun's ultraviolet (UV) radiation. A severe decrease in the concentration of ozone in the ozone layer could lead to the following harmful effects:
-An increase in the incidence of skin cancer.
-A large increase in cataracts and Sun burning.
-Suppression of immune systems in organisms.
-Adverse impact on crops and animals.
-Reduction in the growth of plankton found in the Earth's oceans.
-Cooling of the Earth's stratosphere and
-Global Warming.