Tag: ozone and its depletion

Ozone layer is present in the stratosphere which absorbs the harmful ultraviolet radiation Ultraviolet rays cause heritable mutational changes. They have the capability to destroy plants and animals and can cause skin cancer, cataracts to human beings. Existence of life on earth is possible only because of the presence of ozone layer around the earth. The main cause of the ozone hole was found to be gases that contained chlorofluorocarbons (CFCs), halons and freons. Found commonly in aerosol cans and released by many electronic appliances, these decrease the level of ozone in the stratosphere. All of these gases contain chlorine, which is a major cause behind the thinning of the ozone layer. The presence of chlorine within CFCs break down the ozone gases in ozone layer which increases the chances of ozone depletion. CFCs have accounted for about 80% of ozone depletion. 

Polar spring, also known as the Antarctic Spring is the period from late August to early October and the strong westerlies circulate around the Antarctic continent creating a polar vortex. The polar vortex results in the formation of the polar stratospheric clouds which trap most of the gases including the ozone-depleting factors like CFCs, methyl bromide etc. 

The discovery of the ozone hole over Antarctica was done by British Antarctic Survey Scientist Farman, Gardiner and Shanklin and reported in the Nature journal in May 1985. The ozone hole is defined as the area in the atmosphere where the value of the ozone is less than 220 DU. Paul Crutzen, Mario Molina and Sherwood Rowland gave the observation of CFCs in degradation of the ozone.

The ozone layer in the stratosphere is created by the interaction of the UV radiation from the sun and the oxygen. It is capable of absorbing the most damaging type of UV radiation called the UV-B. The ozone hole refers to the depletion of the ozone by the pollutants like CFCs, HCFCs and HFCs. The pollutants split up due to UV radiation and the nascent chlorine reacts with the ozone molecules to form the oxygen. Over Antarctica, the ozone is highly depleted and so the widest ozone hole is seen there. This is because of the presence of the stratospheric cloud in abundance.

Ozone layer depletion is caused due to CFC's. So, chlorine nitrate, which is found in the stratosphere causes break down of the ozone layer. Chlorine is highly reactive and it interacts with ozone and hence destroys the ozone layer.

Freons are chlorofluorocarbons and are responsible for depletion of ozone layer. 

The severe depletion of the Antarctic ozone layer known as the ozone hole occurs because of the special atmospheric and chemical conditions that exist there and nowhere else on the globe. The very low winter temperatures in the Antarctic stratosphere cause polar stratospheric clouds (PSCs) to form. These clouds contain Chlorine nitrate $(ClNO _3)$

Option (B) is correct.

The ozone layer protects us from harmful ultraviolet rays of the sun.

Ozone is formed as a result of the action of U.V. light on oxygen and it forms a layer in upper layers of the atmosphere. 

Ozone is a form of elemental oxygen. In its most stable form, elemental oxygen exists as diatomic molecules (O2). The molecules of ozone contain three oxygen atoms (O3) and are unstable with respect to O2. Ozone is a very reactive gas, and even at low concentrations it is irritating and toxic. It occurs naturally in small amounts in the Earth's upper atmosphere, and in the air of the lower atmosphere after a lightning storm. 

Ozone has been implicated to have an adverse effect on plant growth: "... ozone reduced total chlorophylls, carotenoid and carbohydrate concentration, and increased 1-aminocyclopropane-1-carboxylic acid (ACC) content and ethylene production. In treated plants, the ascorbate leaf pool was decreased, while lipid peroxidation and solute leakage were significantly higher than in ozone-free controls. 

Ozone, along with reactive forms of oxygen such as superoxide, singlet oxygen, hydrogen peroxide superoxide, singlet oxygen, hydrogen peroxide, and hypochlorite ions, is naturally produced by white blood cells and other biological systems (such as the roots of marigolds) as a means of destroying foreign bodies. 

Thus Option B is correct.