Tag: causes of greenhouse effect

Free radicals have unpaired electrons. These are extremely reactive. As one chlorine free radical can remove 11000 ozone molecules from stratosphere.

• Nitrous oxide is stable at ground level and breaks down when it reaches the stratosphere to form nitrogen oxides, that trigger ozone-destruction. 
  
• The main cause of ozone depletion are halocarbon refrigerants, such as chlorofluorocarbons (CFCs), HCFCs, halons).
  
• So, the correct option is 'Both B and C'.
  

Ozone layer is formed in the stratosphere of the atmosphere by the action of UV rays on the oxygen molecules. This ozone layer acts as absorbant for the harmful UV radiations and so, these radiation do not cross the troposphere to reach the earth's surface. However, the ozone depleting pollutants like chlorofluorocarbons reach the stratosphere and break when exposed to the UV rays. This process releases the reactive chlorine which further reacts with ozone to form simple oxygen. That is how the ozone layer is depleted. Hence, the correct answer is 'Chlorofluorocarbons'.

Ultraviolet radiations cause photochemical splitting of oxygen molecules in the stratosphere. The nascent oxygen combines with molecular oxygen to form ozone. In troposphere nascent oxygen comes from nitrogen dioxide.

ODS refers to the ozone-depleting substances like chlorofluorocarbons, methyl bromide, methyl chloroform, carbon tetrachloride, hexaflurocarbons that release the chlorine and oxides of chlorine. These react with the UV rays and ozone to release the nascent oxygen. 

The ozone depleting substances include the chlorofluorocarbons, oxides of nitrogen, methyl bromide, carbon tetrachloride etc because these split up when exposed to UV radiations and release the reactive chlorine and bromine. These reactive species of chlorine and bromine then react with ozone to release the nascent oxygen. Sulphur dioxide and carbon dioxide are greenhouse gases. Carbon monoxide is an air pollutant.

Ozone hole refers to the depletion of the ozone layer present in the stratosphere of the atmosphere. The chlorofluorocarbons are the paraffinated halogens that enter the stratosphere with winds and split up when exposed to the UV rays. They release reactive chlorine which further reacts with the ozone to release diatomic oxygen. The ozone hole shows a low concentration of ozone which is less than 220 DU. It is more prominent over Antarctica due to polar vortex and formation of the polar stratospheric clouds.

The ozone layer in the stratosphere is useful because it absorbs the UV radiations from the sun and prevents them from reaching the earth's surface. The depletion of the ozone by the ozone-depleting substances causes the break down of the ozone resulting in the ozone depletion. Due to this, the lives on the earth's surface are exposed to the UV rays. These UV rays induce mutations in the DNA by distorting its structure, leading to the erroneous function and replication of the DNA. The uncontrolled errors at times cause uncontrolled cell proliferation, causing skin cancer.