Previous Year Question
Which of the following substances is/are ozone depleting?
Select the correct answer from the codes given below:
Chlorofluoro Carbons
Halans
Carbon tetrachloride
Codes:
1 only
1 and 2 only
2 and 3 only
1, 2 and 3
Correct Answer: D
Detailed Solution
Ozone-Depleting Substances (ODS) are chemical compounds responsible for the depletion of the Ozone Layer present in the Stratosphere. The Ozone Layer is a region of relatively high ozone concentration located approximately 15–35 kilometres above the Earth's surface. It absorbs most of the harmful Ultraviolet Radiation from the Sun, particularly UV-B radiation. Chlorofluorocarbons (CFCs), Halons, and Carbon Tetrachloride (CCl₄) are all ozone-depleting substances.
Chlorofluorocarbons (CFCs) are chemical compounds composed of Carbon, Chlorine, and Fluorine. They were previously used extensively in refrigerators, air conditioners, Aerosol Propellants, and foam manufacturing. These compounds remain relatively stable in the Troposphere and can reach the Stratosphere. There, exposure to Ultraviolet Radiation causes their decomposition, releasing chlorine atoms that catalyse the destruction of ozone (O₃). During this process, a single chlorine atom can destroy a large number of ozone molecules before being removed.
Halons are mainly bromine-containing halogenated organic compounds that have been widely used in Fire Suppression Systems. For example, Halon-1211 and Halon-1301 are important ozone-depleting compounds. Bromine released from their decomposition in the Stratosphere plays a significant role in ozone destruction. Carbon Tetrachloride (CCl₄) is a chemical compound composed of Carbon and Chlorine, previously used as an Industrial Solvent and in the manufacture of various chemicals. It contributes to ozone depletion by acting as a source of chlorine in the Stratosphere.
The Montreal Protocol was adopted in 1987 to protect the Ozone Layer and entered into force in 1989. It introduced the phased regulation of the production and consumption of ozone-depleting substances. Under the Montreal Protocol, CFCs and Halons are listed in Annex A, while Carbon Tetrachloride is included in Annex B as a controlled substance. Depletion of the Ozone Layer can allow more UV-B radiation to reach the Earth's surface, increasing the risks of skin cancer, cataracts, and damage to vegetation and aquatic ecosystems.