Chlorofluorocarbons (CFCs) are stable in the lower atmosphere. However, when they reach the stratosphere, they are broken down by ultraviolet (UV) radiation from the sun, releasing chlorine atoms (Cl). These free chlorine atoms then act as catalysts in a chain reaction that destroys ozone molecules (O₃). A single chlorine atom can destroy thousands of ozone molecules before it is removed from the stratosphere.
On the ozone layer, the CFC has continuing their effects as :
Asked in OPSC CS Prelims 2021 · Topic: Ozone Layer (Mechanism of Ozone Depletion in the Stratosphere)
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Answer: C. In reactions, the Cl atoms formed by them serve as catalysts leading to the degradation of ozone.
More Environment and Ecology questions
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- CFCs (and other halogenated hydrocarbons like halons) are transported to the stratosphere where UV radiation breaks them down, releasing reactive chlorine and bromine atoms. These halogen atoms catalyze the destruction of ozone (O3). Thus, statement 1 is correct. 2. In polar regions during winter, extremely cold temperatures and the presence of the polar vortex (circumpolar winds) lead to the formation of Polar Stratospheric Clouds (PSCs), which can consist of ice crystals or nitric acid particles. These clouds provide surfaces for heterogeneous chemical reactions that convert less reactive halogen compounds into highly reactive forms (like Cl2). When sunlight returns in spring, these reactive forms are photolyzed, releasing large amounts of chlorine and bromine atoms, leading to rapid ozone depletion (the ozone hole). Thus, statement 2 is correct. 3. Ozone destruction primarily occurs through catalytic cycles involving reactive species. A key cycle involves chlorine monoxide (ClO) and oxygen atoms (O). Chlorine atoms react with ozone (Cl + O3 -> ClO + O2). Chlorine monoxide then reacts with an oxygen atom (ClO + O -> Cl + O2), regenerating the chlorine atom. The oxygen atoms (O) in the stratosphere are formed by the photolysis of oxygen molecules (O2) by UV light; these can be in ground (triplet) or excited (singlet) states, and both react with ClO. Thus, statement 3 refers to the reactive intermediates and partners involved in the catalytic destruction cycle and is correct. 57. Depletion of the stratospheric ozone layer occurs when molecules of ozone are destroyed by chemicals such as
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