- Statement 1 is correct: Chlorofluorocarbons (CFCs) are very stable in the lower atmosphere (troposphere) and do not easily react or break down. Over time, they slowly migrate upwards through diffusion into the stratosphere. - Statement 2 is correct: Once in the upper atmosphere (stratosphere), CFC molecules are exposed to high-energy ultraviolet (UV) radiation from the sun, which breaks the carbon-chlorine bond, releasing highly reactive free radical chlorine atoms (Cl•). A chlorine radical then reacts with an ozone molecule (O₃) to form chlorine monoxide (ClO•) and oxygen (O₂). - Statement 3 is correct: The chlorine monoxide radical (ClO•) is also highly reactive. It can react with a free oxygen atom (O) (which is naturally present in the stratosphere from the breakdown of O₃) to form another chlorine radical (Cl•) and oxygen (O₂). The regenerated chlorine radical can then attack another ozone molecule, continuing the cycle. This chain reaction allows a single chlorine atom to destroy many thousands of ozone molecules before it is eventually removed from the stratosphere by other processes. This catalytic cycle leads to significant depletion of the ozone layer.
Consider the following statements about Chlorofluorocarbons (CFCs) : 1. CFCs remain inert in the troposphere but slowly diffuse into the stratosphere. 2. CFCs in the upper atmosphere are subjected to UV radiations, generating free radical chlorine that immediately reacts with O₃ to form a radical called chlorine monoxide (ClO). 3. Each ClO can initiate a series of chemical reactions, leading to the destruction of the ozone layer. How many of the statements given above is/are correct ?
Asked in UPSC Geoscientist 2024 · Topic: Ozone Layer (Mechanism of Ozone Depletion in the Stratosphere)
More Environment and Ecology questions
- On the ozone layer, the CFC has continuing their effects as :
- Collapsing of polar vortex contributes to the stabilization of the ozone layer because it :
- Which of the following processes would explain ozone losses in the atmosphere? When ozone is exposed to 1. CFCs and UV radiation. 2. long winter circumpolar winds to form ice crystals. 3. singlet oxygen atom and chlorine monoxide. Select the correct answer using the code given below :
- 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
- The supersonic jets cause pollution by the thinning of
- Statement (A) : Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen molecule. Statement (B) : The decrease in ozone has been linked to synthetic chemicals like chloro-fluoro-carbons (CFCs). - Question not attempted
- Select the incorrect statement from the following - (1) In stratosphere chlorine atoms are released from Chlorofluorocarbons (CFCs) by UV rays. (2) Chlorofluorocarbons (CFCs) added to the stratosphere, have permanent and continuing effects on Ozone. (3) The ‘Kyoto protocol’ is for the substances that deplete Ozone layers. (4) In stratosphere, chlorine atoms act as a catalyst for degrading ozone.
- Which one is responsible for Ozone holes ?