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 :
1, 2 and 3
2 and 3 only
1 and 2 only
1 and 3 only
Answer is Right!
Answer is Wrong!
This question was previously asked in
UPSC CAPF – 2011
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.