Question

which of the following mechanism represent the formation of zone hole in stratosphere? a. o3 + o3 -> 3 o2 b. clo + o3 -> cl + 2 o2 c. cl + o3 -> clo + o2 d. o3 + uvb -> o + o2

Explanation:

Step1: Understand ozone - layer depletion mechanism

Chlorine radicals (\(Cl\)) play a crucial role in ozone (\(O_3\)) depletion. The overall mechanism of ozone depletion by chlorine - containing compounds (like CFCs which release \(Cl\) radicals in the stratosphere) involves a series of reactions.

Step2: Analyze each reaction

• For option A: The reaction \(O_3+O_3

ightarrow3O_2\) is not a common or significant reaction in the context of ozone - hole formation. Ozone - ozone reactions are not the main cause of large - scale ozone depletion.

• For option B: The reaction \(ClO + O_3

ightarrow Cl+2O_2\) is part of the cycle, but it is not the initiating step for ozone destruction by chlorine.

• For option C: The reaction \(Cl + O_3

ightarrow ClO+O_2\) is the key initiating step. Chlorine radicals (\(Cl\)) react with ozone (\(O_3\)) to form chlorine monoxide (\(ClO\)) and oxygen (\(O_2\)). Then \(ClO\) can react further (e.g., \(ClO + O
ightarrow Cl+O_2\), where \(O\) is from \(O_3\) photolysis \(O_3+h
u
ightarrow O_2 + O\)) to regenerate \(Cl\) radicals. So, a single \(Cl\) radical can destroy many \(O_3\) molecules in a catalytic cycle.

• For option D: The reaction \(O_3 + UVB

ightarrow O+O_2\) is the natural photolysis of ozone. While it is part of the ozone - oxygen cycle (\(O_3+h
u
ightarrow O_2 + O\), \(O + O_2+M
ightarrow O_3+M\) where \(M\) is a third body), it is not the reaction that is enhanced due to anthropogenic activities (like CFC release) to cause ozone - hole formation.

Answer:

C. \(Cl + O_3
ightarrow ClO + O_2\)