Question

Polar stratospheric clouds facilitate the formation of:

• A. \(CIONO_2\)
• B. \(HOCL\)
• C. \(CIO\)
• D. \(CH_4\)

Answer 1

The Correct Option is B

To understand why polar stratospheric clouds facilitate the formation of \(HOCl\), we need to look at the chemistry involved in the stratosphere, particularly around the polar regions.

Polar Stratospheric Clouds (PSCs): These clouds form in the stratosphere at high latitudes during the winter when temperatures drop below -78°C. PSCs provide surfaces for chemical reactions that lead to the depletion of the ozone layer.

Key Reactions in PSCs:

• PSCs contain frozen ice particles and compounds like nitric acid that become critical sites for reactions involving chlorine compounds.
• When the sun returns to the polar regions after the winter, the following reaction can occur on the surface of PSCs: \(ClONO_2 + H_2O \rightarrow HOCl + HNO_3\)

Formation of \(HOCl\): The above reaction shows the formation of hypochlorous acid (\(HOCl\)) from chlorine nitrate (\(ClONO_2\)) and water (\(H_2O\)) on PSCs. Hypochlorous acid is a significant species involved in catalyzing ozone depletion when it breaks down and releases reactive chlorine (Cl).

Explanation of Options:

• \(CIONO_2\): Chlorine nitrate is actually a reactant in the formation of \(HOCl\), not the product.
• \(CH_4\): Methane is not involved in these stratospheric reactions associated with PSCs.
• \(ClO\): While \(ClO\) is an important chlorine radical for ozone depletion, it is not directly formed by reactions on PSC surfaces, but rather from further photodissociation processes.

Therefore, the correct answer is \(HOCl\).