Question

Which of the following statements are correct with reference to Photochemical Smog?
A. It is an oxidizing smog.
B. It is formed by the reaction between NO\(_2\) and hydrocarbons.
C. It is a reducing smog.
D. It is formed in the presence of UV-radiation.
Choose the most appropriate answer from the options given below:

• A. A, B and D only
• B. A and B only
• C. C and D only
• D. B, C and D only

Hint:

Break down the name "Photochemical Smog":

\textbf{Photo}: Needs sunlight (UV radiation).
\textbf{Chemical}: Involves chemical reactions of primary pollutants (NOx + VOCs).
\textbf{Smog}: Forms a haze containing secondary pollutants, which are strong \textbf{oxidizing} agents (Ozone). \end{itemize}

Answer 1

The Correct Option is A

Step 1: Concept Overview:
Photochemical smog, or Los Angeles-type smog, is air pollution prevalent in industrialized cities with many cars. The question asks about its defining traits.

Step 2: Statement Analysis:
- Statement A: Correct. Photochemical smog features high oxidizing agent concentrations, mainly ozone (O\(_3\)), making it oxidizing smog.
- Statement B: Correct. Nitrogen oxides (NOx, including NO\(_2\)) and volatile organic compounds (VOCs), or hydrocarbons, are the primary pollutants causing photochemical smog, largely from vehicle emissions.
- Statement C: Incorrect. This contradicts statement A. Reducing smog, also known as classical or London-type smog, contains high sulfur dioxide (SO\(_2\)) levels from coal burning and has a reducing chemical composition.
- Statement D: Correct. "Photochemical" means sunlight is necessary. Solar ultraviolet (UV) radiation powers the chemical reactions between NOx and VOCs, producing secondary pollutants like ozone.

Step 3: Conclusion:
Statements A, B, and D are correct. Thus, option (A) is the answer.