Question

The photochemical smog does not generally contain :

• A. NO
• B. NO₂
• C. SO₂
• D. HCHO

Answer 1

The Correct Option is C

Photochemical smog is a type of air pollution that occurs in urban areas with significant automobile activity. It is a complex mixture formed by the reaction of sunlight with pollutants such as nitrogen oxides (NO_x) and volatile organic compounds (VOCs) in the atmosphere. This type of smog is characterized by the presence of the following components:

• Nitric oxide (NO): Emitted during fuel combustion in vehicles and industrial processes.
• Nitrogen dioxide (NO₂): Formed from the further oxidation of NO in the presence of sunlight, contributing to the characteristic brownish haze.
• Ozone (O₃): A secondary pollutant formed by the photochemical reactions involving NO_x and VOCs under sunlight.
• Formaldehyde (HCHO): A type of VOC involved in the formation of photochemical smog, and contributes to the peroxyacyl nitrates (PANs) found in smog.

Now, let's examine each option to identify the component not generally found in photochemical smog:

1. NO is a precursor involved in the formation of photochemical smog.
2. NO₂ is a significant component of photochemical smog, known for its role in creating ozone through photochemical reactions.
3. HCHO (Formaldehyde) is another key component involved in the smog formation process.
4. SO₂ is primarily associated with industrial pollution and traditional (sulfurous) smog, not photochemical smog. It is not generally a part of the photochemical smog components as seen in urban areas.

Based on the components typically involved in photochemical smog, SO₂ is identified as the compound not generally found in photochemical smog. Instead, SO₂ is more relevant in forming classical industrial smog, also known as 'London smog'.

Correct Answer: SO₂