The photochemical smog does not generally contain :

CONCEPT:

Photochemical Smog

• Photochemical smog is a type of air pollution produced when sunlight reacts with nitrogen oxides (NO_x) and volatile organic compounds (VOCs) in the atmosphere.
• Common components of photochemical smog include ozone (O₃), peroxyacetyl nitrate (PAN), nitrogen dioxide (NO₂), and aldehydes such as formaldehyde (HCHO).
• Sulfur dioxide (SO₂) is typically not a component of photochemical smog; it is more associated with industrial smog and acid rain.

EXPLANATION:

• NO (nitric oxide) and NO₂ (nitrogen dioxide) are precursors in the formation of photochemical smog.
• HCHO (formaldehyde) is also a component of photochemical smog due to its formation from VOCs in the presence of sunlight.
• SO₂ (sulfur dioxide) is not typically involved in the chemical reactions that lead to photochemical smog.

The correct answer is 3) SO₂.