Photochemical smog (Los Angeles type smog) is chemically distinct from classical London smog. Which pollutant is the PRINCIPAL secondary pollutant in photochemical smog that causes its characteristic eye and respiratory irritation?

• A Peroxyacetyl nitrate (PAN) and ozone (O3) ✓
• B Sulphur dioxide (SO2)
• C Carbon monoxide (CO)
• D Particulate matter (PM10)

Explanation

Photochemical smog forms when ultraviolet radiation reacts with primary pollutants (NO from vehicle exhaust, volatile organic compounds) to produce secondary pollutants — chiefly peroxyacetyl nitrate (PAN), ozone (O3), and acrolein. PAN causes intense eye, nose, and throat irritation and is phytotoxic. London smog (classical, reductive smog) is sulfurous — SO2 from coal combustion mixed with fog and soot causing bronchospasm in cold, calm conditions. CO causes systemic hypoxia without direct irritation. PM causes respiratory and cardiovascular effects.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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