Photochemical smog: Formed when sunlight acts on nitrogen oxides (NOx) and hydrocarbons (unburnt fuel), producing secondary pollutants like ozone (O3), peroxyacetyl nitrate (PAN), formaldehyde, etc. It is also called Los Angeles smog or summer smog. It mainly occurs in warm, dry, and sunny climates. Option A: It is controlled by the use of catalytic converters in automobiles. Correct. Catalytic converters reduce emissions of NOx and hydrocarbons, which are precursors of photochemical smog. Option B: It causes corrosion of metals. Correct. Ozone and other oxidants in photochemical smog can corrode metals. Option C: It is a mixture of SO2, smoke, and fog. Not correct. This describes classical smog (also called London smog or reducing smog), which occurs in cool, humid conditions and is a mixture of SO2 and particulates with fog. Photochemical smog, on the other hand, contains NOx, hydrocarbons, and oxidants such as ozone-not SO2-based smoke and fog. Option D: It causes extensive damage to plant life. Correct. Ozone and PAN damage leaves and affect photosynthesis.
