Q.An example of secondary air pollutant is

Sanitary landfills replaced open dumping/burning of waste.

Open dumping and burning of solid municipal waste in heaps causes air pollution, foul smell, breeding of pests and contamination of surroundings. Sanitary landfills were developed as a safer alternative: waste is dumped in a lined depression and compacted, then covered with soil each da …

Secondary pollutants form in the air from reactions of primary pollutants; PAN, a component of photochemical smog, is the example here — the answer is (d).

• Primary air pollutants are released directly into the atmosphere from a source — e.g. sulphur dust, hydrocarbons, carbon monoxide (CO) (options a, b, c).
• Secondary air pollutants are not emitted directly; they form in the atmosphere by chemical/photochemical reactions among primary pollutants. …