Which of the following are examples of secondary air pollutants?

1.Sulphate

2.Nitric oxide (NO)

3.Photochemical smog

4.Peroxyacetyl nitrate (PAN)

5.Polycyclic aromatic hydrocarbons (PAH)

A1, 2, 3 & 4 only

B3, 4 & 5 only

C2, 3 & 4 only

D1, 3 & 4 only ✓ Correct

Correct answer: (D) 1, 3 & 4 only

Explanation

Secondary pollutants form in the air by reactions, and sulphate, photochemical smog and peroxyacetyl nitrate all do so.

Statement 1 sulphate arises when sulphur dioxide is oxidised in the atmosphere.

Statement 3 photochemical smog is created by sunlight driven reactions among other pollutants.

Statement 4 peroxyacetyl nitrate forms in that same photochemical mix.

Nitric oxide and polycyclic aromatic hydrocarbons are emitted directly, so they are primary pollutants.

Primary pollutants are released straight from sources while secondary ones appear only after reactions.

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