Which of the following is NOT a secondary air pollutant?
DSSSB JE - 2023,
Answer: D
Nitrogen oxide is not a secondary pollutant. It is a primary pollutant, released directly from combustion in vehicles, furnaces and power plants. Secondary pollutants are not emitted directly but are formed in the air by reactions of primary ones: ozone forms from nitrogen oxides and hydrocarbons in sunlight, formaldehyde forms in the photochemical oxidation of hydrocarbons, and sulphuric acid forms when sulphur dioxide is oxidised and combines with water vapour.
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