Answer: Is formed in the atmosphere by reaction between primary pollutants.
- A Is formed in the atmosphere by reaction between primary pollutants
- B Is emitted directly from a source such as a vehicle exhaust
- C Is always less harmful than a primary pollutant
- D Exists only in the stratosphere
Correct answer: A. Is formed in the atmosphere by reaction between primary pollutants
Explanation: Secondary pollutants (e.g., ozone, PAN) are not emitted directly but are produced by chemical reactions among primary pollutants in the atmosphere.
Classical smog is a reducing mixture of SO₂ and fog, while photochemical smog is an oxidising mixture generated by UV-driven reactions of NOx and hydrocarbons.
Concept context
Understand how human activities alter the atmosphere, water, and soil. Covers air pollutants, smog types, ozone depletion, acid rain, greenhouse effect, water and soil pollution, and the principles of green chemistry.