Answer: vehicle exhaust.
- A plant respiration
- B vehicle exhaust
- C ocean spray
- D volcanic ash
Correct answer: B. vehicle exhaust
Explanation: High-temperature combustion in vehicle engines produces the NOₓ that seeds photochemical smog.
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.