Which components of smog are most likely released from automobile exhaust?

• A. Nitrogen oxides and volatile organic compounds
• B. Sulfur dioxide and ammonia
• C. Particulate matter and carbon monoxide
• D. Ozone and sulfur trioxide

Answer: (A)

Photochemical smog forms when nitrogen oxides and volatile organic compounds released by automobile exhaust react in sunlight to produce ground-level ozone and other oxidants. Cars emit both NOx and VOCs, so these two components are the primary precursors that drive the sunny, hazy smog associated with vehicle pollution. The other options don’t fit as well: sulfur dioxide and ammonia aren’t the main car exhaust precursors for smog formation; particulate matter and carbon monoxide are pollutants emitted by vehicles but not the key pair that creates the photochemical smog in sunlight; ozone is a secondary pollutant formed in the atmosphere rather than directly emitted by cars, and sulfur trioxide isn’t a common vehicle emission.