Photochemical smog is a form of air pollution that forms in urban areas when sunlight acts on substances emitted by vehicle exhausts. Which combination of primary pollutants causes photochemical smog to form?
- Acarbon dioxide and water vapour
- Bcarbon monoxide and unburnt hydrocarbons
- Cnitrogen oxide and unburnt hydrocarbons
- Dsulfur dioxide and water vapour