An air sample analysed at noon in a sunny city shows a strong peak of ozone and peroxyacetyl nitrate, little sulphur dioxide, and high levels of nitrogen oxides and hydrocarbons from traffic. Which description of the smog and its effective control is correct?

1. AOxidising (photochemical) smog; remove $\mathrm{SO}{}_2$ using limestone scrubbers
2. BReducing (classical) smog; fit electrostatic precipitators to chimneys
3. COxidising (photochemical) smog; reduce vehicle $\mathrm{NOx}$ and hydrocarbon emission with catalytic converters
4. DReducing (classical) smog; remove $\mathrm{SO}{}_2$ from coal combustion using scrubbers