Which pollutants are targeted by catalytic converters in vehicle exhaust?

• A. Sulfur dioxide and methane
• B. Carbon monoxide, nitrogen oxides, and hydrocarbons
• C. Ozone and particulates
• D. Water vapor and oxygen

Answer: (B)

Catalytic converters are designed to cut the main harmful gases that come from car exhaust by turning them into less harmful substances as the exhaust passes through. The pollutants they target are carbon monoxide, nitrogen oxides, and unburned hydrocarbons. Carbon monoxide is toxic, so it’s oxidized to carbon dioxide. Nitrogen oxides contribute to smog and acid rain, so they’re reduced to nitrogen and oxygen. Hydrocarbons, which are unburned fuels, are oxidized to carbon dioxide and water. This is achieved with a mix of catalysts (such as platinum, palladium, and rhodium) that accelerate these reactions at the exhaust temperature. Ozone and particulates aren’t the direct targets of catalytic converters, and water vapor and oxygen are not pollutants in this exhaust context.