What pollutants are primarily reduced by a catalytic converter in vehicles?

• A. Carbon Monoxide (CO), Non-Methane Hydrocarbons (NMHCs), and Nitrogen Oxides (NOx) are reduced by a catalytic converter.
• B. Sulfur Dioxide, Methane, and Ozone.
• C. Lead, Cadmium, and Mercury.
• D. Phosphates, Nitrates, and Sulfates.

Answer: (A)

Catalytic converters in vehicles are designed to cut the three main gaseous pollutants produced by gasoline engines: carbon monoxide, non-methane hydrocarbons, and nitrogen oxides. The three-way catalyst (typically platinum, palladium, and rhodium) promotes reactions as exhaust passes through. CO reacts with oxygen to form carbon dioxide; non-methane hydrocarbons are oxidized to carbon dioxide and water; and nitrogen oxides are reduced to nitrogen and oxygen. This combination targets the most harmful components emitted in typical exhaust, especially under near-stoichiometric engine conditions.

Other substances listed aren’t the primary targets of this device. Sulfur dioxide and various sulfur-containing or particulate pollutants come from fuel sulfur and other industrial sources, not mainly from the exhaust pollutants the catalytic converter is optimized to treat. Lead and some heavy metals were a concern with older fuels, but catalysts are poisoned by lead, and modern engines use unleaded fuel and separate control measures. Phosphates, nitrates, and sulfates are more associated with fertilizers, air pollution from different sources, or environmental deposition than with the core exhaust pollutants addressed by catalytic converters.