Topic 17 of 34
Combustion products have different environmental effects
A catalytic converter reduces several pollutants but does not remove carbon dioxide emissions.
A-Level 9476 (2026-2027)
Combustion products have different environmental effects
A catalytic converter reduces several pollutants but does not remove carbon dioxide emissions.
| Emission | Origin and consequence | Catalytic treatment |
|---|---|---|
| CO | Incomplete combustion; interferes with oxygen transport in the body. | 2CO + O2 → 2CO2. |
| NOx | Nitrogen and oxygen react under high-temperature engine conditions; contributes to air pollution, acidic deposition and photochemical smog. | A representative reduction is 2NO + 2CO → N2 + 2CO2. |
| Unburnt hydrocarbons | Fuel escapes complete combustion; contributes to photochemical pollution with NOx in sunlight. | Oxidise to CO2 and H2O on the catalytic surface. |
| CO2 | Product of complete combustion; increased atmospheric amounts contribute to the enhanced greenhouse effect. | Ordinary exhaust catalysts do not remove it. |
Gases such as CO2, CH4 and N2O absorb outgoing infrared radiation. Increasing their atmospheric abundance strengthens the greenhouse effect and changes the climate energy balance. Distinguish this mechanism from ozone depletion and from local toxicity: a pollutant can contribute to more than one problem, but the chemical causes are not interchangeable.
A catalyst needs suitable temperature and contact with active sites. Removing CO, NOx and hydrocarbons improves exhaust composition, while fuel use and carbon content still determine the associated carbon dioxide production. Assess a proposed fuel using energy output, incomplete-combustion products and wider emissions rather than one chemical label alone.