Poorly maintained motor vehicles can emit up to 10 times more pollutants than regularly serviced
vehicles. Many countries now require exhaust emission tests at regular
intervals. This ensures that vehicles are properly maintained and the test also reveals the effectiveness of the emission system.
The main emissions are: nitrogen gas (N2),carbon dioxide (CO2) and water vapour (H2O). These emissions are mostly harmless although it is considered that carbon dioxide contributes to global
warming. But as the combustion process is not perfect, some smaller amounts of more harmful emissions are also
produced: carbon monoxide (CO) - a poisonous gas. Hydrocarbons or volatile organic compounds
(VOCs) - produced mostly from unburned fuel that evaporates and which reacts with sunlight to create high ozone
levels. Nitrogen oxides (NO and NO2, called NOx) contribute to smog and acid
rain. Since January 1993, all new petrol-engined vehicles sold in the EU must be fitted with a catalytic
converter. This is made up of a very thin layer of platinum group metals on a honeycomb
structure. The surface area is huge, about the equivalent of two football
pitches. As exhaust gasses pass through the catalytic converter, a chemical reaction converts CO, VOCs and NOx to less harmful compounds
(water, nitrogen and carbon dioxide). |
