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The main exhaust products and their effects on the environment and our health
European rules affecting exhaust emissions from cars first came into force in 1970 and have been tightened up progressively ever since. This means that cars are cleaner now then they have ever been and are set to get cleaner still.
The limits form part of the European type approval regulations – a collection of safety and environmental tests which a new vehicle must pass before it can be sold in the European Union. Euro standards affect the construction of the car and although this will impact on MoT testing, the tests are not the same.
After the first standard in 1970 the next big change came in 1992 with the introduction of the Euro 1 standard. This heralded the compulsory fitting of catalytic converters to petrol cars to reduce carbon monoxide (CO) emissions.
Euro 2 was introduced in January 1996 and further reduced the acceptable limit of carbon monoxide emissions. It also reduced the combined levels of unburned hydrocarbons and oxides of nitrogen for both petrol and diesel vehicles.
Euro 3 came into force in January 2000 and modified the test by eliminating the 40-second engine warm-up period previously allowed before the beginning of the emission sampling. It further reduced permitted carbon monoxide emissions from petrol and diesel cars well.
Euro 4 (January 2005) and Euro 5 (September 2009) have concentrated on cleaning up emissions from diesel cars, especially reducing particulate matter(PM) and oxides of nitrogen (NOx). Some Euro 4 diesel cars were fitted with particulate filters, but all diesel cars need particulate filters to meet the requirements of Euro 5.
In theory, you should be able to burn a 'hydrocarbon' fuel (petrol, diesel, gas etc) with air in an engine to produce just carbon dioxide (CO2) and water (H2O). The rest of the exhaust would be the nitrogen (N2) that came in with the air.
Unfortunately the fuels we burn comprise hundreds of differently structured hydrocarbons that burn in different ways and at different rates. This means that in practice the exhaust contains some that were partially burned, some that reacted with others and some that reacted with the nitrogen.
The main exhaust products and their effects on the environment and our health.
(23 February 2012)