diagram: exhaust filter
Picture courtesy of Johnson Matthey, USA.



title: Reducing Risk

Ceramic filters reduce risks from PM10's

Advanced ceramics have high strength, can survive high temperatures, are chemically inert and light. These properties make them excellent in the production of filters for exhaust fumes.





Self-cleaning filter

Exhaust filters become blocked by the carbon particles, so they need to be replaced regularly. This makes them unsuitable for many vehivles but Johnson Matthey have developed a filter that can clean itself.

Exhaust gases pass over a platinum catalyst which converts Nitrogen monoxide into Nitrogen dioxide. Particulates are filtered out by a ceramic honeycombe. When the temperature of the exhaust rises over 250oC, the Nitrogen dioxide allows the carbon particles to burn off and regenerate a clean filter.





The filters are made out of a ceramic material called silicon carbide. This has a microscopic structure containing millions of pores that can trap the carbon particulates. The ceraminc is light and can withstand the high temperatures of the exhaust gas.

Tests show that the filter removes up to 90% of the PM10's. In central London, this could reduce the average levels of PM10's from 48 to 20 microgrammes per cubic metre.




European limits on PM10's

Particulate filters will help vehicles to meet the increasingly tough emissions regulations and clean up the air in our cities.

EU PM10 limits from diesel engines:

1996 - 0.08 g.km-1
2000 - 0.05 g.km-1
2005 - 0.025 g.km-1


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