5. What kinds of vehicles are fitted with exhaust aftertreatment systems? For many years only passenger cars were fitted with catalysts, but now heavy duty trucks, buses and also construction equipment have catalysts and filters. Autocatalysts have been used on cars sold in America and Japan since 1974, now most of the new cars in the world need catalysts in order to meet increasingly stringent legislative limits. Vehicleandenginemanufacturershavemadesignificantprogressovertheyearsin reducingemissionsfromtheirengines, butlegislatedlimitsaresuchthatexhaust aftertreatmentisalsoneeded. Aftertreatmenttakestheformofoneormorecatalysts whichconvertthegaseouspollutantstoharmlessgases, adieselparticulatefilter( DPF) totrapthePM, orboth. Therearelegallimitsforthelevelofimpuritiesinfuel, themostimportantbeingsulphur. Sulphuractsasapoisontomanycatalysts, andthecontentinfuelhasbeenreducedfrom severalthousandpartspermillion( ppm) inthe1970sand1980s, tolessthan15or10ppm inmuchoftheworldtoday. 64. What is being done to reduce pollution? Legislationthateffectivelyrequirednewheavydutyvehiclestobefittedwith aftertreatmentdevicescamemuchlater. Thevastmajorityofthesevehiclesare diesel- fuelledandsomayneedadieseloxidationcatalystaswellasaDPFand/ or NOxreductioncatalyst, dependingonwhichpollutantlimitstheyhavetomeet. 1970 Today

6. Can aftertreatment systems be fitted to old vehicles? Exhaust aftertreatment technology has been successfully fitted to older heavy duty diesel ( HDD) vehicles since the mid- 1990s. This has enabled cities in particular to reduce their ambient pollution levels. Many have made it a prerequisite of low emission zone ( LEZ) schemes, that vehicles have to have a DPF fitted if their emissions do not meet the required legislative standard. This is known as retrofit. Filters can also be retrofitted to passenger cars, although space and design constraints make it difficult to use DPFs that are as efficient as those on larger vehicles. Now heavy duty trucks, buses and also construction equipment have catalysts and filters 7 Filters can also be retrofitted to passenger cars