United Nations Environment Programme

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Tool 11: Emissions control technologies for diesels

Emissions control technologies for diesels can substantially reduce harmful emissions. These technologies can be installed by the manufacturer as a standard feature in new vehicles or be installed afterwards in older vehicles (i.e. retrofitted). However, in order to function, all emissions control technologies require low (<500 ppm) or ultra-low (<50 ppm) sulphur diesel.

The primary emissions control technologies available are:

These technologies reduce particulate matter (PM), hydrocarbons (HC) and carbon monoxide (CO). Reducing nitrous oxides (NOx) is more complicated in a diesel engine; some new technologies are now available:

Emissions control technologies in your new vehicles: Newer and stricter regulations on emissions in several industrialized countries and regions – such as Tier II regulations in the US and Euro V in the European Union – are soon to be enacted. These regulations require the adoption of advanced emissions control technologies on new diesel vehicles.

Some new diesel passenger cars already have DPFs as a standard feature. Peugeot was the first vehicle manufacturer to offer DPFs as standard equipment in one of their 2005 models. Today, Mercedes, Citroen, and Audi all offer diesel cars with DPFs. The extra cost is not disclosed but is assumed to be around $500 for a passenger car, which is the same price as that for 3-way catalysts 12 years ago (in Europe), when they became mandatory for petrol vehicles. In many European countries, fiscal incentives are offered for diesel vehicles equipped with PM-filters because they qualify as “environmental cars”.

For trucks, DPFs will soon become mandatory as a result of tougher regulations in the US. In the EU, DPFs are increasingly installed in new trucks and buses driving in sensitive areas such as city centers. Upcoming regulations will also increase the demands on low NOx technologies such as exhaust gas recirculation (EGR) and selective catalytic reduction (SCR). EGR systems are already widely used in new trucks the US and in the EU. SCR systems are introduced in trucks within the EU as a result of upcoming Euro V regulations.

Mexico City has recently undergone a major retrofit programme for their city buses. Photo Diana Navarrete

Installing emissions control technologies in older vehicles - retrofits. Some of the emissions control technologies not only apply to new vehicles but can, at a reasonable cost, be installed or “retrofitted” into older in-use vehicles.

Retrofitting is an appropriate option for heavy-duty diesel vehicles, since these vehicles tend to be used extensively, have a long lifetime, and also have high emissions. Retrofitting is also done for many trucks and buses driving in city centers. Good contact with fuel suppliers and retrofit technology suppliers is helpful before starting a programme to retrofit older vehicles or buy new vehicles already equipped with emissions control technologies.

The Action-in use vehicles Sheet in the Inventory and Options (Tool 18) will give you an estimate of emission reduction when retrofitting your in-use vehicles.

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