United Nations Environment Programme

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Tool 10: Low-sulphur diesel

For diesel vehicles, always use the lowest sulphur fuel available. Using low-sulphur diesel has a number of benefits, such as: decreasing emissions of sulphur oxides (SOx) and fine particles (PM2.5); extending engine life; and enabling the use of emission control technologies.

Low-sulphur diesel contains less than 500 ppm (parts per million) of sulphur. Sulphur levels as high as 5,000 to 10,000 ppm can be found in some places in the world. In Japan, Republic of Korea, parts of Europe (such as in Scandinavia and Germany) and in some parts of the US, diesel with sulphur levels as low as <15 ppm is currently used.

Photo: Thomas Harrison-Prentice

Direct environmental and health effects from choosing low-sulphur fuels:

Sulphur is emitted from tailpipes as sulphate or sulphur oxides. Sulphate and sulphur oxides are major contributors to the most dangerous pollutant for human health, ultra-fine particles (i.e. PM2.5). Environmental effects from these emissions include forest declines and deterioration of stone buildings. The quick link SOx provides a detailed description of the various impacts of sulphur emissions and the sheet named ‘Action-Clean Diesel’ in the Inventory and Options (Tool 18) will give you an estimate of SOx reduction by using low sulphur fuel.

Most of the sulphur emissions responsible for environmental damage (such as forest declines in Eastern Europe) were emitted from coal-burning power plants and industries using high-sulphur coal. However, just as the use of high-sulphur coal is decreasing, the use of high-sulphur diesel must also be minimised.

Using high-sulphur fuel prohibits effective emission controls: A significant disadvantage of high-sulphur fuel is that it prevents the use of effective tailpipe emission control technologies. For petrol vehicles, 3-way catalysts can still function, but their effectiveness is drastically reduced. For diesel vehicles, high sulphur levels clog and damage devices such as particulate filters, oxidation catalysts or other emission control technologies, making them useless.

Natural sulphur levels: Sulphur occurs naturally in crude oil and thus also in diesel and petrol, unless the fuels have been desulphurised. Diesel and petrol have different levels of sulphur because they use different fractions of the crude in the production process. The sulphur level in crude also varies globally, from very low “sweet crude” (around 1,000 to 5,000 ppm) to “sour crude” (around 10,000 ppm to 33,000 ppm). The resulting “natural” sulphur level in diesel can thus be from 1,000 ppm to more than 10,000 ppm. Typically, sulphur levels are approximately 2,000 to 5,000 ppm if the diesel has not been desulphurized. For petrol, the “natural” sulphur level is generally between 50 ppm to 1,000 ppm.

Producing low-sulphur diesel:Fuel sulphur levels depend predominately on the natural sulphur level found in the crude oil, which vary by region. However, several technologies exist to desulphurize diesel and petrol at the refinery, such as hydro treating or sulphur adsorption. Costs for upgrading or reconfiguring the refinery equal approximately 2 to 10 cents per gallon of fuel. Experience has shown that it is more cost-effective to move directly to the lowest sulphur level (<15 ppm), as opposed to taking incremental steps. Experience around the world has also shown that the benefits arising from lower sulphur levels – such as better air quality and less wear and tear on vehicle engines – outweigh the costs. 

Availability of low-sulphur diesel: The map below shows the sulphur levels globally as they were in 2006. For more up-to-date information and to see your own region in detail, please check the PCFV website and click on your region.

Figure 7: Worldwide sulphur levels in diesel fuel (2009). Source: PCFV/UNEP

For more info on low sulphur diesel >> www.theicct.org,