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Transport and sustainability
Transport and sustainability

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4 Petrol and diesel emissions

Petrol (known as gasoline or 'gas' in the USA) and diesel are refined from crude petroleum. More energy is required to 'crack' crude petroleum to produce shorter chains of hydrocarbons, which is why diesel needs less energy to refine than petrol (only about half as much).

Internationally, there has been a trend towards introducing cleaner conventional fuels through the removal of lead, sulfur and other additives and impurities. Lead was added as an octane rating improver, but owing to proven health risks (particularly its effect on the mental development of young children), leaded fuels have been phased out in most developed countries and have been banned in the EU since 2000.

European fuel specifications have also led to reduced sulfur content. Fuels that meet these requirements include ultra-low sulfur diesel (ULSD) and ultra-low sulfur petrol (ULSP). Since 2005, all petrol and diesel fuels sold in the EU have had to qualify as ULSD or ULSP, with a maximum sulfur content of 50 ppmv – whereas previous specifications allowed up to 500 ppmv sulfur content. [Recall that 'ppmv' stands for 'parts per million by volume'.] Going even further than this, 'sulfur-free' petrol and diesel (which in practice means a maximum of 10 ppmv) has been required in the EU since 2009.

Emissions in use, manufacture and disposal

Conventional road transport leads to environmental pollution as a result of vehicle and fuel manufacture, the vehicles in use and the disposal of scrap vehicles. These impacts can be assessed using life-cycle analysis, which traces all the environmental impacts of a product – from the extraction and processing of raw materials through to manufacture and delivery of the product, its use and what happens at the end of its life. For petrol- and diesel-engine cars, the energy consumed in use (vehicles in operation) makes up most of the impact (see Figure A.2 and also studies such as Teufel et al., 1993; Mildenberger and Khare, 2000; Ecolane, 2006; Concawe, 2007; and Patterson et al., 2011). Therefore this free course focuses on the emissions associated with vehicle operation, which includes fuel production as well as use on the road.

Figure 2 Typical car life-cycle emissions

There are also environmental impacts associated with road construction, road maintenance and the development of the transport and fuel-supply infrastructure. All these other impacts are important, but here I will concentrate on the energy used for the vehicle operations themselves.