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# 5 Petrol and diesel emissions

Petrol (known as gasoline or ‘gas’ in the USA) and diesel are refined from crude petroleum. Most of the world’s crude oil supplies are of ‘heavy oil’ which needs to be ‘cracked’ (heated and broken down) to produce shorter chains of hydrocarbons suitable for petrol and DERV fuel. Diesel fuel consists of longer hydrocarbon chains than petrol and needs only about half as much energy to refine. Note, however, that oil produced from ‘fracking’ is relatively light and more suitable for petrol than diesel.

Internationally, there has been a trend towards introducing cleaner conventional fuels through the removal of lead, sulfur and other additives and impurities. Lead was originally added to petrol early in the 20th century 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. The ban is now almost worldwide.

European fuel specifications have a low sulfur content. This has been necessary not just to reduce acid pollution emissions, but also to prevent poisoning of vehicle catalytic converters designed to reduce NOx emissions. ‘Sulfur-free’ petrol and diesel (which in practice means a maximum of 10 parts per million by volume (ppmv)) has been required in the EU since 2009.

It is also worth pointing out here that sulfur dioxide emissions from the diesel engines of shipping are a matter of concern globally and particularly in port cities. Starting in 2020, the sulfur limit for shipping diesel has been reduced from 3.5% (35 000 ppmv) down to 0.5% (5000 ppmv). Note: ppmv = parts per million by volume.

## Emissions in use, manufacture and disposal

Conventional road transport also 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 can be less than 20% of the total life cycle energy use (Rosendfeld et al., 2019). However, for electric vehicles operating on renewable energy, the proportion is likely to be higher. The actual CO2 emissions involved in manufacture will depend on the fuels used. They are likely to be higher for vehicles manufactured in a coal-based country such as China than in the UK.

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 course concentrates on the energy used for the vehicle operations themselves.

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