Which is greener diesel or petrol

The US National Institutes of Health indicates that diesel particulates are "reasonably anticipated to be a human carcinogen", although the link is not definitive despite the figures. Diesel exhaust is a complex combination of products, with the mix highly dependent on the type of engine, the speed the engine is running at and the load. The fuel also contributes to this cocktail.

Low loads produce fewer particles but more organic compounds and engines struggling under high loads produce fewer organics but more particulates. The small invisible particles measured less than a millionth of a metre across, get into the alveolar tissues, carrying with them polyaromatic hydrocarbons and nitroarenes. One answer is to install passive filters or active filtration that includes a reactive chemical that neutralises the particles. Of course, diesel fuels also cause the release of other chemicals.

Nitrogen oxide, NOx is one, a characteristic shared with petrol. Diesel also used to be a significant source of sulphur dioxide, a chemical that produces acid rain when washed out of the atmosphere. Environmental controls have forced down sulphur levels in diesel to counter this. Please update your payment details to keep enjoying your Irish Times subscription. Wed, Oct 29, , More from The Irish Times Motors. Home energy upgrades are now more important than ever.

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Top We count down the best cars for Sign In. Don't have an account? Forgot Password? Meanwhile, manufacturers are also trying to make petrol engines more efficient and economical - using so-called "direct injection" technology.

But that improvement comes at a price. It can mean they produce much higher levels of particulates. So there is a risk petrol engines could actually become dirtier.

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Diesel scrappage scheme considered. Image source, Getty Images. Modern diesel engines are equipped with filters to reduce particulate emissions. However, most vehicle fleets are dominated by the older and considerably more polluting, earlier emission standard vehicles. It will take many years for these vehicles to make their way out of operation.

During this time, human health will continue to be damaged by diesel emissions. The Conversation is checking claims made by public figures. Statements are checked by an academic with expertise in the area. A second academic expert then reviews an anonymous copy of the article. Please get in touch if you spot a claim you would like us to check by emailing us at uk-factcheck theconversation. Please include the statement you would like us to check, the date it was made, and a link if possible.

For example, diesel cars have been promoted, as they produce less CO and HC on average when compared to petrol cars, and they have greater fuel economy producing less CO 2 per km. However recent health concerns about particulate matter have given diesels a less environmentally-friendly image, as have the higher emissions of nitrogen oxides compared with petrol cars.

As a comparison, petrol cars produce virtually no particulate matter, take longer to warm up, produce more carbon dioxide per mile on average, and emissions of the regulated pollutants are higher. A method of pollution reduction currently being utilised involves the use of cleaner petrol and diesel. It is cheaper to improve conventional fuels than to use many of the alternatives and no investment is needed for new storage tanks and service stations.

Ultra low sulphur petrol is now widely available in the UK. To replace pollutant fuels petrol and diesel , alternative fuels are currently being developed. Those put forward as alternatives to petrol and conventional diesel include: compressed natural gas CNG ; liquefied petroleum gas LPG ; city diesel; hydrogen; alcohol fuels; and battery operated vehicles.

Indeed, emissions of CO from CNG powered vehicles are of the same order as those emitted by diesel vehicles. However, emissions of total hydrocarbons THC from CNG vehicles are relatively high because of methane, the major component of natural gas.

Although methane is a small contributor to the formation of low level ozone it is a major factor in global warming.