Which is the Worst Pollutant – Petrol or Diesel?

For years, carmakers and drivers have preferred diesel-powered vehicles. This has changed, though, as more people nowadays wouldn’t want anything to do with diesel vehicles, especially with the UK’s scheduled switch to electric vehicles (EVs) happening in 2040.

The debate between diesel and petrol supporters (or believers?) is ongoing. Some believe that diesel vehicles are better than petrol while others believe petrol is better and diesel-powered engines are the worst pollutants.

Both petrol and diesel have advantages and disadvantages. Choosing which one is better for the environment and human health involves more than just listening to people’s opinions.

Petrol and diesel: differences

Aside from their weight – petrol or gasoline is lighter than diesel – there are several significant differences between the two fuels.

In terms of hydrocarbons, petrol has five to 12 carbon atoms compared to diesel’s average of eight to 21 carbon atoms.  The larger/longer hydrocarbons a fuel has, the more stable it is.

Diesel is at least 10 and 15% denser than petrol per litre or gallon.

Petrol or gasoline fuel use spark-fired engines, which need a spark plug to ignite the cylinder of an engine. Diesel engines are compression-fired, which is considered less polluting and more energy-efficient.

Compression-fired fuel has more thermal efficiency compared to spark-fired engines, only both cannot be considered 100% thermally efficient. Petrol’s thermal efficiency is only around 20 to 25%, with the remaining energy released by the vehicle’s exhaust. The thermal efficiency of diesel fuels is somewhere between 30 and 45%.


The most significant difference between petrol and diesel engines is in what each one emits into the air.

Although diesel engines have more carbon dioxide (CO2) – 2.68 kg per litre compared with petrol’s 2.31 kg per litre, they release lesser CO2 throughout their lifetimes or during long-distance drives.  Additionally, the DfT or Department for Transport said that diesel engines emit lower volumes of CO2 for every kilometre a vehicle travelled because of higher efficiency.

The big difference is in nitrogen oxide (NOx) emissions.

As mentioned earlier, diesel vehicles mix fuel and air to generate more efficient fuel use. As a result of this, the vehicles release NOx, which contains nitric oxide (NO) and nitrogen dioxide (NO2), a toxic combination.

Petrol-powered vehicles, on the other hand, release NOx at volumes that are at least 30% less than that of diesel engines. Nevertheless, they can still cause adverse effects on the environment and human health.

NOx emissions have devastating effects, particularly on the environment and human health.

Which one is the worst pollutant?

Both petrol and diesel vehicles contribute to air pollution. Choosing one or the other will not give you an environmentally safe alternative.

It would be safer to choose the cleaner alternative – electric vehicles (EVs). Some drivers prefer hybrid vehicles, especially those who are not yet ready for EVs. Whichever you choose, you’re sure that your vehicle won’t be releasing dangerous nitrogen oxides.

Nitrogen oxide

Nitrogen oxide is responsible for producing acid rain, smog, and ground-level ozone, which also helps in the formation of ground-level ozone, a pollutant responsible for weakening and damaging vegetation, such as plants and crops.

NOx also triggers depression, anxiety, and other mental health-related issues. Additionally, exposure to NOx emissions can lead to dementia as a result of your cognitive abilities weakening.

The most devastating effects of NOx emissions, however, are on a person’s overall health. Here are some of the health impacts you might have:

  • Asthma
  • Bronchitis, emphysema, and other respiratory issues
  • Pulmonary oedema
  • Difficulty in breathing/shortness of breath
  • Asphyxiation
  • Laryngospasm
  • Cardiovascular diseases
  • Cancer
  • Premature death

Diesel vehicles are known to emit volumes upon volumes of NOx, and this was never more evident than during the Dieselgate diesel emissions scandal.

The diesel emissions scandal

The Dieselgate scandal first broke out in September 2015 after the Volkswagen Group received a notice of violation from US authorities for their alleged use of illegal defeat devices in Audi and Volkswagen vehicles sold to American consumers.

A defeat device detects when a vehicle is being evaluated so it can automatically lower emissions to levels that are within the World Health Organization’s (WHO) legal limits. This makes the vehicle appear emissions-compliant. However, this is only true during testing conditions.

When the vehicle is taken out of the lab and driven on real-world roads, it reverts to emitting massive amounts of nitrogen oxides. These levels are often 40 times over the WHO and EU limits. As such, a defeat device-equipped vehicle is a heavy pollutant.

VW is not the only carmaker accused of using defeat devices; there are other carmakers accused by authorities as well, including Mercedes-Benz, luxury vehicle manufacturer BMW, and Vauxhall.

These manufacturers deceived their customers, so authorities are encouraging affected drivers to file a diesel claim against their carmaker.

How do I start my diesel claim?

If you believe your vehicle is equipped with a defeat device, you can work with an emissions expert in bringing your carmaker to court. However, you should first verify your eligibility to file a diesel claim. It’s easy; all you have to do is visit ClaimExperts.co.uk and get all the information that you need. Once you’ve confirmed your eligibility, you’re ready to start your emission claim.