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Petrol vs Diesel – Why The Thinking Changed

For decades, the UK’s official stance was that diesel vehicles were the better choice for the environment, compared to their petrol counterparts. This notion has radically shifted in recent years, with diesel now seen as the greater environmental villain. So, what changed?

Let’s first clarify the fundamental differences between petrol and diesel. Petrol and diesel fuels are both derived from crude oil, but they are refined differently, resulting in distinct combustion processes. Petrol engines ignite fuel using a spark plug, whereas diesel engines use compression. Diesel fuel is denser and contains more potential energy than petrol, making diesel vehicles more fuel-efficient. Thus, they produce less CO2, a key greenhouse gas – this was the foundation of the earlier preference for diesel.

The turning point came when studies began to reveal the darker side of diesel: nitrogen oxides (NOx) and particulates. Diesel engines emit significantly more of these pollutants, which are harmful to human health, leading to conditions like asthma, lung cancer, and cardiovascular issues. The ‘Dieselgate’ scandal of 2015, where Volkswagen admitted to cheating emissions tests, brought this issue into sharp relief.

In 2017, the UK government announced plans to ban the sale of new diesel and petrol cars from 2040, as part of their Clean Air Strategy. This marked a significant shift in their stance, acknowledging the detrimental impact of diesel on air quality. The date was subsequently brought forward to 2035, and then to 2030, reflecting the urgency of the situation.

Another milestone was the introduction of Clean Air Zones (CAZs) in several cities, including London’s Ultra-Low Emission Zone (ULEZ), where drivers of older, more polluting vehicles, particularly diesels, have to pay a charge. This policy, designed to discourage the use of such vehicles, has been a clear demonstration of the government’s pivot away from diesel.

The UK’s shift in position was also influenced by evolving scientific knowledge and technology. Hybrid and electric vehicles (EVs) have come to the fore as a cleaner, more sustainable alternative. The UK government has pledged to invest heavily in EV infrastructure, further solidifying the move away from fossil fuels.

So, why the change in thinking? While diesel cars do emit less CO2 than petrol, the high levels of NOx and particulates they produce outweigh this benefit, especially given the direct harm they cause to human health. This, coupled with the rise of cleaner alternatives, has led to a U-turn in official policy.

The story of diesel vs petrol in the UK is a cautionary tale of how initial perceptions can be misleading, and a reminder of the need for comprehensive evidence when making environmental decisions. It also demonstrates the importance of flexibility in policymaking, as new information and technologies emerge. Today, the UK is steering a clear course towards a cleaner, greener transport future. Diesel, once the darling of eco-conscious driving, is now firmly in the rear-view mirror.

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