The late 19th century was a time of new inventions, including the first vehicle powered by a gasoline engine. In 1893, Rudolf Diesel successfully built the first diesel engine prototype, and since then, the world has relied on petrol and diesel vehicles, which continue to pollute the environment with carbon dioxide.
The growing focus on sustainability and concerns about climate change have sparked serious debate over which fuel type is more sustainable for the environment. The reality is that diesel and petrol vehicles generate millions of tons of carbon dioxide each year. Despite the rise of electric cars in the automobile market, petrol and diesel vehicles continue to pollute the air with CO2. According to the World Health Organization (WHO), the U.S. Environmental Protection Agency (EPA) and other independent studies, vehicular emissions are responsible for almost 30% of air pollution in urban areas.
Which fuel is more sustainable? In this article, we will examine the environmental impact of these fuel types, integrating data from several studies, expert insight, and emerging technologies to answer the question about the sustainability of these fuel types.
Which Is More Eco-Friendly: Petrol or Diesel?
Lifecycle Emissions: A Holistic Analysis
Determining which fuel is more sustainable requires more than just considering emissions rates. A full lifecycle analysis (LCA) assesses the environmental impact of a fuel’s production, refinement, combustion, transportation, and disposal.
#1. Extraction and Refining
Both petrol and diesel are extracted from crude oil, but the refining process of the latter is energy-intensive. A study by the International Council on Clean Transportation (ICCT) discovered that carbon emissions from the refining process of diesel are 18% higher compared to petrol. However, diesel fuel is more energy-dense, meaning less fuel is needed to travel the same distance as a petrol vehicle would and this offsets some of the emissions during combustion.
#2. Combustion
Compared to gasoline-powered vehicles, diesel engines emit about 20% less CO2 per kilometre due to their higher fuel efficiency. However, a study suggests that diesel engines still release higher amounts of nitrogen oxides (NOx) and particulate matter (PM2.5), which are toxic to the environment and human health.
On the other hand, petrol vehicles emit more CO2 but produce lower levels of nitrogen oxides and particulate matter. The carbon emissions from petrol vehicles continue to pollute the environment and remain one of the large contributor to climate change.
#3. End-of-Life Impacts
Both petrol and diesel contribute similarly to end-of-life emissions, with vehicle scrapping, recycling, and disposal generating environmental burdens. However, diesel engines are more durable and tend to last longer than petrol engines.
Expert Insight: Dr Michael Anderson, Environmental Health Specialist
“While petrol engines contribute more to global warming due to CO2 emissions, diesel’s higher NOx and particulate emissions pose an immediate risk to urban air quality and human health. This makes the environmental impact of diesel more pressing in the short term, especially in cities.”
Conclusion on Lifecycle Emissions
While diesel vehicles have higher fuel efficiency than petrol vehicles, their lifecycle emissions are somewhat higher due to their energy-intensive production and refining processes as indicated by the International Council on Clean Transportation (ICCT) study.
Health Impacts: Diesel vs. Petrol
Diesel Emissions and Public Health
Public opinion on diesel engines has criticized the fuel type for its harmful impact on human health. According to a report by the World Health Organization (WHO), diesel exhaust was classified as a Group 1 carcinogen in 2012, meaning that there is evidence that exposure to fumes may cause cancer in humans. According to the California Air Resources Board, PM2.5 emitted by diesel engines can lead to serious health problems like:
- Respiratory diseases, bronchitis, asthma, and chronic obstructive pulmonary disease (COPD).
- Cardiovascular diseases, including strokes and increased risk of heart attacks.
- Cancer, as long-term exposure to toxic fumes, can also cause lung cancer.
A 2017 study published in DW estimated that exposure to fumes from diesel engines causes about 70,000 premature deaths each year in Europe alone. This is particularly concerning, especially in densely populated cities with poor air quality.
Petrol Emissions and Health
Petrol engines emit less particulates and nitrogen oxides than diesel engines. However, while diesel vehicles are more fuel-efficient, petrol vehicles emit more CO2. Although nitrogen oxides and PM2.5 are more potent and toxic to human health compared to CO2, other pollutants such as carbon monoxide (CO) and volatile organic compounds (VOCs) may still cause serious respiratory health issues.
Expert Insight: Dr Emily Turner, Automotive Engineer
“The health risks posed by diesel vehicles are well-documented, particularly in urban settings where pollution levels are high. While petrol engines also contribute to air pollution, the particulate matter from diesel is far more dangerous for human health in the long run.”
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Conclusion on Health Impacts
Fumes emitted by diesel engines are more harmful to human health due to the higher output of nitrogen oxides and PM2.5. Although petrol vehicles still release significant amounts of CO2 into the atmosphere, they pose a lesser threat to public health compared to diesel vehicles
Environmental Impacts: Petrol vs. Diesel
Diesel and Climate Change
With higher fuel efficiency, diesel engines may appear to be a more sustainable option in terms of greenhouse gas emissions. According to a study by the European Environmental Agency (EEA), diesel vehicles emit about 15 to 20% less CO2 per kilometre driven than comparable petrol vehicles of the same class. However, the U.S. Environmental Protection Agency (EPA) states nitrogen oxides emitted by diesel vehicles have a 300 times greater global warming potential than carbon dioxide over 100 years.
Petrol and Climate Change
A 2021 study by the International Council on Clean Transportation found that petrol vehicles generate more CO2 per kilometre drive compared to diesel vehicles because they are less fuel-efficient, meaning that petrol vehicles produce higher CO2 emissions over their lifetime than diesel vehicles. However, petrol vehicles do not exacerbate air quality problems to the same extent as their diesel counterpart. This is because diesel engines produce more harmful nitrogen oxides (NOx) and particulate matter (PM).
Case Study: London’s Air Quality Strategy
The city of London provides an excellent case study to evaluate the impacts of petrol versus diesel emissions. In 2019, London introduced the Ultra Low Emission Zone (ULEZ), an initiative that charges owners of vehicles that do not meet strict emissions standards. The ULEZ was introduced to lower nitrogen oxide emissions from diesel vehicles, which studies have shown are responsible for almost 50% of the city’s nitrogen oxide emissions. Since the ULEZ was introduced, nitrogen oxide levels in central London have reduced by 44%.
Expert Insight: Dr Jason Moore, Environmental Scientist at the University of Cambridge
“While diesel vehicles are more fuel-efficient and emit less CO2, the trade-off in terms of air pollution is severe. NOx and particulate matter contribute to smog, acid rain, and respiratory issues, making diesel particularly damaging in urban areas.”
Conclusion on Environmental Impacts
Although diesel vehicles are more fuel-efficient and emit less carbon dioxide per kilometre, their level of nitrogen and PM2.5 emissions remains a threat to the environment and public health. Petrol vehicles emit more CO2 but may have less effect on air quality.
Technologies Advancements in Emissions Reduction
Over the last few decades, the automobile industry has made efforts to reduce emissions from both diesel and petrol vehicles.
Diesel Innovations: Selective Catalyst Reduction (SCR)
Selective Catalyst Reduction (SCR) is one of the significant innovations for the diesel engine. This technology uses Diesel Exhaust Fluid (DEF) to convert nitrogen oxides into nitrogen and water, hence reducing the NOx emissions by approximately 90%. Additionally, Diesel Particulate Filters (DEF) in modern diesel vehicles are helping with CO2 emissions by trapping up to 99% of soot and particulate matter.
Despite these advancements in reducing CO2 emissions, the Transport and Environment (T&E) believes that these technologies are not effective enough. The European research organization has pointed out that diesel vehicles continue to emit more NOx than petrol vehicles.
Petrol Innovations: Gasoline Direct Injection (GDI)
Gasoline Direct Injection (GDI) systems are one of the new technologies to improve fuel efficiency in petrol engines. The GDI system works by delivering fuel directly into the combustion chamber, reducing the amount of fuel required. However, this can increase particulate emissions, which has led to the introduction of Gasoline Particulate Filters (GPF) in newer petrol vehicles.
Expert Insight: Professor Robert Johnson, Automotive Researcher
“The advancements in emissions control for both diesel and petrol vehicles have narrowed the gap between the two in terms of environmental impact. However, even with SCR and DPFs, diesel engines still pose significant challenges, particularly regarding NOx emissions.”
Conclusion on Technological Advancements
Technological innovation has been made to reduce emissions from petrol and diesel engines, yet these vehicles continue to emit toxic harmful pollutants, especially in urban areas where congested traffic is common. Petrol engines equipped with GPF and GDI have reduced particulate emissions, making them a more favourable option when compared with diesel engines.
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Government Policies and Regulations
Strict government regulations can drive change to reduce carbon emissions from petrol and diesel engines. Many countries worldwide are imposing strict emissions regulations and incentivizing the transition to cleaner technologies.
European Union
The European Union Euro 6 standards, introduced in 2014, set strict limits on carbon dioxide, nitrogen oxides, and particulate matter emissions for diesel and petrol engines. Diesel vehicles faced stricter nitrogen oxide limits, forcing automobile manufacturers to adopt DPF and SCR technologies.
In 2020, the European Commission proposed even stricter Euro 7 standards. These stricter regulations on diesel engines aim to phase out internal combustion engines (ICEs) and transition to zero-emission vehicles by 2035.
United States
The United States has also imposed a similar standard through the EPA’s Tier 3 regulations, which limits nitrogen emissions for diesel vehicles. California, through its Advanced Clean Cars Program, is at the forefront of transitioning to zero-emission vehicles. The state’s sustainability plan also includes a ban on the sale of new petrol and diesel cars by 2035.
China
China introduced its China IV emissions standards—and as the largest automobile market in the world—the country is aggressively pushing for the adoption of electric vehicles, and plans to phase out petrol and diesel cars by 2040.
The Future: Hybrid and Electric Alternatives
As countries continue to impose stricter regulations on petrol and diesel vehicles, the future for automobiles is with hybrid, electric and alternative fuel vehicles.
Hybrid Diesel and Petrol Vehicles
Hybrid vehicles operate efficiently by combining internal combustion engines with electric motors. They generate less emissions but maintain the range and convenience of traditional vehicles. Due to their higher cost of managing nitrogen oxide emissions, hybrid diesel vehicles are less common compared to hybrid petrol vehicles.
A study by the International Council on Clean Transportation (ICCT) found that hybrid petrol vehicles emit about 20% to 27% less CO2 over their life cycle compared to traditional petrol vehicles.
Electric Vehicles
Electric vehicles are the best option for a zero-emission future. Many countries worldwide, especially in Scandinavia, are transitioning to electric vehicles. Major cities also plan to go fully electric, with cities like London, Paris, and Los Angeles soon to ban petrol and diesel vehicles from city centres by 2030.
The International Energy Agency (IES) projects that the widespread adoption of electric vehicles could reduce global carbon emissions by 1.5 gigatons annually by 2040 if current purchase trends continue.
Expert Insight: Dr Sarah Williams, Energy Policy Analyst
“The future of eco-friendly transportation lies in electric and hybrid technologies. While petrol and diesel vehicles will dominate the roads for the next decade, advancements in EV infrastructure and battery technology are rapidly closing the gap.”
Verdict: Which is More Eco-Friendly?
Considering factors such as lifecycle emissions, air pollution, public health impact, and recent technological advancements, the answer to which fuel type is more eco-friendly is not straightforward.
Diesel vehicles are highly fuel-efficient and emit less CO2; however, their high NOx and particulate matter output remain a major concern for public health.
Petrol vehicles on the other hand generate lower levels of NOx and particulate matter but emit more CO2 per kilometer, causing air pollution, especially in urban areas.
Final Verdict
In terms of long-term climate change mitigation, diesel engines hold a slight edge over petrol engines due to their fuel efficiency. However, for improving air quality and reducing immediate health risks, petrol vehicles are a better option than diesel engines. Nevertheless, both petrol and diesel vehicles are harmful to the environment, and plans are in place to phase them out in favour of hybrid and electric vehicles.
Conclusion: The Road Ahead
Petrol and diesel vehicles continue to release millions of tons of CO2 into the atmosphere, contributing to climate, air pollution, and public health risks. While diesel engines emit about 20% less CO2 per kilometre due to their higher fuel efficiency, they still release higher amounts of nitrogen oxides (NOx) and particulate matter. Petrol vehicles produce more CO2 but lower levels of NOx and particulate matter.
Ultimately, electric and hybrid vehicles present the best option for a zero-emission future. Major cities are already preparing to transition fully to electric vehicles, with cities like London, Paris, and Los Angeles planning to ban petrol and diesel from city centres by 2030, according to a document.