The Downfall of Diesel: Why Clean Diesel Was Too Good to Be True

The Rise of Diesel

During Superbowl XLIV in 2010, Audi released a highly praised advertisement that characterized clean diesel technology as something that environmentalists should love. When paired with an advanced Audi engine, the clean diesel technology was said to have been able to use an effective emissions control system to achieve nearly zero fine particulate emissions and smog forming compounds like nitrogen oxide. Additionally, the proven energy efficiency of new diesel technology was highlighted as a way to achieve cleaner air, reduce greenhouse gas emissions, and enhance environmental sustainability. However, only five years later, it was publicly announced that Volkswagen, Audi, and a number of other automobile manufacturers had been illegally rigging diesel-powered cars to manipulate air pollution tests and appear much cleaner than they actually were. Since then, the decline of diesel-powered vehicles has started to accelerate in countries around the world.

Diesel was once advertised as a wonder fuel that would reduce emissions, save consumers money on fuel, and provide superior performance on the road. Governments, industry executives, and science itself had compelled countless consumers around the world to buy diesel-powered vehicles to cut greenhouse gas emissions as the world shifted into a new eco-conscious era (Forrest, 2017). Advances in diesel engine technology, particularly during the late 1990s, contributed to an increasing demand for diesel fuel. The superior fuel efficiency, the lower cost of ownership, and the dependability of a diesel engine were the driving factors that made owning a diesel-powered vehicle popular for both car and truck owners alike. As global concerns began to intensify about carbon emissions and global warming, European governments started advertising campaigns to convince citizens to switch from driving a vehicle powered by gasoline to one powered by diesel fuel.

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The Cracks Appear

One of the biggest boosts for diesel occurred in 2001, when the United Kingdom’s chancellor of the Labor Party, Gordon Brown, significantly reduced taxes on diesel vehicles to help shift the country’s citizens away from gasoline. However, a little over a decade later in 2012, the cracks started to appear in the diesel market after a major research study unveiled some truly disconcerting health impacts related to diesel emissions. The European Environment Agency found that nitrogen dioxide from diesel emissions had been causing around 71,000 premature deaths across the European continent every year (Forrest, 2017). During the same year, the World Health Organization and the France-based International Agency for Research on Cancer declared that after extensive research, the organizations had found enough compelling evidence to declare that diesel exhaust was a known carcinogen and a cause of lung cancer that placed it in the same category as mustard gas, arsenic, tobacco, and asbestos.

The gripping reports from the European Environment Agency, the World Health Organization, and the International Agency for Research on Cancer had a tremendous impact on diesel vehicle sales. During the time that the reports were released, diesel-powered vehicles were almost entirely confined to commercial vehicles outside of Europe and India. However, this came as a significant blow to German carmakers’ plans of trying to raise awareness of the fuel’s greater efficiency in the United States, where the long-distance highway travel would best suit new diesel engine technology in passenger cars and trucks. The European Automobile Manufacturers Association almost immediately dismissed the reports after they were made public by saying that the latest diesel technology had become much cleaner than it previously was in the past. Moreover, industry spokeswoman Sigrid de Vries signaled that the European automakers were working on new technology to address the health concerns.

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Troubling Research Reports

Prior to the 2012 health reports, the International Agency for Research on Cancer has previously labeled diesel engine exhaust as a probable carcinogen to humans. It took nearly twenty years of research for the organization to switch its stance from probable carcinogen to definite carcinogen. In addition to European industry criticism, American industry executives also questioned the decision to switch the carcinogenic rating. Allen Schaeffer, the executive director of the American-based Diesel Technology Forum, stressed how diesel engine and equipment makers had been investing billions of dollars in research into new technologies and strategies to limit the emissions from diesel-powered vehicles (Kelland, 2012). Even with the pushback from the auto industry, global health experts and environmentalists say that while historic tax breaks and other incentives led diesel vehicles to make up nearly one-third of Europe’s fleet, they also clogged cities like London and Paris with dangerously high levels of air pollution that ultimately caused thousands of premature deaths (Plumer, 2015).

In 2013, a study conducted by renowned researchers Michel Cames and Eckard Helmers found that Europe’s push to switch consumers over to diesel vehicles didn’t have any impact on reducing levels of global warming. While the reduction in carbon dioxide emissions had originally compelled lawmakers to incentivize diesel engines, Cames and Helmers reported that the reduction in carbon dioxide emissions was offset by the high levels of soot that were emitted by diesel engines. Moreover, the study highlighted the perils of Europe’s fixation on diesel vehicles rather than making progress to expand the adoption of electric vehicles. While the global demand for electric vehicles is predicted to rise sharply in the coming decades, Europe has lagged behind global adoption rates because of the many years that policymakers spent on incentivizing a future characterized by diesel rather than electricity.

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Rapid Vehicle Growth

Rapid population growth and rising incomes in developing countries like China and India are projected to fuel an increasing supply of vehicles on the road. The ongoing growth in the global population of automobiles is projected to increase from one billion vehicles in 2016 to over two billion vehicles by 2040 (Sioshansi & Webb, 2019). Morgan Stanley economic analysts forecast that the global demand for gasoline will triple by the mid-2030s (Domm, 2018). Moreover, projections by McKinsey & Company, a global management and consulting firm, show that by 2030, electric vehicles (including battery electric vehicles and plug-in hybrids) could rise to nearly 20 percent of annual global vehicle sales and nearly 35 percent of sales in Europe (Hensley et al, 2018). While the world will continue to see a rise in both gas-powered vehicles and electric vehicles in the coming decades, the future of diesel-powered vehicles has come into question in recent years because of the mounting health and environmental implications of diesel emissions.

The Diesel Scandal

In September of 2015, as Volkswagen was vying with Toyota for the title of world’s biggest car company, the German automaker rocked the industry by admitting that it had cheated on emissions control tests after the U.S. Environmental Protection Agency (EPA) issued the company with a notice of violation of the Clean Air Act. Volkswagen was found to have intentionally programmed its turbocharged direct injection (TDI) diesel engines to initiate emissions controls only during specific emissions testing. Since 2009, Volkswagen had deliberately installed an elaborate cheating software system in 482,000 “clean diesel” vehicles sold to Americans (Plumer, 2015). The software allowed Volkswagen vehicles to secretly emit a plethora of hazardous and smog-forming chemicals into the atmosphere without alerting U.S. regulators. Volkswagen later admitted that the software had been installed on a total of 11 million clean diesel cars sold worldwide. While the automaker’s cars were supposed to offer exceptional fuel economy and low levels of pollution, researchers found that the cars actually emitted 15 to 35 times as much nitrogen oxide as international environmental laws had permitted (Plumer, 2015).

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The Science of Diesel

Great gas mileage and supposedly low levels of pollution were two of the main reasons why Europe embraced diesel cars throughout the 1980s and 1990s. For the majority of the 20th century, automakers primarily designed cars to run on gasoline, which is more flammable and ignites easier than diesel through the use of sparkplugs. While gasoline is much more combustible than diesel, diesel is known to contain more energy per gallon produced. After crude oil is extracted from production wells, it is sent to oil refineries for processing. The refineries convert the crude oil into useable fuel that is separated into lighter and heavier mixtures. The lightest mixture of hydrocarbons becomes gasoline, while the heavier hydrocarbons are converted into diesel fuel. Since diesel contains more energy than gasoline, diesel engines are able to work more efficiently than gas engines, allowing a vehicle to travel up to 30 percent farther on a single gallon of fuel (Plumer, 2015).

A unique aspect of a diesel engine is that the fuel is ignited not by a spark as it is in gasoline engines, but it is ignited by the heat produced by compressed air in a cylinder. In addition to diesel fuel being refined from traditional crude oil, it is possible to produce a synthetic type of diesel known as Fischer-Tropsch diesel, which can be developed from natural gas, synthesis gas obtained from coal, biogas derived from biomass materials, and biodiesel, which can be made from oily plants and soybean oil (Augustyn et al, 2019). Alternative forms of diesel fuel are often blended with traditionally refined diesel as a way to reduce environmental impacts and dependence on sources of petroleum.

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More Efficiency and More Pollution

Even though diesel fuel allows a car to travel longer distances with less fuel, diesel emits more nitrogen oxides, particulate matter, ground-level ozone, and smog than gasoline. To address this problem, U.S. environmental organizations like the EPA have established a variety of standards for the sulfur content of diesel fuel and for emissions from diesel engines. The EPA standards include a requirement that the petroleum industry must produce Ultra Low Sulfur Diesel (ULSD) fuel, which is a cleaner-burning type of diesel fuel that contains a maximum of 15 parts-per-million of sulfur. The reduction in sulfur is said to reduce smog and other harmful tailpipe emissions. While ULSD fuel has reduced some diesel-related emissions, diesel fuel use still contributes significantly to air pollution in North America. According to 2018 data from the U.S. Energy Information Administration, diesel fuel consumption in the U.S. transportation sector contributed to 461 million metric tons of carbon dioxide being released into the atmosphere, which equates to nearly 24 percent of all U.S. transportation sector emissions (EIA, 2019).

Following decades of diesel vehicle promotion, automakers are starting to shift away from diesel technology toward electric vehicles. While diesel engines may be more fuel-efficient and emit less carbon emissions than gasoline engines, the higher levels of other air pollutants and smog-forming compounds can worsen heart and lung disease, exacerbate asthma attacks, and even cause premature death. David King, the United Kingdom’s former chief scientific adviser on climate change, has admitted that the country made a huge mistake by promoting diesel as a clean fuel (Forrest, 2017). Moreover, lawmakers in Athens, Paris, Madrid, and Mexico City have recently revealed that they are all developing plans to remove diesel vehicles from their roadways by 2025 (Coren, 2018). Limited bans on some older diesel-powered vehicles in the cities of Paris, Madrid, and Hamburg have already prompted many drivers to abandon diesel engines in droves. Over the last few years, governments and automakers around the world have rolled out a variety of initiatives to incentivize electric vehicles. In the coming decades, it appears that the war on diesel vehicles will continue to expand as countries look to more environmentally friendly initiatives.


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Domm, P. (2018). “Electric vehicles: The little industry that could take a bite out of oil demand.” CNBC.

EIA. (2019). “Diesel fuel explained.” Energy Information Administration.

Forrest, A. (2017). “The death of diesel: Has the one-time wonder fuel become the new asbestos?” The Guardian.

Hensley, et al. (2018). “Three Surprising Resource Implications from the Rise of Electric Vehicles.” McKinsey Quarterly: 00475394, 2018, Issue 2

Kelland, K. (2012). “Diesel exhaust fumes cause lung cancer, WHO says.” Reuters.

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Sioshansi, F., & Webb, J. (2019). “Transitioning from conventional to electric vehicles: The effect of cost and environmental drivers on peak oil demand.” Economic Analysis and Policy.

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