|Fig. 1: Map of excess emissions produced by VW vehicles from 2008 - 2015.  (Source: Wikimedia Commons)|
Diesel-fueled vehicles can be incredibly fuel-efficient and diesel-fueled vehicles have become increasingly popular over the past decade. But, Volkswagen took advantage of this trend as they knowingly deceived devices to allow their vehicles to pass government testing, while actually emitted up to 40 times the nitrogen oxides (NOx) emission limits.
Recent technological advances and particulate filters have allowed diesel engines to burn cleaner, eliminating the black smoke long associated with diesel vehicles. In addition, in 2006, ultra-low sulfur diesel fuel was introduced to the market. Ultra-low sulfur diesel contains 97% less sulfur than the previously sold diesel fuels and allows diesel cars to meet emissions standards so that they could be more widely sold. 
While hybrid cars (battery and gas-fueled) have very low emissions and very high gas mileage, the engines are not powerful, deterring many consumers. Another benefit to diesel engines is that, despite costing slightly more than gasoline, diesel fuel is between 25 to 30% richer in energy; these cars can more efficiently utilize one gallon of fuel as compared to gasoline-fueled vehicles. Finally, it is estimated that putting one million diesel cars on the road, equating about 7% of vehicles, would reduce expected emissions of eight million tons of carbon emissions and 24 million barrels of crude oil.  Given these technological advantages and fuel benefits , diesel-fueled vehicles have created demand for fuel-efficient vehicles and resulted in the increase of production of such vehicles.
In 2015, the Environmental Protection Agency (EPA) issued Volkswagen a Clean Air Act Notice of Violation. The EPA accused Volkswagen of installing software in their diesel-fueled vehicles that allowed the vehicles to pass EPA certification testing, but outside of the laboratory in real-world conditions these cars released up to 40 times the nitrogen oxides emission limits.  The software, referred to in court documentation as a defeat device, reduces the usage of the vehicles exhaust filter and emission control system, as it required extra fuel to operate these pollution controls.  In an effort to increase vehicles fuel economy and sell more vehicles, Volkswagen knowingly installed these defeat devices that were not initially discovered by the EPA in lab testing.
With 600,000 vehicles (11 million worldwide) and nearly 40 times the permissible amount of nitrogen oxide for each vehicle, Volkswagens defeat devices have a significant and detrimental effect on the environment.  Without the defeat devices and assuming full compliance with EPA regulations, the vehicles were calculated to theoretically only emit 1,000 tons of nitric oxide annually. But, Volkswagen vehicles in the US are actually responsible for 9,000 to 41,000 extra tons of NOx each year.  And, as Volkswagen vehicle containing defeat devices have been on the roads since 2009, the amount of toxic fumes released overall is actually eight times that approximation. (See Fig. 1 for a depiction of the excess emissions and their origin in the United States.) As Volkswagen admitted to creating 11 million vehicles total with such devices, these estimations do not encompass the other 10.5 million cars on the roads internationally that also use defeat devices to bypass emission controls.  The EPA regulates nitrogen oxides closely because of the detrimental health and environmental effects. NOx is a key contributor to the formation of ground level ozone, and in turn, creates smog. It also can cause nutrient enrichment problems in bodies of water, like excessive algae or phytoplankton. This can cause bodies of water to be uninhabitable by plants and marine life alike.  Also, excessive amounts of NOx react with sulfur and ammonia in the air to create acid decompositions that return to earth in the form of acid rain. Boosted NOx levels increase the risk of the health issues that stem from pollutants. Those with asthma and respiratory problems experience worse and more frequent attacks and issues.  When inhaled, nitrogen oxides cause damage to the lung and respiratory system and cause diseases like emphysema and bronchitis. Also, lung cancer and other illnesses have been linked to excessive exposure to NOx. 
The harmful and long-term effects of excessive NOx from diesel-fueled vehicles require the federal government to create policy that will protect Americans, their health, and the environment. From the finalized Volkswagen settlement to the pending Fiat Chrysler suit, the possibility of a greater number of high NOx emission-releasing vehicles exists. The government must implement policy to offset the detrimental environment effects from these diesel-fueled vehicles and deter the possibility of other companies deceiving the EPA emission testing.
© Mary Caballero. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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 "Technical Bulletin: Nitrogen Oxides (NOx), Why and How They are Controlled, U.S. Environmental Protection Agency, EPA 456/F-99-006R, November 1999.
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