Ethanol Can Help Reduce Toxic Gasoline Aromatics

Source: By Savannah Bertrand, EESI • Posted: Wednesday, March 2, 2022

Every gallon of gasoline sold in the United States contains toxic chemicals called aromatic hydrocarbons—mainly mixtures of BTEX chemicals, which stands for benzene, toluene, ethylbenzene, and xylene—that increase octane. Higher octane levels prevent engines from prematurely combusting, or knocking, which can damage the engine and make its operation less efficient.

Aromatic hydrocarbons made up an average of 20 percent of the gasoline sold in the United States in 2016. When gasoline aromatics are combusted, they produce ultra-fine particle matter and other air pollutants that are harmful to human health. The Environmental Protection Agency (EPA) classifies BTEX chemicals as toxic air pollutants known to cause cancer, adverse reproductive effects, and other health issues.

Ethanol, a biofuel made from biomass feedstocks such as corn, barley, and sugar cane, can be blended with gasoline as a direct substitute for aromatics. According to the EPA, “ethanol’s high octane value has allowed refiners to significantly reduce the aromatic content of the gasoline.” To be exact, increased ethanol in gasoline allowed the United States to reduce the total volume of aromatics in gasoline from about 25 percent in 2005 to about 20 percent in 2016. High-octane ethanol blends also improve vehicle performance and efficiency.


While widespread adoption of electric vehicles (EVs) is the ultimate goal to shift away from fossil fuel-powered transportation, it will be many yearsbefore EVs are more prevalent than internal combustion engine (ICE) vehicles. In the meantime, ICE vehicles will continue to spew toxic air pollutants and greenhouse gases like carbon dioxide that contribute to the climate crisis and harm communities across the country. During the transition from ICE vehicles to EVs, biofuels such as ethanol are a readily available solution to reduce the climate and health impacts associated with transportation.

Compared to conventional gasoline, corn ethanol has 19-48 percent fewer life-cycle greenhouse gas emissions, depending on a number of factors including farming practices. A 2020 Argonne National Lab study found that corn ethanol emits 40 percent fewer greenhouse gases over its lifetime than gasoline. A 2019 U.S. Department of Agriculture study found similar results, with a 39 percent reduction in greenhouse gas emissions. Widespread adoption of conservation agriculture and ethanol refinery efficiency improvements could lead to additional greenhouse gas emission reductions.

Between 2005 and 2019, corn ethanol helped reduce greenhouse gas emissions by 500 million tons, equal to taking more than 96 million cars off the road. While corn ethanol is already contributing to lower emissions and health impacts, continued advances in biofuels will lead to additional benefits. For example, cellulosic ethanol—produced from non-food crop sources such as corn husks—can reduce life-cycle greenhouse gas emissions by over 88 percent. However, cellulosic ethanol currently only makes up a small percent of biofuels produced in the United States.

Over the past 20 years, the use of ethanol has steadily risen from about 1.65 billion gallons in 2000 to 14.5 billion gallons in 2019, primarily because the nation’s leading biofuel policy, the Renewable Fuel Standard (RFS), has required a certain volume of biofuel to be mixed into U.S. transportation fuel since 2005. The EPA announces the volume requirements annually and is set to announce potential changes to the program this year.

Because of the standard, almost all gasoline in the United States currently contains ethanol, typically as a blend of 10 percent ethanol and 90 percent gasoline, known as E10. E10 is a “drop-in” fuel, meaning it can be used in vehicles without engine modifications.

Every year, E10 reduces aromatics in gasoline by 7 to 8 billion gallons. This substitution of toxic aromatics for ethanol reduces the health impacts associated with gasoline. A University of California Riverside study found that low-aromatic, high-ethanol blended gasoline can reduce tailpipe emissions of particulate matter, carbon monoxide, BTEX, and other pollutants. Despite somewhat higher emissions of formaldehyde and acetaldehyde, overall toxic pollutants decreased with higher ethanol blends.

Additionally, a study—in collaboration between the Energy Resources Center at the University of Illinois Chicago and the Hormel Institute at the University of Minnesota—found that ethanol-blended fuels produce fewer toxic emissions known to cause cancer. According to Dr. Steffen Mueller, principal economist at the Energy Resources Center and co-author of the study, “ethanol is a beneficial substitute for carcinogenic aromatics.”


Switching to higher blends of ethanol would result in more benefits and could be undertaken relatively easily. The EPA has approved E15 for use in 2001 or newer vehicles. Virtually all cars currently on the road in the United States–over 96 percent–could use E15. A 2020 report found that expanding ethanol blends from E10 to E15 would reduce greenhouse gas emissions by over 17.5 million tons per year.

“Increasing octane and reducing the carbon content of liquid transportation fuels using mid-level blends of ethanol as a substitute for carcinogenic aromatic compounds in gasoline is a win-win-win option,” according to Ernie Shea, president of Solutions from the Land, a nonprofit advocating land management solutions to environmental challenges. “Doing so can improve vehicle efficiency, reduce emissions, improve public health while also boosting the economies of those rural areas that produce the bulk of those cleaner fuels.”