Ethanol at the Gas Pump May Be Hurting, Not Helping Air Quality, Study Says

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Proving there’s no easy solution to environmental challenges, a new study published by the U.S. National Academy of Sciences concludes that ethanol may have a more negative effect on air quality and other environmental factors than gasoline does.Ethanol has until now been assumed to be helping the environment and contributing to lower greenhouse-gas emissions.A previous USDA study concluded that ethanol use was delivering a major improvement in environmental quality compared with gasoline.

If you wonder whether the use of ethanol as an ingredient to fuel our vehicles has a complicated political, environmental, or financial history, the answer is yes to all three. But at least ethanol at the pump helps with the problem of greenhouse-gas emissions, right? Well, maybe not. A study just released in the Proceedings of the National Academy of Sciences concludes that the corn-based fuel likely has a negative effect on air quality compared with gasoline. The additional use of cropland, fertilizers, and equipment associated with growing all that extra corn is the main culprit, the study says.

The new study, as first reported by Reuters, examined the life-cycle emissions of ethanol. Its conclusion contradicts a 2019 USDA study that claimed major air-quality advantages for ethanol compared with gasoline.

The study’s name is Environmental Outcomes of the U.S. Renewable Fuel Standard, and it was authored by a group of scientists, researchers, and professors from the University of Wisconsin, Kansas State University, University of California, and University of Kentucky. It reviews the effects of the U.S.’s Renewable Fuel Standard (RFS), which was passed into law in 2017 and mandates annual increases in biofuel use. In 2022, the standard calls for the utilization of about 15 billion gallons of ethanol. Much of that corn-based biofuel finds its way into the gasoline we fill our cars with at the pump.

The researchers considered the effect of the RFS on every aspect of ethanol production, from field to fuel tank—the full life cycle of a gallon of ethanol. And they found that “the carbon intensity of corn ethanol produced under the RFS is no less than gasoline and likely at least 24 percent higher.” In other words, the overall environmental effect of ethanol, which includes greenhouse gases, is at best equal to—but probably significantly worse than—that of gasoline. Note that the RFS requires ethanol’s carbon intensity to be 20 percent lower (better) than gasoline’s.

The scientific team’s calculations included changes in land use—the number of acres of cropland converted to grow corn, and even how much additional fertilizer was required to do so—and the resultant effect on water and soil quality, as well as on greenhouse-gas levels.

The conclusion is not encouraging: “The production of corn-based ethanol in the United States has failed to meet the policy’s own greenhouse-gas emissions targets and negatively affected water quality, the area of land used for conservation, and other ecosystem processes.” The lead author of the study, Tyler Lark, an assistant scientist at the University of Wisconsin-Madison Center for Sustainability and the Global Environment, told Reuters, “Corn ethanol is not a climate-friendly fuel.”

The study contradicts a similarly extensive USDA investigation from just two years ago that called ethanol far more eco-friendly than gasoline. That USDA study concluded that corn ethanol’s current GHG [greenhouse gas] profile is 39 to 43 percent lower than gasoline’s.

What to Believe?

Not surprisingly, the ethanol trade lobby has pushed back hard against this new study. Reuters quoted Geoff Cooper, president and CEO of the Renewable Fuels Association, calling the study “completely fictional and erroneous” and accusing the authors of employing “worst-case assumptions [and] cherry-picked data.”

This controversy leaves us consumers and—even more important—policy makers without a definitive answer about whether adding ethanol to gasoline is helping or hurting the country’s air quality. That’s especially troubling because the RFS’s required national biofuel-use level—the number of gallons of ethanol that must be produced and consumed—must be reset for 2023 and beyond.

The RFS study states, “As policy-makers worldwide deliberate the future of biofuels, it is essential that they consider the full scope of the associated tradeoffs, weighing the greenhouse gases and other environmental externalities alongside each fuel’s benefits.” True, but with two credible studies opposing each other so starkly, the value of corn-based ethanol is thrown into question. We can only hope that, in the not-too-distant-future, science can render a verdict on ethanol that makes it clear whether its use should be expanded or eliminated.

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