A trade publication that covers ethanol production is suggesting that American ethanol producers are using outdated methods to the measure levels of nitrogen oxide (NOx) that they’re putting out.

It’s long been debated whether ethanol is a cleaner, more environmentally-friendly fuel than gasoline, and if ethanol producers are underestimating the amount of NOx that they’re putting into the atmosphere, that would mean ethanol and its production are harming the environment more than previously thought.

SEE ALSO: EPA Sets Ethanol Increases 25 Percent Below Original Standard

The Clean Air Act measures nitrogen dioxide, or NO2, in place of NOx, as a surrogate of sorts, and 40 years ago, NO2 was believed to make up five to 20 percent of NOx emissions. Now, however, it’s been found that calibration methods have been inaccurate, and now NO2 may actually account for 80 percent of NOx emissions. That means ethanol factories could be causing more environmental damage than previously realized.

SEE ALSO: Clinton Campaign Says Candidate Supporting Ethanol Blend But Not Low-Carbon Fuel Standard

This follows a University of Michigan study from last month that showed that regulators might be wrong to assume that carbon dioxide emissions from biofuels were being offset by the growth of the plants, such as corn, that are used to produce the biofuels.

On the other hand, the study was funded by the American Petroleum Institute, although the lead author claimed it was peer-reviewed. The Environmental Protection Agency hasn’t filed a report in five years, which prevents further clarification.

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