Ethanol refining may release more of some pollutants than previously thought
ethanol fuel refineries could be releasing much larger amounts of some ozone-forming compounds into the atmosphere than current assessments suggest, according to a new study that found emissions of these chemicals at a major ethanol fuel refinery are many times higher than government estimates.
New airborne measurements downwind from an ethanol fuel refinery in Decatur, Illinois, show that ethanol emissions are 30 times higher than government estimates. The measurements also show emissions of all volatile organic compounds (VOCs), which include ethanol, were five times higher than government numbers, which estimate emissions based on manufacturing information. VOCs and nitrogen oxides react with sunlight to form ground-level ozone, the main component of smog.
If emissions at the more than 200 fuel other ethanol refineries in the U.S. are also being underestimated, these plants could be a higher source of VOC emissions than currently thought, according to the new findings accepted for publication in the Journal of Geophysical Research: Atmospheres, a publication of the American Geophysical Union.
The new study is one of the first and most detailed investigations of emissions from ethanol fuel refining, according to its lead author Joost de Gouw, a scientist at the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder and NOAA's Earth System Research Laboratory in Boulder, Colorado. Information about the refining process is one piece of examining the entire lifecycle of ethanol fuel emissions, from growing the corn used to make the fuel to the effect of emissions on urban air quality, he said.
"Over the past decade, because of the renewable fuel mandate, we have added 10 percent of ethanol to all the gasoline that is sold in the U.S. and so the question is: what does that do to the environment," de Gouw said. "That is a very complicated question and it has many different aspects. One of the aspects is the air-quality implications and, to get at them, we have to know what are the emissions associated with producing ethanol and using ethanol. That is where this study fits in."
To make the measurements they report, de Gouw and his colleagues flew an airplane downwind of an Archer Daniels Midland ethanol refinery, the third largest producer of fuel ethanol in the U.S., and took air-quality readings at three different distances from the plant. The researchers used those to calculate emissions of various gases, including VOCs, nitrogen oxides and sulfur dioxide.
They then compared their findings with government emissions estimates from 2011. Emissions of sulfur dioxide and nitrogen oxides - compounds generated by the coal-burning plant - were in-line with government estimates, but emissions of VOCs, including ethanol, were higher than government estimates. De Gouw said the VOC emissions are likely generated by the refining process, not the coal-burning that powers it.
The researchers also used government estimates and ethanol production numbers from the Renewable Fuels Association to analyze emissions from all fuel ethanol refineries in the U.S. and compare those to emissions from burning ethanol in motor vehicles.
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