If emissions at the more than 200 fuel other fuel ethanol refineries in the US 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 fuel ethanol production, 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 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. 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.

—Joost de Gouw

To make the measurements, 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 US, 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 NO_x—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 production process, not the coal-burning that powers it.

The team also observed chemical transformations of the emissions from Decatur, including formation of new particles, nitric acid, peroxyacyl nitrates, aldehydes, ozone and sulfate aerosol.

The researchers used government estimates and ethanol production numbers from the Renewable Fuels Association to analyze emissions from all fuel ethanol refineries in the US and compare those to emissions from burning ethanol in motor vehicles.

Prevailing estimates had indicated that refining ethanol fuel and burning it in cars and trucks generate equivalent amount of VOCs, including ethanol. But, the new emissions measurements from the Decatur plant show that ethanol emissions from production of one kilogram of ethanol at the refinery are 170 times higher than what comes out of a vehicle burning the same amount of ethanol, de Gouw said. If the Decatur refinery is like most other refineries in the US, he added, “the higher emissions of ethanol and VOCs that we calculated from our data would make the refining process a larger source of these gases than burning the ethanol fuel in your car.”

Obviously, this was just one refinery that we looked at, so we’d like to do more and see if these findings are more universal or if this plant was just exceptional.

—Joost de Gouw

Resources

• J.A. de Gouw et al. (2015) “Airborne Measurements of the Atmospheric Emissions from a Fuel Ethanol Refinery” Journal of Geophysical Research: Atmospheres doi: 10.1002/2015JD023138