2015 News & Events

Refining ethanol may release more of some pollutants than burning it in vehicles.

After quantifying the airborne emissions from the nation's third largest ethanol refinery, a team led by NOAA and University of Colorado-Boulder researchers has found that for some gases, refining ethanol releases more to the atmosphere than previously thought – and in some cases more than is ultimately released by burning the fuel in vehicles. The emissions can contribute to the formation of ozone, a regulated pollutant that can affect human health. Results are published in the paper "Airborne measurements of the atmospheric emissions from a fuel ethanol refinery," just accepted for publication in the Journal of Geophysical Research.

For the new study, researchers made measurements in the summer of 2013 downwind of a large refinery in Decatur, Illinois, using a NOAA WP-3D research aircraft loaded with instruments to measure airborne emissions. Though the amounts found for some gases were in line with estimates in national emissions inventories (e.g., sulfur dioxide and nitrogen oxides), others were higher. Volatile organic compounds (VOCs) were five times higher than inventories estimated, and emissions of ethanol itself were about 30 times higher. Nitrogen oxides and VOCs react in the atmosphere in the presence of sunlight to form the pollutant ozone.

Over the past decade, the use of fuel ethanol produced from corn has grown and ethanol is now 10 percent of the volume of gasoline used in the United States. More than 200 ethanol refineries dot the U.S. landscape, mostly in the corn-producing states of the Midwest. The new study is one of the first and most detailed studies of emissions generated by ethanol fuel refining.

"Information about the refining process is one part of the entire cycle of production and use of ethanol as a fuel," said the study's lead author, Joost de Gouw, a scientist with the Cooperative Institute for Research in Environmental Sciences (CIRES) at CU-Boulder and the Chemical Sciences Division of NOAA's Earth System Research Laboratory. De Gouw led the 2013 "Southeast Nexus" field campaign (SENEX 2013) that gathered the data.

Some of the largest ethanol refineries in the country, including the Decatur plant studied by the researchers, use coal as the energy source to convert corn into ethanol. Other studies have found that using coal rather than natural gas tends to boost the emissions of nitrogen oxides and sulfur dioxide coming from the refining process.

But are the emissions from refineries significant in the scheme of things?

The new study answers that question by comparing refinery emissions (which are released in mostly corn-producing areas of the Midwest) to what comes out of the tailpipes of vehicles when the ethanol is burned (released predominantly in large metropolitan areas across the nation). To make a broad comparison, the authors used the numbers in the national emissions inventories, which rely on manufacturing information. Inventory numbers suggest that refining a pound of ethanol emits similar amounts of nitrogen oxides and VOCs, but more sulfur dioxide, compared with burning the pound of ethanol in cars and trucks.

However, if the atmospheric measurements gathered by the researchers for the Decatur refinery can be generalized to other refineries, the inventory numbers are too low for some gases, especially ethanol itself and VOCs in general.

"If the Decatur refinery is like most other refineries in the country, our measurements suggest that the ethanol refining process puts more VOCs into the air than burning the ethanol fuel in your car," said de Gouw.

The new study indicates that the refining process should be on the ledger sheet when accounting for the atmospheric effects of ethanol production and use.

"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. It has many different aspects, but 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, and that is where this study fits in."

The new study is published online in the Journal of Geophysical Research in preprint form, and will appear in final form in a few weeks. Coauthors of the study are from NASA, Harvard University, University of Wisconsin, University of Maryland Baltimore County, and the Swiss Federal Institute of Technology-Zürich.