Burning ethanol as a transportation fuel may cause more air pollution than gasoline combustion, according to a new study from the University of Minnesota.

For the study, which compared pollution levels from gasoline fuel and 10 alternative energy vehicles, researchers looked at tailpipe emissions from various fuels and calculated the entire pollutant stream. The authors included everything from growing the corn to the process used to turn it into ethanol.

“And we found that some options available to us, like corn ethanol or electricity from coal used in electric vehicles, actually make the air much worse,” assistant professor Jason Hill told CBS Minnesota.

The study also found that a battery-electric car is also worse than gasoline if the power used to recharge the batteries is generated from burning coal.