"Our work highlights the need to expand the biofuels debate beyond its current focus on climate change to include a wider range of effects such as their impacts on air quality," said Jason Hill, lead author of the report.

Published in Proceedings of the National Academy of Sciences, the study examined combined environmental and human health costs of gasoline, corn-based ethanol and cellulosic fuels. It found corn ethanol to be the most costly.

Cellulosic ethanol made from wood, grasses and plant biomass produces less emissions of fine particulate matter, emits lower levels of greenhouse gases and has fewer effects on human health. Although environmental and health costs of cellulosic ethanol are less than half that of corn-based biofuels, it is far from being ready for commercial use.