Switching from gasoline or corn-based biofuels to cellulosic ethanol–made from the stalks and stems of plants–could have more health and environmental benefits than previously recognized, according to a study of different types of transportation fuels.

The environmental and health costs associated with cellulosic ethanol are less than half those of gasoline and of corn ethanol, the study found.

The analysis looked at the impacts of cellulosic and corn-based biofuels and of gasoline. It accounted for many possible impacts, including those from the energy used in refineries, the pollutants pumped out of car tailpipes, and the consequences of cultivating corn or other plants used to make biofuel.

This is the first study to focus not just on the environmental impacts of fuels, which have already been the subject of considerable scrutiny and debate, but also on the consequences for human health. Air pollutants emitted as a result of fuel production and consumption can cause breathing problems and aggravate asthma, and have been linked to premature death.

“We wanted to see which fuels are in the best interests of society to develop,” says Jason Hill, a resident fellow in the University of Minnesota’s Institute on the Environment and the lead author of the study, which was published online in the Proceedings of the National Academy of Sciences on February 2.

Cellulosic ethanol was the clear winner in the analysis. Switching to cellulosic ethanol from gasoline could significantly reduce the amount of pollutants emitted during fuel production and consumption, Hill and his colleagues found. Ethanol burns more cleanly than gasoline, and crops cultivated to produce biofuel also absorb carbon dioxide. Cellulosic ethanol is a better alternative to corn ethanol because it requires less fertilizer than corn ethanol to produce, and there’s no energy required for heat at biorefineries. Biorefineries that produce cellulosic ethanol actually generate excess electricity by burning lignin.

Biofuel produced from corn grains has environmental and health costs that are equal or greater than those of gasoline, depending on whether natural gas, coal, or corn stover is used to generate heat during the production process, the study found.

The findings aren’t unexpected, according to Roger Sedjo, a senior fellow with Resources for the Future, a nonprofit group that conducts independent research on environmental, energy, and natural-resource issues. But he adds that they are “interesting and important.”

Lester Lave, a Carnegie Mellon University professor who has written extensively on energy economics, lauds Hill and his colleagues for their efforts to quantify fuel impacts. “It’s a brave paper,” he says. “It does as good a job as you can do at this stage.”

To estimate the environmental and health costs of fuel production and consumption, Hill and his colleagues focused on the two most harmful emissions: fine particulate matter, which can aggravate lung diseases and has been linked to heart attacks in people with heart problems, and greenhouse gases. They used an analysis from the U.S. EPA to monetize the health impacts of fine particulate matter, including lost work days, hospital visits, and early deaths. They also used independent estimates of carbon mitigation costs, carbon market prices, and the social cost of carbon to calculate the cost of greenhouse gases.

Hill and his colleagues calculated the emissions associated with a billion-gallon increase in ethanol production and consumption, or the equivalent amount of gasoline–about the same as the rise in U.S. gasoline production from 2006 to 2007.

For gasoline, the combined climate-change and health costs of that increase are $469 million, the researchers concluded; for corn ethanol, they range from $472 million to $952 million, depending on the production method; and for cellulosic ethanol, they are between $123 million and $208 million, depending on the plant material that’s used to produce it.

Evidence against corn ethanol has been accumulating in recent years. It takes a lot of energy to grow corn and to ferment the kernels to produce ethanol, and considerable amounts of greenhouse gases are produced in the process. Hill’s analysis suggests that corn ethanol could also create more health problems than gasoline.

However, Satish Joshi, an environmental economist at Michigan State University, who wasn’t involved in Hill’s study, says that he “wouldn’t rule out corn ethanol” yet: “It’s proven, well-established technology.” Although Joshi says that he’s pleased to see more evidence of the advantages of cellulosic ethanol, it’s a newer development, and there isn’t yet a way to produce it economically. Conversely, “corn has the longer history and the established manufacturing base … Cellulosic ethanol is still technologically unproven,” Joshi says.

Hill’s study compared three ways of making ethanol from corn–using natural gas, coal, or corn stover to generate heat at biorefineries–and four processes that produce cellulosic ethanol–from corn stover, switchgrass, prairie grasses, or Miscanthus, a tall perennial grass–and he says that the results show how much difference production methods can make in the overall impacts associated with fuels.

The impacts associated with fuels vary according to where the fuel is produced, Hill found. The health costs associated with airborne particles vary considerably, he says, depending on atmospheric conditions and population density.

“Maybe there’s a way to spatially locate production of biofuel to get maximal health benefits” out of a switch from gasoline, Hill says–something that he plans to investigate.

His analysis assumes, for the sake of simplicity, that the additional corn or other plant material needed to produce biofuel is grown on grasslands that are currently part of the U.S. Conservation Reserve Program. Hill says that in reality, increased biofuel production will likely encroach on land that’s now used to produce other crops, triggering a cascade of land-use changes. If rain forests in other countries are cleared to make way for crops, for example, the impacts in terms of climate change could negate the benefits of switching to biofuel to reduce greenhouse-gas emissions.

By taking into account the health consequences of fine particles, Hill looked at “one additional thing off a huge list” of possible effects that also include erosion, pesticide contamination, and petroleum spills”, says Soren Anderson, an assistant professor at Michigan State University, who focuses on biofuels as part of his research on energy and environmental economics. “That additional thing made clear that corn ethanol is actually worse than gasoline, and cellulosic ethanol looks to be better.”