Ethanol derived from corn--already under fire for higher-than-expected greenhouse gas emissions--is also more harmful to public health than either cellulosic ethanol or traditional gasoline, according to a new study.
Researchers, who published their findings in the 'Proceedings of the National Academy of Sciences' this month, calculated emissions of greenhouse gases and fine particulate matter from petroleum-based gasoline as well as from corn-based and cellulosic ethanol.
They then quantified the social cost of these emissions over the entire lifecycle of the different fuels, using a combination of market prices for carbon, carbon capture and storage costs, and health care costs resulting from pollution.
The authors calculated that the combined climate change and health costs associated with the production and combustion of 1 billion gallons of traditional gasoline in the US amount to $469 million.
The same quantity of ethanol derived from corn was found to have a cost ranging from $472 million to $952 million, depending on the source of the heat used to power the biorefinery and other technological variables.
Meanwhile, production and combustion of cellulosic ethanol from a variety of feedstocks led to a comparable cost of just $123 million to $208 million.
The study was conducted by researchers at the University of Minnesota, Stanford University, Argonne National Laboratory, and Cambridge-based Industrial Economics.
Breaking down the numbers further, corn-derived ethanol produced using electricity generated from natural gas--as is common in today's biorefineries--was found to have a combined social cost of $614 million.
In an 'advanced' corn ethanol scenario--with major improvements in corn production and conversion technology--the social costs fall to $472 million but still exceed those of gasoline.
For cellulosic ethanol, the costs range from $128 million when the fuel is derived from various prairie grasses to $208 million when derived from switchgrass.
Focusing specifically on the health impacts over the lifecycle of the different fuels, the study found that corn ethanol--regardless of the source of energy used during production--has higher health costs resulting from emissions of fine particulate matter than gasoline.
On the other hand, cellulosic ethanol leads to the lowest health-related costs of the three types of fuel, with prairie grasses imposing the very lowest burden on human health.
The study noted that 'unlike long-lived [greenhouse gas] emissions, which globally mix in the atmosphere, the formation and health effects of [fine particulate matter] are regional.'
So in the case of ethanol derived from corn, fuel production has concentrated health impacts on the US Midwest, where much of the country's corn is grown.
The authors of the study found that 'growing perennial biomass crops for cellulosic ethanol in this same region results in lower [fine particulate matter] levels than corn ethanol because less fossil fuel and fertilizer are required.'
A growing number of studies in the last two years have questioned the perceived environmental benefits of corn-derived ethanol. Typically, such studies have concluded that each barrel of oil used to grow the corn and process it results in production of only 1.2 to 1.5 barrels of ethanol.
This latest study added a new dimension to the debate about corn-based ethanol by focusing on how it can affect public health.
Such findings have important implications in the US, where ethanol derived from corn has dominated domestic production of the alternative fuel.
And the contribution of corn-based ethanol to the US fuel mix is set to rise in the coming years as gasoline blenders work to meet the aggressive targets laid out in the Energy Independence and Security Act.
The Act, which was signed into law in 2007, set a production goal of 36 billion gallons of biofuels per year by 2022 (OD Dec.26'07,p1). US production of ethanol hit 9 billion gallons last year.
Although the contribution of ethanol and biodiesel derived from feedstocks other than corn is mandated to increase over time, the development of these alternatives has been a slow process (OD Dec.9,p6).
Casey Sattler, Houston
