Ethanol and other biofuels are often touted for their ability to reduce greenhouse gas emissions by replacing fossil fuels. Traditional biofuels like ethanol can reduce greenhouse gas emissions by 19-48 percent compared with gasoline, while advanced or cellulosic biofuels can reduce emissions by more than 100 percent. A less-recognized benefit of biofuels is their ability to reduce other harmful emissions that are found in gasoline exhaust.
A new study out of the Swiss Federal Laboratories quantifies the emissions reductions that ethanol blends like E10 (10 percent ethanol) and E85 (85 percent ethanol) achieve compared with traditional gasoline, or E0. The study analyzed and compared emissions of nanoparticles, polycyclic aromatic hydrocarbons (PAHs), and alkyl- and nitro- PAHs. The authors found that using ethanol blends significantly decreased these harmful emissions. A flex-fuel vehicle was used for the experiments.
Types of Emissions
Nanoparticles, one type of emissions considered in the study, are very fine particulate matter. Nanoparticles are smaller than 0.1 micrometers. Particulate matter can be carcinogenic, and has been linked to developmental and neurodegenerative disorders, cancers, and cardio-pulmonary effects.
Polycyclic aromatic hydrocarbons, or PAHs, are organic contaminants emitted from burning motor oil, coal, or cigarettes, manufacturing tires, and other sources. PAHs are composed of six atom benzene rings with many different configurations and varieties. Those with fewer rings are usually more toxic, soluble, and volatile, while PAHs with more rings are carcinogenic and more easily attach to sediments. For more on PAHs and their effects on human health and the environment, see EESI briefing PAHs Increasing in Urban U.S. Lakes.
Depending on the chemical configuration of the PAHs, some are classified as alkyl- or nitro- PAHs. Alkyl-PAHs are more abundant, and survive in the environment for longer periods of time. Nitro-PAHs, which can be created from parent PAHs or directly emitted, can sometimes be more toxic than parent PAHs.
Reduced Emissions from Ethanol
The study authors compared emissions from a flex-fuel vehicle when fueled with E0, E10, and E85. E10 is already the most commonly used fuel in the United States as a result of the Renewable Fuel Standard (RFS). Both E10 and E85 reduced particulate matter emissions by more than 95 percent when compared with E0, providing a substantial health benefit.
In addition, PAH emissions from E10 gasoline were 67-96 percent lower than E0, while PAH emissions from E85 were 82-96 percent lower than E0. The relative toxicity of these emissions also decreased—72 percent lower with E10 and 83 percent with E85. These results suggest that switching to higher ethanol blends in our gasoline can have positive effects for human health, as well as the positive effects on greenhouse gas emissions.
Author: Rebecca Chillrud
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