Emissions
When environmentalists concern themselves with emissions from combustion engines there are four primary types of pollutants scientists study. These emissions are hydrocarbons (HC), oxides of nitrogen (NOx), carbon monoxide (CO) and carbon dioxide (CO2 ). Because E85 is predominantly ethanol the tailpipe emissions are much different than that of regular gasoline. There have been numerous studies done to compare and contrast the different emissions and the effects these emissions have on the environment but the tests have been inconclusive. The tests have shown very little consistency if any at all because there are too many variables involved. The make and model of the vehicle, the way in which the ethanol was produced and the vehicles overall fuel efficiency all play a large role in the overall outcome of each study. To address the problem of inaccuracy, engineers at the National Renewable Energy Laboratory combined data from all applicable emissions studies and compiled them into one data set. This compiled set of data showed that on average all emissions that are federally regulated showed a decrease or no statistically relevant difference between E85 and gasoline.
EPA's stringent tier-II vehicle emission standards require that FFVs achieve the same low emissions level regardless of whether E85 or gasoline is used. However, E85 can further reduce emissions of certain pollutants as compared to conventional gasoline or lower-volume ethanol blends. For example, E85 is less volatile than gasoline or low-volume ethanol blends, which results in fewer evaporative emissions. Using E85 also reduces carbon-monoxide emissions and provides significant reductions in emissions of many harmful toxics, including benzene, a known human carcinogen. However, E85 also increases emissions of acetaldehyde. EPA is conducting additional analysis to expand our understanding of the emissions impacts of E85.
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