One of the main motivations for using E85 is its ability to help reduce the impact of vehicle emissions on the environment. E85 provides major reductions in some tailpipe emissions compared to gasoline. E85 is also less toxic than gasoline. Furthermore, the ethanol used in E85 can be derived from renewable resources, thus reducing net greenhouse gas emissions.

Vehicle Tailpipe Emissions

Determining the effect of E85 on vehicle emissions is complex, since many factors influence the emissions of vehicles. Further, E85 use is a politically charged issue, effecting the environment, domestic employment, and petroleum imports. Finding reliable emissions data is, therefore, challenging. Actual emissions will vary with engine design and calibration. One of the more recent sources, the U. S. Environ­mental Protection Agency (EPA), reports potential substantial tailpipe emissions benefits when using E85 relative to conventional gasoline.18 These benefits are shown in Figure 8.1. This source suggests these benefits for an engine optimized to operate on E85. The EPA also reports that fewer total toxics are produced, and that the hydrocarbon emissions have a lower reactivity. The use of E85 does produce higher ethanol and acetaldehyde emissions than gasoline.

Other sources provide different values, but most sources tend to show sub­stantial reductions in carbon monoxide. For example, the Renewable Fuels Asso­ciation reports a reduction of 25%.19 E85 typically results in slightly reduced levels of unburned hydrocarbons. Emissions of nitrous oxides (NOx) are slightly

Emissions Species

FIGURE 8.1 Estimated emissions reductions for an engine optimized to use E85 com­pared to those when operating on gasoline. Source: Data compiled from U. S. Environ­mental Agency, EPA420-F-00-035, Mar. 2002.

reduced with some sources showing slight increases and others showing decreases. Again, much of the data is subject to the test schedule used, and the vehicle and its optimization for E85.

Data from a snowmobile powered by a four-stroke, spark-ignited engine modified to operate using blends up to E85 is shown in Figure 8.2.20

If the ethanol used in E85 comes from renewable resources such as corn, E85 can show substantial reductions in greenhouse gas emissions. In 1998, the U. S. DoE Argonne National Laboratory estimated that 1 gallon of E85 reduces greenhouse gas emissions by 16-28% compared to gasoline.21 Other references suggest higher reductions exceeding 50%.22