E85 Emissions
Although it is an alternative fuel, the use and storage of E85 (85% ethanol, 15% gasoline) result in the emission of regulated pollutants, toxic chemicals, and greenhouse gases. These emissions are primarily released by fuel evaporation and combustion from light-duty vehicles. However, emissions from E85 sources are generally reduced compared to those of gasoline. The different E85 emissions and how they compare with gasoline emissions are described below.
Evaporative Emissions
Emissions of evaporated E85 or gasoline enter the air through permeation, fuel tank venting, and fuel or vapor leaks. Permeation vapors are released through fuel-line materials. This type of emission is more of an issue for regular gasoline and gasoline with low levels of ethanol such as E5 (5% ethanol, 95% gasoline) and E10 (10% ethanol, 90% gasoline) than E85. For more information on ethanol's influence on permeation rates at different blend levels, see the Coordinating Research Council's permeation report (PDF 657 KB). Download Adobe Reader.
Fuel tank venting occurs when fumes escape the tank during refueling and when gasoline vapors expand on warm days. Since model year (MY) 2000, fuel tank venting is controlled by onboard refueling vapor recovery devices installed in all cars running on E85 or gasoline. Evaporative emissions also come from fuel or vapor leaks. These emissions are less prevalent in cars running on either type of fuel because of ongoing improvements in leak-resistant materials and fittings.
Tailpipe Emissions
Tailpipe emissions come from fuel combustion in a vehicle's engine and are emitted from its exhaust system. Most often the emissions of primary concern include hydrocarbons, oxides of nitrogen (NOx), carbon monoxide (CO), air toxics, and carbon dioxide (CO2). Numerous studies have compared the emissions of E85 to those of gasoline. These studies do not tell a consistent story due to the large number of variables involved. However, in 2008, engineers at the National Renewable Energy Laboratory combined data from all applicable emissions studies into one robust data set. They analyzed this data set and compared the changes in emissions of E85 in a flexible fuel vehicle (FFV) with gasoline in an FFV or a similar non FFV. On average, all regulated emissions either decreased or showed no statistically significant difference with E85 compared with gasoline. Emissions that increased with the use of E85 included formaldehyde, acetaldehyde, and methane.
| Emission | Comparison | Average Change (%) | 95% Confidence Range (%) | Number Tested | P Value For Paired t test |
|---|---|---|---|---|---|
| Total Hydrocarbons |
E85 vs. gasoline in same FFV | -8 | -19 4 | 89 | 0.20 |
| E85 vs. gasoline in similar non FFV | -18 | -28 -7 | 71 | 0.00 | |
| Nonmethane Organic Gas | E85 vs. gasoline in same FFV | 12 | -56 182 | 6 | 0.43 |
| E85 vs. gasoline in similar non FFV | -43 | -43 -43 | 1 | NA | |
| Nonmethane Hydrocarbon | E85 vs. gasoline in same FFV | -10 | -17 -3 | 72 | 0.03 |
| E85 vs. gasoline in similar non FFV | -27 | -37 -16 | 72 | 0.00 | |
| Benzene | E85 vs. gasoline in same FFV | -70 | -82 -50 | 6 | 0.16 |
| E85 vs. gasoline in similar non FFV | -86 | -86 -86 | 1 | NA | |
| 1,3-Butadiene | E85 vs. gasoline in same FFV | -62 | -83 -13 | 6 | 0.01 |
| E85 vs. gasoline in similar non FFV | -91 | -91 -91 | 1 | NA | |
| NOx | E85 vs. gasoline in same FFV | -18 | -27 -9 | 93 | 0.00 |
| E85 vs. gasoline in similar non FFV | -54 | -60 -46 | 73 | 0.00 | |
| Particulate Matter | E85 vs. gasoline in same FFV | -34 | -98 -2395 | 3 | 0.00 |
| E85 vs. gasoline in similar non FFV | |||||
| CO | E85 vs. gasoline in same FFV | -20 | -39 4 | 93 | 0.00 |
| E85 vs. gasoline in similar FFV | -18 | -27 8 | 73 | 0.00 | |
| Formaldehyde | E85 vs. gasoline in same FFV | 63 | 51 75 | 92 | 0.00 |
| E85 vs. gasoline in similar non FFV | 56 | 39 76 | 72 | 0.00 | |
| Acetaldehyde | E85 vs. gasoline in same FFV | 1786 | 1424 2233 | 92 | 0.00 |
| E85 vs. gasoline in similar non FFV | 2437 | 2130 2786 | 72 | 0.00 | |
| Methane | E85 vs. gasoline in same FFV | 92 | 72 114 | 86 | 0.00 |
| E85 vs. gasoline in similar non FFV | 91 | 75 108 | 71 | 0.00 |
Source: Effect of E85 on Tailpipe Emissions from Light-Duty Vehicles (PDF 660 KB) Download Adobe Reader. Journal of the Air & Waste Management Association, February 2009.
Note: A low P value (especially <.05) means the emission difference between the two groups is significant.
Life-Cycle GHG Emissions and Petroleum Use
Evaluating life-cycle greenhouse gas (GHG) emissions requires tracking all GHG emissions released to produce and distribute E85 as well as those emitted while driving. Researchers at Argonne National Laboratory found that corn-based E85 reduces GHG emissions 17% to 23% below that of regular gasoline on a per-mile basis. They also found that E85 reduces petroleum use by 70%. The Environmental Protection Agency is currently assessing an additional variable, indirect land use, and the effect it will have on the overall GHG emissions from corn-based ethanol.