Flexible
Fuel Vehicle Emissions
Using
ethanol as a vehicle fuel provides local and global benefits
- reducing emissions of harmful pollutants and greenhouse
gases.
Ethanol has been blended in low levels (10% or less) with
gasoline for many years. This use of ethanol as an "oxygenate"
promotes more complete combustion of the fuel, which can reduce
exhaust emissions of carbon monoxide - a regulated pollutant harmful
to human health - by 20% to 30% compared with pure gasoline.
FFVs fueled with E85 also emit less carbon monoxide than gasoline-powered vehicles.
Emissions from E85-fueled FFVs of other regulated pollutants,
such as hydrocarbons and nitrogen oxides, are similar to those
from gasoline-powered vehicles.
Tests indicate that vehicles fueled with ethanol blends produce
lower emissions of some toxic compounds, such as benzene and
1,3 butadiene, than vehicles fueled with pure gasoline. However,
evidence suggests that ethanol might increase toxic aldehyde
emissions. In addition to exhaust emissions, all vehicles
emit hydrocarbons due to evaporation of fuel from their tanks
and fueling systems, especially in warm weather. The common
oxygenate blend E10 (10% ethanol, 90% gasoline) has a higher vapor pressure
than pure gasoline and thus produces higher evaporative emissions. E85's vapor pressure is lower than gasoline's,
so it produces lower evaporative emissions.
Mid-level ethanol blends, such as E15 and E20, can be used
in FFVs but currently not in standard gasoline-powered vehicles.
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