Regulation of Fuels and Fuel Additives: Renewable Fuel Standard ...

Table VIII.A.1.b-2
Effect of MTBE and Ethanol in Conventional Gasoline on Tier 0 Vehicle Emissions
Relative to a Typical Non-Oxygenated Conventional Gasoline a
Pollutant Source 11 Volume 10 Volume
Percent MTBE Percent Ethanol b
Exhaust VOC EPA Predictive Models -9.2% -7.4%
NOx
2.6% 7.7%
CO c
MOBILE6.2 -6% / -11% -11% / -19%
Exhaust Benzene EPA Predictive and
-22% -27%
Formaldehyde Complex Models
+10% +3%
Acetaldehyde -8% +141%
1,3-Butadiene
-12% -27%
Non-Exhaust VOC MOBILE6.2 Zero +17%
Non-Exhaust Benzene MOBILE6.2 & Complex
Models
-10% +13%
a
Average per vehicle effects for the 2012 fleet during summer conditions
b
Assumes a 1.0 psi RVP waiver for ethanol blends
c
The first figure shown applies to normal emitters; the second applies to high emitters
As was the case with the RFG blends, the two oxygenated blends both reduce
exhaust VOC and CO emissions, but increase NOx emissions. The MTBE blend does
not increase non-exhaust VOC emissions, but the ethanol blend does due to the
commonly granted waiver of the RVP standard. Both blends have lower exhaust benzene
and 1,3-butadiene emissions. As above, ethanol increases non-exhaust benzene and
acetaldehyde emissions.
The exhaust emission effects shown above for VOC and NOx emissions only
apply to Tier 0 vehicles in our primary analysis. For example, MOBILE6.2 estimates
that 34% of exhaust VOC emissions and 16% of NOx emissions from gasoline vehicles
in 2012 come from Tier 0 vehicles. In the sensitivity analysis, these effects are extended
to all gasoline vehicles. The effect of RVP on non-exhaust VOC emissions is
temperature dependent. The figures shown above are based on the distribution of
temperatures occurring across the U.S. in July.
c. Nonroad Equipment
To estimate the effect of gasoline quality on emissions from nonroad equipment,
we used EPA’s NONROAD emission model. We used the 2005 version of this model,
NONROAD2005, which includes the effect of ethanol on permeation emissions from
most nonroad equipment.
Only sulfur and oxygen content affect exhaust VOC, CO and NOx emissions in
NONROAD. Since sulfur level is assumed to remain constant, the only difference in
exhaust emissions between conventional and reformulated gasoline is due to oxygen
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