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

Unlike VOC and NOx, emissions of CO and benzene from gasoline and diesel
vehicles and equipment were estimated to decrease when the use of renewable fuels
increased. Reductions in emissions of CO varied from as low as 1.3 percent to as high as
3.6 percent for the nation as a whole, depending on both the renewable fuel volume
scenario and assumptions regarding the amount of ethanol used in reformulated versus
conventional gasoline. Benzene emissions from gasoline vehicles and equipment were
estimated to be reduced from 1.7 to 6.2 percent.
We do not have sufficient data to predict the effect of ethanol use on levels of
either directly emitted particulate matter (PM) or secondarily formed PM, but do expect a
net reduction in ambient PM levels to result due to the secondary PM impacts as
discussed in section VIII.C. However, data on direct PM emission impacts is available
for biodiesel. We estimate that reductions in emissions of direct PM from the projected
increase in the use of biodiesel to be about 100 tons nationwide, equivalent to less than
0.5 percent of the diesel PM inventory.
The emission impact estimates described above are based on the best available
data and models. However, it must be highlighted that most of the fuel effect estimates
are based on very limited or old data which may no longer be reliable in estimating the
emission impacts on vehicles in the 2012 fleet with advanced emission controls 3 . As
such, these emission estimates should be viewed as preliminary. EPA hopes to conduct
significant new testing in order to better estimate the impact of fuel changes on emissions
from both highway vehicles and nonroad equipment, including those fuel changes
brought about by the use of renewable fuels. We hope to be able to incorporate the data
from such additional testing into the analyses for other studies required by the Energy Act
in 2008 and 2009, and into a subsequent rule to set the RFS program standard for 2013
and later.
We used the Ozone Response Surface Model (RSM) to estimate the impacts of
increased use of ethanol on ozone levels for the 7.5 billion gallon use scenario
representing the required volumes under the RFS program. We did not evaluate other
renewable fuel volumes scenarios due to the limited amount of time available for
completing this NPRM. The ozone RSM approximates the effect of VOC and NOx
emissions in a 37-state eastern area of the U.S. Using this model, we projected that the
changes in VOC and NOx emissions could produce a very small increase in ambient
ozone levels. On average, ozone levels increased by 0.06 ppb, which represents less than
0.1 percent of the standard. Even for areas expected to experience a significant increase
in ethanol use, ozone levels increased by only 0.1 - 0.2 ppb, less than 0.2 percent of the
standard. These ozone impacts do not consider the reductions in CO emissions
mentioned above, or the change in the types of compounds comprising VOC emissions.
Directionally, both of these effects may mitigate these already small ozone increases.
The ozone impacts also do not consider the impact of increased emissions from ethanol
and biodiesel production facilities or any corresponding decrease in emissions from
refineries.
3 Advanced emission controls include close-coupled, high density catalysts and their associated electronic
control systems for light-duty vehicles, and NOx adsorbers and PM traps for heavy-duty engines.
- 19 -