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

of their more approximate nature. Their geographical concentration also makes it more
difficult to simulate with the Ozone RSM.
The Ozone RSM was created using multiple runs of the Comprehensive Air
Quality Model with Extensions (CAMx). Base and proposed control CAMx
metamodeling was completed for the year 2015 over a modeling domain that includes all
or part of 37 Eastern U.S. states, plus the District of Columbia. For more information on
the Ozone RSM, please see the Chapter 5 of the DRIA for this proposal.
The Ozone RSM limits the number of geographically distinct changes in VOC
and NOx emissions which can be simulated. As a result, we could not apply distinct
changes in emissions for each county. Therefore, two separate runs were made with
different VOC and NOx emissions reductions. We then selected the ozone impacts from
the various runs which best matched the VOC and NOx emission reductions for that
county. This models the impact of local emissions reasonably well, but loses some
accuracy with respect to ozone transport. No ozone impact was assumed for areas which
did not experience a significant change in ethanol use. The predicted ozone impacts of
increased ethanol use for those areas where ethanol use is projected to change by more
than a 50% market share are summarized in Table VIII.C.1-1. As shown in the Table
5.1-2 of the DRIA, national average impacts (based on the 37-state area modeled) which
include those areas where no change in ethanol use is occurring are considerably smaller.
Table VIII.C.1-1
Impact on 8-hour Design Value Equivalent Ozone Levels (ppb) a
Primary Analysis Sensitivity Analysis
Min RFG Use Max RFG Use Min RFG Use Max RFG Use
Minimum Change -0.030 -0.025 -0.180 0.000
Maximum Change 0.395 0.526 0.637 0.625
Average Change b
0.137 0.171 0.294 0.318
Population-
0.134 0.129 0.268 0.250
Weighted Change b
a In comparison to the 80 ppb 8-hour ozone standards
b Only for those areas experiencing a change in ethanol blend market share of at least 50 percent.
As can be seen, ozone levels generally increase to a small degree with increased
ethanol use. This is likely due to the projected increases in both VOC and NOx
emissions. Some areas do see a small decrease in ozone levels. In our primary analysis,
where exhaust emissions from Tier 1 and later onroad vehicles are assumed to be
unaffected by ethanol use, the population-weighted increase in ambient ozone levels in
those areas where ethanol use changed significantly is 0.129-0.134 ppb. Since the 8-hour
ambient ozone standard is 80 ppb, this increase represents about 0.16 percent of the
standard, a very small percentage.
In our sensitivity analysis, where exhaust emissions from Tier 1 and later onroad
vehicles are assumed to respond to ethanol like Tier 0 vehicles, the population-weighted
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