Renewable Fuel Ass. Says NRC Report on Oxygenates Confuses The Debate
12 May 1999
Renewable Fuel Association Says NRC Report on Oxygenates Confuses The Debate; Critical Questions Remain WASHINGTON, May 11 -- By reaching far beyond the original
charge put forth by the Environmental Protection Agency, a report released
today by the National Research Council, "Ozone-Forming Potential of
Reformulated Gasoline," falls short of answering critical questions regarding
the benefits of oxygenates generally, and the air quality impacts of ethanol
fuels specifically. But the report does provide EPA with guidance regarding
the role of CO in ozone and the need to evaluate high emitting vehicles which
could enhance ethanol's role in RFG.
"The National Research Council (NRC) was asked by EPA to provide guidance
on whether changes to the existing program (e.g., credit for reductions in
carbon monoxide) were justified on the basis of ethanol's increased oxygen
content," said Eric Vaughn, President of the Renewable Fuels Association.
"The Committee, however, took it upon itself to go beyond its original charge
and examined the efficacy of the RFG program itself. In doing so, the
Committee did not have the benefit of public comment on these complex issues
nor fully availed itself of the scientific data regarding the air quality
benefits of oxygenates. It is simply impossible to draw conclusions about the
efficacy of oxygenates in RFG without considering the dilution effect of
oxygenates and the impact on air quality of the gasoline components that might
be used to replace the large volume and octane lost if oxygenates were not
used in RFG. As the NRC report did neither, its conclusions regarding the air
quality impacts of oxygenates are unjustified."
With regard to the NRC's explicit charge to evaluate the relative ozone
impacts of 10% ethanol and 11% MTBE fuels, Vaughn expressed dismay that the
Committee did not do a more robust analysis, choosing instead to simply
restate the conclusions of a 1998 California Air Resources Board study that
was extremely limited in its scope (only six vehicles tested) and which failed
to evaluate the impact on emissions from high emitting vehicles. Still,
Vaughn noted the NRC did support several critical points the ethanol industry
has been making regarding the need to account for all of ethanol's emissions
impacts when assessing the ozone equivalency of ethanol and MTBE blended
gasolines. Specifically, the NRC report made the following points that
warrant additional consideration:
* Carbon monoxide (CO) in exhaust emissions from motor vehicles contribute
about 20% to the overall reactivity of motor vehicle emissions. Further, as
VOC emissions from mobile sources continue to decrease in the future, CO
emissions might become proportionately an even greater contributor to ozone
formation. CARB data shows that CO reductions from ethanol-blended fuels are
twice that of MTBE fuels.
* A sizeable portion of the ozone-precursor emissions from gasoline-fueled
vehicles appears to be associated with a relatively small number of high
emitting vehicles. But most emissions tests have been completed on normal-
emitting vehicles. There is evidence to suggest, however, that oxygenates
have a beneficial impact on emissions from higher emitting vehicles. For
example, a 1994 EPA study found significant decreases in exhaust VOC (10%)
and CO (11%) emissions when comparing ethanol to MTBE. Recognizing the
importance of high emitters to overall emissions, the NAS recommended further
tests to discern the effects of oxygenates.
* The Committee concluded that for normal emitting vehicles the increase
in evaporative emissions from ethanol-blended fuels tends to outweigh the
decrease in exhaust reactivity emissions. But the Committee's fundamental
conclusion was the overall impact on ozone of allowing the use of ethanol-
containing fuel "would likely be quite small in any case." The report
concludes, "the use of ethanol, as opposed to MTBE, as an oxygenate would lead
to a decrease in the effectiveness of RFG's, but not a total cancellation.
The net effect on ozone concentrations would be extremely small and almost
certainly not discernable from the ambient ozone concentration data."
Vaughn concluded that "while the report confuses some issues because of
its lack of focus, it does provide EPA with some guidance regarding potential
improvements to the RFG program. Clearly, we need to work to find a way to
assess the impact of CO on ozone formation. We need to fully understand the
impact of ethanol and oxygenates on high emitters. And we should appreciate
that the overall impact on ambient ozone air quality from small increases in
evaporative emissions is likely to be trivial in any case." Vaughn stated the
RFA would continue working with the U.S. EPA on these important issues to
assure the continued success of the RFG program.
