1. Evaluation of MTBE as a Component of Reformulated Gasoline
Catherine P. Koshland
Donald Lucas
Robert F. Sawyer
Pamela M. Franklin
University of California, Berkeley
EPA Blue Ribbon Panel
Sacramento, CA
March 25, 1999
Good afternoon. My name is Pamela Franklin. Today I’d like to describe research conducted at the University of California, Berkeley, with Professors Cathy Koshland and Robert Sawyer and Dr. Donald Lucas at the Lawrence Berkeley National Laboratory.
We conducted this research as part of a University of California - wide, comprehensive evaluation funded by state legislation to investigate the effects of MTBE, including health effects, effects of groundwater and surface water, remediation techniques, and overall costs and benefits. The purpose of this research was intended to provide the Governor with input to make a decision about MTBE in California.
While our research included a lot of technical data, today I’d like to provide you with an overview of the context in which we conducted this study and some of the political / policy implications for this research.

2. Objectives
Evaluate published literature of vehicle emissions from conventional fuels, oxygenated fuels, and reformulated fuels
Laboratory studies
Vehicle dynamometer studies
On-road studies
Evaluate Auto/Oil database
Conduct experimental laboratory reactor study to identify combustion byproducts
Our effort focused on an evaluation of the effects of MTBE on automotive combustion byproducts. To this end, we performed three tasks:
1. we conducted an extensive investigation into the existing literature on laboratory, vehicle, and on-road studies, ranging from pure MTBE reaction at ambient and elevated temperatures, to vehicle dynamometer testing with selected fuel formulations, to real-world vehicles and complex fuel mixtures.
2. we also evaluated an extensive database compiled by the Auto/Oil study, a collaborative effort of 14 oil companies and 3 domestic auto manufacturers, which speciated over 150 hydrocarbon emissions (engine out + exhaust) for different vehicle technologies and fuel formulations.
3. Finally, we conducted original laboratory experiments in a flow reactor in order to simulate “worst-case” automotive engine-out emissions, to fill in data gaps we identified, to better identify contribution of MTBE to specific combustion byproducts.

3. Gasolines Conventional fuel = hydrocarbons
“Oxyfuel” = conventional fuel + oxygenate
Goal: reduce CO emissions
Reformulated gasoline (RFG)
Goal: reduce ozone precursors, toxic emissions
Federal RFG (1995):
Requires minimum 2.0 wt% oxygen
California Phase 1 RFG (1992)
Eliminated lead, reduced vapor pressure, required detergents
California Phase 2 RFG (1996)
More stringent than Federal RFG requirements
Limits eight fuel parameters
Requires wt% oxygen unless predictive model used
It’s helpful to begin by describing some of the different “flavors” of gasoline.
Different gasoline formulations are regulated by federal statute under the 1990 Clean Air Act. California also has special privilege to make its own fuel regulations.
Conventional fuel may have low levels of oxygenates (2-3 vol%), primarily as octane booster.
Oxyfuels and RFGs - do not mandate any particular oxygenate.
MTBE is the refiners’ “oxygenate of choice” - technical, economic reasons.

4. MTBE combustion byproducts Laboratory reactor measurements
Increase in MTBE emissions, byproduct emissions (especially isobutylene, formaldehyde) when MTBE is a component of reformulated gasoline
Methanol (pure MTBE byproduct) not observed as byproduct of MTBE-fuel at elevated temperatures
TBF (pure MTBE byproduct under atmospheric conditions) not observed at elevated temperatures
Observed combustion byproducts consistent
Laboratory studies of pure MTBE
Vehicle and on-road studies of gasoline with MTBE
Our experimental studies concur with other laboratory studies in flow reactors at elevated temperatures.

5. California Phase 2 RFG vs
California Phase 2 RFG vs. Conventional Gasoline Vehicle and tunnel measurements
Reduces hydrocarbons: %
Reduces CO: %
Reduces NOx: %
Reduces benzene: %
Increases aldehydes when oxygenates are included in fuel formulation
These results encapsulate a wide range of vehicle dynamometer and on-road studies comparing exhaust emissions from reformulated fuel (typically with 11 vol% MTBE) and conventional gasoline.

6. Impact of fuel formulations on automotive emissions
Oxyfuel vs. conventional gasoline
Reduces CO exhaust emissions
Reduces emissions of total hydrocarbons, benzene, and aromatics by dilution effect
RFG vs. conventional gasoline
Reduces ozone-forming potential of emissions
Larger emission reductions of total hydrocarbons, benzene, and aromatics
Reduces evaporative emissions
Improves effectiveness of catalytic converter
CaRFG2 with MTBE vs. non-oxygenated CaRFG2
Produce similar reductions in ozone-forming potential and mass emissions of total hydrocarbons, benzene, and aromatics
MTBE-fuel increases direct (exhaust) formaldehyde emissions
Similarly, these broad-stroke comparisons of the impact of different fuel types on vehicle emissions are based on vehicle dynamometer and on-road studies.

7. Conclusions: MTBE’s role as a fuel component
MTBE (as well as other oxygenates) helps reduce automotive CO emissions in older cars and increases formaldehyde emissions from all vehicles
RFG - with or without MTBE - has significant air quality benefits
In newer vehicles, non-oxygenated CaRFG2 provides essentially the same emissions benefits as CaRFG2 with MTBE
Fully-compliant CaRFG2 can be produced without MTBE
Fuel formulation changes are one dimension of a comprehensive strategy to reduce auto emissions in California
Here are some of the conclusions / policy implications we’ve drawn from our review of the available information and our own study, in terms of how these results impact policy decisions.

8. Response to reviewer comments: Scientific support for conclusions
“Based only on Auto/Oil study”
Conclusions based on totality of evidence
Auto/Oil study results compelling
“Does not directly compare two fuels identical except for MTBE”
Impossible to compare identical CaRFG2 formulations with and without MTBE
California is the only place where “RFG” is not synonymous with “oxygenated RFG”
Auto/Oil study:
CaRFG2 with 11 vol% MTBE vs. a non-oxygenated CaRFG2
“Advanced technology,” MY; 1989 MY; Federal Tier I (1993 California, rest of US)
published Auto/Oil study; also database
few studies: tunnel studies (e.g., Kirchstetter et al.) haven’t tested CaRFG2 without MTBE as a comparison!
impossible to compare two “identical” RFGs with and without MTBE:
- differences in octane number

9. “MTBE plays an important role in reducing CO emissions”
Response to reviewer comments: MTBE’s contribution to reduced vehicle emissions
“MTBE plays an important role in reducing CO emissions”
Oxygenates lower tailpipe CO by % per wt% oxygen
Wide variation: vehicle technology, ambient temperature
“Conclusion ignores the contribution of CO to reduced ozone-forming potential”
CO has low reactivity, but is emitted at higher levels than most HCs
California predictive model does not include OFP per se
Auto/Oil urban airshed ozone models do include the impact of reduced CO emissions
“MTBE reduces toxic emissions via ‘dilution effect’ ”
True for “oxy-fuels” (conventional gas + oxygenate)
Not accurate description of oxygenated RFG
Reduced CO emissions:
2 - 10% per wt % oxygen
varies widely depending on vehicle technology
uncertain effects at low temperatures
ambient CO - confounding factors: meteorology, fleet turnover
not really an issue in California anymore
CO and OFP:
CO has low MIR compared to other HCs but is emitted at higher levels: uncertainty about net contribution: 10-20% of HC OFP?
California predictive model doesn’t include OFP per se
Auto/Oil: urban airshed model projects peak ozone formation - includes impact of reduced CO emissions
Reduction in toxic emissions via “dilution effect”
accurate description of “oxyfuels” = conv. gas + oxygenate
not at all accurate for RFGs - “match blended”
We concur with ARB’s comment: “Oxygenates do provide value in that they have blending properties that facilitate meeting the overall specifications for CaRFG2 …. We believe it is more accurate to conclude that oxygenates are effective in making gasoline with lower emitting properties but that alternative gasoline formulations that are equally effective and do not use oxygenates are also feasible to produce.”

10. “Evaluation of other hydrocarbon species not considered”
Response to reviewer comments: Benzene vs. other automotive toxic emissions
“Evaluation of other hydrocarbon species not considered”
Incorrect. We evaluated numerous hydrocarbon byproducts, including:
Formaldehyde
Direct emissions
Secondary atmospheric formation important
Acetaldehyde
1,3-butadiene
US EPA: “US EPA does not believe that decreases in other toxic compounds should be ignored on the basis of their statistical significance.”

11. Response to reviewer comments: Advanced Technology Vehicles
“ ‘Advanced Technology’ vehicles (Auto/Oil study) not defined”
Mid-1990s prototypes at time of study
3-way catalysts, exhaust gas recirculation, sequential or port fuel injection
“ ‘Advanced Technology’ vehicles represent only a small fraction of California fleet”
Growing proportion of on-road fleet
Vehicle turnover important
Significant fraction of vehicle miles traveled and mobile source emissions

12. “Evaporative emissions not considered”
Response to reviewer comments: Extrapolation of studies to the real world
“Vehicle dynamometer studies have limitations and should not be extrapolated to real-world”
Evaluated wide range of studies, including on-road
Auto/Oil study included older vehicles, high-emitting vehicles
“Evaporative emissions not considered”
Evaluated in Auto/Oil study; incorporated in their conclusions
“High-emitting vehicles and ‘gross polluters’ not considered”
Relatively few vehicles contribute disproportionately to automotive pollution
Fuel formulation may not be the most effective way to address this aspect of auto pollution

13. Response to reviewer comments: Role of oxygenated fuels in reducing automotive CO emissions
“Relying on fleet turnover is insufficient to reduce CO emissions and ensure compliance with CO standards”
Compliance with NAAQS for CO a decreasing problem in California
Vast improvements in vehicle technology are having an important effect
“Oxygenates are needed to reduce emissions from high-emitting vehicles”
Fuel formulation changes are one way to address this problem, but may not be the most effective way to reduce emissions from gross polluters, malfunctioning vehicles

14. Response to reviewer comments: Other benefits from oxygenated fuels
“Reduced particulate matter (PM) emissions benefits ignored”
Increasing concern over ultra-fine particulate emissions
Few data are available
High aromatic fuel content may be important precursor
“Emission reduction benefits in off-road vehicles ignored”
Contribution to mobile source emissions varies according to pollutant type
As on-road fleet turns over, new vehicle technology, off-road sources will become increasingly important