United States
Environmental Protection
Agency
Air and Radiation
EPA420-F-98-022
May 1998
Office of Mobile Sources
vvEPA Announcement/
Update
EPA Staff Paper on Gasoline
Sulfur Issues
The Staff Paper on Gasoline Sulfur Issues presents EPA 's current
understanding of the impact of gasoline sulfur on emissions from
current andfuture motor vehicles. Based on the data and
information obtained to date, EPA staff believe that some level of
gasoline sulfur control is appropriate.
Background
The Staff Paper includes a discussion of the latest information on
sulfur impacts on vehicle emission controls and summarizes various
approaches to controlling sulfur levels in gasoline. It contains an
exploration of what gasoline producers and automobile
manufacturers can do to reduce sulfur's impact on vehicle emissions.
EPA recently published a draft Tier 2 Study of the air quality need
for and the feasibility and cost-effectiveness of emissions reductions
from light-duty vehicles and light-duty trucks beyond those required
by the existing Tier 1 emission standards. EPA plans to follow this
study with a proposal for this next level of emission standards, Tier 2
standards, by the end of 1998.
Impacts of Gasoline Sulfur on Emission
Control Systems
Sulfur in gasoline inhibits the performance of catalytic converters,
which are used on all current gasoline-fueled vehicles to reduce

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hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen
(NOx). Although future improvements in catalyst and engine designs
may reduce the impact of sulfur, it is unlikely that the impact of
sulfur can be completely eliminated. As tighter emission standards
require catalysts to be more efficient, the impact of sulfur will
become more dramatic.
Recent tests conducted by auto manufacturers and oil companies
demonstrate a significant emissions impact from gasoline sulfur,
especially on NOx emissions. No vehicle tested was completely
insensitive to sulfur, although some were more sensitive than others.
The testing shows that current vehicles designed for lower emissions
are much more sensitive to sulfur than earlier vehicles. Advanced
vehicle designs, aimed at lower emissions and higher fuel efficiency,
may depend on low sulfur levels.
Reducing the Sulfur Content of Commercial
Gasoline
A number of refinery options are available to reduce the level of
sulfur in gasoline. Significant sulfur reduction would likely require
investment in new refinery equipment and increases in operating
costs. Refinery modeling estimates from a variety of sources indicate
that to reduce gasoline from today's average levels of more than 300
parts per million (ppm) to levels similar to California's low sulfur
gasoline (regulated to an average of about 40 ppm) could cost 5 to 8
cents per gallon of gasoline with current technology; promising new
technologies could reduce this to 2 cents per gallon.
Steps Toward a Solution
Near term solutions are to redesign vehicles to be more tolerant of
sulfur, to reduce the sulfur level of commercial gasoline, or both.
Several interested parties, including domestic and import vehicle
manufacturers, manufacturers of emission controls, environmental
groups, and states support a nationwide gasoline sulfur level capped
at 80 ppm and averaging 40 ppm or less. Oil industry representatives
support a more limited, summertime-only program that would
control sulfur to an average of 150 ppm in 22 eastern states and
certain other ozone nonattainment areas.
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The Staff Paper presents a recommendation that EPA propose
gasoline sulfur standards to be implemented at the same time as the
implementation of the planned proposed Tier 2 vehicle emission
standards for passenger cars and light trucks.
Issues to Be Addressed in Future Rulemaking
Action
A number of issues must be addressed before gasoline sulfur control
could be implemented, including the issues of vehicle emission
sensitivity to sulfur, and options and costs for the refinery control of
sulfur. Additional issues are the air quality and health benefits of
gasoline sulfur control, the question of regional versus national
programs, and the potential for reversing the sulfur effect on
catalytic converters if the vehicle is exposed to higher-sulfur fuel.
The Staff Paper is intended to encourage further dialog and research
on outstanding issues. In addition, EPA will hold a public workshop
to discuss gasoline sulfur issues on May 12, 1998, from 10:00 a.m. to
5:00 p.m. at Quality Hotel, 1200 N. Courthouse Road, Arlington,
Virginia 22201 (telephone: (703) 524-4000).
For More Information
A copy of the report EPA Staff Paper on Gasoline Sulfur Issues is
available electronically from the EPA Internet server at:
http://www.epa.gov/OMSWWW/tr2home.htm
For further information on the Staff Paper, please contact Susan
Willis at:
U.S. Environmental Protection Agency
Office of Mobile Sources
2565 Plymouth Road
Ann Arbor, MI 48105
734-668-4432 (after May 8, 734-214-4432)
willis.susan@epa.gov

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