U. S. Environmental Protection Agency

May 3, 1999

Document Released for Stakeholder Review and Comment

Fuel Sulfur Effects on Exhaust Emissions

Report Number EPA420-P99-008

The Office of Mobile Sources, Assessment and Modeling Division
announces the release of "Fuel Sulfur Effects on Exhaust
Emissions" for stakeholder review and comment.  This document
EPA420-P99-008 also known as document M6ful001 is available at
the MOBILE6 section of the OMS Web Site
(http://www.epa.gov/oms/m6.htm)

This document describes EPA's effort to estimate empirical
relationships between fuel sulfur content and exhaust emissions
of hydrocarbons (HC), non-methane hydrocarbons (NMHC), nitrogen
oxides (NOx), and carbon monoxide (CO) as a function of vehicle
technology and vehicle emitter classification for
gasoline-powered vehicles.  MOBILE6 will use these relationships
to adjust exhaust emission rates in response to fuel sulfur
levels input by the user.  The vehicle technologies addressed in
this analysis include: Tier 0, Tier 1, Low-Emitting Vehicles
(LEVs), and Ultra Low-Emitting Vehicles (ULEVs).  Where possible,
the vehicle technology data are further stratified by passenger
car (PC), Light-Duty Truck Class 1 (LDT1), and heavier Light-Duty
Truck classifications (LDT2/LDT3/LDT4).  

Wherever possible, normal and high emitters are also addressed
and analyzed separately.  Diesel-powered heavy-duty vehicles are
not considered in this analysis as very little data exists to
describe sulfur's effect on emissions from these vehicles.

Comments on this report and its proposed use in MOBILE6 should be
sent to the attention of Venkatesh Rao.  Comments may be
submitted electronically to mobile@epa.gov, by fax to 
(734) 214-4939 or to MOBILE6 Review Comments US EPA Assessment
and Modeling Division, 2000 Traverwood Drive, Ann Arbor, MI
48105.  Electronic submission of comments is preferred.  In your
comments please note clearly the document you are commenting on,
including the report title and the code number listed.  Please be
sure to include your name, address, affiliation and any other
pertinent information.

This document is being released and posted on May 3, 1999. 
Comments will be accepted for sixty (60) days.  EPA will then
review and consider all comments and will provide a summary of
those comments and how we are responding to them in a follow-up
document. 

Thank you for your continuing interest in the development of
MOBILE6.

Sincerely,

Emission Inventory Group
Assessment and Modeling Division
US EPA
Office of Mobile Sources