U.S. Environmental Protection Agency

                        May 17, 1999
                                
      Document Released for Stakeholder Review and Comment
                                
Basic Exhaust Emission Rates of Open Loop Vehicles for MOBILE6:

Exhaust Emissions at High and Low Altitudes for Engine Starts and
Running Emissions for Motorcycles, Light Duty Diesel Vehicles and
Trucks and Pre-1981 Model Year Light Duty Gasoline Vehicles and
Trucks
                                
                 Report Number EPA420-P-99-020

The Office of Mobile Sources, Assessment and Modeling Division,
announces the release of "Basic Exhaust Emission Rates of Open
Loop Vehicles for MOBILE6:Exhaust Emissions at High and Low
Altitudes for Engine Starts and Running Emissions for
Motorcycles, Light Duty Diesel Vehicles and Trucks and Pre-1981
Model Year Light Duty Gasoline Vehicles and Trucks" for
stakeholder review and comment. This document, also known as
M6.EXH.005, is available at the MOBILE6 section of the OMS Web
Site (http://www.epa.gov/oms/m6.htm).

"Open loop" is a term that refers to vehicles which do not use
electronic feedback systems to control the delivery of fuel to
the engine cylinders.  Most current light-duty vehicles make use
of feedback systems.  However, motorcycles, older light-duty
vehicles and most diesel vehicles are open-loop.  This report
discusses how the basic rates for both engine starts and exhaust
running emissions for these open loop vehicles will be estimated
for MOBILE6.  The MOBILE6 basic exhaust emission rates for heavy
duty trucks and 1981 and newer light-duty vehicles and trucks are
discussed in separate reports.

Comments on this report and its proposed use in MOBILE6 should be
sent to the attention of David Brzezinski. Comments may be
submitted electronically to mobile@epa.gov, by fax to
(734)214-4939, or by mail 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 that 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. Data sets for
this document will be provided in electronic format if requested.

This document is being released and posted on May 17, 1999.
Comments will be accepted for sixty (60) days. EPA will then
review and consider all comments received, and will provide a
summary of those comments and how we are responding to them in
the form of a followup 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