U.S. Environmental Protection Agency

                May 3,1999
                                
      Document Released for Stakeholder Review and Comment
                                
 Determination of NOx and HC Basic Emission Rates, OBD and I/M
           Effects for Tier 1 and Later LDVs and LDTs
                                
                 Report Number EPA420-P-99-009

The Office of Mobile Sources, Assessment and Modeling Division,
announces the release of "Determination of NOx and HC Basic
Emission Rates, OBD and I/M Effects for Tier 1 and Later LDVs and
LDTs" for stakeholder review and comment. This document, also
known as M6.EXH.007, is available at the MOBILE6 section of the
OMS Web Site (http://www.epa.gov/oms/m6.htm).

This document describes the methodology used to develop NOx and
HC basic emission rates, OBD (On-board Diagnostics II) effects,
and I/M (Inspection / Maintenance) credits for Tier 1 vehicles,
TLEVs (Transitional Low Emitting Vehicles), LEVs (Low Emitting
Vehicles), and ULEVs (Ultra Low Emitting Vehicles). This document
also describes the modeling for several program types (i.e., with
and without OBD checks, with and without exhaust I/M testing) and
combinations of these types. The methodology for CO emissions is
described in a separate document (M6.EXH.009).

Comments on this report and its proposed use in MOBILE6 should be
sent to the attention of John Koupal. 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.

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 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