October 27, 1998


Document Released for Stakeholder Review and Comment

Development and Use of Heavy-Duty NOx Defeat Device Emission
Effects for MOBILE5 and MOBILE6

Report Number M6.HDE.003

     The Office of Mobile Sources, Assessment and Modeling
Division, announces the release of "Development and Use of Heavy-
Duty NOx Defeat Device Emission Effects for MOBILE5 and MOBILE6"
for stakeholder review and comment.  This document M6HDE003.PDF
is available at the MOBILE6 section of the OMS Web Site
(http://www.epa.gov/oms/models.htm).    

     This document describes the methodology used to estimate
excess NOx emissions produced by heavy-duty diesel vehicles
(HDDV)as the result of built-in defeat devices.  Also, presented
in the document are emission estimates based on two programs
designed to mitigate the effect of the defeat device on fleet NOx
emission levels. These include the incorporation of more
stringent HDDV standards earlier than originally required (pull
ahead), and accelerated engine rebuild programs (rebuild) to get
in-use engines into better compliance.  The document describes
two basic models. The first model is an Excel spreadsheet model
(Spreadsheet Model)used to calculate excess HDDV NOx emission
effects in units of tons per year.  

     Both a MOBILE6 and a MOBILE5 version of the spreadsheet
model were developed. The excess NOx emission results in tons
from this spreadsheet model are compared with the official EPA
heavy-duty defeat device inventory emission results prepared by
EPA's Office of Compliance and Enforcement (OECA).  The second
model is the heavy-duty defeat device module that is built into
the MOBILE6 emission factor model.  It was developed and
programmed into MOBILE6 using parameters from the spreadsheet
model.  The specific methodologies, parameters, procedures and
their incorporation in the MOBILE6 model (the second model) are
also discussed in this document.

     Comments on this report and its proposed use in MOBILE6
should be sent to the attention of Ed Glover.  Comments may be
submitted electronically to mobile@epa.gov, or 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 October 27,
1999.  Comments will be accepted for sixty (60) days, ending
December 27, 1999  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 follow-up document within
30 days after the close of the comment period.
  
Thank you for your continuing interest in the
development of MOBILE6.
                                 
Sincerely,

Emission Inventory Group 
Assessment and Modeling Division 
Office of Mobile Sources 
US Environmental Protection Agency