In-Use Exhaust Deterioration and I/M Benefits of 1981
     and Newer Model Year Cars and Trucks Proposed for Use
                           in MOBILE6

Package of Related Material Released for Stakeholder Review and
                            Comment
                                
                          May 3, 1999
                                
           U.S. EPA Assessment and Modeling Division

NOTE: In-use exhaust deterioration refers to the modeling of
exhaust emissions as a function of mileage.

Contents:

         Overview of Methodology for Tier 0 In-Use Deterioration and
     Key Issues for Comment (M6.EXH.008)
          The overview describes the basic methodology being proposed
     for comment, describes the key issues, and compares the
     results to estimates obtained with MOBILE5. By way of this
     document, EPA is soliciting comments and/or information
     pertaining to the key issues.

         Draft Tier 0 In-Use Deterioration Papers for Public and
     Stakeholder Review
          There are four draft papers that document the proposed
     findings on the in-use exhaust deterioration of 1981-1993
     model year (Tier 0) cars and trucks:

                    The Determination of Hot Running Emissions from FTP Bag
          Emissions (M6.STE.002)
     
                    Determination of Start Emissions as a Function of
          Mileage and Soak Time for 1981-1993 Model Year Light-
          Duty Vehicles (M6.STE.003)
     
                    Determination of Running Emissions as a Function of
          Mileage for 1981-1993 Model Year Light-Duty Cars and
          Trucks (M6.EXH.001)
     
                    Analysis of Emissions Deterioration Using Ohio and
          Wisconsin IM240 Data (M6.EXH.002)
     
          Abstracts and the full reports are provided. The abstracts
     contain details regarding the procedure and deadline for
     submittal of comments.

          Peer review comments on these draft papers have also been
     solicited and received from three reviewers. These
     independent peer review comments are being made available to
     assist public and stakeholder reviewers. The papers have not
     yet been revised to incorporate our response to the peer
     review comments. The independent peer review comments and
     others received will be addressed together following the
     general comment period. Followup documents containing EPA's
     response to all the comments will then be provided.

         Summary of Peer Review Comments on the Draft Tier 0 In-Use
     Deterioration Papers

         Individual Peer Review Comments on the Draft Tier 0 In-Use
     Deterioration Papers
                    Mr. Kevin Green
                    Dr. Stephen L. Gerritson
                    Dr. Larry Caretto

         Other Draft Papers Related to In-Use Deterioration for Public
     and Stakeholder Review

                    MOBILE6 Inspection / Maintenance Benefits Methodology for
          1981 through 1993 Model Year Light Vehicles (M6.IM.001)

                    Determination of NOx and HC Basic Emission Rates, OBD and
          I/M Effects for Tier 1 and Later LDVs and LDTs
          (M6.EXH.007)
     
                    Determination of CO Basic Emission Rates, OBD and I/M
          Effects for Tier 1 and Later LDVs and LDTs (M6.EXH.009) 
          [to be posted soon]
     
                    Comparison of MOBILE6 Basic Emission Rates for 1981-1993
          Model Year Light-Duty Cars and Trucks with FTP and IM240
          Data (M6.EXH.010)  [to be posted soon]