U.S. Environmental Protection Agency


       Document Released for Stakeholder Review and Comment

      Estimating Weighting Factors for Evaporative Emissions
                             in MOBILE6 

                  Report Number   EPA420-P-99-023

     In previous documents (M6.EVP.001, M6.EVP.002, and M6.EVP.005),
EPA proposed methods of estimating vehicles' resting loss and diurnal
emissions based (in part) on the vehicles' performance (pass or fail) on the
purge and pressure tests.  EPA plans to compute model-year and age specific
average resting loss and diurnal emissions by weighting together the
emissions of passing and failing vehicles according to their frequency in the
in-use fleet.  This document describes this approach and EPA's proposed
estimates of pass and fail rates as functions of vehicle age.

     Please note that EPA is seeking any input from stakeholders and reviewers
that might aid us in modeling any aspect of resting loss or diurnal evaporative
emissions.

     Comments on this report and its proposed use in MOBILE6 should be sent
to the attention of Larry Landman.  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 July 14, 1999.  Comments
will be accepted for sixty (60) days, ending September 9, 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.