April 1997

NOTE

SUBJECT:   Release of Final Version of MOBILE5b 

FROM:      David Brzezinski, EPA OMS AMD

TO:        All MOBILE Model Users


Two changes have been made to the draft MOBILE5b code since it
was released in September 1996.  The version of MOBILE5b now
available from EPA has the following two changes: 

1) The Detergent Gasoline parameters were stored in two locations
in the code.  Changes were made to one set, but not the other. 
However, as it turns out, the second set is never used.  The
second (unused) set was eliminated from the source code.  This
change has no implications for users.

2) The Retest-Based Hybrid I/M option in MOBILE5b checks the I/M
credits provided by the user to make sure they are indeed
"hybrid" I/M credits before you can use them.  Unfortunately,
there are no hybrid credits for pre-1981 model year vehicles
(none were released with MOB5a_H).  So, anyone trying to use
MOBILE5b to duplicate MOB5a_H hybrid I/M runs would get an error
for that run if the I/M program included older vehicles. MOBILE5b
was changed so that it only checks the I/M credits for the newer
model years (the IMDATA.D file).  This will not change the
results, but will allow users to use MOBILE5b for hybrid I/M
runs.

Both of these changes are technical and do not affect the results
of the model.  Therefore, any work done using the earlier version
of MOBILE5b will be identical to results from the new version. 
However, users who wish to make use of the Retest-Based Hybrid
I/M option will need to use the final version.  The draft version
will not be able to model Retest-Based Hybrid I/M programs that
include older model years.

The final version of MOBILE5b is now the version available on the
EPA Web site (http://www.epa.gov/omswww/models.htm) or contact
OMS via fax (313-741-7939) or e-mail (mobile@epamail.epa.gov).