Model Change Bulletin
              
                                    MCB#4                         11/02/98

                             ISCST3 (dated 98226)


    This Model Change Bulletin documents changes made to the Industrial
Source Complex Short Term (ISCST3) Dispersion Model (see Code Changes below).

[NOTE:  New ISC3 users are urged to read ISC3 MCB#1, Amendment #1 for
important information.  In addition, this change to the ISCST3 model does
not address the anomalous behavior of the dry deposition algorithm described
in MCB#2.]


CODE CHANGES

    Changes from ISCST3 (dated 97363) include the following:

1.  Incorporates the changes associated with the draft Fortran 90 version
    of the model, called ISCST390 (dated 97365), which has been available
    in the Topics for Review area of SCRAM.  This includes the use of
    allocatable arrays for data storage, the INCLUDED keyword option,
    additional options for specifying the shape of an area source, and
    the EVENT processing formerly associated with the ISCEV3 model.
    With this release, the ISCEV3 program is obsolete, and will no longer
    be supported as a separate processor.

2.  Modifications to the averaging of high-fourth-high (H4H) 24-hour
    averages and annual averages for the new PM10 National Ambient Air
    Quality Standard (NAAQS), promulgated by EPA in July 1997.  This
    change allows for averaging the H4H values across a multiple year
    meteorological data file, and also changes the manner in which
    ANNUAL averages are calculated for multiple year data files.  The
    ANNUAL average option (for PM10 as well as other pollutants) is now
    based on calculating the averages for each individual year, and then
    averaging the annual values across the multiple year period.  As a
    result, the ANNUAL average concentrations are no longer equivalent
    to PERIOD average concentrations for multiple year analyses.  The
    ANNUAL average option and the new PM10 H4H averaging both assume that
    the meteorological data file includes complete years of data.  Any
    data beyond the last complete year will be ignored.


More details on the modifications to the user interface for this version
of ISCST3 are included in the Addendum to Volume I of the User's Guide,
which is available in the model documentation area of SCRAM in
WordPerfect 6.1 format as file ISC3ADD1.ZIP.


                           *****************
                           *   IMPORTANT   *
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    This program will henceforth be identified by its name and a Julian date,
i.e.: ISCST3 (dated 98226).  Future changes to this model will be identified
by an updated Julian date found at the beginning of the model source code
and followed by a reference to a SCRAM Model Change Bulletin (MCB#n)
which will explain the nature and contents of the changes.  All Model Change
Bulletins for this program will always be available for back reference on
this website.  In the future, notification of changes (MCBs) to this program
will be made in the SCRAM ALERTS section of this website.