Model Change Bulletin
              
                                    MCB#5                         12/14/98

                             ISCST3 (dated 98348)


    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.  Also, refer to the IMPORTANT NOTE below for informations
regarding additional problems with the dry depletion algorithm.]


CODE CHANGES

    Changes from ISCST3 (dated 98226) include the following:

1.  Corrections to errors with the new post-1997 PM10 routines
    involving leap years and the 24-hour PLOTFILE option.  The user
    may now model either 24-hour or annual averages separately
    for post-1997 PM10 analyses.

2.  A correction to the 'NO ECHO' option.

3.  A correction to a potential problem with the MAXTABLE option
    when MaxNum = 1.

4.  The status message written to the screen has been modified to
    include the year of data being processed.

5.  General code clean-up, including additional variable declarations
    and the inclusion of an IMPLICIT NONE statement throughout the code,
    and minor cosmetic changes.  For example, The PCALC2, VCALC2, ACALC2,
    and OCALC2 routines for EVENT processing have been removed, and the
    PCALC, VCALC, ACALC, and OCALC routines have been modified to handle
    both "normal" and EVENT processing.

6.  The file unit for the runstream input file (INUNIT) has been
    changed from 5 to 7, and the file unit for the main printed output
    file (IOUNIT) has been changed from 6 to 8.  This change in file units,
    and much of the code clean-up, is to improve portability of the model
    to the Lahey LF95 Fortran 95 Compiler (Version 5.0).

7.  A new PARAMETER called ILEN_FLD has been added to MAIN1, which is
    initially assigned a value of 80.  This PARAMETER is now used to
    specify the maximum length of individual fields on the input
    runstream image, and also to declare the length of all filename
    and format variables.  The user may therefore specify file/pathnames
    of up to 80 charaters for all input and output files.

8.  The integration routine for the area source integral has been replaced
    by the same integration routine used for depletion (QATR).  Other
    optimizations have also been made to the area source integration.
    This may cause relatively minor changes to the results for area
    sources, but should improve model runtimes for most area source
    applications.


IMPORTANT NOTE ON DRY DEPLETION:

    An error has been identified in SUBROUTINE DEPCOR involving an
    undefined variable 'x' being used for comparison to the plume
    touchdown distance, 'xtd', and in a subsequent call to SUBROUTINE
    SZSETL.  While it appears that the variable being used in this context
    should be 'xr', such a correction leads to anomalous behavior for
    ground-level, non-buoyant sources (such as area sources).  Therefore,
    EPA is not correcting the known error (i.e., changing 'x' to 'xr') at
    this time.  Corrective action will be deferred until the problems
    with the SZSETL routines can be further investigated and appropriate
    solutions developed and tested.  Users are therefore encouraged to
    use extra caution when applying and interpreting the dry depletion
    algorithm.



                           *****************
                           *   IMPORTANT   *
                           *****************

    This program will henceforth be identified by its name and a Julian date,
i.e.: ISCST3 (dated 98348).  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.