
                        Model Change Bulletin

                                MCB#5                      04/13/2011

                        AERMOD (dated 11103)

This Model Change Bulletin (MCB) documents changes made to the AERMOD
Dispersion Model.  A brief description of the changes is provided
below.  Additional details are available in the Fortran source code.
Changes to the user instructions associated with this update are
documented in an updated AERMOD User's Guide Addendum.


This revised version of AERMOD (dated 11103) includes the following
modifications relative to the previous version (dated 11059):

--  Bug Fixes:

    1.  Modified subroutine MXDLYFL to include an IF-THEN block 
        to account for cases with NHIMXDLY = 1, i.e., only the 
        1st-highest rank was selected on the RECTABLE keyword.  
        The previous version (11059) resulted in all short-term 
        values being 0.0 if only the 1st-highest rank was selected 
        for applications involving the special processing for 
        daily maximum values (24hr PM25, 1hr NO2 and 1hr SO2).
        This bug did not affect the results for applications
        that included other ranks on the RECTABLE keyword,
        including single ranks other than 1st-highest or any
        range of ranks, or applications that do not utilize
        the special processing for the 24hr PM25, 1hr NO2 and 
        1hr SO2 NAAQS.

--  Miscellaneous:

    1.  Modified subroutines O3FIL and BACK_GRND to include checks
        for potential problems with the Fortran format specifier 
        for hourly ozone files and hourly background files.  The 
        hourly ozone and/or background concentrations may have been 
        assigned values of zero (0) in previous versions of AERMOD 
        if the user-specified Fortran format includes an integer 
        (I) format to read the concentration values.  This could
        significantly affect modeled concentrations for the OLM
        and PVMRM options based on hourly ozone data, without any
        clear indication of a problem.  The user-specified format
        must use an integer format to read the date variables and
        a real format (F, E, or D) to read the concentration 
        variable.  Warning messages will be generated if the format
        does not meet these requirements.  In addition, the compiler
        options for the AERMOD executable distributed on SCRAM have 
        been modified to include an option to check for consistency 
        between variable types and format specifiers, which will 
        cause AERMOD to issue a fatal error when reading the file 
        in cases where real variables are read with an integer
        format, or vice versa.  The AERMOD User's Guide Addendum 
        has also been modified to clarify the requirements for 
        user-specified Fortran formats with these options.


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                        *   IMPORTANT   *
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This program will henceforth be identified by its name and a Julian date,
i.e.: AERMOD (dated 11103).  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 content 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 Recent Additions section of the SCRAM website.
