
                        Model Change Bulletin

                                MCB#1                       12/07/2006

                        AERMOD (dated 06341)

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


   This revised version of AERMOD (dated 06341) includes the following            
   modifications relative to the previous version (dated 04300):                                                       
                                                                        
   Bug Fixes:                                                           
                                                                        
   1.  A bug causing inconsistencies in estimated concentrations for
       area sources was fixed by initializing the effective plume 
       height (HE) to equal the release height (HS) prior to first 
       call to ADISY in subroutines ACALC and OCALC.                                     
                                                                        
   2.  The logical variable lbd was undefined in calls to WAKE_XSIG. 
       The calling argument lbd was replaced with .TRUE. to ignore 
       BID for the "outside" cavity source in subroutine CAV_SRC.                                           
                                                                        
   3.  Subroutine PRMDELH was modified to save L_INWAKE to a local            
       variable to avoid potential problems on some computer
       systems.                                                        
                                                                        
   4.  Modified subroutines WAKE_DFSN and WAKE_DFSN2 to initialize      
       dummy variables zkdum and ykdum to 0.0.  Otherwise these         
       variables may be undefined in subroutine WAKE_SIG under         
       some circumstances.                                              
                                                                        
   5.  Moved call to RSDUMP for MULTYR option from subroutine           
       HIPER to MAIN to resolve minor discrepancy in ANNUAL             
       averages for MULTYR option.                                      
                                                                        
   6.  Added arrays to store WDSIN and WDCOS by source for use          
       in determining the wind direction for the dominant source        
       in the PVMRM option.                                             
                                                                        
   7.  Deleted code in subroutine PCALC that adjusts DHCRIT based       
       on distance to well-mixed layer for stable conditions for        
       consistency with Model Formulation Document.                     
                                                                        
   8.  Added error checking for missing GASDEPOS inputs.                
                                                                        
   9.  Corrected variable type from INTEGER to REAL for variable        
       NEWRAD (effective radius) in subroutine GENCIR for AREACIRC      
       sources. Use as an integer variable may have resulted in 
       some truncation of the effective radius.                                                        
                                                                        
   Enhancements:                                                        
                                                                        
   1.  A new 'BETA' option has been added to the CO MODELOPT card to      
       identify and allow for new features to be added to the model     
       that are still in a draft BETA-test status.  The BETA option     
       is a non-DFAULT option, and will be overridden if the DFAULT     
       option is specified.  
       
       The following two draft enhancements are included in this 
       update to AERMOD under the BETA option:                     
                                                                        
       a) options for capped stacks (source type = POINTCAP) and for    
          horizontal releases (source type = POINTHOR); and
                     
       b) the PSDCREDIT option for PVMRM to account for NO/NO2 plume      
          chemistry in the computation of PSD increment consumption 
          with credits.  
       
       Inclusion of these draft BETA-test options does not imply
       any endorsement of their use for regulatory or non-regulatory
       applications of the model. In addition, the designation of
       BETA-test to these draft enhancements does not imply that 
       these options have completed rigorous internal (Alpha) testing
       prior to being included in a public release of the model.
                                                                       
   2.  Additional options included under EMISFACT keyword to vary 
       emissions by month, hour-of-day, and day-of-week (MHRDOW and 
       MHRDOW7).     
                                                                        
   3.  Expanded urban option to allow multiple urban areas to be         
       defined in a single run through multiple URBANOPT cards.       
       A new URBAN-ID parameter has been added to link sources with           
       specific urban areas.  Existing input files with a single        
       urban area do NOT need to be modified to run with this           
       new version of the model.                                            
                                                                        
   4.  The following changes have been made to ensure consistency 
       with the current PM NAAQS:
       
       a) Added special processing for PM-2.5 to calculate design          
          values in accordance with the PM NAAQS.  The design value    
          for 24-hour averages is based on the high-eighth-high (H8H)      
          averaged over N years, as an unbiased surrogate for the 98th     
          percentile.  The long-term design value for PM-2.5 is based      
          on the highest annual average concentration averaged over        
          N years using the ANNUAL keyword on the AVERTIME card.          
                                                                        
       b) The "post-1997" PM-10 processing based on H4H averaged over 
          N years has been removed since that standard was vacated.  
          The PM-10 design value for 24-hour averages is based on the 
          high-sixth-high (H6H) over five years (for NWS data), or more 
          generally by the high-N+1-high value over N years. This can 
          be accomplished using the existing CO MULTYEAR option with 
          multiple 1-year input met data files, or using single 
          five-year data files without the MULTYEAR option.                                               
                                                                        
   5.  Added option to specify initial in-stack NO2 ratio for           
       PVMRM and OLM options with CO NO2STACK card.  Default ratio      
       without the NO2STACK card for OLM is 0.10.  No default ratio     
       has been determined for PVMRM, so user must either use the       
       CO NO2STACK card to initialize ratio for all sources, or         
       specify ratio for each source using the SO NO2RATIO card.        
       The SO NO2RATIO card can be used to override the value           
       specified on the CO NO2STACK card for specific sources.
       
   6.  The maximum number of vertices for an AREAPOLY source is now
       allocated dynamically at runtime.  The previous version of 
       AERMOD allowed a maximum of 20 vertices.  The maximum number
       of vertices allowed for AREACIRC sources is not allocated 
       dynamically.  However, if both AREAPOLY and AREACIRC sources 
       are included in the same model run, then the maximum number 
       of vertices identified for the AREAPOLY sources will also define 
       the maximum number allowed for the AREACIRC sources. In addition,
       the maximum number of vertices allowed for AREACIRC sources will 
       always be at least 50.
                                                                        
   Miscellaneous:                                                       
                                                                        
   1.  Added range check on value of vertical potential temperature      
       gradient above ZI (variable VPTGZI), to avoid problems with      
       data provided from sources other than AERMET.  A minimum         
       value of 0.005 K/m is applied for consistency with AERMET,       
       and a warning message is also generated for values larger        
       than 0.10 K/m.                                                   
                                                                        
   2.  Refined the process of dynamically allocating array storage
       to skip allocation of arrays that are not needed based on the
       model options selected, in order to reduce unnecessary memory
       usage.    
                                                                        
   3.  Removed calls to subroutines VDP and SCAVRAT from subroutine     
       PLUME_VOL.
       
   4.  Removed references to obsolete BOUNDARY keyword for receptors
       in RECSIZ and PREREINC subroutines to allocate receptor arrays,
       and in subroutines PRTANN, SPRTHT, and PRTPM25 of OUTPUT.FOR.

   5.  Changed AMAX1/AMIN1 intrinsics to MAX/MIN.                       
       
       
       
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This program will henceforth be identified by its name and a Julian date,
i.e.: AERMOD (dated 06341).  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 SCRAM ALERTS section of this website.
                                                                 