Errors with Hg Bidirectional Flux Simulations

[chogrefe]

Description

CMAQ simulations for mercury with the CTM_HGBIDI option set to T will fail due to two issues in the current CMAQ code except for when using the STAGE dry deposition option for a single day simulation. The first issue affects only the M3Dry dry deposition option and causes a model crash if CTM_HGBIDI is set to T but CTM_ABFLUX (bidirectional flux option for NH3) is set to F. The second issue affects both the M3Dry and STAGE dry deposition options and leads to a model crash on the second day of the simulation when using a MEDIA_CONC restart file.

Scope and Impact

The current CMAQ code with not complete successfully for mercury simulations with the CTM_HGBIDI option set to T for multi-day simulations for both the M3Dry and STAGE dry deposition options. For M3Dry, the code will not complete successfully even on the first day of the simulation unless the CTM_ABFLUX is also set to T.

Solution

The first issue is caused by the land use fraction array needed by the Hg bidirectional calculations not being allocated and assigned a value in the M3Dry version of ASX_DATA_MOD.F. To fix this issue, change these statements on lines 557 and 638 from

   If ( ABFLUX) Then

To

   If ( ABFLUX .or. HGBIDI ) Then 

The second issue is caused by subroutine INIT_BIDI in BIDI_MOD.F being called twice in both M3Dry and STAGE, leading to a duplicate allocation error. To fix this issue, the beginning of that subroutine should be modified as follows:

Current code (lines 75 – 80 in the M3Dry version of BIDI_MOD.F):

     Integer         :: STATUS
     
    C--------------------------------------------------------------------------
     ! Set Mercury BiDi Processing Flag equal to false if there is
     ! no mercury gas-phase species.
     If ( INDEX1( 'HG', N_GC_DDEP, GC_DDEP ) .EQ. 0 ) HGBIDI = .FALSE.

Updated code:

     Integer         :: STATUS
     Logical, SAVE   :: INITIALIZED = .FALSE.

     C--------------------------------------------------------------------------
     C Prevent initilializing the code twice 
     If ( INITIALIZED ) Return 

     INITIALIZED = .TRUE.

     ! Set Mercury BiDi Processing Flag equal to false if there is
     ! no mercury gas-phase species.
     If ( INDEX1( 'HG', N_GC_DDEP, GC_DDEP ) .EQ. 0 ) HGBIDI = .FALSE.

For STAGE, corresponding changes would have to be made in lines 73 – 76 of the STAGE version of BIDI_MOD.F

Additional context

These issues will be fixed in the next release of CMAQ.

[kmfoley]

This issue is resolved with the release of CMAQv5.4.