Turning off process like Dry Deposition or BC in CMAQ

  1. What would be the right way to switch off a process like dry deposition altogether, or just switch off ozone dry deposition to leaves stomata only in CMAQ (newest version)?
  2. What is the easiest way of setting input CMAQ BC of select species to zero?

You should be able to turn off dry deposition for a specific gas phase species by editing the GC namelist file, specifically by changing the factor in the β€œFAC” column to the right of the β€œDRYDEP SURR” column from 1 to 0. For example, to switch off ozone dry deposition, change the beginning of the GC namelist file from

&GC_nml

GC_SPECIES_DATA =

!SPECIES ,MOLWT ,IC ,IC_FAC,BC ,BC_FAC ,DRYDEP SURR ,FAC ,WET-SCAV SURR ,FAC ,GC2AE SURR ,GC2AQ SURR,TRNS ,DDEP ,WDEP ,CONC
β€˜NO2’ , 46.0 ,’’ ,-1 ,’’ ,-1 ,β€˜VD_NO2’ , 1 ,β€˜NO2’ , 1 ,β€˜NO2’ ,’’ ,β€˜Yes’ ,β€˜Yes’ ,β€˜Yes’ ,β€˜Yes’,
β€˜NO’ , 30.0 ,’’ ,-1 ,’’ ,-1 ,β€˜VD_NO’ , 1 ,β€˜NO’ , 1 ,’’ ,’’ ,β€˜Yes’ ,β€˜Yes’ ,β€˜Yes’ ,β€˜Yes’,
β€˜O’ , 16.0 ,’’ ,-1 ,’’ ,-1 ,’’ ,-1 ,’’ ,-1 ,’’ ,’’ ,’’ ,’’ ,’’ ,β€˜Yes’,
β€˜O3’ , 48.0 ,’’ ,-1 ,’’ ,-1 ,β€˜VD_O3’ , 1 ,β€˜O3’ , 1 ,’’ ,β€˜O3’ ,β€˜Yes’ ,β€˜Yes’ ,β€˜Yes’ ,β€˜Yes’,

to

&GC_nml

GC_SPECIES_DATA =

!SPECIES ,MOLWT ,IC ,IC_FAC,BC ,BC_FAC ,DRYDEP SURR ,FAC ,WET-SCAV SURR ,FAC ,GC2AE SURR ,GC2AQ SURR,TRNS ,DDEP ,WDEP ,CONC
β€˜NO2’ , 46.0 ,’’ ,-1 ,’’ ,-1 ,β€˜VD_NO2’ , 1 ,β€˜NO2’ , 1 ,β€˜NO2’ ,’’ ,β€˜Yes’ ,β€˜Yes’ ,β€˜Yes’ ,β€˜Yes’,
β€˜NO’ , 30.0 ,’’ ,-1 ,’’ ,-1 ,β€˜VD_NO’ , 1 ,β€˜NO’ , 1 ,’’ ,’’ ,β€˜Yes’ ,β€˜Yes’ ,β€˜Yes’ ,β€˜Yes’,
β€˜O’ , 16.0 ,’’ ,-1 ,’’ ,-1 ,’’ ,-1 ,’’ ,-1 ,’’ ,’’ ,’’ ,’’ ,’’ ,β€˜Yes’,
β€˜O3’ , 48.0 ,’’ ,-1 ,’’ ,-1 ,β€˜VD_O3’ , 0 ,β€˜O3’ , 1 ,’’ ,β€˜O3’ ,β€˜Yes’ ,β€˜Yes’ ,β€˜Yes’ ,β€˜Yes’,

This is the approach I took for a brute force sensitivity simulation in CMAQv5.0.2 but I have not tested it in newer versions.

To modify and/or switch off specific dry deposition pathways (e.g. stomatal), you would have to work directly with the M3DRY and/or STAGE code. Since modifying that code without in-depth knowledge of its workings can be error-prone, you probably would want to reach out to the developers before embarking on such an analysis.

You can set boundary conditions of selected species to zero by a) using a tool like β€˜combine’ to modify your existing BCON files to explicitly set these concentrations to zero, b) using a tool like β€˜combine’ or β€˜m3xtract’ to remove the species you want to be set to zero from your existing BCON files (CMAQ will set boundary conditions to zero - or a very small number - if a given species cannot be found in the BCON file), or c) setting the β€˜BC_FAC’ column in the GC namelist file to zero for the desired species.

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