Activate VBS SOA module in CMAQ5.3.1

Dear all,
I would like to know how to activate the VBS mechanism in SOA module with in CMAQv5.3.1 model. Could you please give me some hints?

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I found the following documentation in the src code:

aero/aero6/AERO_DATA.F: Integer, Parameter :: n_vbs_bin = 5

! Primary Organic Aerosol Volatility Distributions

  Integer, Parameter :: n_vbs_bin = 5

  Character( 10 ) :: poa_name( n_vbs_bin ) = (/ 'LVPO1', 'SVPO1', 'SVPO2', 'SVPO3', 'IVPO1' /)

  Real, Parameter :: poa_op_vf( n_vbs_bin ) = (/ 0.09,  0.09,  0.14,  0.18,  0.5 /)  ! Aggregated

! The Following Volatility Distributions are alternative options

! but at this point can only be implemented indivdually for the

! entire POA suite of compounds.
There is documentation on vbs described for an older version of CMAQ. CMAQv5.0.2-VBS - CMASWIKI
and 1.5-Dimensional volatility basis set approach for modeling organic aerosol in CAMx and CMAQ - ScienceDirect
This doesn’t fully answer your question, but is a starting point.

Hi Liz,
Thanks a lot for pointing it out. And my question is whether there is an available option for activate VBS module in CMAQv5.3.1?


CMAQ v5.3.1, by default, uses a mixture of volatility-driven and aqueous-mediated (solubility) SOA pathways. Volatility-driven pathways can be represented by a VBS which we do for several systems in aero7. You can set your POA volatility distribution in the emission control file (the code Liz noted is for POA). Note that VBS refers to the use of log10C* bins and does not necessarily include gas-phase aging OH reactions.

See for references for the different SOA systems as well as the v5.3 (and 5.3.1) release notes on aero7

Hi Ryan,

Thanks for your question. The short answer is that you don’t have to do anything. The model is making assumptions consistent with the VBS out-of-the-box.

There are essentially two detailed parts to the answer.

  1. CMAQv5.3.1 is equipped with model species for organic aerosols that are in line with VBS approaches. In other words, the species have saturation concentrations spanning from low volatility to intermediate volatility with an order of magnitude separation. You can see this in the table in SOA_DEFN.F. Partitioning and chemical aging of POA species proceed in line with other models employing VBS techniques, but the assumptions vary for different SOA pathways (see Havala’s post above).

  2. The emissions are what you are probably worried about specifically. You should use the Emission Control file (EmissCtrl_{MECH}.nml) to properly distribute nonvolatile primary organic emissions (i.e. POC, PNCOM) to higher volatility bins. These are the lines of interest:

    ! Fine-Mode Primary Organic Aerosol Scaling
    ! There are a series of species available for propagating emissions of primary
    ! organic particles and vapor. APOC and APNCOM are nonvolatile species that
    ! age chemically in the particle phase. Traditionally, all POC (primary organic
    ! carbon) and PNCOM (primary non-carbon organic matter) have been represented
    ! by these species.
    ! It is more correct to use semivolatile species to account for the gas-particle
    ! partitioning of this POA mass. Several particle and gas-phase species are
    ! provided for this task, and these species vary in their volatility, which is
    ! quantified with the metric C*. See Donahue et al. (ES&T, 2006).
    ! Gas Species : VLVPO1 VSVPO1 VSVPO2 VSVPO3 VIVPO1
    ! Particle Species : ALVPO1 ASVPO1 ASVPO2 ASVPO3 AIVPO1
    ! C* (ug m-3) : 0.1 1 10 100 1000
    ! (Mostly Particle) (Mostly Vapor)
    ! To enable semivolaitle partitioning, you may direct a fraction of mass from the
    ! nonvolatile emission surrogates (POC and PNCOM) to each of these semivolatile
    ! CMAQ species. To conserve mass, the total of the scale factors should sum to 1.
    ! Note: Each of the semivolatile species accounts for both OC and NCOM mass, so
    ! rules should come in pairs (one for POC and one for PNCOM) in order to
    ! conserve the total. For Example,
    ! ‘EVERYWHERE’, ‘ALL’ ,‘POC’ ,‘VSVPO2’ ,‘GAS’ ,0.14 ,‘MASS’,‘a’,
    ! ‘EVERYWHERE’, ‘ALL’ ,‘PNCOM’,‘VSVPO2’ ,‘GAS’ ,0.14 ,‘MASS’,‘a’,
    ! Note: To avoid large swigns in repartitioning after emission, it’s a good idea
    ! to split mass between gas and particle phases, with all mass going to
    ! the particle in the C* = 0.1-1 range and all gas for C* = 100-1000.
    ! Species with C*=10 can generally have mass split between gas and particle
    ! or be put in all gas if conditions are very clean. If too much mass
    ! evaporates or condenses upon emission, the aerosol size distribution
    ! will be affected.
    ! Note: It is common to specify different volatility distributions for different
    ! emission sources. Please use this interface to specify your model
    ! parameters.
    ! --> Nonvolatile POA
    ‘EVERYWHERE’, ‘ALL’ ,‘POC’ ,‘APOC’ ,‘FINE’,0. ,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘PNCOM’ ,‘APNCOM’ ,‘FINE’,0. ,‘MASS’,‘a’,
    ! --> Semivolatile POA
    ‘EVERYWHERE’, ‘ALL’ ,‘POC’ ,‘VLVPO1’ ,‘GAS’ ,0. ,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘PNCOM’ ,‘VLVPO1’ ,‘GAS’ ,0. ,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘POC’ ,‘VSVPO1’ ,‘GAS’ ,0.045,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘PNCOM’ ,‘VSVPO1’ ,‘GAS’ ,0.045,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘POC’ ,‘VSVPO2’ ,‘GAS’ ,0.14 ,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘PNCOM’ ,‘VSVPO2’ ,‘GAS’ ,0.14 ,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘POC’ ,‘VSVPO3’ ,‘GAS’ ,0.18 ,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘PNCOM’ ,‘VSVPO3’ ,‘GAS’ ,0.18 ,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘POC’ ,‘VIVPO1’ ,‘GAS’ ,0.50 ,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘PNCOM’ ,‘VIVPO1’ ,‘GAS’ ,0.50 ,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘POC’ ,‘ALVPO1’ ,‘FINE’,0.09 ,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘PNCOM’ ,‘ALVPO1’ ,‘FINE’,0.09 ,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘POC’ ,‘ASVPO1’ ,‘FINE’,0.045,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘PNCOM’ ,‘ASVPO1’ ,‘FINE’,0.045,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘POC’ ,‘ASVPO2’ ,‘FINE’,0. ,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘PNCOM’ ,‘ASVPO2’ ,‘FINE’,0. ,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘POC’ ,‘ASVPO3’ ,‘FINE’,0. ,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘PNCOM’ ,‘ASVPO3’ ,‘FINE’,0. ,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘POC’ ,‘AIVPO1’ ,‘FINE’,0. ,‘MASS’,‘a’,
    ‘EVERYWHERE’, ‘ALL’ ,‘PNCOM’ ,‘AIVPO1’ ,‘FINE’,0. ,‘MASS’,‘a’,

Below these lines are more emission rules that govern the use of potential-combustion SOA, which is also on by default:
! pcSOA is a CMAQ species introduced to account for missing pathways for SOA
! formation from combustion sources. It includes IVOC oxidation as well as other
! phenomena (Murphy et al., ACP, 2017). It was parameterized primarily in LA,
! where vehicle exhaust continues to dominate.
‘EVERYWHERE’, ‘ALL’ ,‘POC’ ,‘PCVOC’ ,‘GAS’ ,6.579,‘MASS’,‘a’,
‘EVERYWHERE’, ‘ALL’ ,‘PNCOM’ ,‘PCVOC’ ,‘GAS’ ,6.579,‘MASS’,‘a’,
! However, the added pcSOA is probably inappropriate for Fire sources, especially
! in its current configuration. This pathway should be zeroed out for all fire
! and wood-burning related sources.
‘EVERYWHERE’, ‘PT_FIRES’ ,‘ALL’ ,‘PCVOC’ ,‘GAS’ ,0.0 ,‘MASS’,‘o’,

Good luck and let us know if we can clarify anything further.

Dear @Havala.Pye @Ben_Murphy,
Thanks a lot for your answers. They are really helpful!!
I really appreciate your help!