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Release Date: Sep 24, 2013


The volatility basis set (VBS) approach provides a unified framework for gas-aerosol partitioning of both primary and secondary OA (POA and SOA) and their chemical aging. It uses a set of semi-volatile OA species whose volatility is equally spaced in a logarithmic scale (the basis set), and they react further in the atmosphere (chemical aging) leading to changes in their volatilities (i.e., shifting between volatility bins).

The VBS scheme implemented in CMAQ uses four basis sets to distinguish different OA groups observed in atmosphere:

Basis Set Description
AVB SOA or oxygenated POA (OPOA) from anthropogenic sources
BVB SOA or OPOA from biogenic sources
PVB fresh POA from anthropogenic sources
FVB fresh POA from biomass-burning

Each basis set includes 5 volatility bins (i=0 to 4) ranging from 0 to 1e3 ug/m3 in saturation concentration.

Build Instructions

The CMAQv5.0.2 VBS installation includes a build script for compiling a version of the CCTM instrumented with VBS.

For installing CMAQ-VBS, first download, install, and build the base version of the model. Then download the CMAQ VBS tar file and untar into the CMAQv5.0.2 home directory:

cd $M3HOME/../
tar xvzf CMAQv5.0.2_VBS.Apr2014.tar.gz

Use the bldit.cctm.vbs script as you would the base cctm build script.

cd $M3HOME/scripts/cctm_vbs
./bldit.cctm.vbs |& tee bldit.cctm.vbs.log

The VBS scheme is currently available with CB05TUCL gas-phase chemistry mechanism and AE6 aerosol mechanism. To build CMAQ with the VBS module, the following settings should be used in the build script:

set ModEmis   = emis/emisvbs
set ModGas    = gas/ebi_cb05tucl_ae6vbs
set ModAero   = aero/aero6vbs
set ModCloud  = cloud/cloud_acm_ae6vbs
set Mechanism = cb05tucl_ae6vbs_aq

For the equivalent version of standard CMAQ, AERO6 and associated modules should be selected:

set ModEmis   = emis/emis
set ModGas    = gas/ebi_cb05tucl_ae6
set ModAero   = aero/aero6
set ModCloud  = cloud/cloud_acm_ae6
set Mechanism = cb05tucl_ae6_aq

Note that you will need to have the libraries (I/O API, netCDF, MPI, Stenex, and Pario) and model builder (bldmake) required by the base model to compile this version of the code. See the base model README for instructions on building these components.

Run Instructions

A sample run script is provided in the CMAQ VBS release package under $M3HOME/scripts/cctm_vbs. The CMAQ VBS test run uses the same input data as the base CMAQv5.0.2 distribution package. To run the CMAQ VBS test case:

  1. Download the base CMAQv5.0.2 distribution, including the model and input data to obtain/prepare inputs for CMAQ VBS.
  2. Run the ICON and BCON processors from the base model package to create initial and boundary conditions input files for the CMAQ VBS test case.
  3. Point the VBS run script to the emissions and ICBC data from the base CMAQv5.0.2 distribution
  4. Execute the CMAQ VBS run script the same way that you would run the base model

CMAQ VBS Input/Output Data

Emissions Input Data

In addition to the usual hydrocarbon precursors (i.e., aromatics, monoterpenes, etc.), users should supply emissions of intermediate-volatility organic compounds (IVOCs; volatility ranges 1e4 to 1e6 ug/m3) from anthropogenic sources (IVOC_P) or biomass burning (IVOC_F). If not provided, IVOC emissions are estimated equal to 1.5 times the POA emissions by default. Users can also provide POA emissions separately by source category: POA_GV for gasoline vehicles, POA_DV for diesel vehicles, POA_OP for other anthropogenic sources, and POA_BB for biomass burning. If standard AE6 emissions are used, emissions of POC and PNCOM are summed and allocated to volatility bins using default emission factors (of POA_OP).

VBS Output Data

Versions of the CCTM instrumented with VBS will output additional variables to the concentration files. Table 1 lists the additional VBS concentration variables.

Table 1. CMAQ VBS Output Variables
Variable Description
SV_AVB[1-4] Anthropogenic SOA/OPOA concentrations in the gas-phase
SV_BVB[1-4] Biogenic SOA/OPOA concentrations in the gas-phase
SV_PVB[1-4] Anthropogenic POA concentrations in the gas-phase
SV_FVB[1-4] Biomass-burning POA concentrations in the gas-phase
IVOC_P Anthropogenic IVOC concentrations
IVOC_F Biomass-burning IVOC concentrations
A_AVB[0-4]J Anthropogenic SOA/OPOA concentrations in the aerosol-phase
A_BVB[0-4]J Biogenic SOA/OPOA concentrations in the aerosol-phase
A_PVB[0-4]J Anthropogenic POA concentrations in the aerosol-phase
A_FVB[0-4]J Biomass-burning POA concentrations in the aerosol-phase


Koo, B., Knipping, E., Yarwood, G. 2014. 1.5-Dimensional volatility basis set approach for modeling organic aerosol in CAMx and CMAQ. Atmos. Environ., 95, 158-164.

Koo, B. et al., Implementing VBS Algorithm for OA Formation in CMAQ v5, AAAR Annual Conference, Minneapolis, MN, 2012.


Bonyoung Koo, ENVIRON International Corporation


The work to develop CMAQ VBS was performed by ENVIRON International Corporation with sponsorship from the Electric Power Research Institute (EPRI).