The calculation mechanism of ASO4s

Hello CMAQ users, my name is Yuya.

I would like to know how the concentrations of ASO4I, ASO4J and ASO4K are calculated.

Does anyone know which file to see?

I use CMAQv5.2 and saprc07_tc_ae6_aq as a chemical mechanism.

Thank you and best regards.


Hi Yuya,

To look into how ASO4I/J/K calculated in CMAQ, you have to look into the source codes under AERO

your path/CMAQ_v5.2/CMAQ_REPO/CCTM/src/aero

In aero6, you can do

grep ASO4 *

In AEROSOL_CHEMISTRY.F and/or ISORROPIA files (file with iso***.f), there are the SO4 aerosol chemistry related codes. Also when the aerosols grow, some ASO4I might become ASO4J etc.

Hope this helps,


Hi Joey,

Thank you for your reply , I will check the source codes.



Hi Yuya,
Small amounts of ASO4I,J,K can be directly emitted from sources.

The majority of ASO4I,J,K is produced from gas-phase or aqueous oxidation of SO2. Gas-phase reaction resulting in sulfuric acid (which will condense to particles) is available in mech*.def:
SO2 + OH = SULF + HO2 + SULRXN # 4.50E-31^-3.9 & 1.30E-12^-0.7 &0.53 &1.1;

Aqueous reactions with H2O2 and O3 (and others) are handled in the cloud chemistry module. No aqueous-aerosol reactions currently produce sulfate. The aero module will indicate how condensed sulfuric acid is allocated among the sizes (I, J, etc). ISORROPIA does not produce ASO4* species, but does use them to predict other inorganic species (ammonium, nitrate, etc).


Hi, Havala,

Thank you for your reply!

In gas phase reaction, I would like to know how SULRXN or SULF turns into ASO4I,J,K in the model.
Do you know which file handles the reaction of SULRXN or SULF → ASO4I,J,K?

I could find some calculation mechanisms of aqueous oxidation of SO2 in cloud/acm_ae6/aqchem.F and I would like to search other files in cloud directory.

Thank you for your information about AERO module.

Thank you for your help!