# The calculation mechanism of ASO4s

**URL:** <https://forum.cmascenter.org/t/the-calculation-mechanism-of-aso4s/1204>\
**Category:** Chemistry and Aerosols\
**Created:** [December 25, 2019, 9:17am UTC](https://forum.cmascenter.org/t/the-calculation-mechanism-of-aso4s/1204 "2019-12-25T09:17:42Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![yuya](https://avatars.discourse-cdn.com/v4/letter/y/76d3ee/32.png) [@yuya](https://forum.cmascenter.org/u/yuya)\
**Post date:** [December 25, 2019, 9:17am UTC](https://forum.cmascenter.org/t/the-calculation-mechanism-of-aso4s/1204/1 "2019-12-25T09:17:42Z")

</div>

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.

Yuya

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**Author:** ![huangj1311](https://avatars.discourse-cdn.com/v4/letter/h/8edcca/32.png) [@huangj1311](https://forum.cmascenter.org/u/huangj1311)\
**Post date:** [December 30, 2019, 8:47pm UTC](https://forum.cmascenter.org/t/the-calculation-mechanism-of-aso4s/1204/2 "2019-12-30T20:47:59Z")

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Hi Yuya,

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

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

```

In aero6, you can do

```auto
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,

Joey

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<div class="post-metadata">

**Author:** ![yuya](https://avatars.discourse-cdn.com/v4/letter/y/76d3ee/32.png) [@yuya](https://forum.cmascenter.org/u/yuya)\
**Post date:** [December 31, 2019, 4:02am UTC](https://forum.cmascenter.org/t/the-calculation-mechanism-of-aso4s/1204/3 "2019-12-31T04:02:10Z")

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Hi Joey,

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

Regards

Yuya

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**Author:** ![Havala.Pye](https://avatars.discourse-cdn.com/v4/letter/h/67e7ee/32.png) [@Havala.Pye](https://forum.cmascenter.org/u/Havala.Pye)\
**Post date:** [January 2, 2020, 5:03pm UTC](https://forum.cmascenter.org/t/the-calculation-mechanism-of-aso4s/1204/4 "2020-01-02T17:03:18Z")

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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).

Havala

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<div class="post-metadata">

**Author:** ![yuya](https://avatars.discourse-cdn.com/v4/letter/y/76d3ee/32.png) [@yuya](https://forum.cmascenter.org/u/yuya)\
**Post date:** [January 3, 2020, 3:12pm UTC](https://forum.cmascenter.org/t/the-calculation-mechanism-of-aso4s/1204/5 "2020-01-03T15:12:48Z")

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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!

Regards

Yuya