# SOA photolysis rate in CMAQ

**URL:** <https://forum.cmascenter.org/t/soa-photolysis-rate-in-cmaq/4535>\
**Category:** Chemistry and Aerosols\
**Tags:** cmaq, research-topic\
**Created:** [November 10, 2023, 2:16pm UTC](https://forum.cmascenter.org/t/soa-photolysis-rate-in-cmaq/4535 "2023-11-10T14:16:19Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![hlbutterfly](https://avatars.discourse-cdn.com/v4/letter/h/57b2e6/32.png) [@hlbutterfly](https://forum.cmascenter.org/u/hlbutterfly)\
**Post date:** [November 10, 2023, 2:16pm UTC](https://forum.cmascenter.org/t/soa-photolysis-rate-in-cmaq/4535/1 "2023-11-10T14:16:19Z")

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Hi,

Is SOA photolysis considered in CMAQ (for example, CMAQ 5.3.2)? I tried to dig into the source code and look for signs. But I did not find any signs of SOA photolysis except SOA oligomerization. I want to make sure about this.

Thanks  
Ling

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**Author:** ![manishsoni](https://avatars.discourse-cdn.com/v4/letter/m/c2a13f/32.png) [@manishsoni](https://forum.cmascenter.org/u/manishsoni)\
**Post date:** [November 10, 2023, 8:15pm UTC](https://forum.cmascenter.org/t/soa-photolysis-rate-in-cmaq/4535/2 "2023-11-10T20:15:31Z")

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Hi Ling,

Can you look at this post.

```auto
https://forum.cmascenter.org/t/about-soa-species-in-cmaq-v5-3/3858/4

```

Also you can refer this article

```auto
https://gmd.copernicus.org/preprints/gmd-2020-345/gmd-2020-345.pdf

```

I also suggest you can also contact @ben_murphy for more clarification.

Also you may look at third bullet point in the link below.

```auto
https://github.com/USEPA/CMAQ/wiki/CMAQv5.4-Series-FAQ#chemistry

```

Manish

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<div class="post-metadata">

**Author:** ![hlbutterfly](https://avatars.discourse-cdn.com/v4/letter/h/57b2e6/32.png) [@hlbutterfly](https://forum.cmascenter.org/u/hlbutterfly)\
**Post date:** [November 11, 2023, 1:05am UTC](https://forum.cmascenter.org/t/soa-photolysis-rate-in-cmaq/4535/3 "2023-11-11T01:05:14Z")

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Hi Manish,

Thank you for the reply! However, I still haven’t found any clues on SOA photolysis in CMAQ.

Thanks  
Ling

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<div class="post-metadata">

**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:** [November 14, 2023, 2:45pm UTC](https://forum.cmascenter.org/t/soa-photolysis-rate-in-cmaq/4535/4 "2023-11-14T14:45:40Z")

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Hello,  
You can find the peer-reviewed references for CMAQ’s SOA treatment here: [How to Cite CMAQ | US EPA](https://www.epa.gov/cmaq/how-cite-cmaq#Particle_Microphysics_and_Chemistry)

Photolysis of SOA is not considered in CMAQ. Oligomerization is not modulated by photolysis and is a condensed phase process. Photolysis of SOA has been implemented in work that is under review (Vannucci et al.) and is under consideration for operationalizing in CRACMM3. The work by my student (Vannucci et al.) could be published in the next 2-3 months.

Havala

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<div class="post-metadata">

**Author:** ![lizadams](https://avatars.discourse-cdn.com/v4/letter/l/49beb7/32.png) [@lizadams](https://forum.cmascenter.org/u/lizadams)\
**Post date:** [November 17, 2023, 8:40pm UTC](https://forum.cmascenter.org/t/soa-photolysis-rate-in-cmaq/4535/5 "2023-11-17T20:40:15Z")

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<div class="post-metadata">

**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:** [February 5, 2024, 6:23pm UTC](https://forum.cmascenter.org/t/soa-photolysis-rate-in-cmaq/4535/6 "2024-02-05T18:23:54Z")

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Hi Ling,  
In work just published by Vannucci et al. ([ACS ESC 2024](https://doi.org/10.1021/acsearthspacechem.3c00333)), we examined a photolysis loss of SOA to reduce overestimates in OA and its association with temperature in the eastern U.S. during summer. The reactions like those listed below were added to mech\*.def and use a photolysis rate that is 1% of the NO2 rate based on previous experimental studies (see references in Vannucci et al.). In most cases, we fragmented the SOA to some unknown and untracked product. In the case of AELHOMJ dimers, we fragmented it to AHOMJ monomers. This type of loss should have a product specified to better conserve mass. To implement similar chemistry in another mechanism, you’d want to use the relevant NO2 rate for that mechanism. To propagate this type of update to the CMAQ Fortran code and executable, you can use the Autochem process (See [Section 2.2.b of the mechanism tutorial](https://github.com/USEPA/CMAQ/blob/main/DOCS/Users_Guide/Tutorials/CMAQ_UG_tutorial_chemicalmechanism.md#22b-cmaq-autochem-mechanism-build-process)) or manually run chemmech and create\_ebi (See [CMAQ Utilities Guide](https://github.com/USEPA/CMAQ/tree/main/UTIL)).

AHOMJ = # 0.01/\<NO2\_RACM2\>;  
 AELHOMJ = 2.0\*AHOMJ # 0.01/\<NO2\_RACM2\>;  
 ASOATJ = # 0.01/\<NO2\_RACM2\>;  
 AGLYJ = # 0.01/\<NO2\_RACM2\>;  
 AORGCJ = # 0.01/\<NO2\_RACM2\>;  
 AOP3J = # 0.01/\<NO2\_RACM2\>;  
 AROCN2ALKJ = # 0.01/\<NO2\_RACM2\>;  
 AROCN1ALKJ = # 0.01/\<NO2\_RACM2\>;