SOA photolysis rate in CMAQ

CMAQ Chemistry and Aerosols
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1

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

2

Hi Ling,

Can you look at this post.

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

Also you can refer this article

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.

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

Manish

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3

Hi Manish,

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

Thanks
Ling

4

Hello,
You can find the peer-reviewed references for CMAQ’s SOA treatment here: How to Cite CMAQ | US EPA

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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6

Hi Ling,
In work just published by Vannucci et al. (ACS ESC 2024), 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) or manually run chemmech and create_ebi (See CMAQ Utilities Guide).

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>;

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