I have model CESM model output "OC" and "SOA", does this OC refer to primary organic carbon (POC)?

[Hemraj]

Hi, CESM community,
I just want to be clear about the model output so as to clearly interpret my model results. I have "OC", and "SOA" in my model output.

Are these OC and SOA completely isolated? OC refers to primary organic aerosol (POA), and SOA refers to Secondary organic aerosol. This is my current understanding. I just want to make sure this is right.

Thank you so much.

-Hemraj

 

[dbailey]

Moving this to CAM-CHEM.

 

[Duseong]

Hi Hemraj,

I think you are correct. Which variables are you looking at? I think "POM" is used for POA in CESM generally.

Best,
Duseong

 

[Hemraj]

Dear @Duseong ,
Thank you for your prompt action. I am using
"CAM_NML_USE_CASE" value="2000_cam4_trop_chem" & "LND_TUNING_MODE" value="clm5_0_cam6.0" in FMOZ compset with code base CESM2_1_3.

There is no output called "POA" in CAM output. My objective is to calculate PM2.5 manually since I didn't see PM2.5 in the output list (maybe because I used CAM4). Thus, following the conversion factor and equation from Hand et al., 2012 (10.1029/2011JD017122) and Ford et al., 2018 (10.1029/2018GH000144), I used this equation to calculate PM2.5:

PM2.5 = 1.375 × SO42– + 1.8 × OC + BC + NH4NO3 + SOA

I excluded natural sources, such as dust and sea salt, in the PM2.5 calculation.

I hope to this point, it is ok.

My concern is I am doing OC*1.8 to convert OC to OM and adding SOA as well in PM2.5 calculation. My current understanding is OM is primary organic aerosol (POA), which is completely isolated from SOA (secondary organic aerosol), and summing them doesn't double count while calculating PM2.5 using the above equation.

This is my understanding. Please correct me if I am wrong. I just wanted to make sure I am doing it correctly.

Thank you again.

Best,
Hemraj

 

[Duseong]

Hi Hemraj,

I see, I actually never used CAM4 so I hope other people can answer this as well.
But generally, chemistry models do separate POA and SOA, and don't mix them during the calculation, as SOA needs partitioning calculation but POA doesn't.
There could be some exceptions like the semi-volatile POA approach, but I don't think this is the case for CAM4.

For the OM/OC factor, CAM6 already simulates POA as OM mass, so you shouldn't apply this factor, but it looks like CAM4 is different from CAM6.
As a side note, the OM/OC factor can be 1.4 near the emission source but 2.1 in remote/rural regions, so there are already a lot of uncertainties when using this constant OM/OC factor.

Best,
Duseong

 

[Hemraj]

Thanks a lot, @Duseong. I am looking forward to hearing from other experts. I just don't want to make a wrong interpretation of my results.
Look forward.
Thanks again.