PM1AC factors depending on CMAQ version

[jaeeun]

Hi everyone,

I have a question about organic aerosol concentrations depending on the CMAQ version. As far as I know, CMAQv5.2.1 and CMAQv5.3.2 use the same SOA yields data, so even though they apply different SOA formation schemes—2-product and VBS respectively—they usually give similar concentration results.

However, in my simulations, PM1_OM results from CMAQv5.2.1 and CMAQv5.3.2 show noticeable differences. As shown in Figure(left, the black line is observation), the vertical profile of PM1_OM at the same location indicates that CMAQv5.2.1 gives higher values, which is contrary to what I expected.
Interestingly, when I compared the vertical profiles of PM25_OM at the same point, the two versions gave similar results, as I had anticipated.

To investigate this, I briefly compared the average values of the factors that determine PM1_OM and PM25_OM—namely, PM1AT, PM1AC, PM25AT, and PM25AC. I found that the PM1AC value in CMAQv5.3.2 was significantly lower than that in CMAQv5.2.1, while PM25AT and PM25AC were similar between the two versions.

what might be causing this difference? And how can this issue be resolved?

Thanks
Jaeeun

[Ben_Murphy]

Hello Jaeeun,

Thank you for sharing these informative figures. Here are the aerosol-relevant release notes records for the model versions between 5.2.1 and 5.3.2:

CMAQ/DOCS/Release_Notes at 5.3 · USEPA/CMAQ

New Aerosol Modules AERO7 and AERO7i

• Overview of AERO7 and AERO7i
• Monoterpene SOA
• Reorganization of anthropogenic SOA species
• Added uptake of water onto hydrophilic organic aerosol
• Corrected the conversion of inorganic to organic sulfate
• Nonvolatile POA Option in CMAQv5.3
• Streamlined SOA Module

Other Aerosol Processes

• Aerosol Dry Deposition Algorithm Updated
• Fix to Gravitational Settling Sub-Time-Step Calculation
• Simplify Propagation of Aerosol Surface Area to Heterogeneous Chemistry Algorithm

The update that could have potentially had the most impact is the Dry Deposition Algorithm Update (CMAQ/DOCS/Release_Notes/aerosol_dry_deposition.md at 5.3 · USEPA/CMAQ · GitHub). We found in Shu et al. (2022) that the dry deposition of Aitken mode particle would increase with the deposition update (Figs. 3 and 4i). This could explain the decrease you are seeing in PM1.0.

Best,
Ben Murphy

[Havala.Pye]

Hi Jaeeun,
According to my notes in Figure 1 of this article (Pye et al., 2024 EM, Leveraging Scientific Community Knowledge for Air Quality Model Chemistry Parameterizations - NASA Technical Reports Server (NTRS)) and Appel et al., 2021 (GMD - The Community Multiscale Air Quality (CMAQ) model versions 5.3 and 5.3.1: system updates and evaluation), there were changes to SOA in CMAQv5.3 aero7.

Note that size cuts can be affected by all other aerosol species. For example, changes in oxidants can affect sulfate formation and shift the size distribution propagating to changes in deposition (a function of size) and the fraction of each model below a specific size cut.

Havala