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:
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