How you approach this depends on what processes you are considering and the CMAQ model options. If
you are using the M3Dry deposition option:
Constants related to cuticular and soil resistances by deposition species are found in:
AS_DATA_MOD.F
All other surface resistances are estimated in:
m3dry.F
The aerodynamic and stomatal resistances are passed down from the meteorological model
All modifications will require a recompile of the code. Documentation can be found in Pleim and Ran 2011 (Atmosphere | Free Full-Text | Surface Flux Modeling for Air Quality Applications)
If you are using the STAGE compile time deposition option:
Constants related to cuticular and soil resistances by deposition species are found in:
CMAQ_Control_STAGE.nml
All other surface resistances are estimated in
STAGE_FUNCTIONS.F
Aerodynamic and stomatal resistances are currently normalized to the meteorological model output and can be modified in:
MOSAIC_MOD.F
Modifications to do not require a re-compile while modifications to STAGE_FUNCTIONS.F or MOSAIC_MOD.F will require recompiling the code.
Additionally, there is a box model version of the STAGE option Walker et al. 2023 (BG - Atmospheric deposition of reactive nitrogen to a deciduous forest in the southern Appalachian Mountains) available here (Bash and Wu 2023; STAGE bidirectional air-surface exchange model | Zenodo). I have found this to be useful in the development of updated deposition parameters.