[Draft] Scale aerosol number concentrations based on change in bulk masses

[jimmielin]

This is a science update.

At present, CESM-GC only scales up/down the MAM4 aerosol masses (e.g., so4_a1-3) based on change in SO4 from GEOS-Chem chemistry, but not the MAM4 aerosol numbers (num_a1-3).

• For the current approach, only scaling up the mass means that (GEOS-Chem) chemistry only grows or shrink aerosols (changing their distribution) since the number is unchanged.
• For this commit, we scale the aerosol number concentration based on the change in bulk masses. This allows for GEOS-Chem chemistry to keep the distribution fixed but proportionally add/remove aerosol particles to change the mass.

This commit will update the aerosol number concentrations for a consistent distribution after GEOS-Chem chemistry. The impacts are minimal for most aerosol species except sulfate.

Changes in aerosol concentrations (sulfate) before/after update (blue is new, orange is old)

a2 aitken mode

a1 accumulation mode

a3 coarse mode

Changes in aerosol number concentrations (all species) before/after update

a2

a1

a3

[lizziel]

Hi @jimmielin, what is the status of this PR?

[jimmielin]

Hi @lizziel I haven't used this for a while since I've moved the aerosol implementation later for the science paper (I'll make a separate PR for it.) but I'll mark it as a draft so it's out of the view. I'll probably close/revisit this soon. Thanks for the reminder.

[jimmielin]

Closing this out since it was not adopted in the ACP manuscript.