Extension: offAOD/AERONET operator parity for BrC bins

[maxcharvey]

Problem

The wiki flags that online and offline AOD/AAOD operators can disagree for BrC bins, especially hydrophobic DBRCPOA/PBRCPOA and split hygroscopic bins. Column validation against AERONET should not proceed until online/offline mapping is explicit.

Wiki basis

• wiki/projects/brc-modeling/current-brc-implementation-checklist.md: verify offAOD mapping before science interpretation.
• wiki/projects/validation/brc-observation-operator-notes.md: offAOD mapping notes.
• registries/run_matrix.yml: OFFAOD and AERONET operators.

Needed

• Define model fields used by offline AOD/AAOD for each BrC species.
• Keep DBRCPOA/PBRCPOA hydrophobic in offline optics unless design changes.
• Compare online AODHyg* + BrCDryAOD* against offline bins for a controlled run.
• Record AERONET operator assumptions: AOD, AAOD, AAE, SSA, humidity, vertical profile.

Acceptance

• Online/offline BrC AOD agree within tolerance for a short test.
• AERONET comparison scripts cannot silently omit dry BrC AOD.

Wiki audit: [[brc-implementation-audit-2026-06-30#Future Branch Backlog]]

[maxcharvey]

offAOD validation run completed on max/full_test.

The Python wrapper could not run in the module environment because netCDF4 is missing, so I ran the compiled Fortran gc_aod binary directly against a StateMet-enabled 1h run. It wrote AOD/AAOD/SSA output successfully.

550 nm column comparison vs online AOD: BCPI/SALA/SALC/BRCSOA/WTC within about 0.5%; OCPI about 7%; SO4/NPBRC/DBRC about 17-18%. Good enough for an independent offAOD smoke; keep exact parity work open if required.

Branch: max/full_test.

Pinned commits:

• GCClassic: 475ffbd9cbf0adf0ee5f74eed06eb5e3739d1fe3
• GEOS-Chem: e586d1f207701ca31af2f50c55a26b5607c17664
• Cloud-J: 52407dbc3ab47874dafa7d9b87ed53ece3750945
• HEMCO: 3bdab085e8c6c5cf562a425251f655044ea7bb34

Validation completed:

• 1h fullchem scheme 4: pass
• 1h fullchem scheme 0: pass
• 1h RRTMG BrC smoke: pass
• 24h fullchem scheme 4 to 2019-07-02 00:00: pass
• StateMet-enabled offAOD prep run: pass
• offAOD Fortran core: pass

Caveat: a separate 0100->0200 restart mini-run hit HEMCO PS_NEXTDAY handling in the temporary met setup. The 24h run crossed the day boundary and wrote the final restart, so this does not look like a BrC-code issue.