MEGAN extension is turned on by default in GCHP run directory

[yantosca]

Your name

Bob Yantosca

Your affiliation

Harvard + GCST

What happened? What did you expect to happen?

The HEMCO MEGAN extension is turned on by default when creating a GCHP run directory. Found by @yuanjianz.

Offline biogenic emissions are recommended for standard full-chemistry GCHP simulations. Having both offline biogenic VOC and MEGAN turned on may double count some emissions.

What are the steps to reproduce the bug?

Created a GCHP run directory and look at the HEMCO_Config.rc

Please attach any relevant configuration and log files.

No response

What GEOS-Chem version were you using?

14.4.0

What environment were you running GEOS-Chem on?

Local cluster

What compiler and version were you using?

gcc10

Will you be addressing this bug yourself?

Yes

In what configuration were you running GEOS-Chem?

GCHP

What simulation were you running?

Full chemistry

As what resolution were you running GEOS-Chem?

14.4.0

What meterology fields did you use?

MERRA-2

Additional information

No response

[yuanjianz]

I would suggest that this happens to other configurations like GCClassic as well. See:

geos-chem/run/GCClassic/HEMCO_Config.rc.templates/HEMCO_Config.rc.fullchem

Line 197 in 1ef3d7f

108 MEGAN : on ISOP/ACET/PRPE/C2H4/ALD2/MOH/EOH/MTPA/MTPO/LIMO/SESQ/SOAP/SOAS

[msulprizio]

This was originally done on purpose for the implementation of MOH in version 12.7 (see pull request #175 and commit 3e2a48f). From that commit message:

Update initialization phase to not define certain species (ISOP, ACET, ALD2, C2H4, LIMO, MTPA, MTPO, PRPE, SESQ, SOAP, SOAS, EOH) when the OFFLINE_BIOGENICVOC option is turned on in HEMCO_Config.rc. This will allow use of offline biogenic VOC emissions for those species and online MEGAN emissions will be used for the rest of the species. Right now, just MOH from MEGAN will be fed back into the model and the remaining monoterpene species, methyl butenol, formic acid, and acetic acid will be used for diagnostic purposes only.

At that time, MOH was not included in the offline biogenic emissions so we still needed to call MEGAN to compute the emissions for just that species. MOH is now included in the offline biogenic VOC files (I'm not sure of the exact date of when that occurred) so I'm confirming that we no longer need to call MEGAN when offline biogenic emissions are used.

[msulprizio]

A fix for this can go into dev/no-diff-to-benchmark since offline emissions are not used in benchmark simulations.

[yantosca]

Thanks @msulprizio for confirming.

[msulprizio]

The fix for this (#2372) has been merged into 14.4.2. We can close this issue.

In a separate PR, @lizziel will fix a lingering issue where HEMCO_Diagn.rc for MOH still lists the MEGAN extension as its source instead of the base emissions (i.e. offline emissions).

EmisMOH_Biogenic   MOH    108    -1  -1   2   kg/m2/s  MOH_emission_flux_from_biogenic_sources

should be

EmisMOH_Biogenic   MOH      0    4  -1   2   kg/m2/s  MOH_emission_flux_from_biogenic_sources