Variable names for MEGAN emissions

[Seb Eastham]

Dear CESM land modeling community,

We are seeking to archive hourly emissions from MEGAN 2.1 in CESM2.1.3 with CLM5. Using the standard outputs, we are seeing that we can get 10 different emissions (acetaldehyde, acetic acid, acetone, carene-3, ethanol, formaldehyde, isoprene, methanol, a-pinene, and "thujene-a"). In each case the variable name was just preceded by "MEG_". However we had two questions we were hoping you could help with.

First, there are several classes of emission which MEGAN 2.1 calculates, but which are not included in the standard outputs. Specifically myrcene, sabinene, limonene, b-pinene, b-caryophyllene, a-farnesene, 232-MBO, CO, other monoterpenes, other sesquiterpenes, bidirectional VOC, stress VOC, and other VOC. Some of these we could probably guess but we were hoping somebody might have a comprehensive list of those which MEGAN can provide through CESM.

Second (and part of the reason we are looking for an authoritative list), I was hoping there was some data on what exactly is included in each. The reason is that a-thujene is just one of the species within the "other monoterpenes" class, so I'm wondering if the variable MEG_thujene_a is actually the total emissions of other monoterpenes or if there has been an effort to further break down the emissions classes.

Any information that anyone can provide is much appreciated! Please also let me know if this should be posted in the atmosphere forums instead.

 

[slevis]

You may have already looked at these, but I will recommend this chapter of the clm5 technical description and relevant references included in that section:

2.30. Biogenic Volatile Organic Compounds (BVOCs) — ctsm release-clm5.0 documentation

and Guenther et al. (2012).

For more information, it's likely best to reach out to the developers of MEGAN 2.1.

 

[slevis]

Something else to say about your first question:
If I understand you correctly, the CESM version of MEGAN calculates classes of emission not sent to history. If so, you may wish to familiarize yourself with the history-writing part of VOCEmissionMod.F90 where MEG_* fields get written and see if you can add more compounds to the existing loop. I suggest this not knowing your programming skill level, so it may or may not be an option for you.

 

[Seb Eastham]

Thanks @slevis - that's a big help! We had looked through the documentation but couldn't find the variable names which were used specifically in CLM/CTSM. I'll take a look at VOCEmissionMod.F90 and see what I can tease out. Hopefully we can get what we need by just messing with namelists but I'm not above hardcoding if necessary. I'll report back here once I've had a chance to formulate a plan.

 

[Seb Eastham]

Thanks again for all your help! For future users, the full list of compounds which can be output through MEGAN is specified based by the 'megan_factors_file' specified in the MEGAN namelist (megan_emis_nl). In CESM 2.1.3 with CLM5, that file is inputdata/atm/cam/chem/trop_mozart/emis/megan21_emis_factors_78pft_c20161108.nc. It looks like the variable called 'comp_name' in that file provides a list of all the species for which emissions can be calculated and then specified in the MEGAN emissions namelist.