SCM Failures due to RRTMG Update

So, this is a fun one and I'm not sure how to solve it. In the latest version of GEOSgcm_GridComp we incorporated changes from @dr0cloud that detects negative inputs into RRTMG (#393). And this is a Good Thing™ as negative inputs to RRTMG are usually not wanted.

But, it turns out, some of the SCM cases seem to have negative inputs as last night's tests showed:

• TRMM_LBA

 file:rrtmg_lw_rad.F90, line:         378
 minval(cfc12vmr): -8.1840096E-22
negative values in input: cfc12vmr

• arm_97jul

 file:rrtmg_lw_rad.F90, line:         378
 minval(cfc12vmr): -1.5127862E-20
negative values in input: cfc12vmr

• merra_arm97jul

 file:rrtmg_lw_rad.F90, line:         378
 minval(cfc12vmr): -1.9174425E-20
negative values in input: cfc12vmr

• merra_armsgp

 file:rrtmg_lw_rad.F90, line:         378
 minval(cfc12vmr): -1.0579275E-20
negative values in input: cfc12vmr

• merra_namecore

 file:rrtmg_lw_rad.F90, line:         378
 minval(cfc12vmr): -7.2872787E-23
negative values in input: cfc12vmr

• merra_trmm

 file:rrtmg_lw_rad.F90, line:         378
 minval(cfc12vmr): -5.3364247E-22
negative values in input: cfc12vmr

• merra_twp

 file:rrtmg_lw_rad.F90, line:         378
 minval(cfc12vmr): -4.6316816E-23
negative values in input: cfc12vmr

In each case, it's cfc12vmr that triggers it. It's possible there are other negative inputs, but cfc12vmr is the first to trigger, and the Fortran stops.

I tried to look around GEOS and I'm sort of certain CFC12 is coming from the pchem.species.CMIP-5.MERRA2OX.197902-201706.z_91x72.nc4 file. I took a look and I'm pretty sure it's never negative in the file.

Now the question is: who to ask for help...because who is causing it to be negative?

I'll mention @gmao-esherman and @amolod as they are the SCM gurus I know of. And maybe @mmanyin as an overall knower of Chemistry knowledge.

Perhaps, though, this is due to GF/Moist so maybe @srfreita or @narnold1 or @wmputman ? I do see this in the log file:

 GF is doing transp and wet removal of: CFC12

so perhaps GF did something weird?