Tolerance for negative emissions in the DESID module

CMAQ
1

I was trying to do a zero-out CMAQ (v5.4) run where emissions from a source sector were eliminated. I was subtracting the source sector emissions from merged emissions at runtime using the DESID module.
The run failed with the following error message:

     ERROR: Invalid Negative emission rate -1.192E-07 has been
      detected for CMAQ species NUMACC.
     Please inspect the Emission Control Namelist File (Search for
     "Reading Emission Control Namelist" in this Log File).

I understand that subtraction operation in the DESID module could possibly result in small negative mass. Upon examining desid_module.F, however, I realize that a single tolerance value of -1.0e-7 is applied to all variables; that is, not just mass variables but also aerosol number and surface area variables.
I wonder whether you should apply a different tolerance value to the aerosol number variables since their values are typically many orders of magnitudes greater than mass concentrations?

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2

That’s good advice Bonyoung, and we’ll consider adding it for v6.0. If you want to apply that discrimination yourself and you haven’t already found the following variables, you may use DIFF_MASK_NUM( IDIFF ) and DIFF_MASK_SRF( IDIFF ) to filter for the indices in VDEMIS_DIFF that correspond to number and surface area. respectively. They are in the VDIFF_MAP module that is already used in the header of DESID_CHECK_NEG to access the variable DIFF_SPC.

Best regards,
Ben

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