Unused surrogates NVOL, UNR, VOC_INV in all input emission sectors in CMAQ log file

How alarming is it to have ‘unused surrogates’ NVOL, UNR, and VOC_INV for all emission sectors - both gridded and elevated - in CMAQ output log file?

How can we enable CMAQ to use these unused surrogates?

These species are most often unused by CMAQ as NVOL and UNR (by design) don’t have an impact on chemistry (i.e. ozone formation). VOC_INV is generally used as a diagnostic variable in emissions processing. In future mechanisms, species previously assigned to NVOL or UNR may be remapped to IVOC species and used for SOA formation. VOC_INV could be used to scale new species that you want to introduce.

But the bottom-line is that for current CMAQ operation, you do not need to use these species.

Thanks a lot for the insight - it really helps me understand the unused SMOKE species for CMAQ simulation!

I am also inclined to ask a similar question about the 2D merged emissions (MRGGRID_2D stream in the screenshot above): besides the point source surrogates NVOL, UNR and VOC_INV you just explained, the 2D merged emissions stream MRGGRID_2D also has UNK, N2O_INV surrogate species that are unused by CMAQ and I was wondering if they have any importance for CMAQ simulation?

No, neither UNK nor N2O_INV are used by the chemical mechanisms in CMAQ. N2O_INV is especially rare.