Hello everyone,
When running smkmerge with the setting setenv MRG_GRDOUT_UNIT moles/s, I noticed that species defined in the GSPRO with split factor, divisor, and mass fraction of 1.0, 1.0, 1.0 (e.g., PEC, POC, VOC_INV) are being processed in g/s units.
Could any of the teachers please confirm if that is correct? If so, does it mean that these species cannot be processed in CMAQ directly, since it requires inputs in moles/s?
Hi Mason,
First of all, for CMAQ there are two different units in emission inputs: moles/s for gaseous species (e.g., NOX, CO, SO2) and g/s for aerosol species (PEC, PSO4, POC). Similarly, GSPRO has two types of speciations values for gaseous and aerosol species. As you observed, the defined values for aerosol species always have divisor = 1 because SMOKE is converting mass-base emissions from inventory raw data (e.g., ton/yr in NEI, internally convert to g/s in SMOKE) to mass-base mode ready outputs (g/s). Whereas, the divisors for gaseous species essentially are their molecular weight, which are required to convert mass-base emission inputs to mole-base model ready outputs (moles/s). The split factor and mass fraction are set to 1 only if we are mapping emission species to model species in 1-to-1 fashion (eg., PEC in raw emission data to PEC in model ready output, NOX to NOX), they are typically less than 1 when we are speciating a single emission species to multiple model species (e.g., TOG = 0.0147 ACET + 0.0736 CH4 + …)
VOC_INV is often included as tracer species and does not participate in any physical/chemical processes in CMAQ, and so it keeps its original mass-base unit.
So the bottom line is what you are seeing is correct. I hope this helps.
Dear Dr. Tran,
Thank you for your detailed and insightful response. Your explanation has greatly clarified my understanding of the processing steps.