Using bi-directional NH3 flux module in CMAQ

My understanding is that, to use CMAQ’s bi-directional NH3 module, you should provide NH3 emissions from fertilizer separately (as NH3_FERT) to avoid double-counting.
Then, CMAQ uses total NH3 emissions (NH3) minus NH3_FERT in the emissions module, and the soil NH4 contents estimated by EPIC (through FEST-C) will completely replace the conventional soil NH3 emissions from NEI (NH3_FERT). Is that correct?

Yes, that is correct. However, if you do not have NH3 emissions from fertilizer already you can specify this array in the emissions file(s) as 0.0 and estimate these emissions with the bidirectional exchange option in-line.

Take care,

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