The value of agricultural source contribution in ISAM simulation results is 0

Hello everyone,
When I use CMAQ-ISAM for source apportionment, the emission inventory I use has only NH3 for agricultural emissions.
This will make the concentration of agricultural source contribution in my result to be 0. How can I solve this problem? Is it impossible to resolve the contributing concentration with only ammonia emissions?

Which TAG CLASSES did you define in your isam_control.txt file, and which SA_ACONC species did you look at? The only tag class NH3 emissions would contribute to is AMMONIUM, providing the contribution of (tagged) NH3 emissions to simulated NH3, ANH4I, and ANH4J concentrations.

Thank you for your reply, I am now using ISAM for ozone source apportionment and getting a result of 0 contribution from agricultural sources, I have attached my ISAM_CONTROL file below for your review. I noticed that AMMONIUM is not added in my TAG CLASSES, is it relevant here?
Thanks again for your answer!
isam_control_cctm.txt (3.4 KB)

Since NH3 does not participate in gas phase chemistry (it is specified in the NR / non-reactive namelist), agricultural NH3 emissions to not contribute to ozone. NH3 emissions do contribute to NH3, ANH4I, and ANH4J concentrations, so if you add AMMONIUM to your tag classes, you should see the agricultural contributions to these species (but still not for ozone).

If you had agriculture-related NOx and/or VOC emissions (e.g. from farming equipment), you could track the contribution of those emission sources to ozone.

Thank you for your answer!
In the PM2.5 source apportionment, is it also possible that only NH3 is emitted from agriculture and thus the concentration contributed by agricultural sources is 0?

I might be misunderstanding your question.

ISAM does not have a generic “PM2.5” source apportionment, but instead offers apportionment of specific PM2.5 species to emissions of the relevant precursors species via the SULFATE, NITRATE, AMMONIUM, EC, OC and PM25_IONS TAG CLASSES. The list of the relevant species is provided in the definition of each TAG CLASS.

If the source you are tracking only contains NH3 emissions, it can only have a non-zero contribution to the AMMONIMUM TAG CLASS and the three species listed for that TAG CLASS. However, given that ANH4I and ANH4J are part of CMAQ’s representation of PM2.5, this still means that the contribution to total PM2.5 would also be non-zero because you’re quantifying how much of simulated ANH4I and ANH4J (which is part of simulated PM2.5) is due to your agricultural NH3 emissions.