# CMAQ5.5 Zero Out NH3\_fert and Soil NOx emissions **URL:** \ **Category:** CMAQ\ **Tags:** emissions\ **Created:** [October 10, 2025, 6:56pm UTC](https://forum.cmascenter.org/t/cmaq5-5-zero-out-nh3-fert-and-soil-nox-emissions/6027 "2025-10-10T18:56:24Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![hosok004](https://avatars.discourse-cdn.com/v4/letter/h/9f8e36/32.png) [@hosok004](https://forum.cmascenter.org/u/hosok004)\ **Post date:** [October 10, 2025, 6:56pm UTC](https://forum.cmascenter.org/t/cmaq5-5-zero-out-nh3-fert-and-soil-nox-emissions/6027/1 "2025-10-10T18:56:24Z")
Hello, I am running a CMAQ5.5 simulation over CONUS using CRACMMv2 and I was interested in testing the effects of zeroing out certain emissions. Specifically, I would like to test out the effects of having zero NH3 fertilizer emissions or zero soil NOx emissions in two runs. To zero out NH3\_fert, should I simply set CTM\_abflux to N? For context, I am using ag emissions files from the EQUATES Project that only include NH3 from livestock. For soil NOx I am a bit confused on how to proceed. From what I understand, soil NOx is calculated using the inline BEIS biogenic emissions. To adjust the biogenic emissions, would I need to edit the NO split factor from 1.0 to 0.0 in the gspro\_biogenics.txt file (screenshots below)? ![image](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/7/746172cb8160f4f3405394b325a4510c02d997b1.png) ![image](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/9/986c50131978655a2c36e8b8dbd66688e3da77d6.png) ---
**Author:** ![slfarrell](https://avatars.discourse-cdn.com/v4/letter/s/e9bcb4/32.png) [@slfarrell](https://forum.cmascenter.org/u/slfarrell)\ **Post date:** [October 23, 2025, 1:20pm UTC](https://forum.cmascenter.org/t/cmaq5-5-zero-out-nh3-fert-and-soil-nox-emissions/6027/2 "2025-10-23T13:20:16Z")
Hello - Do you mind sending me your run script so I can better answer your Ag NH3 question? For Soil NO, you can zero out those emissions by placing this line in your CMAQ\_Chem\_Control file like so: ![image](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/b/b5f1f5d51c41455f67352ca4b1aa029676d333d3.png) And then to ensure that these emissions are being zero’d out you can add this as a stream in your CMAQ\_Control.nml file like so: ![image](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/2/2ddc25e2cd0465aeaf7b8fcea5ae7f49b92ab016.png) ---
**Author:** ![hosok004](https://avatars.discourse-cdn.com/v4/letter/h/9f8e36/32.png) [@hosok004](https://forum.cmascenter.org/u/hosok004)\ **Post date:** [October 23, 2025, 3:06pm UTC](https://forum.cmascenter.org/t/cmaq5-5-zero-out-nh3-fert-and-soil-nox-emissions/6027/3 "2025-10-23T15:06:29Z")
Hi, Thanks for your advice! Here is my cctm run script for more clarification. I am modeling over the 12km CONUS domain for Summer 2005 using the CRACMM2 mechanism and BEIS biogenic emissions. [run\_cctm\_2005\_12US1\_CRACMM2.csh.txt](https://forum.cmascenter.org/uploads/short-url/i12mFbhHQ0Czmv6cckgOlT19RVb.txt) (39.6 KB) ---
**Author:** ![slfarrell](https://avatars.discourse-cdn.com/v4/letter/s/e9bcb4/32.png) [@slfarrell](https://forum.cmascenter.org/u/slfarrell)\ **Post date:** [October 23, 2025, 8:37pm UTC](https://forum.cmascenter.org/t/cmaq5-5-zero-out-nh3-fert-and-soil-nox-emissions/6027/4 "2025-10-23T20:37:25Z")
Hello Again, I have an addendum to my original response. Hopefully this will be more helpful! And have a solution to your fertilizer NH3 question as well thanks to @nash.skipper. 1. When I refer to the CMAQ\_Control.nml file, for you that would be the CMAQ\_Control\_DESID.nml file and then when I refer to the CMAQ\_Chem\_Control file, I’m referring to your CMAQ\_Control\_DESID\_cracmm2.nml file. 2. For zero’ing out NO emissions from soil in BEIS you would insert the scaling rule I screenshotted before in your CMAQ\_Control\_DESID\_cracmm2.nml file, but instead of “a” under the Op column, you would change this to “o” (which stands for override). 3. To zero out NH3 emissions from fertilizer (from both Bidirectional Fluxes and from your offline EQUATES emissions file - which should be the emissions stream labeled “GRIDDED\_EMIS” in your runscript), you would indeed set CTM\_ABFLUX to N and then in your CMAQ\_Control\_DESID\_cracmm2.nml you would add this line: ![image](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/1/13ebd21034af138b4fef34d3329cd01c48a170fe.png) Note that the “a” is retained (meaning add) as you are negatively adding NH3 from fertilizer from your total NH3 emissions (or in plain speak: subtracting). As a sanity check you can output these streams as I mentioned before by modifying your CMAQ\_Control\_DESID.nml file. Your NO from the BIOG DESID stream should be 0, and your NH3 from your GRIDDED\_EMIS should be less than if you ran without setting that scaling factor to -1. Hope this helps and good luck with your project! -Sara ---
**Author:** ![hosok004](https://avatars.discourse-cdn.com/v4/letter/h/9f8e36/32.png) [@hosok004](https://forum.cmascenter.org/u/hosok004)\ **Post date:** [October 24, 2025, 1:06am UTC](https://forum.cmascenter.org/t/cmaq5-5-zero-out-nh3-fert-and-soil-nox-emissions/6027/5 "2025-10-24T01:06:17Z")
Thank you for all the help! I’ll let you know if I run into any issues. ---
**Author:** ![system](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/1X/9a72c78e529465c3f1053af404e3033b0875428c.png) [@system](https://forum.cmascenter.org/u/system)\ **Post date:** [October 31, 2025, 1:06am UTC](https://forum.cmascenter.org/t/cmaq5-5-zero-out-nh3-fert-and-soil-nox-emissions/6027/6 "2025-10-31T01:06:38Z")
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