# How can CMAQ output the concentration of specific aerosols like NH4NO3

**URL:** <https://forum.cmascenter.org/t/how-can-cmaq-output-the-concentration-of-specific-aerosols-like-nh4no3/5517>\
**Category:** CMAQ\
**Created:** [January 15, 2025, 3:31am UTC](https://forum.cmascenter.org/t/how-can-cmaq-output-the-concentration-of-specific-aerosols-like-nh4no3/5517 "2025-01-15T03:31:07Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Fortuna](https://avatars.discourse-cdn.com/v4/letter/f/ea666f/32.png) [@Fortuna](https://forum.cmascenter.org/u/Fortuna)\
**Post date:** [January 15, 2025, 3:31am UTC](https://forum.cmascenter.org/t/how-can-cmaq-output-the-concentration-of-specific-aerosols-like-nh4no3/5517/1 "2025-01-15T03:31:07Z")

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Hi all,

I’m using CMAQv5.4 now. And I notice that the aerosol part of the CMAQ output file only contains the sum of ANO3-, ASO42- and other inorganic salts. Is there a way to get the concentration of specific aerosol species such as NH4NO3 from ANH4+ or ANO3- variables?  
Thanks for your help.

Liu

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**Author:** ![Havala.Pye](https://avatars.discourse-cdn.com/v4/letter/h/67e7ee/32.png) [@Havala.Pye](https://forum.cmascenter.org/u/Havala.Pye)\
**Post date:** [January 21, 2025, 2:22pm UTC](https://forum.cmascenter.org/t/how-can-cmaq-output-the-concentration-of-specific-aerosols-like-nh4no3/5517/2 "2025-01-21T14:22:34Z")

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Hi Fortuna,  
CMAQ uses ISORROPIAII to calculate inorganic aerosol (including NH4+ and NO3-) formation. You can see the system of equations in [Table 2 of Fountoukis and Nenes 2007](https://acp.copernicus.org/articles/7/4639/2007/acp-7-4639-2007.pdf) which highlights the connected system. The aqueous NH4+ could be associated with sulfate, bisulfate, or Cl- in addition to nitrate. If you had the form of sulfate vs bisulfate and all other inorganic constituents, you could do a charge balance on fine mode aerosol to get the ammonium specifically associated with nitrate. Bisulfate would have to be saved out. Alternatively, you may be able to back calculated things from pH (or AH3OP).  
Havala

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**Author:** ![Fortuna](https://avatars.discourse-cdn.com/v4/letter/f/ea666f/32.png) [@Fortuna](https://forum.cmascenter.org/u/Fortuna)\
**Post date:** [February 24, 2025, 11:31am UTC](https://forum.cmascenter.org/t/how-can-cmaq-output-the-concentration-of-specific-aerosols-like-nh4no3/5517/3 "2025-02-24T11:31:08Z")

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Hi Havala,

Thanks for your reply. I have found the corresponding ISORROPIA module aero\_subs.F, which seems to be mainly responsible for the relevant calculation. May I ask whether the ISORROPIA method is still used to calculate the relevant inorganic aerosol concentration in the WRF-CMAQ two-way coupled model?

Liu

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**Author:** ![Havala.Pye](https://avatars.discourse-cdn.com/v4/letter/h/67e7ee/32.png) [@Havala.Pye](https://forum.cmascenter.org/u/Havala.Pye)\
**Post date:** [February 24, 2025, 2:15pm UTC](https://forum.cmascenter.org/t/how-can-cmaq-output-the-concentration-of-specific-aerosols-like-nh4no3/5517/4 "2025-02-24T14:15:42Z")

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Online and offline CMAQ both use ISORROPIA.

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**Author:** ![Fortuna](https://avatars.discourse-cdn.com/v4/letter/f/ea666f/32.png) [@Fortuna](https://forum.cmascenter.org/u/Fortuna)\
**Post date:** [February 25, 2025, 1:11am UTC](https://forum.cmascenter.org/t/how-can-cmaq-output-the-concentration-of-specific-aerosols-like-nh4no3/5517/5 "2025-02-25T01:11:46Z")

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Thanks for your reply, I will check it out in coupled model.