# Is CMAQ-ISAM possible to tag for Particle Number variable (NUMATN, NUMACC, or NUMCOR)?

**URL:** <https://forum.cmascenter.org/t/is-cmaq-isam-possible-to-tag-for-particle-number-variable-numatn-numacc-or-numcor/4135>\
**Category:** CMAQ-ISAM\
**Created:** [May 23, 2023, 8:19pm UTC](https://forum.cmascenter.org/t/is-cmaq-isam-possible-to-tag-for-particle-number-variable-numatn-numacc-or-numcor/4135 "2023-05-23T20:19:02Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![kkkghs0828](https://avatars.discourse-cdn.com/v4/letter/k/ce7236/32.png) [@kkkghs0828](https://forum.cmascenter.org/u/kkkghs0828)\
**Post date:** [May 23, 2023, 8:19pm UTC](https://forum.cmascenter.org/t/is-cmaq-isam-possible-to-tag-for-particle-number-variable-numatn-numacc-or-numcor/4135/1 "2023-05-23T20:19:02Z")

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Hello.  
I am curious if CMAQ-ISAM can tag for particle numbers.

In the isam\_control.txt file,  
I can choose only 9 options.  
e.g. !!! Choose any/all from the list of nine: SULFATE, NITRATE, AMMONIUM, EC, OC, VOC, PM25\_IONS, OZONE, CHLORINE

Should I change SA\_DEFN.F to tag a new variable?

Best regards,

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**Author:** ![Ben\_Murphy](https://avatars.discourse-cdn.com/v4/letter/b/74df32/32.png) [@Ben\_Murphy](https://forum.cmascenter.org/u/Ben_Murphy)\
**Post date:** [June 6, 2023, 4:36pm UTC](https://forum.cmascenter.org/t/is-cmaq-isam-possible-to-tag-for-particle-number-variable-numatn-numacc-or-numcor/4135/2 "2023-06-06T16:36:54Z")

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Hello!

Unfortunately, number and surface area are currently not included, and it is not clear how the ISAM source-tagging approach could be extended to handle these metrics since they are not conserved like mass is.

For example, if a small particle and large particle from to sources collide, what is the source allocation of the resulting particle? Surface area would in theory be more tractable since it is a continuous quantity, but it would be difficult to determine how one thinks about particle morphology and source distribution. It would not be a very meaningful prediction at this point.

My recommendation (if you have a limited number of sources you are considering) would be to zero out each source of concern and quantify the impact on particle number.

Best wishes,  
Ben

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**Author:** ![kkkghs0828](https://avatars.discourse-cdn.com/v4/letter/k/ce7236/32.png) [@kkkghs0828](https://forum.cmascenter.org/u/kkkghs0828)\
**Post date:** [June 7, 2023, 8:10pm UTC](https://forum.cmascenter.org/t/is-cmaq-isam-possible-to-tag-for-particle-number-variable-numatn-numacc-or-numcor/4135/3 "2023-06-07T20:10:31Z")

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Hello Ben,

Thank you for your comment and recommendation.  
From my understanding, it is the BFM method, right?  
i.e. running CMAQ with and without each source.

Best regards,  
Darby

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**Author:** ![Ben\_Murphy](https://avatars.discourse-cdn.com/v4/letter/b/74df32/32.png) [@Ben\_Murphy](https://forum.cmascenter.org/u/Ben_Murphy)\
**Post date:** [June 7, 2023, 9:54pm UTC](https://forum.cmascenter.org/t/is-cmaq-isam-possible-to-tag-for-particle-number-variable-numatn-numacc-or-numcor/4135/4 "2023-06-07T21:54:34Z")

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That’s absolutely right. I think brute force is the best way to go for this question at the moment.

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**Author:** ![Jano](https://avatars.discourse-cdn.com/v4/letter/j/9dc877/32.png) [@Jano](https://forum.cmascenter.org/u/Jano)\
**Post date:** [September 1, 2026, 12:11am UTC](https://forum.cmascenter.org/t/is-cmaq-isam-possible-to-tag-for-particle-number-variable-numatn-numacc-or-numcor/4135/5 "2026-09-01T00:11:20Z")

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Hello Ben, I hope this message finds you well. I had the same question. I imagine that until now (CMAQv5.5), we have only calculated source apportionment for particle number using the Brute Force Method, right?

Kindest regards,

Alejandro Delgado Peralta (Jano)

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**Author:** ![sergey](https://avatars.discourse-cdn.com/v4/letter/s/9fc348/32.png) [@sergey](https://forum.cmascenter.org/u/sergey)\
**Post date:** [September 21, 2026, 12:04pm UTC](https://forum.cmascenter.org/t/is-cmaq-isam-possible-to-tag-for-particle-number-variable-numatn-numacc-or-numcor/4135/6 "2026-09-21T12:04:39Z")

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We are still only supporting apportionment of particle mass. There are currently no plans to address particle number with ISAM. Brute-force method continues to be your best way forward.

Sergey