# Can ISAM only track O3?

**URL:** https://forum.cmascenter.org/t/can-isam-only-track-o3/2827
**Category:** CMAQ-ISAM
**Created:** [November 18, 2021, 9:08am UTC](https://forum.cmascenter.org/t/can-isam-only-track-o3/2827 "2021-11-18T09:08:18Z")
**Posts on this page:** 2
**Page:** 1

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### Author: ![bmbmnb](https://avatars.discourse-cdn.com/v4/letter/b/94ad74/32.png) [@bmbmnb](https://forum.cmascenter.org/u/bmbmnb)
#### Post date: [November 18, 2021, 9:08am UTC](https://forum.cmascenter.org/t/can-isam-only-track-o3/2827/1 "2021-11-18T09:08:18Z")

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Hello CMAQ stuffs,

I’m running a ISAM case for ozone source apportionment, but all NITRATE species and VOC species(which I don’t need) are included if ‘TAG CLASSES’ is set to OZONE. This really push the computer memory to the limit so that I have to split it to run multiple times, which cost so much time.  
Is there any ways to only track O3 for ISAM?

Yunqing

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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: [December 23, 2021, 7:26pm UTC](https://forum.cmascenter.org/t/can-isam-only-track-o3/2827/2 "2021-12-23T19:26:39Z")

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Sorry, there is not a way to avoid tracking NITRATE and VOC species, because these are precursors to ozone formation.