# How can I find PM2.5 in CMAQ output (ACON)

**URL:** <https://forum.cmascenter.org/t/how-can-i-find-pm2-5-in-cmaq-output-acon/3099>\
**Category:** CMAQ\
**Created:** [March 13, 2022, 7:11pm UTC](https://forum.cmascenter.org/t/how-can-i-find-pm2-5-in-cmaq-output-acon/3099 "2022-03-13T19:11:32Z")\
**Posts on this page:** 5\
**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:** [March 13, 2022, 7:11pm UTC](https://forum.cmascenter.org/t/how-can-i-find-pm2-5-in-cmaq-output-acon/3099/1 "2022-03-13T19:11:32Z")

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I want to use PM2.5 but there is no variable for PM2.5.  
Should I sum all A(Chemical\_name) I/J (ex ASO4I + ASO4J) ? or Is there a module to sum up automatically?  
 ![image](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/8/881543052c49390e955b34f815a3338f8b53feeb.png)

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**Author:** ![hogrefe.christian](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@hogrefe.christian](https://forum.cmascenter.org/u/hogrefe.christian)\
**Post date:** [March 13, 2022, 8:02pm UTC](https://forum.cmascenter.org/t/how-can-i-find-pm2-5-in-cmaq-output-acon/3099/2 "2022-03-13T20:02:04Z")

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In the current and previous versions of CMAQ, you need to compute PM2.5 by summing up the CMAQ aerosol species and accounting for the size distribution of the I, J, and K modes. There are tools in the CMAQ system that you can use for this task, specifically the `combine` utility and the “Species Definition” files available for each mechanism. Future versions of CMAQ will support including total PM2.5 in the output files. Please see the following documentation link and forum discussion threads for further details:

[Users guide chapter on analyzing CMAQ output](https://github.com/USEPA/CMAQ/blob/main/DOCS/Users_Guide/CMAQ_UG_ch08_analysis_tools.md#82-aggregating-and-transforming-model-species)

Related forum threads:

[How do I compute PM2.5, PM10 or PM1 from CMAQ output?](https://forum.cmascenter.org/t/how-do-i-compute-pm2-5-pm10-or-pm1-from-cmaq-output/47)  
[PM25 composition and estimation of PM25 water (CMAQv5.3.1)](https://forum.cmascenter.org/t/pm25-composition-and-estimation-of-pm25-water-cmaqv5-3-1/2980)  
[How to calculate PM25\_TOT/PM25 Concentration from CMAQv5.3.2-ISAM results?](https://forum.cmascenter.org/t/how-to-calculate-pm25-tot-pm25-concentration-from-cmaqv5-3-2-isam-results/2109)  
[CMAQ Computing PM2.5](https://forum.cmascenter.org/t/cmaq-computing-pm2-5/2261)

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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:** [March 13, 2022, 10:01pm UTC](https://forum.cmascenter.org/t/how-can-i-find-pm2-5-in-cmaq-output-acon/3099/3 "2022-03-13T22:01:48Z")

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Where can I find combine tool??  
Is it in IOAPI??

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**Author:** ![hogrefe.christian](https://avatars.discourse-cdn.com/v4/letter/h/74df32/32.png) [@hogrefe.christian](https://forum.cmascenter.org/u/hogrefe.christian)\
**Post date:** [March 13, 2022, 10:21pm UTC](https://forum.cmascenter.org/t/how-can-i-find-pm2-5-in-cmaq-output-acon/3099/4 "2022-03-13T22:21:30Z")

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It is part of the POST tools in the CMAQ github repository:

[README](https://github.com/USEPA/CMAQ/blob/main/POST/combine/README.md)  
[Source Code](https://github.com/USEPA/CMAQ/tree/main/POST/combine/src)  
[Scripts](https://github.com/USEPA/CMAQ/tree/main/POST/combine/scripts)

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**Author:** ![Ryan](https://avatars.discourse-cdn.com/v4/letter/r/a8b319/32.png) [@Ryan](https://forum.cmascenter.org/u/Ryan)\
**Post date:** [March 13, 2022, 11:26pm UTC](https://forum.cmascenter.org/t/how-can-i-find-pm2-5-in-cmaq-output-acon/3099/5 "2022-03-13T23:26:16Z")

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You can find the COMBINE tool under the directory of YourCMAQPath/POST/combine