# How to Compute PM2.5 Source Contributions Using IPR in CMAQ? **URL:** \ **Category:** Evaluation\ **Tags:** cmaq, process-analysis\ **Created:** [July 11, 2025, 2:08am UTC](https://forum.cmascenter.org/t/how-to-compute-pm2-5-source-contributions-using-ipr-in-cmaq/5906 "2025-07-11T02:08:19Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![active3734](https://avatars.discourse-cdn.com/v4/letter/a/43a26b/32.png) [@active3734](https://forum.cmascenter.org/u/active3734)\ **Post date:** [July 11, 2025, 2:08am UTC](https://forum.cmascenter.org/t/how-to-compute-pm2-5-source-contributions-using-ipr-in-cmaq/5906/1 "2025-07-11T02:08:19Z")
I found the PM2.5 calculation method in the file `SpecDef_cb6r3_ae7_aq.txt`, and the formula is as follows: `PM25_TOT = ATOTI[0] * PM25AT[3] + ATOTJ[0] * PM25AC[3] + ATOTK[0] * PM25CO[3]` However, I couldn’t find any formula for IPR calculation. So I have two questions: **First** , does `PM25_TOT` refer to PM2.5 mass concentration? **Second** , can I calculate IPR for PM2.5 using the same approach as the PM25\_TOT calculation? For example, I found that: `ATOTK = ASOIL[1] + ACORS[1] + ASEACAT[1] + ACLK[1] + ASO4K[1] + ANO3K[1] + ANH4K[1]` Each of these components has its own IPR terms, such as `ZADV_ASOIL`, `HADV_ASOIL`, and `EMIS_ASOIL`. Can I calculate the IPR of PM2.5 by applying the same formula used for PM25\_TOT, but using the IPR values of each species instead? ---
**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:** [July 11, 2025, 5:12pm UTC](https://forum.cmascenter.org/t/how-to-compute-pm2-5-source-contributions-using-ipr-in-cmaq/5906/2 "2025-07-11T17:12:14Z")
Yes, PM25\_TOT refers to PM2.5 mass concentration, and yes, you can aggregate the IPR terms for the various aerosol species in the same way you would aggregate the species concentrations.