# Questions in CMAQ-ISAM output **URL:** \ **Category:** CMAQ-ISAM\ **Tags:** cmaq, cmaq-isam\ **Created:** [July 3, 2025, 8:44am UTC](https://forum.cmascenter.org/t/questions-in-cmaq-isam-output/5891 "2025-07-03T08:44:57Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Bailey](https://avatars.discourse-cdn.com/v4/letter/b/8491ac/32.png) [@Bailey](https://forum.cmascenter.org/u/Bailey)\ **Post date:** [July 3, 2025, 8:44am UTC](https://forum.cmascenter.org/t/questions-in-cmaq-isam-output/5891/1 "2025-07-03T08:44:57Z")
Hello teachers, I encountered a problem while processing the ISAM output file. I have enabled the ISAM source apportionment function in the CMAQ 5.3.2 version. The ISAM control file has been uploaded. I would like to know the contribution of biogenic emissions to ozone formation. ![1751531675377](https://canada1.discourse-cdn.com/flex027/uploads/cmas/original/2X/7/790f23ffc28705a9fefcc05aeff11ab9537bc474.png) However, after extracting the information “O3\_MEG” from CCTM\_SA\_ACONC\_v532\_intel\_china7\_\*.nc, the result I obtained was that all the contribution values were zero. I have uploaded the LOG file for one of the days. Could a teacher please check it for me? Thanks! [CTM\_LOG\_038.v532\_intel\_china7\_20200720.txt](https://forum.cmascenter.org/uploads/short-url/iX8Girs7XAn3AKUfgJaOOyjnjSQ.txt) (499.2 KB) ---
**Author:** ![sergey](https://avatars.discourse-cdn.com/v4/letter/s/9fc348/32.png) [@sergey](https://forum.cmascenter.org/u/sergey)\ **Post date:** [July 15, 2025, 3:52pm UTC](https://forum.cmascenter.org/t/questions-in-cmaq-isam-output/5891/2 "2025-07-15T15:52:58Z")
Hi Bailey, It is certainly unusual to get all zeros in the output file for ISAM. Some questions for you. 1. Is the standard concentration output for ozone reasonable (CONC or ACONC)? 2. Can you track a different stream and get reasonable output? 3. Are the emissions values in the file GRIDDED\_MEGAN reasonable? Sergey