Combining ELMO and ISAM in CMAQv5.4 to Customize Tracked Species and Reduce Output Variable Count

CMAQ-ISAM
1

Hello all,

I am currently using CMAQv5.4 ISAM to track OA_TOT. However, due to the large number of TAG NAME entries, the resulting variable count becomes overwhelming, often leading to the error:

Could not open SA_CONC_1 : Maximum number of files already opened.

To address this, I would like to reduce the number of output variables by customizing species within the ELMO module. Specifically, I would like to aggregate certain variables into new user-defined species and have ISAM track these aggregated species directly.

Additionally, I noticed that CMAQv5.5 introduces changes that expand ISAM capabilities to quantify source contributions to total secondary organic aerosol (SOA) and individual species. However, I have not yet tested this version and am unsure whether it can fulfill my requirements.

Could you please provide guidance on:

  1. How to define and track custom species in ISAM using the ELMO module in CMAQv5.4?
  2. Whether CMAQv5.5 offers a built-in solution for this issue or requires further customization?

Thank you for your insights and suggestions!
@Ben_Murphy @hogrefe.christian @sergey

Best regards,
Jin

2

Hello Jin,

unfortunately, using ELMO-defined species in ISAM is not possible in either CMAQv5.4 or CMAQv5.5. It is a feature that is planned for the next CMAQ release in 2026. While full SOA apportionment was already supported in CMAQv5.4, there were a few subsequent bug fixes (released in CMAQv5.4.0.1 and CMAQv5.4.0.2) that are incorporated in CMAQv5.5 so we recommend using that latest version for your work.

Given that using ELMO-defined species in ISAM is not possible, you will have to address the error you reported above. When you compiled CMAQ ISAM, did you use the “large” I/O API library (as described here) recommended for DDM3D and ISAM applications with many output variables?

3

Thank you for your reply and clarification. I will try using the “large” I/O API library as you suggested. I truly appreciate your guidance and am excited to see the advancements in the next CMAQ release!