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

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?

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

Related forum threads:

How do I compute PM2.5, PM10 or PM1 from CMAQ output?
PM25 composition and estimation of PM25 water (CMAQv5.3.1)
How to calculate PM25_TOT/PM25 Concentration from CMAQv5.3.2-ISAM results?
CMAQ Computing PM2.5

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

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

Source Code

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