Hi Ryan,
The tag ENX is defined in the sensinput.cmas.dat
It was defined as the sensitivity of ozone to NO and NO2.
The tag ESX is defined in the sensinput.cmas.dat as the sensitivity of ozone to SO2.
https://www.airqualitymodeling.org/index.php/CMAQ_version_5.2_DDM_Technical_Documentation
There was another issue in this forum that describes the setup for determining the sensitivity to NOX from the transportation sector that may be helpful.
https://forum.cmascenter.org/t/cmaq-ddm-3d-sensinput-file-setting-about-ddm3d-es-emissions-split-into-categories-sensitivity/632
Liz