The 2-D CMAQ integral average concentration file (ACONC) includes average model species concentrations for each model hour, as opposed to instantaneous concentrations at the end of each output time step. The species written to the ACONC file are set by the user in the CCTM run script using the variable AVG_CONC_SPCS. The model layers across which to derive the integral average concentration are also set in the CCTM run script using the variable ACONC_BLEV_ELEV.