The 3-D CMAQ hourly concentration file (CONC) is the most commonly referenced CMAQ output file. Containing gas-phase species mixing ratios (ppmV) and aerosol species concentrations (μg/m3), CONC files include instantaneous model species concentrations at the end of each model hour. The number and types of species contained in the CONC files is dependent on the chemical mechanism and aerosol model configurations selected when compiling the CCTM. The species concentration include files (CONC.EXT) within the mechanism include directories list the species that are written to the CONC files for each mechanism configuration. The GC_CONC.EXT file lists the gas-phase species and the AE_CONC.EXT file lists the aerosol species written to the CONC file. You can remove species from these CONC.EXT files to reduce the number of species written to the CONC file.