The program BCON prepares chemical boundary conditions for the CCTM from either ASCII vertical profiles, from an existing CCTM output concentration (CONC) file, or from a larger-scale (e.g., global) CTM. The boundary conditions created by BCON can be static in time and space (i.e. time-invariant with uniform concentrations in all boundary grid cells), dynamic in both time and space, or a combination of these two. The ASCII vertical profiles are primarily used to create static boundary conditions. Dynamic boundary conditions can be extracted from CONC files on either the same horizontal grid spacing (i.e., as a windowed modeling domain) or for a finer resolution model grid (i.e., for a nested simulation), or they can be interpolated from a larger-scale CTM simulation (which is analogous to defining lateral boundary conditions for MM5 or WRF-ARW).

There are two distinct modes of operation for BCON, and each depends on the nature of the input data. When creating BCON executables, the user must specify whether the input data will be ASCII vertical profiles or a CONC file by selecting either “profile” or “m3conc,” respectively, for the setting of the ModInpt variable. This variable determines the input module to use when creating a BCON executable.