The CMAQ installation includes a tutorial dataset for benchmarking the model on your system. Unpacking the different tar files of the distribution in the M3HOME directory installs the CMAQ source code, scripts, and tutorial data files in a directory structure recognized by the default run and build scripts. The M3HOME directory is the base location of the CMAQ installation for a specific application. Under M3HOME, the scripts directory contains the build and run scripts, the models directory contains the CVS archive of model source code, the data directory contains the input and output data for the model, and the lib directory contains the compiled binary library files required to build the CMAQ executables. The CMAQ scripts use the following environment variables to alias the locations of these different directories:

Using environment variables to specify the CMAQ directories generalizes the CMAQ scripts by only requiring that the user specify the location of the M3HOME directory on their system and then setting the rest of the CMAQ directories relative to M3HOME. While this directory structure works well for the tutorial case and most CMAQ applications, other configurations are possible.