The PARIO library contains modules for controlling the model input and output in parallel multi-processor computing environments. In addition to a series of CMAQ-specific routines, it contains special implementations of several of the I/O API modules for multi-processor computing environments.

The PARIO library is only necessary when compiling the CCTM for parallel multi-processor environments; single processor versions of the CCTM and the other CMAQ programs do not use the PARIO library.