SMOKE can accommodate a variety of chemical mechanisms for the models it supports. From the emissions processing perspective, the chemical mechanism is the mapping of the pollutants provided in the emissions inventory to the species needed by the AQM of interest. For example, SMOKE can support by default five chemical mechanisms for the CMAQ model: Carbon Bond 4 (CB4), CB4 with particulates, Regional Acid Deposition Model, 2 (RADM2), RADM2 with particulates, and an early research version of CB4 with toxics. Note that the early version of CB4 with toxics has already been changed to an updated research version. As of this writing, the default version of SMOKE will not support this newer version; however, as described in the next paragraph, it is possible to run SMOKE for the newer research version, as well as for any other chemical mechanism. For example, there are versions of CMAQ available at EPA that include mercury species as additional species in several of the chemical mechanisms.

In Section 4.5.10, “Use a different speciation mechanism or change speciation inputs”, we provide the settings needed in the Assigns file in order to use one of the default chemical mechanisms with SMOKE. However, SMOKE is not constrained to the default mechanisms provided with it. If you need to process other data (e.g., a tracer species) with SMOKE, they can be added to several input files, including the chemical mechanism file, to be output to the AQM. Some additions to chemical mechanisms are easier than others, and we explain in Section 4.5.10, “Use a different speciation mechanism or change speciation inputs” how to determine whether you can create the files you need for your situation. Also in Section 4.5.10, “Use a different speciation mechanism or change speciation inputs”, we give instructions on how add species to the chemical mechanism files and how to make sure that the inventory pollutants are mapped to the correct chemical species.

SMOKE users must know what chemical mechanism will be used in the AQM for which the SMOKE output emissions are intended. Once that has been determined, the following files must be configured to be consistent with the inventory being used and the chemical mechanism: the inventory table (INVTABLE), speciation profiles (GSPRO), speciation cross-reference (GSREF), and the mobile processes file (MEPROC) when creating on-road mobile emissions with MOBILE6 through SMOKE.