The Geofac program provides a means for adjusting emissions by grid cell after SMOKE has already created model-ready inputs. For example, the program could be used to zero emissions from all grid cells that intersect a certain state, which would be a rough approximation of removing that state’s inventory from the model-ready files. Although it is more accurate to modify the emissions using the Cntlmat program, that approach takes longer and is possible only if the SMOKE input files used to create the model ready emissions are still available. Geofac is useful in situations where speed and simplicity are more important than the accuracy of the emissions, or when only the gridded model-ready inputs are available and the inventories used to create them are not.

Geofac reads in a gridded 2-D or 3-D SMOKE emissions file (output from the Smkmerge program) and multiplies the emissions with a user-supplied adjustment factor for each individual species in the emissions file. The factors are assigned by grid-cell regions, which are defined by the input “mask” file. Each grid cell either receives the factors or it does not (the mask is simply an on-off switch). The resulting hourly, gridded, speciated emissions data are output to a new I/O API file with the same spatial and temporal resolution and the same model species with different values.