On-road mobile processing using MOBILE6 requires a number of additional steps in the Temporal program. First, Temporal must determine which hours of emission factors are needed. Since emission factors are stored by local time, Temporal determines which hours are needed based on start and end time and output time zone. The earliest time needed will be the start time in the time zone farthest from the output time zone. If this time is before 6:00 a.m. local time, then Temporal needs the previous day’s emission factors as well because the emission factor files start at 6:00 a.m. (based on the MOBILE6 convention). The latest time needed is the end time in the time zone closest to the output time zone; if this time is before 6:00 a.m. local time, then the last day is not needed because the previous day’s emission factor file will cover through 5:00 a.m.

Temporal also uses the ungridding matrix (MUMAT) from the Grdmat program to identify sources that are outside of the grid. This is needed because the meteorology data used for computing emission factors depend on the grid, so emission factors are available only for those sources that are inside the grid.

Temporal must determine the correct names of the emission factors that it will use. To do this, it first reads the emission processes file (MEPROC) and creates a list of valid emission factor names. This file describes the correct process-pollutant combinations that are available from MOBILE6 for the pollutants of interest. Not all pollutants requested exist for all processes, so it is important for Temporal to know from this file what emission factors must be read. Temporal also checks the inventory table (INVTABLE) file to determine whether NONHAPVOC was calculated. This allows Temporal to know whether it should also expect and use emission factors for NONHAPVOC.

Temporal also must open and use the emission factor files, which are listed in a text file called the MEFLIST file. It checks to see which days each file covers and makes sure that all hours needed are covered. There can be emission factor files that use different temporal averaging for the meteorology data: episode average, monthly average, weekly average, and day-specific. If the correct time period of data is available, Temporal reads the emission factors for each source from the appropriate file, because different sources can use different temporal averaging approaches. Finally, Temporal multiplies the correct hourly emission factor for each source by that source’s VMT to compute the hourly emissions by process and pollutant.